View Full Version : Ground loop between pre-amp and power amp?
Simon_LDT
18-01-2016, 09:02
Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.
When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.
What are my options to remove this ground loop (and safely)?
I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?
I'm struggling to really find any decent info on this as most stuff that comes up regarding ground loops is usually to do with TV/Cable/Satellite and not between 2 amps.
Hi Simon.
When I had your power amp, I used it with two different pre-amps and had no problems with hum .. so there is hope! In fact I was taken with how low the hum/noise level was through my sensitive speakers.
My experience with audio systems is that the culprit is is often a digital source interacting with the pre. Try unplugging any cd / dvd / blueray players at the mains, one at a time. If that doesn't give any joy, then disconnect all source boxes. Many such players seem to have been designed with two pin mains markets in mind.
Ground loops can be difficult to trace, but you can introduce a ground lift circuit (safely) into the preamp which, more often than not, will cure the problem.
All you need is a bridge rectifier of sugfficient rating, a capacitor and resistor (in parallel) across the connections from the earth to chassis. A 3.5A bridge rectifier, 100nF cap and 10 Ohm (5 to 10W) resistor is all that is needed.
Here's one that I made up for my old croft preamp which didn't have one:
http://i1140.photobucket.com/albums/n577/24pacman/Hifi/_MG_6359_zps6bdc118b.jpg
The white cable in from top left is a new earth wire soldered to the star-earth point for the RCA signal ground point which was lifted and insulated from the chassis and redirected to the earth lift circuit. It is intrinsically safe to do this. All wiring is 600V rated and can carry full earth fault from a failure of the circuit too. Output is to existing chassis earth point. AC mains ground is retained. On no account lift the earth from the mains to chassis! (either at the plug or the amp, as was often recommended back in the bad-old days).
Light Dependant Resistor
18-01-2016, 09:51
Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.
When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.
What are my options to remove this ground loop (and safely)?
I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?
I'm struggling to really find any decent info on this as most stuff that comes up regarding ground loops is usually to do with TV/Cable/Satellite and not between 2 amps.
Check your RCA connectors, that ground one end is 0.00 ohms, ground the other end. You may have a broken lead. Don't get distracted by 3 pin cables and safety earth
all are there for good reason. Ah ! , UNPLUG FIRST and check your extension lead that it has been wired correctly. If wired incorrectly or earth not connected there is likely your fault.
Always use a properly manufactured extension lead. The typical result with a lead wired wrongly, is 1/2 your AC mains voltage then on all chassis metal. Hence WHY and for other
serious faults AC mains GND must always be connected.
Cheers / Chris
Oldpinkman
18-01-2016, 10:44
Yup - for definite always keep the safety ground. Do not disconnect earth.
If it hums with no inputs connected on the preamp then it is not noise coming in from a digital source interacting with the preamp
Strictly you should blank off the inputs on the pre with null plugs - but I doubt that is the issue
Obviously the preamp may have an internal hum fault. If you can get a simple 2rca to 3.5mm jack, you can listen to the preamp out on headphones and eliminate that possibility
My next favourite to confirm a ground loop is signal lead transformers - but I don't suppose you have one in your locker
A good first try is to make a connection from chassis ground on the pre to chassis ground on the power amp - although if both are grounded to earth using the same electrical socket that would be unusual.
As others have noted, check connecting leads and the multiway are wired properly. It is not uncommon for neutral and earth to get swapped.
Report back -but don't lift safety grounds.
Simon_LDT
18-01-2016, 11:07
Thanks for the replies so far. Will be unplugging everything and doing another check shortly.
Simon_LDT
18-01-2016, 11:43
Right, this is really strange. Unplugged everything and plugged back in the power amp and processor/pre (I've already confirmed that the power amp itself is not causing an issue as with all 3 channels I currently have connected to it are hum-free at this stage).
I then plugged in the surround right rca lead and no hum occurs. I then plug in the surround left rca lead and then the hum starts (and is in both rear channels). Why would plugging in a 2nd rca lead cause this? I even tried a different rca lead and the same thing happens. Even tried a different input (in case it was faulty) and again the same result. I haven't even plugged in anything else (HDMI, Optical, Coaxial, etc) yet the same hum is already there...
British high fidelity
18-01-2016, 11:45
Check your RCA connectors, that ground one end is 0.00 ohms, ground the other end. You may have a broken lead. Don't get distracted by 3 pin cables and safety earth
all are there for good reason. Ah ! , UNPLUG FIRST and check your extension lead that it has been wired correctly. If wired incorrectly or earth not connected there is likely your fault.
Always use a properly manufactured extension lead. The typical result with a lead wired wrongly, is 1/2 your AC mains voltage then on all chassis metal. Hence WHY and for other
serious faults AC mains GND must always be connected.
Cheers / Chris
Definitely check the wiring on the plug end, I bought a iec power cord from a reputable company in Australia and had a serious hum coming though the speakers and couldn't identify the issue, hum was coming through when phonostage was selected on input on pre amp and also cd player, finally found the problem but not after my krell blew a transistor, the issue was the ground pin was live, a major and potential catastrophic accident waiting to happen and basically i used the power cable to run from the wall socket to the power conditioner block, so basically anything that was plugged into the conditioner strip was then live on the ground, the cable made one live ground into 5 live grounds (5 sockets) unbelievable, so please everyone check the pins are correct on the cables before plugging into your prized possessions
Check to see if it is earthing properly with a meter( the socket on amp)
Almost certainly not the problem, but just check all the 7 channels on the nak are switched to rca (not xlr). Can't imagine it would make a difference, but ...
Also, does your processor have any ground switches on the back? Some stuff I've had in the past has a ground lift switch, or one you flip for rca or xlr outputs.
Simon_LDT
18-01-2016, 12:00
Check to see if it is earthing properly with a meter( the socket on amp)
How can I do that? I've got a Voltmeter, is that the right tool? I'm not very tech-savvy when it comes to electrics.
Simon_LDT
18-01-2016, 12:02
Almost certainly not the problem, but just check all the 7 channels on the nak are switched to rca (not xlr). Can't imagine it would make a difference, but ...
Also, does your processor have any ground switches on the back? Some stuff I've had in the past has a ground lift switch, or one you flip for rca or xlr outputs.
Yep, flicked all those to rca soon as I got it wired up with my older AVR. No ground switch on the Emotiva.
EDIT: When adding a third (a final RCA for what I'm using it for - to power center and rears) the hum gets a bit louder. So when I've got a sole rca lead plugged in (and it doesn't matter which output I use from the pre) I get no hum, add a 2nd and I get some low level hum, and then a 3rd the hum gets louder.
Initially i would check on ohms that the outer of rca is grounded ...if one is definately working then initially we can hope it is ok so try a reading from outer to outer between the 2 in case its gone hi resistance...could have a dry connection. If its an earthed chassis then you should get a reading to the earth pin of mains plug too..obviously switched off when on ohms..should read 0.00 or very close
Also you could try moving cablescand units about as you can often get a hum induced from a tx ,psu or mains cable etc.
Right, this is really strange. Unplugged everything and plugged back in the power amp and processor/pre (I've already confirmed that the power amp itself is not causing an issue as with all 3 channels I currently have connected to it are hum-free at this stage).
I then plugged in the surround right rca lead and no hum occurs. I then plug in the surround left rca lead and then the hum starts (and is in both rear channels). Why would plugging in a 2nd rca lead cause this? I even tried a different rca lead and the same thing happens. Even tried a different input (in case it was faulty) and again the same result. I haven't even plugged in anything else (HDMI, Optical, Coaxial, etc) yet the same hum is already there...
If you are confident that you have eliminated the power amp and the interconnect from the equation, and nothing else is plugged in then it would seem to be a problem with the rear channel output on the processor/pre-amp
Simon_LDT
18-01-2016, 13:25
If you are confident that you have eliminated the power amp and the interconnect from the equation, and nothing else is plugged in then it would seem to be a problem with the rear channel output on the processor/pre-amp
I've also tried all the other outputs (7) with each rca lead and the same results. Doesn't matter which output I use or which cable, each time I add a 2nd rca lead the hum begins. Very strange.
EDIT: I also just tried putting some speaker cable between the 2 amp's chassis and nothing happened there either.
Oldpinkman
18-01-2016, 13:37
I've also tried all the other outputs (7) with each rca lead and the same results. Doesn't matter which output I use or which cable, each time I add a 2nd rca lead the hum begins. Very strange.
EDIT: I also just tried putting some speaker cable between the 2 amp's chassis and nothing happened there either.
It doesn't need to be speaker cable - any conductor will do . Are you sure you got bare metal on the chassis? I'm sorry if this sounds daft - but just to check, you didn't try touching cable to painted chassis did you? You need to undo a screw and wrap a bit of mains flex round it to make sure you have a metal to metal connection between the 2 chassis.
Simon_LDT
18-01-2016, 14:20
It doesn't need to be speaker cable - any conductor will do . Are you sure you got bare metal on the chassis? I'm sorry if this sounds daft - but just to check, you didn't try touching cable to painted chassis did you? You need to undo a screw and wrap a bit of mains flex round it to make sure you have a metal to metal connection between the 2 chassis.
I undid a screw on the underside of each amp and wrapped the cable around and tightened it up securely. That no good?
I'm really not good at this kind of stuff. :doh:
Oldpinkman
18-01-2016, 14:32
I undid a screw on the underside of each amp and wrapped the cable around and tightened it up securely. That no good?
I'm really not good at this kind of stuff. :doh:
No - that should be fine. Puzzling. I hate fixing hum problems when they are in front of me, never mind trying to do it remotely.
Oldpinkman
18-01-2016, 14:38
You said you have a volt meter. I take it that is a simple multimeter and you can measure resistance - ohms. Just so I can let go of this bone, try unplugging both devices from the mains and measuring the resistance between the screw you undid and the earth pin on the plug. Confirm you got zero ohms (or very close to zero). You could also fit your chassis ground wire, and measure the resistance from the earth pin on one plug (preamp) to the earth pin on the other plug (power amp). Should be zero or near zero.
If the problem is absent when there is a single connection between the 2 devices, but adding a 2nd channel adds hum, it suggests a ground loop of some sort, but not an easy one!
Simon_LDT
18-01-2016, 14:59
You said you have a volt meter. I take it that is a simple multimeter and you can measure resistance - ohms. Just so I can let go of this bone, try unplugging both devices from the mains and measuring the resistance between the screw you undid and the earth pin on the plug. Confirm you got zero ohms (or very close to zero). You could also fit your chassis ground wire, and measure the resistance from the earth pin on one plug (preamp) to the earth pin on the other plug (power amp). Should be zero or near zero.
If the problem is absent when there is a single connection between the 2 devices, but adding a 2nd channel adds hum, it suggests a ground loop of some sort, but not an easy one!
This is the voltmeter I've got: http://www.amazon.co.uk/Skytronic-600-005-Compact-Digital-Multitester/dp/B000L0OHIK
Which setting do I need? I've currently got it on the 200 setting but I'm getting numbers jumping all over the place.
Oldpinkman
18-01-2016, 15:04
Bottom left hand corner - the 200 ohm green setting next to the black sine wave symbol. Touch the probes together to confirm they give 0 ohms first
Black to centre hole marked com. Red to right hole marked v ohms etc.. Set dial to the green settings at bottom marked ohms. The second one up looks like continuity. Touching the leads together should go to 0 and if continuity selected(not sure its is) then it will bleep
Simon_LDT
18-01-2016, 15:12
Right, got that. So when you say touch the earth pin on the plug - is that the wall socket end or the end which plugs into the amp? Can I touch the earth pin on the inside where the power goes into the amp or does it have to be the underside?
Dont do it with the power on.
Dont do it with the power on.
Sounds like the title of an 'Eighties dance single. ;)
Some good input for locating the cause of hum here:
http://www.psaudio.com/ps_how/how-to-find-and-fix-hum/
Simon_LDT
18-01-2016, 15:37
Dont do it with the power on.
Haha, I'm stupid but not that so, haha. :lol:
Just tried the power amp but got no reading (stayed at .1 which seems the default), reckon I may have to pop the top off or maybe I'm missing where to get a metal contact as the screw I took out didn't seem to give me anything - which also means the wire I tried earlier wasn't effective). I did try a reading from the wall plug earth to the earth hole in the amp end of the cable - which gave me a reading of between 0-20ohm (mostly 0 but it did spike to around 15-20 at times) and the voltmeter buzzed as had it on the right setting for continuity.
I'll have to continue tomorrow as I must get some sleep - otherwise I'll be falling asleep at work tonight!
Oldpinkman
18-01-2016, 15:45
Haha, I'm stupid but not that so, haha. :lol:
Just tried the power amp but got no reading (stayed at .1 which seems the default), reckon I may have to pop the top off or maybe I'm missing where to get a metal contact as the screw I took out didn't seem to give me anything - which also means the wire I tried earlier wasn't effective). I did try a reading from the wall plug earth to the earth hole in the amp end of the cable - which gave me a reading of between 0-20ohm (mostly 0 but it did spike to around 15-20 at times) and the voltmeter buzzed as had it on the right setting for continuity.
I'll have to continue tomorrow as I must get some sleep - otherwise I'll be falling asleep at work tonight!
Get some sleep. When you get back refreshed use your resistance measurement to track up to find the fault. Start with the cables. Earth pin on the plug to earth pin in the iee socket. Then check earth pin on plug to the chassis. On a class 1 device, assuming you have found a bare metal contact point, this should be zero ohms. If its not
You may not have found a bare chassis connection - not always easy - OR
If you have found a bare chassis connection and you don't have zero ohms you have a dangerous fault and never mind hum, you needs somebody who knows what they are doing taking a look at it.
If you can find a good chassis connection on both chassis, where you get zero ohms from chassis to earth pin on the plug, then if you connect the 2 chassis, you should get zero ohms (or very few ohms) between the 2 plug earth pins.
Best of luck :)
Haha, I'm stupid but not that so, haha. :lol:
Just tried the power amp but got no reading (stayed at .1 which seems the default), reckon I may have to pop the top off or maybe I'm missing where to get a metal contact as the screw I took out didn't seem to give me anything - which also means the wire I tried earlier wasn't effective). I did try a reading from the wall plug earth to the earth hole in the amp end of the cable - which gave me a reading of between 0-20ohm (mostly 0 but it did spike to around 15-20 at times) and the voltmeter buzzed as had it on the right setting for continuity.
I'll have to continue tomorrow as I must get some sleep - otherwise I'll be falling asleep at work tonight!
Sorry...but its been done lol...
Arkless Electronics
18-01-2016, 16:33
Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.
When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.
What are my options to remove this ground loop (and safely)?
I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?
I'm struggling to really find any decent info on this as most stuff that comes up regarding ground loops is usually to do with TV/Cable/Satellite and not between 2 amps.
I haven't read through the whole thread but yes this should work and retain an earth through the power amp.
Often just removing the earth from the pre or power at the plug is a complete cure but although I sometimes do this in my own system I cant recommend it on safety grounds.... i.e. I trust it enough to do it myself without worries but that's at my own risk and if something happened to you...
I haven't read through the whole thread but yes this should work and retain an earth through the power amp.
Often just removing the earth from the pre or power at the plug is a complete cure but although I sometimes do this in my own system I cant recommend it on safety grounds.... i.e. I trust it enough to do it myself without worries but that's at my own risk and if something happened to you...
Hence why I recommended a ground lift circuit. Price of parts about a fiver. 10 minute job, job done.
Yup it can be quickly tried to see if it works as long as you dont touch anything(just in case) if the hum goes away then youve found the problem.
I had a similar thing with my power pre combo. Thought that was the issue...it wasnt...it was a stray cable too close to another that was inducing it... Resited cables and hum gone
Given that the problem is on the rear channel of an AV set up where audio quality probably isn't 110% critical I would try an in line transformer between - do an search on ebay for "audio hum stopper" or similar cheap ones cost about £3-£5. You can find them with phono plugs and sockets on so its a quick easy and cheap solution but not 100% hifi !!
Oldpinkman
18-01-2016, 18:22
Given that the problem is on the rear channel of an AV set up where audio quality probably isn't 110% critical I would try an in line transformer between - do an search on ebay for "audio hum stopper" or similar cheap ones cost about £3-£5. You can find them with phono plugs and sockets on so its a quick easy and cheap solution but not 100% hifi !!
You can get, and I use for my av, very hifi ones, but they're not cheap. However they are a great way to break a loop between components. I am however a bit phased by why one rca connection between pre and power is not humming but 2 are.
Oldpinkman
18-01-2016, 18:23
Hence why I recommended a ground lift circuit. Price of parts about a fiver. 10 minute job, job done.
It's a neat circuit, from esp I think, but maybe a bit ambitious for a guy who doesn't know which sockets to plug his multimeter probes in
Firebottle
19-01-2016, 08:48
Could it be that the two RCA connections are the actual 'loop' here. I think it is unlikely but can be proven very simply.
Connect the single RCA lead. Then connect the second by inserting fully at one end but only insert at the other end enough for the centre pin to make contact but NOT the outer sleeve/ground.
In other words only partly insert the 2nd end of the 2nd cable. Do this with the volume set low in case of hum pick-up from the input/centre pin.
:)
Oldpinkman
19-01-2016, 10:01
Could it be that the two RCA connections are the actual 'loop' here. I think it is unlikely but can be proven very simply.
Connect the single RCA lead. Then connect the second by inserting fully at one end but only insert at the other end enough for the centre pin to make contact but NOT the outer sleeve/ground.
In other words only partly insert the 2nd end of the 2nd cable. Do this with the volume set low in case of hum pick-up from the input/centre pin.
:)
I wondered that - but can't figure out what would be going on inside the amp to create it. What sort of grounding arrangement? And if the signal pin causes a hum, how are you going to hear if the other hum is there?
How about connecting a bit of wire between the return outers on the RCA's? But why would they not be common anyway? A break in a star ground?
:scratch:
I think I'd want to be sure that we have a proper chassis ground connection before I start going off down other paths, given the later posts. Without seeing it, you are always left wondering what isnt being described
Firebottle
19-01-2016, 13:28
Agreed with what you are saying Richard.
Regarding the hum from the centre pin, I was only thinking of the moment the connection is made, the 2nd lead being fully home at the other end should ensure that the screen of the lead is effective.
I've often wondered if having two separate screen connections to and from the same pieces of equipment, i. e. the 2 RCA leads, could pick up hum due to there being a possible loop.
Given that the 2 leads are generally run together it doesn't offer much of a loop area, plus it would probably need a strong local hum field to cause any problem.
:)
Simon_LDT
19-01-2016, 15:17
Haven't had chance to get back to solving this just yet, but just want to thank everyone for their contributions which are greatly appreciated.
Will see if I can spare an hour or so later to get testing, if not then tomorrow.
This might sound silly, but would the FM antenna on the rear of the pre be a direct metal connection? I'm a bit skeptical about taking the tops off as I've never done it before but it looks like it might be the only way to get to some metal inside to test.
I had a humloop problem when connecting a roksan kandy to a pioneer a400 amplifier.
this caused much nashing of teeth and I tried a few solutions involving extra earthing straps, multiwaypower outlets and rca leads with the shields disconnected...I even resorted to the dreaded earthlift.
then...at my wits end I had a lightbulb moment.
the pioneer a400 is a totally overrated, overbright sounding piece of shit.....I flogged it on and dusted down my trusty nad....happy again!!!
Oldpinkman
19-01-2016, 17:08
Haven't had chance to get back to solving this just yet, but just want to thank everyone for their contributions which are greatly appreciated.
Will see if I can spare an hour or so later to get testing, if not then tomorrow.
This might sound silly, but would the FM antenna on the rear of the pre be a direct metal connection? I'm a bit skeptical about taking the tops off as I've never done it before but it looks like it might be the only way to get to some metal inside to test.
Depends a bit how its earthed / grounded inside but "probably". And probably the outer of any RCA socket will connect to chassis ground too. You can always test with that meter of yours. Just unplug from the mains and check earth pin on the plug to points like an rca shield or the antenna base and see if you get zero ohms (and a continuity buzz if that is switched on). Do the same on the power amp. Connect the 2 chassis points you find, check you have continuity between the earth pins on the 2 plugs (which are both unplugged from the wall for this test), then leave your chassis ground connected, plug both back in and report back the hum has vanished
Or if it hasn't vanished we resume the Sherlock Holmes stuff :)
Simon_LDT
19-01-2016, 18:37
Have just tried the antenna, rca outer shield and not getting any readings on either, nor under any screws I undid yesterday. I even tried touching the earth pin on the amp mains socket but got no reading (is that even possible? Surely that is bare metal for the grounding to actually work?). Looks like I'm going to have to man up and take the tops off (what would I be looking for inside as earth ground?)
I did test the individual IEC cables themselves to make sure none of those are faulty, by connecting the earth from plug to earth hole on the amp end and that gives a good reading of 0ohms and continuity buzzes.
I even tried with both amps on of slowly connecting the 2nd rca lead and I could hear the hum begin as I pushed it in further. Plugging in the 3rd rca makes the hum louder.
Could it be toroid hum? The power amp does hum but sounds normal to me and not overly loud. My 2 Arcam monoblocks (which power the fronts and for stereo) have toroids which hum too, yet the signal going to the speakers is squeaky clean there (via XLR though), although as soon as I switch to AV mode for surround listening, the fronts then begin to hum slightly too (and did even with my old Sony AVR connected up). The common thing here being rca cables going from pre to power. Could they be transferring the noise?
Is it worth trying an rca - xlr cable to go between pre (rca) and power (xlr)?
Might not be a grounded chassis, ... I would be careful.
did you check to see if there is an earth cable in plug or is it an iec... Ive seen not metal cases that dont conduct but look like metal as well
Using directional cables might also be a solution. The shield in your RCA cables might cause a ground loop fight between two components.
Check out the Ground Loop hum section here:
http://archive.oreilly.com/pub/h/4241
You cannot disconnect the shield of a coaxial single ended cable and expect it to work as it also acts as the signal return. It will hum loudly and you will have no common reference to ground (zero volts) between connected pieces of kit. It does not work.
If there is a ground loop problem and all the obvious things have been tried, such as checking connections, checking interconnects are not faulty (swap each pair out, one at a time with a set of the freebee ones or other spares) then it is likely to be a mains earth ground loop.
This introduces differential voltage between connected chassis on the ground plain and with circuit ground, requiring a lift on one of the earth loops to solve the problem. If it is traced to between the pre and power amp, then one or other would require to be fitted with a ground lift. It is a very common problem with a very easy solution that does nothing to upset sound quality. This assumes that both pieces of kit are not double insulated and actually grounded to the mains earth.
It is worth, if lifting lids (obviously safety first....do not poke about unless power is switched off and mains plugs are removed and do not touch any power supply smoothing capacitors which may still be fully charged!) to check that there is no broken or damaged connection on the common signal ground circuit. There should be a bar or wire joining all input RCA grounding collars and this is usually taken to a star-earth point on the chassis. Simply check that none of those connections are damaged or broken on each channel.
If they look ok, then time to try the ground lift. pre or power, doesn't matter which...usually the one with most room inside the casing!
Look to see if there is a little bridge rectifier that the signal grounds are fed to (as per my photo) and that there is a resistor and cap across the terminals. If not, and your ground earth is direct to chassis, then a ground lift will probably work. It is intrinsically safe. The idea is that the mains ground is effectively isolated from signal earth as the easiest way to ground is via the chassis mains earth and not via the signal earth. A smallish value resistor across the connections is enough as shown (10 Ohm) to do the job. Existing mains earth is retained but connected to the bridge rectifier so breaking the low impedance connection with the signal earth. In the event of a high current or dangerous fault occurring on the signal ground, the chssis is still earthed via the original chassis earth. The important thing is that the circuit signal earth is lifted from the chassis ground (insulate or remove the star earth point and run a new wire from here to the rectifier, coupling across the rectifier using a 10R resistor). Here is the circuit:
http://dialedinamps.com/wp-content/uploads/2015/11/lifted_ground.png
Oldpinkman
20-01-2016, 09:51
Using directional cables might also be a solution. The shield in your RCA cables might cause a ground loop fight between two components.
Check out the Ground Loop hum section here:
http://archive.oreilly.com/pub/h/4241
Yup - As Paul says you can't go using the mains earth as the signal return and expect good results. You would get complete silence if one device is double insulated. The direction arrow wouldn't matter as a "ground lift " solution. They don't work that way. Directional cables usually have a signal return inside the shield, and it is only the shield grounded at one end, to make a grounded faraday cage, which can help to reduce noise on the signal cable in some situations but is probably not the issue here.
Looking at a pdf of the manual - the implication is that the preamp is NOT double insulated, in which case there should be a connection between the chassis and earth, and not to have one is the first fault you need to fix before worrying about ground loop lifting (you won't have a ground loop if there is no connection from the amp grounding to earth, so there is nothing to lift).
Next check is a simple one - can you either confirm whether the back panel says the device is class II or double insulated or not, or take a decent photo of it. If it is double insulated, near the CE mark will be one box inside another box. Report back ;)
Simon_LDT
20-01-2016, 11:20
Thanks for the explanation Paul, unfortunately a lot of it goes over my head.
I'm going to be taking the tops off shortly and hoping to solve this issue today. I'll post some photos of the insides as I could really do with some guidance of what to use my probe on to test for resistance ans where to attach an earth strap between the 2 chassis to test that out also.
Richard: Will check for that info in a moment.
Simon_LDT
20-01-2016, 11:33
Can't see any such marks on the rear panel. Ive attached a photo below. I've also attached a photo of a symbol on the underside - mean anything?1602416025
Simon_LDT
20-01-2016, 11:51
This is inside the pre-amp. Looks like an earth wire to me (something I do actually know, heh). If you need any other pics, let me know.
16026160271602816029
Oldpinkman
20-01-2016, 12:12
OK That's a class I device with a chassis ground to which you could fit a ground lifter of the sort Paul mentions. Lets not rush yet. We still haven't solved why you are not getting a continuity (zero ohms) between earth on the plug pin and the equipment chassis. As a basic simple first point to test plug in the mains lead to the unit NOT into the mains - keep the plug on the desk - and put one meter lead on the earth pin on the plug and one on that grounding terminal with the green and yellow wire inside the amp. We should get zero ohms
Report back :)
Can't see any such marks on the rear panel. Ive attached a photo below. I've also attached a photo of a symbol on the underside - mean anything?1602416025
That's look's like a Earth symbol.
Simon_LDT
20-01-2016, 12:35
That is 100% 0ohm, between earth on plug and the earth post inside the amp. What next?
Can you check the same thing for the power amp (if not already done)?
Next, you have to identify the circuit's signal grounding point to the chassis. For a PCB this might be done by a ground track connecting with the PCB connection to the metal PCB mount legs in which case it makes things a little more tricky! If it is via a separate wire which is connected to the chassis, you need to identify this ground wire, lift it from the chassis ground and use the circuit described above to connect it via the bridge rectifier across a 10R resistor with a 100nF cap in parallel. That should eliminate the hum.
It may be easier to achieve inside of the power amp depending on space and how the signal ground is wired, hence you still need to have a look inside that one too.
Oldpinkman
20-01-2016, 13:05
Just before we rush to do ground lifting, lets see if we can bond the chassis grounds as we were trying before. If we establish the chassis is grounded it should be possible to attach a wire to it which will have zero ohms to earth. If we can attach that wire to the chassis of the power amp, we should have (very nearly) zero ohms between the earth pin on the power amp and the earth pin on the preamp when both are unplugged.
If we can get that - plug back in and confirm you still have the hum problem
Simon_LDT
20-01-2016, 13:13
This is the power amp. I can't see any earth cables...
16030
Simon_LDT
20-01-2016, 13:27
Right, think I've found the earth in this power amp. The L and N wires from the power input are attached to the ON/OFF switch, and then there are 2 wires coming from that which are then coiled around a metal circle (see photo) and then they run along side the chasis and towards the front into the power board/section. Seen this before?
16031
Simon_LDT
20-01-2016, 13:29
If anyone needs more photos, let me know. The wire that is coiled around the ring doesn't look to be exposed anywhere (so that the bare wire is touching anything) as it looks like that same cable goes right into the power board.
Looks like its double insulated from the photos Simon as the IEC inlet doesn't appear to have any earth connected to it. That being the case, it ought to have the double insulated markings visible on the rear of the casework, possibly near to the CE markings. Your earth lift would need to be with the preamp that being the case. Power amp should be left alone. Dont connect anything else to its chassis as it is not grounded to mains earth.
Simon_LDT
20-01-2016, 14:28
I'm struggling to find an earth point on the Nak power amp. I'm using the probes and placing 1 end on the plug earth and I've tried the metal on the metal ring and also the earth pin that is sticking out from the IEC socket (which has nothing connected to it as shown in photo). Does this mean the chassis is not grounded? Would the earth be anywhere on the power board?
Go back to the pre..there was a good earth inside that if you need one.. As Paul says there is no earth on the iec socket so must be class 2 or something of that ilk. May be the reason your having probs.
Simon_LDT
20-01-2016, 14:36
Looks like its double insulated from the photos Simon as the IEC inlet doesn't appear to have any earth connected to it. That being the case, it ought to have the double insulated markings visible on the rear of the casework, possibly near to the CE markings. Your earth lift would need to be with the preamp that being the case. Power amp should be left alone. Dont connect anything else to its chassis as it is not grounded to mains earth.
I can't see no double insulated symbol on the rear of the case or nothing to state it is class II. Is there a reason this could cause humming? If the device isn't being earthed at the mains that rules out a ground loop or not?
So going back to the pre, is there anything else I can test to see if the hum can be eliminated?
Firebottle
20-01-2016, 14:40
Simon, you are not that far from me, would you like me to look at your kit if you brought it round to me, near Dudley?
:)
Oldpinkman
20-01-2016, 15:05
The Nakamichi AVP1 assuredly doesn't look double insulated to me. It has a clear CE mark, and no indication of double insulation. And that looks like metal casework next to that mains inlet. Which does beg the question WTF happened to the earth wire?
Connecting an earth wire to its case is not going to do any harm (safety) whatever its construction class - although would be pretty pointless if it is class II
It doesn't look that way to me. So stop worrying about hum and start worrying about why a metal cased amplifier has no earth connection from its mains lead. I would be inclined to take Alan up on his kind offer.
But, if you can get a good metal contact on the Nak and connect that via your "earth bond" wire to a good metal contact on the preamp, which is earthed, that would be interesting to try.
But why is there no earth on that? Is there any chance somebody else has tampered with it? :scratch:
Oldpinkman
20-01-2016, 15:11
http://www.fascinatingtech.com/images/AVP-1_Back.jpg
That's the back of an AVP1. Doesn't look double insulated to me. I bet somebody removed the earth tag on the back of that IEE socket to fix a ground loop!
And relied on the chassis bond connection to an earthed preamp for electrical safety - or spent a lot of time in church on his knees. I would make a good connection from AVP1 to pre as a safety measure pending having the AVP1 properly checked for its missing ground. If it fixes the hum - that's a bonus!
That device should have an earth connection :eek:
No sign of a class 2 marking...very odd. You may well be right Richard. Dodgy thing to do on permenent basis and criminal selling it that way if thats the case... Would take up Alans offer and let him look it over... Hes a genius
Oldpinkman
20-01-2016, 15:24
If anyone needs more photos, let me know. The wire that is coiled around the ring doesn't look to be exposed anywhere (so that the bare wire is touching anything) as it looks like that same cable goes right into the power board.
Yes - that is NOT an earth. There is only one place an earth can get into that amp and that is up the mains lead. And its not connected because that spade terminal is sitting empty. That is almost certainly NOT right.
That device appears to be some sort of choke, maybe to meet RF emmissions - who knows, but its not your earth!
Simon_LDT
20-01-2016, 15:24
Are we sure the Nak isn't doubled insulated but for whatever reason doesn't state it on the rear? (anything I could look for inside?)
My previous AVR (Sony STR-DA2400ES) also does not have Class II or any markings on the rear to state it's double insulated, yet the IEC power lead only has 2 pins (no earth) plus it was causing a hum with my front 2 speakers in a similar situation I'm in now (rca cables to separate power amps). I'll ask on avforums about this issue as they have a dedicated Nak thread there.
So, is there anything I can do here in the meantime (will PM Alan later) which is SAFE?
As long as your pre is earthed and you have a connection between the 2 with your rca cable then that should theoretically earth the power amp. If you are going to touch a casing thats plugged in always first use the back of your hand..one hand only... If you did ever get a shock then you will not grip it and get locked in. That is a general rule with anything electrical that has a metal body.... 50 years expierience talking.
http://www.fascinatingtech.com/images/AVP-1_Back.jpg
That's the back of an AVP1. Doesn't look double insulated to me. I bet somebody removed the earth tag on the back of that IEE socket to fix a ground loop!
And relied on the chassis bond connection to an earthed preamp for electrical safety - or spent a lot of time in church on his knees. I would make a good connection from AVP1 to pre as a safety measure pending having the AVP1 properly checked for its missing ground. If it fixes the hum - that's a bonus!
That device should have an earth connection :eek:
That's what it now looks like to me. That needs earthing!
Oldpinkman
20-01-2016, 15:57
Are we sure the Nak isn't doubled insulated but for whatever reason doesn't state it on the rear? (anything I could look for inside?)
My previous AVR (Sony STR-DA2400ES) also does not have Class II or any markings on the rear to state it's double insulated, yet the IEC power lead only has 2 pins (no earth) plus it was causing a hum with my front 2 speakers in a similar situation I'm in now (rca cables to separate power amps). I'll ask on avforums about this issue as they have a dedicated Nak thread there.
So, is there anything I can do here in the meantime (will PM Alan later) which is SAFE?
I've tried a quick google. I can't find for positive definite a European version. CE markings are an EU requirement. However, the Sony Pre has a mains socket which ONLY has 2 connections - THERE IS NO EARTH, and it has no CE mark on it. Your Nak has a CE Mark AND a 3 pin IEE socket. And double insulation means that there is a barrier between any part of the outer casework and any possible live mains electricity inside the unit. Your NAK does NOT look to be built that way. Maybe the Sony is. Outside the EU the regulations do not require (necessarily) the device to state it is class II, double insulated or bear the box in a box mark.
As Grant says you will have a safety earth of sorts if you have interconnects connected but I would connect a good chassis earth.
My XTZ amplifier only has a 2 pin mains socket and that is metal cased. I have pondered this before. I don't think any of my components has an earth lead but I have no hum problems and not been electrocuted yet either.
No idea if this helps or muddies the water further, I remember reading ages ago that this amp thought to have come out of the same factory as the Emotiva XPA range. A search on hum with the XPA brought up this
http://www.avsforum.com/forum/90-receivers-amps-processors/1481773-emotiva-xpa-5-umc-200-both-have-issues.html#post23530204
and this
http://www.avsforum.com/forum/90-receivers-amps-processors/1481773-emotiva-xpa-5-umc-200-both-have-issues.html#post23673707
I've tried a quick google. I can't find for positive definite a European version. CE markings are an EU requirement. However, the Sony Pre has a mains socket which ONLY has 2 connections - THERE IS NO EARTH, and it has no CE mark on it. Your Nak has a CE Mark AND a 3 pin IEE socket. And double insulation means that there is a barrier between any part of the outer casework and any possible live mains electricity inside the unit. Your NAK does NOT look to be built that way. Maybe the Sony is. Outside the EU the regulations do not require (necessarily) the device to state it is class II, double insulated or bear the box in a box mark.
As Grant says you will have a safety earth of sorts if you have interconnects connected but I would connect a good chassis earth.
The problem with relying on interconnect shields or ground return conductors to earth connected bits of kit is that they are not rated to take a large fault current which could easily burn out some of the small signal wires or even some shields. An interconnect should never be relied upon to act as a safety earth path (even if it does!) as it is not intrinsically safe. Consider also that most RCAs will have bare ground collars which in the event of a fault current to chassis will become live if the chassis isn't earthed to the mains.
If a hifi appliance is not double insulated and carries an IEC 3 pin socket, the earth section must be connected to the chassis. In this particular case, I would most certainly connect it using an appropriately rated wire. There should already be a tapped hole somewhere in the chassis base to use a self tapper. The cable can be terminated in a spade-socket and a spade eyelet bolted or screwed to the chassis, the other end being connected to the IEC earth point.
That may cure the hum problem by introducing a lower impedance earth path for the power amp. If it doesn't then there's always the ground lift circuit as a consideration for the preamp.
Dont think anyone was Paul. Just that it would be there in a metered way. If it should have a mains earth then it neeeds a mains earth hum or no hum.. A safe work a round would need to be found
Agreed Grant. I was just offering a little perspective on why interconnects shouldn't be relied upon as safety earths. It seems from Ian's posting above that the end solution was a signal ground lift on the connected preamp. Interesting as well the comments that the power supply may not be adequately shielded from the PCB on some of these amps, but it's all speculation until the issue is actually resolved. Hopefully Simon has enough to go on.
Oldpinkman
20-01-2016, 18:05
My XTZ amplifier only has a 2 pin mains socket and that is metal cased. I have pondered this before. I don't think any of my components has an earth lead but I have no hum problems and not been electrocuted yet either.
There is no problem with a metal case per se. Double insulation requires the bits that have live mains to be protected from the case . So it may have robust shielding inside and outer metal case. But recent EU product should have a CE mark, and if the product has a CE mark and is Class II it should have the double box, or say it is class II or say it is double insulated.
Hum problems of the sort we have been assuming on this thread come from ground loops. So not having an earth lead helps avoid that (although there are also other ways to get hum problems).
The electrocution point depends on the design. Either the device, like those of your preamp manufacturers are double insulated - so touching the casework has no shock risk, OR if you have not double insulated, then the case needs to be metal and connected to earth.
And finally, "and not been electrocuted yet either" reminds me of the joke about the little old lady boarding a British Airways jumbo jet, and calling one of the cabin crew over
"Excuse me young man, but I am frightened of flying. Can you reassure me. How often do your planes crash?"
"Just once madam" ;)
Oldpinkman
20-01-2016, 18:09
The problem with relying on interconnect shields or ground return conductors to earth connected bits of kit is that they are not rated to take a large fault current which could easily burn out some of the small signal wires or even some shields. An interconnect should never be relied upon to act as a safety earth path (even if it does!) as it is not intrinsically safe. Consider also that most RCAs will have bare ground collars which in the event of a fault current to chassis will become live if the chassis isn't earthed to the mains.
If a hifi appliance is not double insulated and carries an IEC 3 pin socket, the earth section must be connected to the chassis. In this particular case, I would most certainly connect it using an appropriately rated wire. There should already be a tapped hole somewhere in the chassis base to use a self tapper. The cable can be terminated in a spade-socket and a spade eyelet bolted or screwed to the chassis, the other end being connected to the IEC earth point.
That may cure the hum problem by introducing a lower impedance earth path for the power amp. If it doesn't then there's always the ground lift circuit as a consideration for the preamp.
Yes - agreed absolutely. It's what I meant by "but I would have a good chassis earth" but I appreciate I implied you could rely on the i/c's for safety ground, and you absolutely cannot. I should be more precise with my language where electrical safety is concerned :doh:
Simon_LDT
20-01-2016, 18:10
Ian - that thread you linked to seems to describe the problem pretty much exactly. The inside of that XPA-5 also looks very similar to the inside of my Nak...
Have you thought about checking out a ground loop isolator?
http://hallresearch.com/page/GLI-RCA
Here is also a thread from some time back discussing hum and NAK amps:
http://www.hometheaterforum.com/topic/57531-humming-in-power-amps/
Hi ... I thought I'd chip in with my experiences with this very amp.
Firstly, I bought it direct from the distributor (StyleCo in Newton Aycliffe, County Durham). Just to clarify, in relation to post 64, I did not modify or tamper with it in any way before Simon bought it from me. It may be worth talking with the manager there, to see if anyone else has raised similar problems? Also, at least 3 other AoS contributors are currently using this amp in their systems, so might be worth starting another thread, asking for their experiences, or getting a mod to change the title of this thread to 'hum problem with Nakamichi AVP1 amp' or similar, to get their attention?
I had no hum or buzz at all with this power amp, and that was with 96dB speakers, and cranking up the volume to check this very thing. I used two different preamps. One was a transformer-based Music First Audio product, which provided ground lift options, and the other was a regular 'active', valve-based, pre.
Sorry I can't be more help ...
Oldpinkman
22-01-2016, 07:55
Simon - where are we on this. To recap
1) I would take Alan up on his offer to check the amps over
2) The amp with only a 2 pin mains lead is presumed to be a class II device not needing an earth. It has no connection at all to earth, and cannot form a ground loop via an earth connection
3) THe other amp appears to need an earth connection. If it were safe without one there would be non-conductive casework between any live mains wiring and the metal case you can touch, and there isn't. So for safety reasons I would connect a good earth wire (preferably yellow and green) from that earth tab on the IEE socket to a screw in the casework (or I would have thought there would be an earthing point on the case somewhere already - ie something it is easy to fix an earth wire to). That will make the device safe
4) Since your 2 amplifiers will only have one earthing point, through the power amp, you will not get a ground loop through the mains wiring, and shouldn't need a ground lift circuit like the one Paul was showing.
5) maybe the power amp connection to earth will fix your hum . But at least it will be safe and you can report whether it changes your hum problem or not
Firebottle
22-01-2016, 08:20
Amplifiers being looked at later today. Having studied one of the links to the same problem I suspect the wiring/grounding of the power amp is rather less than optimum.
I shall also check on the double insulated or not question and report back. I have my suspicions.
Firebottle
22-01-2016, 13:24
Well it has been an interesting look-see.
It certainly looks like double insulated construction, all the mains wiring and the transformers have two layers of insulation (minimum).
However the all metal case is completely floating, no connection at all to mains earth or any of the amplifier circuitry.
What I think is happening is that a certain amount of 100Hz field is coupled into the (floating) case and it is spread around to the input wiring.
I fitted a proper earth connection from the case to the earth terminal of the IEC320 input and hey presto the buzz reduced considerably, if not disappeared altogether.
So the case is now earthed but the amp circuitry is still floating, but once connected to the preamp that is also grounded via the preamp.
Should now be sorted, Simon will try it when he gets back home.
However the all metal case is completely floating, no connection at all to mains earth or any of the amplifier circuitry.
What I think is happening is that a certain amount of 100Hz field is coupled into the (floating) case and it is spread around to the input wiring.
.
So that arrangement is perfectly safe then?
Well it has been an interesting look-see.
It certainly looks like double insulated construction, all the mains wiring and the transformers have two layers of insulation (minimum).
However the all metal case is completely floating, no connection at all to mains earth or any of the amplifier circuitry.
What I think is happening is that a certain amount of 100Hz field is coupled into the (floating) case and it is spread around to the input wiring.
I fitted a proper earth connection from the case to the earth terminal of the IEC320 input and hey presto the buzz reduced considerably, if not disappeared altogether.
So the case is now earthed but the amp circuitry is still floating, but once connected to the preamp that is also grounded via the preamp.
Should now be sorted, Simon will try it when he gets back home.
Adding the earth should clear any attenna effect of case... Very glad it hadnt be tampered with.
Simon_LDT
22-01-2016, 16:24
Was nice to meet Alan this morning and would like to thank him once again for taking the time to have a look.
I've just plugged it all back in and unfortunately it sounds the same to me. :(
Wonder whether it's my speakers sensitivity that is making it louder because when Alan was testing it with his test speakers even before doing anything the buzz was barely audible and after earthing the case it was hard to hear it at all. I'll have to find out the sensitivity and report back. Strange thing is the my rear speakers (where the buzz is loudest) are B&W 601's and I'm sure the sensitivity is around 88ish which isn't exactly on the high side. The centre speaker being an XTZ 99.26 which the buzz is barely audible there.
Try plugging the rear speakers in with short cable and situate them near the amp. It might be your cable run ..both the 601s and the xtzs will be 88db and both about 8 ohms. That will eliminate the cable to rears.. Also try switching rear speakers with main and see if the hum stays with thespeaker or the amp
Simon_LDT
22-01-2016, 16:47
Will try that. I do get hum in the front speakers too but like the centre they are XTZ's, the difference there being that they are powered by my stereo monoblocks so eliminating the Nak, however the buzz in those is barely audible (and that's with ear pressed to them!), same as the centre. The cables to the rears are pretty long (around 5-6 metres).
I'm at work tonight and will be having a nap soon so will get on to this over the next few days when I can find the time. Will report back.
So glad Alan checked it out and confirmed it's safe and now that the chassis is earthed too I can feel more at ease around it without the fear of being electrocuted.
Oldpinkman
22-01-2016, 17:27
Will try that. I do get hum in the front speakers too but like the centre they are XTZ's, the difference there being that they are powered by my stereo monoblocks so eliminating the Nak, however the buzz in those is barely audible (and that's with ear pressed to them!), same as the centre. The cables to the rears are pretty long (around 5-6 metres).
I'm at work tonight and will be having a nap soon so will get on to this over the next few days when I can find the time. Will report back.
So glad Alan checked it out and confirmed it's safe and now that the chassis is earthed too I can feel more at ease around it without the fear of being electrocuted.
It sounds like it was safe anyway - just the CE mark failed to say it was double insulated.
I would be really surprised if the speakers or their leads are a signifcant issue. So what else has changed from Alans? Were you using the same interconnects? Are they the same length? Do you have the equipment near other equipment which wasn't at Alans? Have you plugged any inputs in? Is it still no hum one lead, hum with 2 or 3 leads?
Firebottle
22-01-2016, 17:37
As discussed with Simon I think that the earth loop or part of it is actually formed by the way the separate amplifier boards are wired.
With the way the power leads for the 0V (common) are all linked back to the virtual star point on the power supply board, I am now thinking that the 'ground loop' is partly inside the amplifier and is completed by connecting two interconnects to external equipment.
I would now be tempted to fit a 10 ohm 'earth' lift resistor in each of the 7 analogue ground leads inside the amplifier.
:scratch:
Simon_LDT
23-01-2016, 10:26
Just had another tinker. I wanted to eliminate the B&W speakers so I unplugged the speaker wire from them and plugged into the fronts (XTZ's) instead. These were near silent before when being run by my monoblocks but funnily enough the buzz comes through them with almost the same loudness as the B&W's (it's a tad quieter but not by much). Again, I unplugged all rca cables and no buzz. Plugged in 1 cable no buzz (or not audible anyway), plug in a 2nd and the dreaded buzz appears.
This was all done without the pre switched on so think we can safely eliminate that altogether.
Alan, do you know what sensitivity those speakers are which you were testing with yesterday? I'm struggling to think why it was barely audible on those, yet on mine the hum is clearly audible from at least 1ft away.
Thats good.. Its removed most things from the equation... We are down to amp really... Alans earth lifts look to be the way forward
Firebottle
23-01-2016, 11:28
I don't know the sensitivity of the test speakers unfortunately.
It does seem peculiar that earthing the case did have an effect when on the workbench but not when you got it back to your place :scratch:
Simon_LDT
25-01-2016, 09:11
Would fitting a 10ohm resister/s or doing something like the link below be a simple enough job for a complete novice (with some guidance/instructions)?
http://www.avsforum.com/forum/90-receivers-amps-processors/1481773-emotiva-xpa-5-umc-200-both-have-issues.html#post23673707)
I've got an old soldering gun in the shed somewhere so that's a start and I'm quite tempted to try it if I know what I need to do.
Firebottle
25-01-2016, 10:11
Before you get the soldering gun out just try attaching the 10 ohm resistor by hand, as it should then indicate if it is going to make a difference or not.
Hold one end against a chassis connection, or under a chassis screw, then touch the other end against the outer ring of one of the RCA inputs.
If there is no difference then it is pointless fitting it internally.
:scratch:
Simon_LDT
25-01-2016, 10:30
Will try that. Any recommendations on what type/brand of 10ohm resisters to use or just pick up anything I can find?
Firebottle
25-01-2016, 13:15
Anything will do for a test, it doesn't have to be 10 ohm, anything close will do, 12, 15, 18 ohm.
Simon_LDT
25-01-2016, 13:42
Does it matter what wattage? I've seen a few different ones already (5w, 10w).
Simon_LDT
30-01-2016, 15:38
Picked up a couple of 10ohm metal oxide resistors this morning. So what do I need to do to test if this'll work or not? I assume I can use speaker wire to connect to each end of the resistor and then place one end on a chassis earth point? Whereabouts do I place the other end?
Should hopefully have some time tomorrow to have a tinker.
Firebottle
30-01-2016, 15:54
See post #96.
Simon_LDT
30-01-2016, 16:29
Thanks Alan, that makes sense!
So I am safe to do this while the amp is on? (without touching the actual bare wire myself of course)
Firebottle
30-01-2016, 17:04
Yes you are perfectly safe, touching the wires as well, as the case is now fully earthed :)
Simon_LDT
01-02-2016, 11:08
Just had a go at adding the 10 ohm resistor but nothing happened. I scraped a little bit of the paint under a screw to get a decent connection to chassis, added the resistor and then touched the other end to the shield on an rca socket (tried a few different ones also). No change in level of hum. I'm still getting louder hum as each rca is plugged in (silent with only 1 in). Seems I might have to live with this. Fortunately, with Alan adding the earth the hum is not as bad as before but it hasn't reduced by much at all.
Would using an rca (pre) - xlr (power) cable help reduce the hum at all? Would there be any point in wasting money on a cable like that?
Just had a go at adding the 10 ohm resistor but nothing happened. I scraped a little bit of the paint under a screw to get a decent connection to chassis, added the resistor and then touched the other end to the shield on an rca socket (tried a few different ones also). No change in level of hum. I'm still getting louder hum as each rca is plugged in (silent with only 1 in). Seems I might have to live with this. Fortunately, with Alan adding the earth the hum is not as bad as before but it hasn't reduced by much at all.
Would using an rca (pre) - xlr (power) cable help reduce the hum at all? Would there be any point in wasting money on a cable like that?
It wont work unless the chassis earth bond between the RCA ground return signals and the chassis is first broken. ALL ground return contacts between RCA sockets and chassis have to be effectively lifted otherwise the lowest impedance pathway remains the mains earth, hence the mains hum from the ground loop created.
Of course if the RCA ground return circuit pathway for the amp is insulated from the chassis, and the PCBs dont have a signal earth connection to the chassis, then an earth lift is of limited (if any) value.
pedalhead
01-06-2018, 14:08
Bit of the thread resurrection here. I've got a similar issue, suspected ground loop between pre and power amps. I read this whole thread & now you've left me on a cliffhanger! Simon, did you ever manage to fix the issue?
Simon_LDT
01-06-2018, 15:16
Bit of the thread resurrection here. I've got a similar issue, suspected ground loop between pre and power amps. I read this whole thread & now you've left me on a cliffhanger! Simon, did you ever manage to fix the issue?
Unfortunately not, I've just learnt to live with it. Luckily it's not audible from listening area but is definitely still there. Think it's just some funky design of the poweramp because my fronts which are powered via my 2 channel set-up amp don't have this problem and it's fed from the same preamp.
StanleyB
01-06-2018, 16:34
Ever since introducing separate Pre and Power amps into my set-up I've had humming coming from my speakers, which I am 99.9% sure is a ground loop. I'm currently running an Emotiva UMC-200 and Nakamichi AVP1, before that I was using my old Sony STR-DA2400ES as a pre into the Nak and also had the humming. Before I ever introduced the Nak I was using the Sony AVR solely and had no humming at all.
When the power amp is connected to the speakers but not the pre, there is no humming so that eliminates the power amp. Soon as the pre is connected up using unbalanced RCA cables the hum appears - before ever connecting any other leads in the pre itself. I can only assume (after thorough research) that because both amps have 3 pin power cables that both are trying to ground and it's throwing something off. Both are plugged into the same power socket via an extension.
What are my options to remove this ground loop (and safely)?
I've read that making up a piece of speaker cable to go between them and connecting it to a screw in each chassis is an option but is that even safe, and will it even work?
In some cases amp designers have a different earth for the case compared to the earth for the signal. Naim is an example that comes to mind. In that case you can try a wire between the case of the pre-amp and the power amp in order to neutralize that problem. It is one of the reason why there is an earth tag on the back of my DACs. Naim owners tend to need that earth tag to stop their amp from humming when connected to my DAC, which has several different earth lines.
pedalhead
01-06-2018, 19:34
Thanks for the update, Simon. Sorry to hear you've not been able to fix it. I've gotten around my similar issue by using a Jensen Iso-Max in between pre and power amps. It's not really addressing the fundamental issue, but at least it fixes the symptom!
Powered by vBulletin® Version 4.2.3 Copyright © 2025 vBulletin Solutions, Inc. All rights reserved.