Technical Question about amps

[dantheman91]

Hi

Quick Question about amplifiers - should they buzz well not buzz more electrical when ear close to speakers but they work fine otherwise. Just wondering. I have an old poineer that does this is it normal for any to do this or.???

:scratch:

[johnwhit]

With the volume level set at maximum or some other point?

I can just about hear mine with the volume set at max (100W), the source selected as CD the CDP on but not playing (obviously) and my ear next to the drive unit with the grille removed.

John

[dantheman91]

Volume set to zero then ear close with no source playing etc. play fine with tv and music.

[johnwhit]

Volume set to zero then ear close with no source playing etc. play fine with tv and music.

Should be deathly quiet, although I must admit never trying with the volume set to zero, I'll give it a try when I get home.

John

[dantheman91]

Should be deathly quiet, although I must admit never trying with the volume set to zero, I'll give it a try when I get home.

John

Well i'm just wondering because i had a nad that also did it.

:rolleyes::scratch:

[johnwhit]

With the volume at zero the silence is deafening, even with an AV component selected such as SKY+ or Pioneer PVR. Normally with a AV component selected and switched on I have some noise at maximum volume due to RF entering the component (I presume) and the fact that both contain HDD's etc.

It sounds as if you may have a ground loop somewhere causing the noise you hear through the speakers.

All my components are connected to the amp by RCA interconnects, the amp chassis is then grounded to my power distribution block, which has a terminal in the middle star earthed on a dedicated cable run from my consumer unit, resulting in a very low noise floor.

John

[istari_knight]

Agree its not normal. Does it still do it with everything disconnected ? [just amp & speakers connected.]

[dantheman91]

Hi

Does not do it when plugged in at the single socket. Thanks guys.

[johnwhit]

If not a ground loop then some EMI or RFI entering the system by a cable.

John

[dantheman91]

Hi

i have a mains block with eight sockets and also has a serge a protection built in. maybe i could invet in main filter ETC.

[johnwhit]

Could be worth a try, it seems you may have some interference from another appliance if all is quiet when plugged into a single socket.

John

[johnwhit]

I found this to be quite interesting, written by a studio engineer IIRC, thought it may be of some help. In my case all my components are double insulated i.e. use a figure 8 (C7) connector with no earth wire connected to the component:

"Just as with the earthed components, the system needs its own reference ground and all the components in the system need to have a connection to that. Usually in Hi-Fi the screen of the RCA connections provides this connection between all the components.

Here's a thing though. Each power supply in the system will have an individual characteristic and will be capacitively, or otherwise, linked to the chassis and the incoming mains in one way or another. This means there is a wild voltage induced on the chassis. When you plug an RCA input to an amp with the amp on (not recommended) when the single centre wire connects, but before the ground part of the RCA makes contact, there is usually a nice hum or noise. This is not interference from the air, I assure you (there just isn't that amount of energy in the air unless you system is inside a power station!). What you are hearing there is the difference in potentials between the two bits of kit. Don't forget they are floating with respect to earth as they are double insulated. Not only is it floating at a random voltage induced from its own power source connection to the mains, but the chassis is also floating and able to pick up noise from any mains supply in the vicinity that is radiating. This is not RF, this is low frequency induced energy

When the RCA connects, all becomes quiet as the RCA ties the two chassis electrically together.

All fine. Well no. There still exists a potential between the chassis, the RCA screen has linked them so the difference in voltage is shorted out. But that means that there is an eddy current flowing in the screen. How close is the screen to the signal cable in the RCA wire? Very, Very close, and that does mean the eddy currents flowing between the chassis through the screens due to induced pick up is capcaitively linking to the signal cable itself and raising the noise floor. You can't get away from it!... but you can mitigate it. In large professional audio and video installations (stadia, film and audio studios, theartres etc) this is a very real problem on an un-ignorable scale that has to be managed in the desinging for the system cable layout. In hi-fi systems it is there, just not as prevalent becuase the scale is so much smaller.

Normally this is not considered a big deal, but on high performance systems it does reduce imagary, and there are the techniques that can improve image by considering this aspect of power supplies, grounding and intereconnections. If, for example, you connect all screens at one end only (I would suggest the Amp) and bind everything with one, nice thick gauge bonding wire, then all possible paths of eddy curretns are removed, except for in the binding system ground wire (We call his a 'technical earth'). It's a shame the old practice of providing a chassis grounding screw (prevalent in the 50's and 60's) was lost- those guys knew what they were about!
This system ground need not be connected to mains earth, though if done safely it does give the system a real reference to the real ground that you, I and the rest of the world share. What I mean is that the entire system will not be then floating at what ever voltage gets induced on it through capactive linkage to the incoming mains through the power supplies".

John

[dantheman91]

Hi

Thanks for the Info well it seems its the sky box and cable was intefering. All fine with CD and DVD. It was a general question thats has been bugging me anyway have a few beers lads its FRIDAY.

[synsei]

Try installing some ferrite rings on the SKY box cables, might sort it ;)

[johnwhit]

Hi

Thanks for the Info well it seems its the sky box and cable was intefering. All fine with CD and DVD. It was a general question thats has been bugging me anyway have a few beers lads its FRIDAY.

As Dave says, ferrite rings may do the job, 8mm snap on type are quite cheap, or a double screened coax if its coming from a socket.

The beer's in the fridge chilling:cool:

John

[walpurgis]

If you can only hear faint hum or other noise from the speakers when no music is playing, I wouldn't worry, especially if it's an older amp.

Some amplifiers have higher levels of residual noise than others and of course what you hear depends on how sensitive (or not) your speakers are. A pair of Lowther horns will highlight the slightest noise from an amp whereas a pair of Celestion SL6 speakers will make your amp sound virtually silent.

Older amplifiers can have noisier backgrounds due to ageing components going out of tolerence and mechanical noise can come from ageing transformer laminations (and mountings) getting a bit loose.

[johnwhit]

Try installing some ferrite rings on the SKY box cables, might sort it ;)

I've had these in my watch list for a while as i was thinking of trying some:

http://www.ebay.co.uk/itm/390425624463?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

http://www.ebay.co.uk/itm/250724456936?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649

I've no connection to the seller.

John

[dantheman91]

Hey


Another question how can you tell when an amplifier giving out DC - Direct Current -.

[johnwhit]

Hey


Another question how can you tell when an amplifier giving out DC - Direct Current -.

Can you elaborate on that?

John

[dantheman91]

Hi
Direct Current.

I think its when the power supply gives out more than it should. Then the amp goes into clipping. it sounds like paper tearing. I think i have ansered my own question.

[Reffc]

Quite often, there's no earth lift within connected components and the resulting hum is the result of chassis current picked up from the circuit earth circuit circulated around the earth loop. One way to successfully break this (if you're handy with a soldering iron) is to install an earth lift within the preamp or the power amp. Its very simple and very safe since you retain all chassis earths and all mains earths (never lift a mains earth!).

Float (or disconnect and isolate from the chassis) the star earth point for the circuit earth. This is separate to the chassis earth in many cases. You then insert a bridge rectifier circuit (a few pounds) with a 100nF cap and a 10 Ohm resistor (both rated for mains voltage to be safe) in parallel with the bridge rectifier. Finally solder the DC output of the rectifier to the circuit earth (connecting both DC outputs together) and the AC side of the rectifier to the chassis earth point.

What this does is to raise the impedance of the earth path from the circuit (signal return) earth to the chassis earth to break the ground loop and eliminate the hum. In the event of a fault circuit, all components are fully protected by chassis earths connected to the mains ground.

Mains hum plagues many systems, but as above, the solution is very straight forwards. I have a similar issue with a croft preamp (no earth lift as these are fitted to the croft power amps and phonostages only) and for about £7, I've bought all the bits needed to make up the earth lift circuit which should cure the problem. "Inky black silences" ahead!

[walpurgis]

Hey


Another question how can you tell when an amplifier giving out DC - Direct Current -.

Yes, you can charge batteries with it!