View Full Version : Music Angel valve pre-amp off ebay
HighFidelityGuy
01-07-2009, 15:04
After reading Jonners post about his Yaqin valve pre-amp that he bought off ebay, I had a look around ebay for something similar to try out and found THIS. (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWNX:IT&item=130304823077) I thought it looked quite nice, the price was good and there seemed to be plenty of spare space in the case for mods. I decided to go for the free ground delivery option to keep costs down. This is my first foray in valve equipment and I just wanted something cheap and upgradeable that I could tinker with and use as a learning tool.
After nearly 2 months of waiting it finaly got delivered today. Import tax only cost just over £15.
Overall the amp seems to be fairly well put together but I have found a few issues. To start with the supplied power cable had no fuse or earth connection, so that's going in the bin. There's also no fusing or earthing inside the amp that I can see, so that will need sorting out. The selector switches and volume pot have a cheap and nasty feel to them and the overall finish on the case isn't as good as in the photos on the auction. The paint is a bit lumpy and the wooden front is a bit over stained and has some imperfections. I'm not really bothered about the paint as it won't be visible once it's in my rack and I think I'll be able to improve the finish of the wood with some TLC.
I'm hopefully going to send the amp to AnthonyTD to get it checked over and have some mods applied. Unfortunately I don't know enough about electronics to know what's right and what's wrong, so I thought it was best to send it to an expert.
The mods I'm hoping to have done are to have the volume pot swapped for a motorised remote controllable version and to have one of the inputs changed so that it bypasses the volume control. I'll then connect the front channel pre-amp output on my AV amp to this input so I can use my power amps and main speakers for stereo and 5.1 without having to to swap wires etc.
I'll post some photos later tonight.
I read on ZG (I think it was) that the basic sonic flavour is big and beefy, but as you say, it definitely benefits from a pot upgrade at the very least and also from your comments above, getting the thing made safe for UK consumption.
AnthonyTD seems the perfect gent to send it to. I'd still avoid spending many hundreds on it though - a Croft at £750 would probably out-perform it - IMO of course...:)
I'll be interested to hear how you get on with this. That amp has caught my eye a couple of times now, and it's certainly cheap enough.
Could be a fun thing to play about with...
HighFidelityGuy
01-07-2009, 18:16
Here's some photos, click to make bigger:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2163.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view¤t=CIMG2163.jpg)http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2168.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view¤t=CIMG2168.jpg)http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2170.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view¤t=CIMG2170.jpg)http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2169.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view¤t=CIMG2169.jpg)
I've also noticed that the power socket has a built in fuse, so that's a bonus.
The gauge of the wiring looks good and the board itself also looks ok with half decent soldering, chunky track and reasonable components. A new volume pot and some tube rolling should work wonders I reckon.
Good luck...
HighFidelityGuy
02-07-2009, 21:26
Thanks Dave, I'm hoping it won't need too much work or expense to get it sounding good.
Since yesterday I've been doing some cosmetic work. After a lot of fiddling I finally managed to remove the front fascia. I had to disconnect the rods that connect the knobs to the volume pot etc. This would have been easy had the rods not been super-glued in place. :doh:
After removing the fascia I used some sand paper to remove the rest of the super-glue from the rods and brass bits and put a nice brushed finish on them.
I also removed the aluminium rings that sit around the knobs on the fascia. These were also glued in place and were a real pain to lever off without causing damage. I then had to soak the rings in hot water to soften up the excess glue so I could scrape it off. Luckily there wasn't any glue left on the wood.
I then started working on the fascia. I first cleaned up the knob recesses (oooer :lol:) with a chisel (ouch) to make sure the knobs turned smoothly. I then started rubbing down the wood to improve the finish. It seems that the wood is naturally a very strong red colour and wasn't over stained as I first thought. That's a shame as I was hoping to tone down the colour quite a lot but never mind. The lacquer finish has a lot of imperfections in it so I'll at least be able to smooth it up and put a propper wax finish on it.
So far I've only rubbed down the top and bottom edges and the left bevelled section.
Here's a photo of the work so far, click to make bigger:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/th_CIMG2171.jpg (http://s2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/?action=view¤t=CIMG2171.jpg)
That's it for now. :)
HighFidelityGuy
07-07-2009, 15:59
Just a quick update to say that I've been continuing to rub down the front panel and I'm currently about half way through. I've removed all the old lacquer and I'm working my way down through the sand paper grades to get a nice smooth finish. I'll post a picture when I've finished that part.
I've also been in touch with AnthonyTD and I'll hopefully be sending the amp to him in a week or two to get it checked over.
Hi Dave, any update on your Music Angel amp, either sonically or aesthetically? Looks an interesting project.
HighFidelityGuy
22-08-2009, 09:48
Hi Alex,
I've not had much time to work on it recently and I've kept finding other opportunities to spend my money on. I'm hoping to send the amp to Anthony TD next month to get the sonic and safety side sorted. I have nearly finished the front panel though so I'll hopefully be able to upload a photo of that soon. :)
HighFidelityGuy
26-08-2009, 13:54
Just a quick update to say that I've managed to get hold of some nice 60's Mullard valves over the last few weeks that should be better than the cheapo Chinese ones supplied with the amp. I've also found an ebay seller that sells ex-millitary Chinese valves and I've order a couple of the full-wave rectifier valves that the amp uses to keep as spares. They were only a couple of quid so I thought I might as well get them while I could. They've not arrived from China yet though. Unfortunately I had to get Chinese one's as no one else seems to make 6Z4 valves with 7 pins. :confused:
I think I've also managed to source some suitable parts to convert the volume control to a remote controlled version. I need to run this past Anthony TD first though before I go ordering anything as I don't know if I'll still need a 100K pot after he's finished changing things. Or if he can source anything better/cheaper.
That's it for now.
Thanks for the update - an interesting project, look forward to the developments.
HighFidelityGuy
05-01-2010, 12:54
Well I've not looked at this project for quite a while due to other things taking priority but as I couldn't get to work today due to the snow I decided to have a tinker.
I was planning on sending the amp to AnthonyTD to check over but I decided today that after giving it a good look over it looked safe enough to try turning on. Depending on it's level of functionality I may then still send it to Anthony to repair.
Upon flicking the switch nothing exploded and I got a nice subtle orange glow from the valves. Phew. After letting it warm up for a few minutes I checked the voltages from the transformer and compared them to what's written on the PCB.
There appear to be 4 power rails, 6.3V, 15V and 260V x2 according to what's written on the PCB. These read as follows on my multimeter: 6.75V, 8.98V, 255.6V and 255.4V. The last two seemed to be fluctuating by a few volts so I took a rough average.
Also if I measure between one of the mains terminals on the back of the IEC socket and the chassis, I get a reading of nearly 150V. :eek: But measuring from the other terminal I get a reading of about 7V.
So the 6.3V rail (heater supply I think) is a bit high and the others are a bit low. I also may have got a dangerous voltage running through the chassis and this doesn't seem to be connected to the IEC socket ground.
Does anyone know whether these results are good or not and how I may be able to resolve any problems?
Thanks. :)
It might be worth giving all the valve pins a good clean and then leaving it powered up for an hour or so. Re-check the voltages again once everything has settled down and see if there's still any fluctuations.
The earthing sounds a bit worrying though... :scratch:
Ali Tait
05-01-2010, 18:01
It does.Also that heater voltage is too high,it won't do your valves any favours.If you solve the other problem though,it may sort this.
anthonyTD
05-01-2010, 18:52
hi dave,
if the chassis is at true earth potential you should get a reading of the full mains if measured between the live terminal on the IEC socket and chassis, and a couple of volts between neutral and chassis [depending on how far away from the distribution transformer you are] if your not sure then dont connect it to any of your other equipment! music angel equipment is notorious for not having bonded earths to chassis, first,,,turn off the equipment and unplug it from the mains then check with a multi-meter on low ohms range between earth pin in IEC socket and chassis you should get a dead short reading, be carefull when checking things.
as ali has stated the heater voltage is too high which leads me to think that this is a 220v model.
hope this helps.
regards,anthony,TD...
CornishPasty
05-01-2010, 19:13
On my Lite Audio psu I have three trim pots to adjust the heater voltages and the B+. I see you have a trim pot on the psu of your pre. That will adjust the heater voltage or the B+. Shouldn't be to hard to find out which.
You will get a reading from the live pin of the IEC to chassis. Chassis will be connected to earth at some point. Can I see a wire from the earth terminal on the IEC going to maybe a mounting bolt on the transformer or something? The earth in the majority of domestic mains is connected to neutral at some point so if you put your meter between live and earth you will get a reading. I would expect to see full mains voltage across live/earth and virtually nothing across neutral/earth. If your domestic earthing arrangement is not up to scratch or you live in a farm house with a TT supply, that could explain those readings.
Maybe you're using some kind of mains conditioner? That would alter the earth reading at the preamp perhaps.
If you're in any doubt get the preamp checked over and maybe get an electrician to carry out an earth loop test on your mains.
Hope that helps.
Rare Bird
05-01-2010, 19:59
Well I've not looked at this project for quite a while due to other things taking priority but as I couldn't get to work today due to the snow I decided to have a tinker.
I was planning on sending the amp to AnthonyTD to check over but I decided today that after giving it a good look over it looked safe enough to try turning on. Depending on it's level of functionality I may then still send it to Anthony to repair.
Upon flicking the switch nothing exploded and I got a nice subtle orange glow from the valves. Phew. After letting it warm up for a few minutes I checked the voltages from the transformer and compared them to what's written on the PCB.
There appear to be 4 power rails, 6.3V, 15V and 260V x2 according to what's written on the PCB. These read as follows on my multimeter: 6.75V, 8.98V, 255.6V and 255.4V. The last two seemed to be fluctuating by a few volts so I took a rough average.
Also if I measure between one of the mains terminals on the back of the IEC socket and the chassis, I get a reading of nearly 150V. :eek: But measuring from the other terminal I get a reading of about 7V.
So the 6.3V rail (heater supply I think) is a bit high and the others are a bit low. I also may have got a dangerous voltage running through the chassis and this doesn't seem to be connected to the IEC socket ground.
Does anyone know whether these results are good or not and how I may be able to resolve any problems?
Thanks. :)
I recon your problem is the 220V primary on the mains transformer, i'd get a UK spec tranny made up..Looks a bit poor anyway.Chinese amps end up blowing up anyway
Ali Tait
05-01-2010, 20:46
I've had two,neither of which have blown up.You could try a bucking transformer,like this-
http://www.forum.diyhifisupply.com/viewtopic.php?f=4&t=12
Or check ebay for a variac.
Fixing that earth problem is the priority though.Check there is continuity between the earth pin in the IEC and the chassis.If not,run a wire from the pin inside to the chassis.
HighFidelityGuy
05-01-2010, 20:49
Thanks for all the replies. :)
I've cleaned all the pins on the valve and left it running for a while and the voltages are much more stable now but are still roughly what I read them as earlier.
On the subject of the earthing, there's no connection between the IEC socket earth pin and the chassis. So should I connect a wire to this and bolt it to the chassis with the usual earth bonding arrangement?
After closer inspection, when checking for a voltage between the neutral pin and the chassis I get a reading of 6.4V and between the live pin and the chassis I get a reading of 144V. So something odd is occurring there. :scratch: Would this simply be due to the chassis not being grounded or is there likely to be a short to ground going on somewhere?
To reply to the comments about my domestic wiring; I live in a 4 year old house built on a new estate, so the wiring should be decent. Also, the preamp is currently connected directly to the mains, no conditioners or surge protectors are being used.
On the subject of the heater voltage adjustment, I'm guessing you mean the little square blue pot next to the oval reg? If so then I guess the pot will control the output of the reg? The reg is outputting 6.14V dc. So if that's the heater voltage then it's actually a bit low, so that's not too bad. Hopefully I've got that bit right. If so I could try adjusting the pot to see if I can get 6.3V.
I'm a bit confused about the other voltages from the transformer being low. I did expect these to be high seen as it's likely a 220V transformer. What could be the reason for this?
Sorry for replying to everyone in one long post but it would have been a bit of a nightmare to quote each person.
Many thanks. :)
HighFidelityGuy
05-01-2010, 20:57
I've had two,neither of which have blown up.You could try a bucking transformer,like this-
http://www.forum.diyhifisupply.com/viewtopic.php?f=4&t=12
Or check ebay for a variac.
Fixing that earth problem is the priority though.Check there is continuity between the earth pin in the IEC and the chassis.If not,run a wire from the pin inside to the chassis.
Thanks Ali, that's useful to know. I currently seem to be getting the opposite problem at the moment, with my voltages mostly being too low, despite the mains input being over 235V at the moment. :scratch:
Rare Bird
05-01-2010, 21:06
If it's a 220V primary transformer it will get hotter than usually & will damage the transformer windings in the long run.
It would be good to have seperate transformer for The H.T & one for the heaters.you have room
HighFidelityGuy
05-01-2010, 21:10
Thanks Andre, I've just checked on the back of the amp and it definitely says 220V, so I'll look into Ali's suggestion as I guess that will cure the over heating problem and be cheaper than swapping the transformer.
Cheers. :)
Rare Bird
05-01-2010, 21:19
Thanks Ali, that's useful to know. I currently seem to be getting the opposite problem at the moment, with my voltages mostly being too low, despite the mains input being over 235V at the moment. :scratch:
Give phil a ring at Bluebell, he'll sort you a transformer out, best a proper transformer
http://www.bluebellaudio.com/
Ali Tait
05-01-2010, 21:24
Good suggestion.If you're not 100% happy making up your own and putting it in a box,get one from Bluebell.
Steve Toy
06-01-2010, 02:06
Send it to Anthony, better safe than sorry. Anthony does very safe.
HighFidelityGuy
06-01-2010, 16:21
Send it to Anthony, better safe than sorry. Anthony does very safe.
Hi Steve, I probably will do that soon but for now I want to see how far I can take it myself so I can learn some new skills.
Today I bolted an earth wire to the chassis and soldered it to the earth pin on the IEC connector. I then connected the amp up the PAT testing machine we have at work and it passed with flying colours. So it's as safe as the government think it should be and that's good enough for me for the purposes of my testing.
I've got another quick question; The 0V rail on the PCB is now connected to earth, I'm guessing via the chassis. I've got a feeling that the 0V rail shouldn't be connected to earth as the earth in many houses floats above true earth. So should I make sure that the 0V rail doesn't short to earth anywhere?
I'm guessing the culprit will be the phono sockets. They look like they're isolated from the chassis but I bet they're not properly.
Cheers. :)
I've got another quick question; The 0V rail on the PCB is now connected to earth, I'm guessing via the chassis. I've got a feeling that the 0V rail shouldn't be connected to earth as the earth in many houses floats above true earth. So should I make sure that the 0V rail doesn't short to earth anywhere?
I'm guessing the culprit will be the phono sockets. They look like they're isolated from the chassis but I bet they're not properly.
Cheers. :)
Float the 0V rail above the chassis earth via a 10R 3W resistor and keep the phono sockets insulated from the chassis. Then check that you see 10ohms between the 0V and the phono socket 'ground' side to the chassis earth...
HighFidelityGuy
06-01-2010, 16:34
I was wrong, it wasn't the phono connectors, they are isolated properly. The actual culprit was a wire that's purposely connected from the input selector switch board to the chassis. So they had purposely connected the 0V output of the transformer to the chassis but hadn't connected the mains earth to the chassis.
After removing the above mentioned connection the 0V rail and chassis/earth are now isolated from each other. So I know I can do this if I need to but I don't know if I should.
After removing the above mentioned connection the 0V rail and chassis/earth are now isolated from each other. So I know I can do this if I need to but I don't know if I should.
OK... I'd connect the 0V rail to the chassis earth via that 10R resistor now. :)
HighFidelityGuy
06-01-2010, 16:39
Float the 0V rail above the chassis earth via a 10R 3W resistor and keep the phono sockets insulated from the chassis. Then check that you see 10ohms between the 0V and the phono socket 'ground' side to the chassis earth...
Thanks Mike. I'll get that sorted asap. Unfortunately I don't think I have any 3W resistors spare so I'll have to make an order. Is there anything I could do in the mean time?
Cheers.
Got any 2W (or higher) resistors? Anything between 10R and 100R would do.
HighFidelityGuy
06-01-2010, 16:54
I'm not sure to be honest. I pilfer most of my components from work as they used to make some electronic products but no longer do, so they have lots of spare stuff that they'll never use. It's mostly low wattage stuff though so I'm not hopeful. I'll have a check tomorrow though.
So would it not be advisable for me to turn on the amp until I've got this sorted?
Cheers.
It shouldn't be dangerous or anything. But it sounds like the 0V rail is currently 'floating' and could cause all sorts of weird voltage variations.
Ali Tait
06-01-2010, 17:20
Yes agreed.Don't worry about using it,but as Mike says,it may be the cause of the weird voltages.
Ali Tait
06-01-2010, 17:20
Do you have a circuit diagram?
HighFidelityGuy
06-01-2010, 17:28
No circuit diagram I'm afraid. :( I've googled the subject but not come across anything other than a guy on one forum saying he had one, so I guess I could try getting in touch with him.
I reconnected the link between 0V and ground and fired her. It still seems to work fine and the voltages from the transformer are still as they were yesturday. However the readings between the live and neutral and earth are all as they should be now. So I've made some progress.
I also had a tinker with the pot that looked like it should control the heater voltage. I've now managed to set this so the reg is outputting 6.3V.
Incidentally, if you have to buy a resistor get a 0.1uF (50V or so) capacitor at the same time.
Put the cap accross the ground lift resistor to help prevent RF problems.
I reconnected the link between 0V and ground and fired her. It still seems to work fine and the voltages from the transformer are still as they were yesturday. However the readings between the live and neutral and earth are all as they should be now. So I've made some progress.
Are the voltages stable now, or still wandering about?
Tying the 0V to earth (which it needs to be) for now without a resistor will be fine. The ground lift resistor and bypass cap is mainly to reduce the possiblity of hum caused by earth loops.
HighFidelityGuy
06-01-2010, 19:16
Thanks mike, if WD get back to me soon and say they can sell me the phono stage PCB's then I'll order these bits at the same time as the bits for the phono stage to save on shipping.
The voltages do seem to be much more stable now. I'm getting 6.73V, 8.97V and the other two are around 255V. These last two do fluctuate a bit but by less than a volt.
To be a bit honest I'm a bit confused my the power supply in this. The 8.97V goes into a diode full wave rectifier and then powers the power on LED but doesn't seem to do anything else that I can see. The tube rectifier must be used to supply power to the other tubes. I'm not sure where the regulator for the heater voltage is getting it's input from. The reg gets very hot so it seems to be getting quite a lot of voltage.
Can anyone shed any light on how it all works?
HighFidelityGuy
07-01-2010, 11:04
Incidentally, if you have to buy a resistor get a 0.1uF (50V or so) capacitor at the same time.
Put the cap accross the ground lift resistor to help prevent RF problems.
Hi Mike,
I've had a rummage at work and I've found some 10R and 100R resistors. There's no info on wattage but they look like 2W to me, so that will do for now I guess. I had a look online and noticed a few people mentione using 100R so I'll use that unless you think 10R will be better.
I've also found various 0.1uF. I have 160V p/carb, 250V poly and 1000V p/prop. I'll be honest and say I have no idea what the abbreviations mean or what the difference is. Would any of these be suitable?
Cheers. :)
anthonyTD
07-01-2010, 12:05
hi dave,
all good advice from both mike and ali, glad you sorted the main earth bonding out first!
let us know if you find out why the +15v is so low.
regards,anthony,TD...
HighFidelityGuy
07-01-2010, 12:31
Hi Anthony,
I thought it would be best to get the ground sorted first for safety before I did any more poking around. The +15V is an odd one, like I mentioned before it only seems to power an LED via a rectifier stage but I guess something else could be connected to it under the board. The LED is getting 3V via a resistor so that seems like it's working correctly as the LED is nice and bright. I'll try and find out if anything else is powered of the +15V.
I also don't understand why the two +260V are low. I'd like to find out what voltage the valves are supposed to be getting so I can check that. The problem with that is I need to test under the board while it's powered and that may prove tricky without death by electrocution. I'll see what I can do.
Cheers. :)
anthonyTD
07-01-2010, 12:39
Hi Anthony,
I thought it would be best to get the ground sorted first for safety before I did any more poking around. The +15V is an odd one, like I mentioned before it only seems to power an LED via a rectifier stage but I guess something else could be connected to it under the board. The LED is getting 3V via a resistor so that seems like it's working correctly as the LED is nice and bright. I'll try and find out if anything else is powered of the +15V.
I also don't understand why the two +260V are low. I'd like to find out what voltage the valves are supposed to be getting so I can check that. The problem with that is I need to test under the board while it's powered and that may prove tricky without death by electrocution. I'll see what I can do.
Cheers. :)
hi dave,
ok, keep us posted, just be carefull, one arm behind the back etc when testing a live high voltage circuit etc.:)
A...
Hi Mike,
I've had a rummage at work and I've found some 10R and 100R resistors. There's no info on wattage but they look like 2W to me, so that will do for now I guess. I had a look online and noticed a few people mentione using 100R so I'll use that unless you think 10R will be better.
I've also found various 0.1uF. I have 160V p/carb, 250V poly and 1000V p/prop. I'll be honest and say I have no idea what the abbreviations mean or what the difference is. Would any of these be suitable?
Cheers. :)
Hi Dave,
100R and any of those caps would be fine. I'd go for the smallest! ;)
I also don't understand why the two +260V are low. I'd like to find out what voltage the valves are supposed to be getting so I can check that.
255V is plenty close enough, I'd not worry about that one as it's well within +/-10%. The 15V is very low though... :scratch: A schematic would be very helpful!
HighFidelityGuy
07-01-2010, 13:42
Right, I've done the resistor and cap thing. Does this look right:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/earth.jpg
Sorry about the quality I only had my iPhone to hand and it's camera is pants.
One end of the resistor goes directly to my new earth bolt and the other is directly soldered to the point where the 0V line from the transformer attaches to the PCB. According to my multimeter I get exactly 100.0R between the PCB 0V and the bolt. :cool:
Cheers. :)
Right, I've done the resistor and cap thing. Does this look right:
Yep! :)
HighFidelityGuy
07-01-2010, 14:04
Excellent. I've switched it back on and everything is still working.So I'm going to let it warm up while I grab a late lunch. Then I'll check the voltages again and see what's what. As I'm at work at the moment the mains input may be a bit different and I've also got a more accurate multimeter here, so it wlll be interesting to see what results I get.
Cheers. :)
HighFidelityGuy
07-01-2010, 14:46
Right, according to a fancy new Fluke meter I'm now getting approx 242V input from the mains. I get about 235-238V at home.
The voltages from the transformer are now, 263V, 263V, 7V and 9.3V.
So I've had an increase across the board but the +15V is still very low.
The point where the +15V connects to the PCB looks a bit shoddily soldered, so I'll try re-flowing that next to see if that helps.
In theory all the voltages from the transformer should be high as it's supposedly wired for 220V on the primary. So if I can get the +15V line to jump to over 15V I'd be much happier that everything was working as it should as I could then sort this out with a bucking transformer as suggested by Ali.
I'll report back later.
as it's supposedly wired for 220V on the primary.
I'm not so sure it is you know... :scratch:
The 260V figure is so close to what it should be. I'd expect it to be closer to 280 (or even more) if it was meant to work on 220V mains.
anthonyTD
07-01-2010, 15:06
I'm not so sure it is you know... :scratch:
The 260V figure is so close to what it should be. I'd expect it to be closer to 280 (or even more) if it was meant to work on 220V mains.
i agree with mike,
there seems to be something wierd going on there dave!:scratch:
A...
HighFidelityGuy
07-01-2010, 15:38
Well I've re-soldered the point where the +15V joins the board. It's in the middle of the diodes that make the bridge rectifier, so the diodes got re-soldered too. I also re-soldered the LED as that connection looked dodgy too.
The voltages from the transformer are all slightly higher again but the mains input also is, so that would explain that. I guess the mains fluctuates here. So the soldering on the +15V was obviously fine.
The bridge rectifier is outputting 10V dc and the LED is now getting 3.3V. Those figures seem so specific and round that I'm beginning to wonder if the +15V line isn't supposed to be 15V at all. I'm wondering if the design has been modified to allow a different transformer to be used with a lower output 3rd winding and still supply 3V to the LED. Perhaps they couldn't get a transformer with the right combination of windings so the got the closest and just changed the resistor before the LED. Is that a likely answer to the conundrum?
Cheers. :)
Ali Tait
07-01-2010, 15:45
Can you find one on ebay and see if it tells you what the current draw is?
I'm wondering if the design has been modified to allow a different transformer to be used with a lower output 3rd winding and still supply 3V to the LED. Perhaps they couldn't get a transformer with the right combination of windings so the got the closest and just changed the resistor before the LED. Is that a likely answer to the conundrum?
It just might! :)
Have you established if that supply feeds anything else?
HighFidelityGuy
07-01-2010, 17:10
Can you find one on ebay and see if it tells you what the current draw is?
I tested it on a clamp meter and that read approx 0.1A. I forget the exact figure as my boss told to go home straight after as it started snowing. I also managed to find an ebay seller who stated it's power consumption was 45W, so that tallies with my readings.
It just might! :)
Have you established if that supply feeds anything else?
Not yet I'm afraid, I'll try to have a better look under the PCB tomorrow.
Once I'd sorted out the grounding today I decided to do some basic testing with an oscilloscope to see if the amp actually did anything with a test signal. I'm happy to report that it seems to work quite nicely. With a 750mA 1KHz test tone it made a little over 5V RMS on the output on both channels at full volume. So it amplifies! Yay. :cool:The output looked nice and clean too.
With the volume set really low there was some noise but I'm not sure if it was bad or not. At least I know it works ok. The output seems rather high though. 5V RMS is double what most CD player etc make. So perhaps the gain is too high.
Anyway, I guess the next stage is to check that different parts of the circuit are getting the correct voltages and try and figure out if the +15V is used for anything else. I guess it will also be a good idea to make sure both channels are the same.
Is there anything else I should check?
Cheers. :)
'Scuse me butting in, but isn't this pre loosely based on the marantz 7 circuit? If so, then the input sensitivities may be rather low and set for older sources with 775mV nominal output..
Just a thought. Can you post some pics of the development of this unit, as it's not expensive..
HighFidelityGuy
07-01-2010, 21:08
Hi Dave,
That's a good point about the input sensitivity, I'll have to check that out.
On the subject of pics; I'll see what I can do. Not much has changed since the first pictures I posted other than the grounding work which is mostly shown in the pic I posted today.
Cheers.
HighFidelityGuy
08-01-2010, 14:19
Quick update:
Today I decided to take the PCB out of the case so I could have a close look at both sides.
It looks like the +15 supply powers the "power on" LED and the heater supply for the ECC82 and ECC83 valves. The output from the rectifier goes directly to the regulator where it gets dropped down to 6.3V. I don't think anything else runs off the +15. So that makes me less worried about the fact that the +15v is actually around +9V, as the LED works and I'm getting 6.3V out of the reg. The reg runs hot enough as it is without having to drop more volts.
On the subject of the reg. I removed it and applied some heatsink compound between it and it's heatsink before re-installing it. I'm hoping this will help it to keep a bit cooler. I've also re-soldered lots of components that had dodgy connections. The two large green caps behind the ECC83's were particularly bad.
I noticed that in several places small bit's of wire had been soldered into spare PCB holes to make rudimentary via's. These appeared to be pointless as components on the same track could be soldered on both sides of the board. So I removed these to tidy things up. It seems that none of the holes in the PCB that go between tracks on both sides of the board are plated inside to make them conductve. So I had to make sure that some components were soldered on both sides of the board. Hopefully I found all the places this needed doing.
I also gave the board a good clean as there were lots of little solder balls and flux all over it.
So now I need to put the board back in the case and test it again. I'll hopefully get that done this afternoon.
HighFidelityGuy
08-01-2010, 21:51
Well I managed to get the board back in the chassis. I also decided to replace three pairs of wires that ran under the board to distribute the heater supply. I used some standard 240V mains wire salvaged from a spare IEC lead I had laying around. I simply extracted the live and neutral wires and twisted them together. This made a lower resistance connection than the original ones.
It took quite a while to do the above so I didn't get chance to do much testing afterwards. It did turn on ok though and the +260V supplies were only just slightly high, so a bit better than before. The +6.3V supply was 6.9V and the +15V around 9V but as I mentioned before I don't think I need to worry about that last one.
I'll check it out on the scope next week to see if it's still fully working.
I'm a little worried that the AC heater supply to the rectifier tube is a bit too high, so I'd be grateful of any advice on how I could lower that to 6.3. I think a bucking transformer would probably lower all the voltages too much, so I think I'll need a solution that only affects the AC heater supply.
Any ideas anyone?
Cheers. :)
HighFidelityGuy
09-01-2010, 14:21
I managed to find some useful info on the full wave rectifier tube used in this amp.
It's tricky to find much info as the tube is only made in China and only seems to be used in Chinese made/designed equipment.
The tube is called a 6Z4 but it's not the same as the American made 6Z4.
Here's the info:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/6z4.jpg
I can't read Chinese but I think this means that the minimum heater voltage is 5.7V, maximum 7V and optimum 6.3V. As my AC heater supply to this valve is around 7V, I am a little worried that I'll burn it out quite quickly. As they're hard to come by, I want to make sure I keep them running as long as possible.
By the way, I found this picture on ebay on an auction for this tube.
I'd like to understand a bit more about heater voltages as I find it interesting that most tubes use 6.3V, whether it be DC or AC. Does anyone know the reason for it being 6.3V specifically and not a nicer round number like 6V or 7V. Also, will tubes that require 6.3V heater supplies run of either 6.3V AC or DC?
If so, would it be a good idea for me to run the 6Z4 tube of a regulated DC supply?
EDIT: Actually, could I not just run the 6Z4 tube's heater off the existing regulated DC supply that runs the other tubes? Or would this cause interference or something?
Cheers. :)
Ali Tait
09-01-2010, 14:48
6.3v is used because years ago a lot of valves were powered by battery,and a single lead-acid cell produces 2.1v,hence 6.3v from three calls.It's the same reason why the high voltage in a valve amp is called B+.B=battery.
Regulated supplies in general are a good idea.They certainly seem to improve sound.
HighFidelityGuy
09-01-2010, 18:03
Thanks Ali, that makes sense.
So is there any reason why I shouldn't run the rectifier tube off the same regulated heater supply as the other tubes?
Thanks. :)
Ali Tait
09-01-2010, 18:47
Yes.You would need to be sure that the winding can supply the needed current first.If not,you would burn out the transformer.
HighFidelityGuy
09-01-2010, 18:59
Ah, good point! Hmm, that will be tricky to establish as there's nothing written on the transformer. Is there any way I could find out how much current that winding could handle by measuring it some how?
Thanks.
Ali Tait
09-01-2010, 19:25
Given the cheap price,I doubt the trannie will be overspecced enough.I could be wrong though!
HighFidelityGuy
09-01-2010, 19:43
I've just been looking at all the ebay auctions for this amp to see if any provide transformer specs. I didn't find that but I did find this:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/schematic.jpg
Which is a nice bonus. :eyebrows:
I've been studying it at it seems to be correct as far as I can tell.
One bit I don't understand is the part that shows the +15V and +6.3V outputs. It looks like the +6.3V output is also used as a primary winding, with the +15V output being the secondary winding. I don't quite understand that. :scratch:
Does anyone know what's going on there?
Thanks. :)
Ali Tait
09-01-2010, 19:53
Nah both secondaries I think,just the way it's drawn.
HighFidelityGuy
09-01-2010, 23:21
Ok, so if the existing heater supply might not be able to cope with powering an extra tube, then I guess I should build a new regulated DC supply instead.
I found this schematic:
http://i2.photobucket.com/albums/y48/DTM2000/Hi-Fi/Valve%20Gear/Music%20Angel%20pre-amp/heaterschematic.png
My idea is to run this off the +6.3V output from the transformer and use it to run the heater on the rectifier tube.
The regulator is 5A which is overkill but that's ok. The bit I don't understand is the two resistors to the right of the regulator. I understand that they are to set the output of the reg and I'm guessing the two values written above relate to them but I don't know which resistor is supposed to be which value. Does anyone know?
Cheers. :)
Ali Tait
09-01-2010, 23:33
Not sure if it matters?
HighFidelityGuy
09-01-2010, 23:55
Ok, I did wonder if that was the case seen as the schematic wasn't specific but I thought I better check.
I'll try to get hold parts soon so I can build one to try out.
Cheers. :)
Ali Tait
09-01-2010, 23:57
Tentlabs and diyhifisupply do regulated supplies.Worth a look.
HighFidelityGuy
15-01-2010, 14:36
I've not really done anything else since the last update as I've been busy with other stuff but today I started thinking about the inputs and outputs and volume control etc. On the subject of the volume control, at the moment this is wired between the output on the PCB and the output sockets. From a sound quality point of view, is it best to have it there or between the input sockets and the input on the PCB?
Cheers. :)
tomatamot
23-01-2010, 11:14
I've not really done anything else since the last update as I've been busy with other stuff but today I started thinking about the inputs and outputs and volume control etc.
Cheers. :)
Hi, Dave how about your thinking?
I`m interested in your progress.
HighFidelityGuy
05-02-2010, 14:56
Hi,
I've not done much just recently but I have decided to leave the volume control on the output. I've been re-wiring the inputs and outputs and doing some tinkering with the volume control. This has helped me to understand a few things about the design.
Once I've finished my tinkering I'm going to finally get it hooked up to an amp and speakers so I can test out the sound quality. :eyebrows:
That's it for now. :)
Hi There - new to posting here (lurking member for some time). Tomek on PFM has one of these and did some basic mods to it - he is very happy with and has been using it for a few years now. On the back of that I also bought one (£80 delivered on the slow boat), but I got something that was the same externally but different internally (different cct board) and the 2 month lead time meant it was too late for a Paypal claim (buyer beware!). However, new selector, volume control and rewiring with a star earth scheme saw major benefits (with decent JJ tubes too) - I used it happily for around 2 years and am changing now only because I am experimenting with valve phono stages too.
You should hook it up for a listen!
Richard
HighFidelityGuy
08-02-2010, 12:38
Hi Richard,
I did a bit of research before I bought mine and read a few favorable reviews from owners that had performed a few basic mods like upgrading the volume pot etc, so I'm looking forward to finally hearing it. It shouldn't be long now until I'm ready to hook it up to a cheap test system. Then once I'm happy it's not going to kill speakers or something nasty like that I'll hook it up to my proper system.
Since my last post I've ordered an Alps Blue Velvet motorized pot off ebay to replace the existing volume pot. I went for a 100K Log version which should match the old one but be better quality. I went for the motorized version so I can add remote control functionality at a later date.
I could have gone for some fancy stepped ladder attenuator type thing or something like that but I wanted to keep the price sensible and make the whole thing as user friendly as possible. I'll post an update with pictures once I've got the pot.
I also tried out the amp with a full line level signal for the first time the other day. I used my Beresford 7520 DAC to feed it some 0dB sine waves to see how the output looked on a scope. Previously I'd just used the headphone output on my iPhone to check it worked. With the DAC feeding the preamp a full 2.5V RMS I got some nasty squaring off the wave peaks. By switching to the DAC's variable output I was able to find out that the preamp likes a maximum input of 1.5V RMS. Anything more that that starts to cause clipping.
Could anyone recommend a mod I could perform to make the preamp able to cope with 2.5V RMS input?
Cheers. :)
HighFidelityGuy
02-03-2010, 17:14
I finally got round to testing this out on my Hi-Fi, so I know what it sounds like now.
It's been a mixed bag of success and failure really. The Chinese valves that came with it sounded supprisingly good compared against my passive preamp. Switching out the Chinese ECC83's for a matched pair of 50's Mullards produced a small improvement but my Mullard ECC82 sounded really bad compared to the Chinese version. I don't think the triodes on the Mullard ECC82 are any where near matched, so I got much less volume from the left channel which screwed up the sound stage. I also tried a Siemens E82CC but that distorted the sound. I'm not sure what was wrong with that as it was supposedly a NOS valve and it's supposedly one of the best ECC82 versions available. :scratch:
I currently have another Mullard ECC82 installed which has matched triodes and that has improved the sound a bit more over the Chinese one. I've also got an RCA ECC82 with matched triodes to try as well.
Will the full set of good Mullards installed the sound is pretty good. I seem to get a bit more mid-range compared to my passive preamp but the sound stage is a bit narrower and there's a slightly compressed feel to the sound. So overall I still prefer the sound of my passive but I do like extra mid-range of the Music Angel.
I think I'm going to try a matched pair of 5751's next to see if they offer any improvements. I also like that these will provide less gain, as I can currently get a ridiculous output voltage which is way more than my power amps require.
I'm also going to look at incorporating some attenuation on the input to prevent the input from being distorted and further limiting the output. I'm hoping that this will help to run the amp at a more optimised middle ground, with the the volume control around the 12 O'clock position.
On the subject of the input attenuation, would anyone be able to tell me what the input impedance of this amp is from looking at the schematic I posted earlier? I believe I need to match the attenuation accordingly but I'm a bit unsure what values to go for. I'd be very grateful if someone could provide some guidance on this.
Cheers. :)
know it's been ten months since the last posting but ,
i have just aquired one of these and it would appear to be the same as you first posted I E no earth etc , so planning to follow your proccess as regards earthing etc :)
also do you still have it and are you using it etc ?
and have you tried any other valves ?
many htanks tommy
I know its an old thread but i have just bought one of these (ebay special + £60 delivery and a £18 customs bill! (about £170 total).
It came i set it up, i didn us the non fused kettle plug but used a fused version instead, it has a removable fuse on the power imputt connection too.
After a couple of songs I heard the sound loosing power then i head some fizzing as i got closer i smelt smoke. It turned it off straight away at the mains but the smoke carried on for four or five minutes, not plooming but certainly noticable with that vile electrical burning smell. I have emailed the vendor in hong kong but dont expect a reply till tomorrow.
Can you give me some ideas what this is likely to be and if I should attempt to rectify it? It will be a royal ball ache returning it and I see a major battle in reclaiming the postal charges.
Thanks
HighFidelityGuy
23-02-2011, 20:32
Oh dear. I'm sorry to hear about that. :(
The list is endless without seeing inside. Could you possibly post some photos of the inside, paying particular attention to anything that's burnt out?
I really don't recommend switching on these cheap Chinese amps until lots of safety checking has been done. They're not really something that can be seen as a finished product as the build quality is so low.
With any luck it's just some caps or resistors that have fried but I fear this could be a cooked transformer. :( I'll try my best to help you get it sorted though. :)
I never really got mine sorted to a good enough level for me to use it in my main system. It started to become a money pit. I'll finish it off one day.
Well I opened it up and it seems to be the transformer. How do you think a new unit could have reacted like this?
it will be a faulty transformer ...
get a replacment from rs or farnel ...might have to buy two to get the voltages you need ...as I remember theres a lot of space in the case ...
I bought one of these about 5yrs ago ...
swapped out the whole of the input and vol pot, replaced it with a relay switched input and stepped attenuator ....
fantastic sound for the cost [less than £100]
but then picked up a beard active passive pre ....which was really a lot better ..[well it should be at about 10x the cost ..back in the mid 80's ish]
HighFidelityGuy
24-02-2011, 14:33
The tricky part here is the question of; Did the transformer die because it was faulty it's self or because the circuit it's connected to is badly wired. If it's the latter then you'll just end up burning out the new transformer.
Really the whole thing needs checking against the schematic I posted earlier in the thread and all the solder joints need checking on both sides of the board. Then you need a new transformer/s and the earthing needs sorting out. That's just to get it working. Then you'll probably need to spend more money and time on mods to get it sounding good. Or alternatively you need to ask the seller for your money back. To be honest based on my experience I'd go for the latter. :(
The vendor responded last thursday and offered to replace or send me a new transformer. I decided on the expensive and less hasstle option, to get a new transformer and replace it myself.
I hope it wasnt a short somewhere else other than the transformer itself...
I would have accepted the offer of one to be sent ...then try and source yourown ...win win !
Reid Malenfant
02-03-2011, 15:29
The tricky part here is the question of; Did the transformer die because it was faulty it's self or because the circuit it's connected to is badly wired. If it's the latter then you'll just end up burning out the new transformer.
The transformer failed because it was only rated at 220V ;) It obviously put out a higher voltage due to the turns ratio & this caused the whole amplifier to draw more current than normal. The end result was that with the over current draw & a significant increase in magnetising current just to add insult to injury - it burnt out.
What you need is a transformer rated for use in the UK & not China or Hong Kong :)
simples
HighFidelityGuy
03-03-2011, 14:09
The transformer failed because it was only rated at 220V ;) It obviously put out a higher voltage due to the turns ratio & this caused the whole amplifier to draw more current than normal. The end result was that with the over current draw & a significant increase in magnetising current just to add insult to injury - it burnt out.
What you need is a transformer rated for use in the UK & not China or Hong Kong :)
simples
That's a possibility but my version of this amp says 220V on the back but it's transformer puts out almost exactly the voltages written on the PCB. That's one of the problems though, the manufacturers are constantly changing the parts they use. So sometimes you fall lucky and get one that mostly works, other times you get one that blows up the moment you turn it on. They don't really do consistancy and quality control. To be honest I don't even think they try turning on most of them before they ship them out. :(
Reid Malenfant
03-03-2011, 14:13
It could also depend on how far you are from a substation :) I'm on top of one & have seen over 250V AC this way, it's regularly in the high 240s. At a distance it may well be nearer 230V which would obviously be a good bit safer :eyebrows:
HighFidelityGuy
04-03-2011, 13:23
It could also depend on how far you are from a substation :) I'm on top of one & have seen over 250V AC this way, it's regularly in the high 240s. At a distance it may well be nearer 230V which would obviously be a good bit safer :eyebrows:
That's a very good point. I usually get quite close to 240V at home, so I'm nicely in the middle. :)
Thanks for the feedback
The replacement transformer still hasnt arrived, a little irratating as I paid for air freight yet hes clearly put it on the boat!
Im thinking about buying a transformer myself, any recomendations?
thanks
Powered by vBulletin® Version 4.2.3 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.