Troubleshooting my cmoy PSU
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Migroo

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Hi everyone.

I've built my cmoy!


However, theres a problem - music is quiet through the left headphone and a good level through the right.

I measured the voltage between + and ground and - and ground, and theres a difference. + to ground is around 1.3 volts, while - to ground is around -7.7 volts. Obviously theres a solder bridge somewhere but I can't see/find it!!

The PSU section was completely fine before with 4.5 and -4.5 volts showing for either side of it respectively when tested.

After putting the remainder of the amp if I've got the problem.

I know I can't really get much help with this, and I'll just have to find it, but I need to know if the problem is going to be around the PSU section or wether it could be anywhere?

All the PSU connections look good, and the main op-amp hook up wires (and connections look fine).

Any tips would be great. I've been following Tangent's guide FWIW.

Cheers
C
 
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n_maher

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Take some good close up shots of both the underside of the board and the top side and odds are someone here will spot the issue. If you had the power section assembled and working it's probably pretty minor.

In the mean time check double check all of your wiring, jumpers and connections. I know it seems obvious but I can't keep track of the number of times that I've found amazingly simply and stupid solutions to the problems I was having.

Best of luck and don't worry, we'll get you up and running soon.

Nate
 
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Pars

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Take a look at this post, and also use the search function, as there are a ton of CMoy troubleshooting threads. Your voltage imbalance is a symptom of the inherent weaknesses in the CMoy voltage divider PSU, but yours seem to be extreme. A voltage difference of a few millivolts or tenths of a volt is normal. See the article on ground schemes on Tangent's site for more info.

This is of course not to say that the CMoy won't work, cuz it does, and its an excellent starter amp. Good luck and have fun, and do as Nate suggested by posting some pics, as its alot easier to help if you have something to look at.
 
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The Monkey

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Another one of those obvious but deadly errors is miswiring the jacks. I did this the other day and couldn't for the life of me figure out why no sound was coming out of the right channel. That is until I realized I had soldered the right channel to the wrong lugs on the jacks. The voltage symptoms you describe seem to be a solder bridge, but you might as well check everything. Keep us posted as your solution will likely help others.
 
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Migroo

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Hi guys.

Many thanks for the responses.

I've had another check this morning and nothing changed (Although for some reason at one point I had a 4.5 / -4.5 PSU split but it was short lived...
Obviously a bad joint somewhere - which I'll try to fix.

Here are some pictures - beware they are rather large..
cmoy from the front/left
cmoy from the back
cmoy tracks

Sorry about the lack of focus in some pics - its the best I could get. Note- the black wires go to the headphone out jack (which is fine as far as I can tell). I'm using croc clips for input at the moment.
 
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Migroo

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I've had a look at the tracks with a magnifying glass and I can't see any bridges (in the wrong place) whatsoever.

How do I clean flux from the board? - I did a search and apparently it can be conductive.

I also measured the impedance of the resistors (R1) in paralell with the PSU capacitors. They aren't 4.7K ohm according to my (cheapsh!t) meter - but they are both 3.66K ohm.. this could be a mis reading by the meter.. either way, are they likely to cause the problem (seeing as both are the same impedance?)

Thanks for any help.
 
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Fresno Bob

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you can try desoldring braid ,which if done right should clean up some of the over solder if you have any. I'm sure some of the more better builders will have a better answer for you.
 
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Migroo

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Thanks. I don't think I have (any) oversolder but I'll get my Dad (major electronics geek to take a look later)..
 
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Migroo

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It works!!

I don't know what I did - I just hooked it up again (the same way). Anyway the PSU is now at 4.3 and -4.6 volts so not too bad. I can't hear a volume difference in the left and right


I can't belive how good it sounds compared to the normal headphone out on my minidisk!! Definately worth doing even if its only a learning exercise!

PS: I know what a good headamp sounds like as I've got a modded xcans.



So far I've tried it with my little senn buds and some HD-25s - which sound rather good (although you can tell when it starts to run out of power).

Thanks to everyone, and to tangent's guide.
 
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skyskraper

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cleaning flux = isopropyl alcohol + brush
 
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Migroo

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Cool, thanks. Definately something to do.
 
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