[diff_lock2]

I bought a cmoy amp off a fellow head-fier. I used it as long as i could, then it started buzzing.

So i took it apart, and tried to put it back together more or less the same way... Remember, that when i bought it was just fine. Now listen... (you gotta download the mp3...hope it works)

 

[diff_lock2]

For those who actually listen, im not playing with anything its doing that all on its own.

 

[Ikrit42]

We can be much more helpful if you post pictures-
Without them, we can't really know what might be the problem.

Was it doing this before you took it apart/reassembled it? If so, I take it you've tried replacing the battery?
Also, make sure that your opamp (the little black chip) is in the socket the right way... there should be alittle arking on one end that corresponds to a similar marking on the socket.

I'm not incredibly knowledgeable, but to me it sounds like a bad opamp. What do other people think?

 

[heatmizer]

fry the opamp?

 

[Joshatdot]

sounds like its shorting or had shorted on the tin metal. but my opa2227p fried/shorted differently, all I got out of it was white/pink noise. try another op-amp and make sure its not shorting on the tin.

 

[Sherwood]

Sounds like your opamp is seriously oscillating. If its mounted in a socket, try replacing it. Aside from that, it's tough to say.

 

[diff_lock2]

I would like to build my cmoy up again, but i have no idea how, i look at the schematics and see 2 problems, i have no idea how the polar caps (anything) are supposed to be wired, cause i don't know what is REALLY negative and whats REALLY positive.

And i can't find a scematic for a single opamp set up, every one just says double for each channel... wow that helps just double it.

 

[balou]

the electrolytic caps are labelled, should be no problem.

and you can't get stereo sound with a single opamp... you need a dual one. one chip, two opamps integrated. you most likely saw a schematic which show one half of the dual opamp in each channel

 

[diff_lock2]

Quote:

Originally Posted by balou /img/forum/go_quote.gif the electrolytic caps are labelled, should be no problem. and you can't get stereo sound with a single opamp... you need a dual one. one chip, two opamps integrated. you most likely saw a schematic which show one half of the dual opamp in each channel

Its a stereo opamp, and even though they are labeled, which way!? the marked side is neg... the REAL negative or the standard positive (red wire)....

 

[Ikrit42]

In schematics, the negative-marked/striped side of polar electrolytic caps is the curved side of the symbol, which is also the direction that conventional current will flow.
That is to say, electrons build up on the negative/striped side of the capacitor, and "positive charges" (which don't really exist) build up on the positive side of the capacitor.

Also, I'm not entirely sure what you're trying to do...
Are you trying to rebuild your cmoy on a new perfboard, from a schematic, using the parts from the old one?
Or are you just trying to reassemble it on the old perfboard?

If you're trying to build it again from "scratch", I'd use Tangent's guide: http://tangentsoft.net/audio/cmoy-tutorial/

Again, pictures are the most helpful thing you could give us.

 

[Pars]

It is also unclear as to whether you are using a dual opamp (ex. OPA2132, OPA2134, etc.) or two single opamps (OPA132, etc.). Chu Moy's original CMoy design on headwize used two single opamps (one for each channel), while Tangent's layout uses a single dual opamp for the L/R channels.

On a DIP-8 opamp, there is a notch on one end of the package. If you hold the opamp with the top up (pins down) and the notch to the left, pin 1 is the left most pin on the bottom row. If it is a dual opamp, power is usually to pin 8 (V+) and pin 4 (V-). Single opamps use pin 7 for V+ and pin 4 for V- usually. As always, check the datasheet for the particular opamp(s) you are using first.