Cmoy Build Problems

Aug 18, 2005 at 11:33 AM Thread Starter Post #1 of 25
Jama211

Jama211

Head-Fier
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Recently I built a headphone amp very similar to the Cmoy amp. It was built correctly (I checked everything) but when i hook it up, the noise is horribly grainy especially in the bass. The thing is it asks for a 15V power, and the only thing i had was a 9V battery, so i tried it with that. firstly is the lowered power from 15V to 9V the cause of the grainyness? Then i tried to wire 2 9V batteries in series to make 18V and it doesn't work! the next thing i tried was wiring 4 1.5V batteries and a 9V to make exactly 15V. it didn't work. if i ever try to wire any battery sequence in series, it doesn't work. i then tried 2 9V batteries, but this time i wired them in parrallel. it worked, but it was still quite grainy especially in the bass, and it was still clipping, and it got worse the louder i made it.
(obviously)

Why won't it let me wire the batteries in series?????

Im afraid i can't post a schematic because i only have a printed version and I don't have a scanner for a day or two
frown.gif
then i will post one.
I am using very cheap portable efficient headphones (Very cheap for the moment in case they blow up)
(later I will use my grado's)
i tried a line out from a hi-fi cd player and i also tried line out from portable cd player and line out from tape rec out from amplifier.
I am using a volume knob, and it would get grainy at about half way (Which isn't very loud at all.)
Unfortunatly I don't know the gain settings for the amp. (Is there an easy way to check?)
The crappyness of the headphones is not the source of the grainyness by the way.

Can anyone help me?
 
Aug 18, 2005 at 12:52 PM Post #4 of 25
Quote:

Originally Posted by Jama211
I am using a TL072 Dual op amp.



that is your problem.. that chip needs high voltage to work well with low impendance
 
Aug 18, 2005 at 1:39 PM Post #5 of 25
Quote:

Originally Posted by Jazper
that is your problem.. that chip needs high voltage to work well with low impendance


but when i try to up the voltage to 18V by connecting 2 9V batteries in series, it does not work.
 
Aug 18, 2005 at 1:43 PM Post #6 of 25
Quote:

Originally Posted by Jama211
but when i try to up the voltage to 18V by connecting 2 9V batteries in series, it does not work.


sounds like there's a problem with the circuit then..maybe with the way you're hooking up the 9v batteries?

are you connecting them (cmoy-) -> (-9v+) -> (-9v+) -> (cmoy+) ?
 
Aug 18, 2005 at 3:34 PM Post #8 of 25
yes i hook it up exactly like that. i then tried hooking everything up but the link between (-9V) and (+9V). i then bypassed one battery and it worked (in its low voltage - one battery kind of way) then i bypassed the other the same way and it worked in the same way. i had previously tested the link and its solders and they all work. but as soon as i attatch the link, it doesn't work. very strange. seems like the circut isn't accepting the higher voltage (18V instead of 15V)??? maybe its triggering some kind of protection cut off???? but i dont remember attaching any kind of protection against catastrophic failure except a 330 kOhm resistor.
 
Aug 18, 2005 at 4:05 PM Post #9 of 25
You keep saying two 9V batteries in series "doesn't work". What do you mean by that? To me it means you have a short in your circuit. Do this:
Put back the two 9V series batteries and turn the circuit on. Then measure the voltage across the batteries. If you don't get near 18V, you have some type of short in your circuitry (causing the circuit to draw too much current). A short will clamp the voltage way down and drain the batteries fast.This problem may not show up with the lower voltage (9V) but the short is still there. That's why the volume is so low at 9V. You need to recheck the circuit carefully.
 
Aug 19, 2005 at 3:11 AM Post #10 of 25
Quote:

Originally Posted by Excalibur
You keep saying two 9V batteries in series "doesn't work". What do you mean by that?


When i say doesn't work i hear a pop when i connect it together (through the phones) but no sound comes through.
it does sound very much like a short but i cant find anything. i will be able to post pictures of a schematic and of the item itself in a few hours.
thanks for all your help.
 
Aug 19, 2005 at 6:10 PM Post #12 of 25
That's not exactly a CMoy. Please post the schematic.
 
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