[streetknight]

ok after searching and 173 threads later, I am posting a questions i cant get answered. i just finshed my first cmoy amp, and i think i have a problem. after testing it and checking all the wires and solding points i tested it with a cdplayer and i can not tell any difference in sound. i followed the assembaly guide and to the point. my question is how can i check if my amp is working?

 

[Sinbios]

if there's sound, then it's working.

 

[Cmoyamphelp]

well let me say this it isn't working,I know i had the same prob,make sure that all your risistors are the right value and POST PIC's,

You would know 100% if it was working,

 

[streetknight]

i get sound even if i dont have the opamp pluged in. i have a Volume control, Panasonic 10K horizontal mount (EVJ-C20), and i can adjust volume but when i go low almost near its full turn i cant hear my right head phone.
also i came to the point of thinking its not working when i unpluged it and tried it straight thru the cd player and it sounded the same. i will post pics later tonight wheni get home.i have checked all the system and it looks like it should be working but i get not noticible difference.

 

[d00dz]

If you get sound even if the opamp is not plugged in, you have a problem...the only way that I can see happening is if your left & right channels are somehow shorted through the amp...

please post some pictures.

 

[james902]

hmm... when the amp is off... i get absolutely no sound

 

[sbelyo]

There is a short somewhere in the amp.

Check with a meter to make sure nothing is grounded that shouldn't be

Also, did you use the standard values on all the components?

 

[streetknight]

heres some pics i have checked most of the circuts and can't seem to find any problems yet

 

[Pars]

Quote:

Originally Posted by Sinbios if there's sound, then it's working.

Wrong. Sound without an increase in volume (large, for a CMoy with 11 gain) , etc. means that somehow the input is shorted to the output.

streetknight: look at Tangent's guide regarding R5... it is EITHER a resistor, OR a jumper (meaning, you put a wire in place of the resistor). You have nothing there. When looking at the schematic, you basically have the feedback loop open because of this, meaning the opamp is doing nothing, and the amp will not work. You would get no sound (unless there is a short from your input somewhere to the output, which would give you the "sounds kinda the same". A working CMoy at a gain of 11 will blow your ears out at full volume, so it isn't subtle whether it is working or not

).

 

[streetknight]

streetknight: look at Tangent's guide regarding R5... it is EITHER a resistor, OR a jumper (meaning, you put a wire in place of the resistor). You have nothing there. When looking at the schematic, you basically have the feedback loop open because of this, meaning the opamp is doing nothing, and the amp will not work. You would get no sound (unless there is a short from your input somewhere to the output, which would give you the "sounds kinda the same". A working CMoy at a gain of 11 will blow your ears out at full volume, so it isn't subtle whether it is working or not

).[/QUOTE]

thanks read it again and i missed that part.

 

[Pars]

Sory, I don't feel like editing pic right now. See your R4 resistor (the 10K, I think from memory), that runs from the opamp out to the edge of the board). On one channel this runs from pin 2 on the opamp, the other side from pin 6. R5 on each side runs from pin 1 and pin 7 on each side, out to the board edge. Look at Tangent's guide again. put a wire in, or a low ohm resistor (100 ohms or less). Parallel to your R4 resistors.

 

[streetknight]

ok just fixed it. now another q. i am running my beyer 250-250ohm what resistor should i add?

 

[sbelyo]

Try 50 ohms or so....

I just built one the other day and I use 25 Ohms and it thumps!!! with my AKG K271S phones.