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-   -   put my pre-amp together and now the left channel is playing distorted :( (http://www.diyaudio.com/forums/solid-state/13256-put-my-pre-amp-together-now-left-channel-playing-distorted.html)

elizard 2nd April 2003 06:17 AM

put my pre-amp together and now the left channel is playing distorted :(
 
Hey guys. I just finished putting together the preamp, and it works, however the left channel gets distorted as the volume is turned past about 1/3 of the way, while the right channel plays just fine even at highest levels.
I tried both the headphones and the speakers, both act the same. As well, I've tried all 4 inputs, and on all 4 the left channel is distorted. I tried switching cables - that didn't fix anything (cable for CD in). I've also tried switching the IC's for the left and right channel, and that does the same thing ..
I've absolutely no clue what it could be. I don't see any obvious soldering faults on the left channel PCB, or on the main PCB.
Do you have any ideas as to what it might be? Or any further suggestions as to what I should check out?

The info, manual, and schematics for the pre-amp can be found at http://www.velleman.be/Product.asp?lan=1&id=342550
Also, the left inputs are contained on their own PCB, but the rest is on the main pcb.

elizard 2nd April 2003 06:23 AM

well i just checked something .. while playing through the amp, i touched the IC (opamp i guess?) that's used for the left channel, and it was warm - getting hotter
i touched the one for right channel (the channel that plays fine) and it was cold .. no hotness whatsoever
does that mean anything?

Netlist 2nd April 2003 06:45 AM

Which opamp is running hot? Position number? Opamp number?
You have a scope?

/Hugo

elizard 2nd April 2003 06:51 AM

Unfortunately the only test equipment I have is a multimeter.

The op-amp number is TLE2071, and its the IC2 position (the one for the left channel).
As I said, I tried swapping the two TLE2071's, and same thing happens. Also, when I don't run the input into the left channel, the op-amp stays cold.

seangoesbonk 2nd April 2003 07:01 AM

Quote:

Originally posted by elizard
Also, when I don't run the input into the left channel, the op-amp stays cold.
If it stays cold when you don't feed it a signal but it gets real hot when you do, maybe it's gain setting is incorrect.

You say that it doesn't distort until the vol is 1/3 of the way up. Is the volume about the same as the right channel before it starts to distort?

Double-check all the components surrounding IC2.

Good luck and keep us posted.

Tomo 2nd April 2003 07:03 AM

Hey,

Did you check your DC offset? You are probably hitting the rail voltage. Also, check the soldering around your IC2. You may also have some shorts etc.

Tomo

elizard 2nd April 2003 07:04 AM

Quote:

Originally posted by seangoesbonk

If it stays cold when you don't feed it a signal but it gets real hot when you do, maybe it's gain setting is incorrect.

You say that it doesn't distort until the vol is 1/3 of the way up. Is the volume about the same as the right channel before it starts to distort?

Double-check all the components surrounding IC2.

Good luck and keep us posted.


well the distortion is not obvious until about 1/3 of the way up .. i just listened some more, seems to be there from the start ..
the volume of both channels is the same mostly .. once the left channel starts distorting its volume seems to drop a little ..

also it doesn't get real hot when i feed it signal .. it gets hotter than the right channel .. the right channel stays completely cold, while the left warms up ..

i've looked at everything that's around ic2 .. seems to be ok ..
there doesn't seem to be any contact between 2 solder points (accidental) .. everything seems to be in check ..
seems of course .. it is 2 am, and its easy to miss stuff when i'm tired like this

elizard 2nd April 2003 07:06 AM

Quote:

Originally posted by Tomo
Hey,

Did you check your DC offset? You are probably hitting the rail voltage. Also, check the soldering around your IC2. You may also have some shorts etc.

Tomo


well there's a 0V offset trimmer for left, and for right channels (separate)
i measured both .. got them to about between 0 and 0.2 mV
i measured it while i was feeding a signal, it goes up to 1.0mV at MOST ..
btw, in the diagram, that's the voltage between ground and J8 (for left, J9 for right) .. and I use the pot found beside IC2/IC3

elizard 2nd April 2003 07:10 AM

well i think i'll hit the sack now .. too tired to even see straight, gonna keep on working on it tomorrow though

PLEASE PLEASE keep suggestions flowing .. i hate this, but i know its a part of diy stuff ..

on a brighter note, i am VERY satisfied with the right channel output i'm getting as observed with my headphones ..
its VERY clean .. compared to the cheapo sony receiver i have right now (yuck) ..
very clean, no annoying hum .. just amazing switching between the two :)
QUITE the difference ..

and i'll be even more pleased when i fix it! :)

thanks guys

Netlist 2nd April 2003 07:22 AM

Quote:

Originally posted by elizard
well i think i'll hit the sack now .. too tired to even see straight, gonna keep on working on it tomorrow though


Best thing to do. Get some good sleep; I'm sure you'll fix it tomorrow.

/Hugo - will keep his coffee ready.


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