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Old 16th July 2012, 07:09 PM   #1
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Talking Channel Distortion

Hello friends,

To make it quick i have just repaired a c-audio sr606 so that it now runs and stays out of protect.

My main issue is that on the left channel i have distortion as i reach higher volumes. This doesnt matter whether i turn the input up and the channel down and vice versa.

I ran some music with loads on terminals and measured the ac.
Right channel about 90v full power.
Left channel abotu 40v full power plus very distorted.

Im guessing that something has either gone in the input stage or driver stage as the fets seemed to test ok and i dont have any dc at idle. Im sure with a meter i would find only half of the output waveform, but i dont have one right now.

SO distortion and half dc voltage hmmmmm.....

Oh ive noticed that the distortion is only really in the bass end of the spectrum im sure i ran it high pass and it sounded ok.

Cheers

Last edited by sketchyphish; 16th July 2012 at 07:19 PM. Reason: Remembered something
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Old 10th October 2012, 09:50 AM   #2
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Talking Tests done

Right o to follow up ive checked the rails, caps and changed the input ic's. Still having issues with the output.
Have now checked the output voltage with a 100hz sine and can confirm at the same volume level the right channel outputs 7.5v and the left only outputs 6.5v.
Im sure i will probably have to take out each of the transistors and check them but i would like some more advice before dismatling the amp.
Also checked the gate resistors against the other channel and they all match.
So either i have a driver issue or a o/p transistor issue.
Tried to contact Lee on this too but no reply.

PLEASE if anyone has any advice can you help as id really like to solve this issue without paying someone else to look at it and charge me the earth for what could be a simple issue.

Next i willbe putting a osc on it to check the output waveform and work my way back through the board (but im not and expert on where i need to check).

Thanks again
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Old 10th October 2012, 05:32 PM   #3
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by sketchyphish View Post
Next i willbe putting a osc on it to check the output waveform and work my way back through the board (but im not and expert on where i need to check).
A logical approach.

You have a working channel to compare the measurements of the faulty channel against. Supply both channels with the same signal and trace both from the input to the output. Where signal in the faulty channels deviates from the good channel is probably where the fault is. The next job will be finding out what the fault is.

From this end of the keyboard, there's not much else that we can do. For trying to offer suggestions, we would at least need schematics and measurements, and even then it can be hard to give advice as this thread will show.

Last edited by jitter; 10th October 2012 at 05:37 PM.
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Old 11th October 2012, 09:58 AM   #4
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Talking Solved

Right o me and a friend went over it with a meter and i believe we have found the issue.
The sine running out of the channel was clipping on the negative side.
Found one transistor with a snapped centre let, probably from having the board in and out over the last few years.
Then traced problem to 9v1 diode in i guess the protection network which had gone open an probably started conducting.
The rest is history.

SO problem solved, brobably blew the diode when the gate drivers went.
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Old 11th October 2012, 05:02 PM   #5
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by sketchyphish View Post
The sine running out of the channel was clipping on the negative side.
Kinda what I expected.

Quote:
Found one transistor with a snapped centre let, probably from having the board in and out over the last few years.
Then traced problem to 9v1 diode in i guess the protection network which had gone open an probably started conducting.
Good to know you fixed it!
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