Accuphase E204 DC offset / bias current adjustment

slam · 25th February 2009, 08:29 AM

Hi,

I am trying to adjust the bias current of my Accuphase e-204. In order to get the bias current to spec (44mv), I need to adjust STK 3082 out¡¦s DC offset to something totally off what the schematic says.

According to the schematic, the DS offset of STK 3082 output should be +/- 1.8V at idle. However here is what I got:

L (Pin 6, 5) +2.825V, -2.667V
R (Pin 11, 10)+2.957V, -2.179V

This is quite a lot more than 1.8 V. Also the difference between +ve and ¡Vve output (particularly on the R channel) worries me quite a bit.

I tried to swap Q4, C22, Q8 and Q12 between L and R channel and it basically makes no differences between the +ve/-ve values on the R channel. I also swapped STK 3082 to another one and it didn¡¦t make any differences.

However, the amp continues to play music and the output wave form seems to be OK. I also checked the capacity and ESR or all the caps and they seem to be OK.

Do you guys think these readings are normal? If not could you suggest ways to further troubleshoot the issue? Here is the schematic:

Thanks in advance!

bosedtobosed · 25th February 2009, 12:17 PM

the 44mv is across the o\ps resisters set that correct, dont worry what the ic o\ps are, they are what that amp measured in the factory and are not absolute values

slam · 25th February 2009, 04:39 PM

Thanks much for your reply. I am pretty new to this and am curious. I probably should measure it less enjoy it more

25th February 2009, 08:29 AM	#1
slam diyAudio Member Join Date: Jan 2005 Location: CA	Accuphase E204 DC offset / bias current adjustment Hi, I am trying to adjust the bias current of my Accuphase e-204. In order to get the bias current to spec (44mv), I need to adjust STK 3082 out¡¦s DC offset to something totally off what the schematic says. According to the schematic, the DS offset of STK 3082 output should be +/- 1.8V at idle. However here is what I got: L (Pin 6, 5) +2.825V, -2.667V R (Pin 11, 10)+2.957V, -2.179V This is quite a lot more than 1.8 V. Also the difference between +ve and ¡Vve output (particularly on the R channel) worries me quite a bit. I tried to swap Q4, C22, Q8 and Q12 between L and R channel and it basically makes no differences between the +ve/-ve values on the R channel. I also swapped STK 3082 to another one and it didn¡¦t make any differences. However, the amp continues to play music and the output wave form seems to be OK. I also checked the capacity and ESR or all the caps and they seem to be OK. Do you guys think these readings are normal? If not could you suggest ways to further troubleshoot the issue? Here is the schematic: Thanks in advance!

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25th February 2009, 12:17 PM	#2
bosedtobosed diyAudio Member Join Date: May 2008	the 44mv is across the o\ps resisters set that correct, dont worry what the ic o\ps are, they are what that amp measured in the factory and are not absolute values

25th February 2009, 04:39 PM	#3
slam diyAudio Member Join Date: Jan 2005 Location: CA	Thanks much for your reply. I am pretty new to this and am curious. I probably should measure it less enjoy it more