Adcom GFA 545 DC offset

seebert · 15th October 2011, 09:11 AM

Hi all. I know DC offset has been done to death here but ...

I just pulled my old Adcom 545 (not the MKII) out for a listen and it sounded just fine, but seeing that it hasn't been used for about 5 months (and being curious as usual) I checked the bias and it was a bit off, not much but I took it back to 6.2mv between TP1 and TP2 using the standard 'crumby' type pot 601 - as close to 6.5 as I could get.

On checking DC offset (no signal - no speakers) however I got 36.4mV left and a whopping 141.7mV on the right channel. Oddly no distortion or loss of ambience on well-known recordings, nothing audible to me at all. I don't want to go to a new matched pair right now so asking : is it okay do you think to go on using the amp with this much offset?

No overheating, no oddities at all, just 'bad' numbers.

Thanks in advance and good listening, Mike.

audiofan · 15th October 2011, 12:30 PM

I would leave the amp ON for a few days ( without load ) and check later after all capacitors had time to form again, moisture had time to get out and everything get to operating tempereature for manay hours.

no cost at all, no risk after that if still some offset try to calibrate again.

seebert · 15th October 2011, 03:40 PM

Many thanks, I'll do that. Best reagrds, Mike.

15th October 2011, 09:11 AM	#1
seebert diyAudio Member Join Date: Sep 2011 Location: Colorado	Adcom GFA 545 DC offset Hi all. I know DC offset has been done to death here but ... I just pulled my old Adcom 545 (not the MKII) out for a listen and it sounded just fine, but seeing that it hasn't been used for about 5 months (and being curious as usual) I checked the bias and it was a bit off, not much but I took it back to 6.2mv between TP1 and TP2 using the standard 'crumby' type pot 601 - as close to 6.5 as I could get. On checking DC offset (no signal - no speakers) however I got 36.4mV left and a whopping 141.7mV on the right channel. Oddly no distortion or loss of ambience on well-known recordings, nothing audible to me at all. I don't want to go to a new matched pair right now so asking : is it okay do you think to go on using the amp with this much offset? No overheating, no oddities at all, just 'bad' numbers. Thanks in advance and good listening, Mike.

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15th October 2011, 12:30 PM	#2
audiofan diyAudio Member Join Date: May 2003 Location: quebec	I would leave the amp ON for a few days ( without load ) and check later after all capacitors had time to form again, moisture had time to get out and everything get to operating tempereature for manay hours. no cost at all, no risk after that if still some offset try to calibrate again.

15th October 2011, 03:40 PM	#3
seebert diyAudio Member Join Date: Sep 2011 Location: Colorado	Many thanks, I'll do that. Best reagrds, Mike.

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