jess28 Posted March 18, 2012 Share Posted March 18, 2012 picked up a dmm to check the offset gettiing readings of r ch - 36.8 l ch - 26.3 it's a cheap dmm testing voltage setting 200m it shouldnt have a - ? my nad with the pre amp problem reads 0.00 both channels what am i if anything doing wrong thanks ahead of time i know I'm posting alot of question but alot of you guys have been such a big help and have tons of knowledge i dont posses yet Quote Link to comment Share on other sites More sharing options...
jess28 Posted March 18, 2012 Author Share Posted March 18, 2012 been checking out the service manual and it says to set the bias to +- 16 mv so its amost double on the l ch and more than double on the left i guess i should have it fixed i've been reading that as long as its under 50mv i wont damage speakers but may be losing some sound quality maybe thats why it doesnt sound a good as my other 555s Quote Link to comment Share on other sites More sharing options...
djk Posted March 19, 2012 Share Posted March 19, 2012 You're confusing bias with off-set. I don't worry unless it is over ±100mV or so. On A GFA555 the off-set should cut in half if you add a 10K~22K resistor across the input to ground. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted March 19, 2012 Share Posted March 19, 2012 picked up a dmm to check the offset gettiing readings of r ch - 36.8 l ch - 26.3 it's a cheap dmm testing voltage setting 200m it shouldnt have a - ? my nad with the pre amp problem reads 0.00 both channels what am i if anything doing wrong thanks ahead of time i know I'm posting alot of question but alot of you guys have been such a big help and have tons of knowledge i dont posses yet When checking DC offset, are you doing it with the speakers disconnected? In my experience it's not always as low as desired, but below 50 mv I wouldn't be overly concerned. How much does it vary between initial turn-on and, say, an hour later? Btw, I'm also in Hunterdon County in case you ever need any help. Regards-- Maynard Quote Link to comment Share on other sites More sharing options...
jess28 Posted March 19, 2012 Author Share Posted March 19, 2012 Yes,Speakers disconnected. I was searching about checking dc offset for the 555 the consensus seemed to be to test with no load so I didn't get any resistors The reason I was concerened is I just bought the amp I always pop the top and look for any physical signs of distress And I found the left channel fuses wrapped in foil . Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted March 19, 2012 Share Posted March 19, 2012 Yes,Speakers disconnected. I was searching about checking dc offset for the 555 the consensus seemed to be to test with no load so I didn't get any resistors The reason I was concerened is I just bought the amp I always pop the top and look for any physical signs of distress And I found the left channel fuses wrapped in foil . Yes, finding fuses wrapped in foil would raise my eyebrows also; but, I've seen worse over the years! Since you have the service manual, and seem familiar with taking measurements, I'd turn on the amp and start verifying voltages after it has been on for an hour. Check the DC offset again (as you are doing it, with no load), verify the bias and adjust it accordingly, and check the power supply rail voltages. If all is well, I'd just enjoy the amp. Quote Link to comment Share on other sites More sharing options...
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