I was following the recommendations at this page, if I understand correctly, they seem to be saying that above 50mV DC offset is not good, and recommend replacing the input differential pairs to fix it : Amplifier Distortion, DC-Offset, and You! - Home Audio Stereo Discussion Forums You're probably right about the electrolytic caps being worn out, I'll have to look into that. Many thanks in advance, looking forward to posting here in the future! Thanks for reading this, hope it wasn't too long. Hope this isn't a problem, maybe they'll help out someone else as well. They are actually RAR files, even though they say ZIP, as this was the only way I could upload them, so please RENAME them to RAR after download. They're not my actual unit, but mine is exactly the same, just less dusty. The owner's manual actually has a better schematic than the shop manual, all on one page. I've attached the service manual and owner's manuals as RAR files (rename them from zip to rar). If I were to replace the output transistors, what would you recommend as substitutes? They are 2 each of NEC 2sb618 and 2sd588. Would this indicate the power trasistors, or the BIAS supply? I felt the chips, and they weren't getting hot.Īnother thing I noticed is that when it starts distorting, the BIAS voltage drops to near zero.
The amp does seem to actually sound better, less distortion, though it still distorts at moderate to high volume. I'm wondering, will I damage anything doing this, should I put them back to where they were? I compromised at 23 mV BIAS for both channels, and now the DC offset is 40 mV for L, and 10 mV for R, which is better, less than half what they were. Is there something wrong here? I tried carefully adjusting them, but they only go to 30mV with the pots fully on, this doesn't seem right to me. In the manual it says should be 40 mV.(!). So I hooked up my voltmeter to the test points, and I got 4 mV on the L, and 8 mV on the R. On a related issue, I'm a bit confused about the BIAS adjustment In the service manual I found the section on BIAS adjustment, and I read online how it can affect the DC offset. Am I right in saying that to fix this I'd have to replace the output transistors? I understand this isn't so good for the L channel at least, but unfortunately this amp doesn't have any DC offset adjustments. I checked the DC offset at the speaker terminals, and the L channel said 100 mV, while the R was 25 mV. Upon using it a bit more, I noticed a bit of distortion at high volume, more so in the left channel. The other week I picked up a nice Kenwood KA-3500 40watt intergrated amplifier in pretty good shape. This is my first post here, so here goes.