Hi all,
This is my first post here, so here goes...
The other week I picked up a nice Kenwood KA-3500 40watt intergrated amplifier in pretty good shape.
Upon using it a bit more, I noticed a bit of distortion at high volume, more so in the left channel. I checked the DC offset at the speaker terminals, and the L channel said 100 mV, while the R was 25 mV. I understand this isn't so good for the L channel at least, but unfortunately this amp doesn't have any DC offset adjustments. Am I right in saying that to fix this I'd have to replace the output transistors?
--
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. So I hooked up my voltmeter to the test points, and I got 4 mV on the L, and 8 mV on the R. In the manual it says should be 40 mV.....(!). 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.
--
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. I'm wondering, will I damage anything doing this, should I put them back to where they were?
The amp does seem to actually sound better, less distortion, though it still distorts at moderate to high volume. I felt the chips, and they weren't getting hot.
Another thing I noticed is that when it starts distorting, the BIAS voltage drops to near zero. Would this indicate the power trasistors, or the BIAS supply?
If I were to replace the output transistors, what would you recommend as substitutes? They are 2 each of NEC 2sb618 and 2sd588.
--
I've attached the service manual and owner's manuals as RAR files (rename them from zip to rar). The owner's manual actually has a better schematic than the shop manual, all on one page. I've also included some pictures. They're not my actual unit, but mine is exactly the same, just less dusty.....
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. Hope this isn't a problem, maybe they'll help out someone else as well........
Thanks for reading this, hope it wasn't too long. Many thanks in advance, looking forward to posting here in the future!
All the best,
Bellarmine
This is my first post here, so here goes...
The other week I picked up a nice Kenwood KA-3500 40watt intergrated amplifier in pretty good shape.
Upon using it a bit more, I noticed a bit of distortion at high volume, more so in the left channel. I checked the DC offset at the speaker terminals, and the L channel said 100 mV, while the R was 25 mV. I understand this isn't so good for the L channel at least, but unfortunately this amp doesn't have any DC offset adjustments. Am I right in saying that to fix this I'd have to replace the output transistors?
--
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. So I hooked up my voltmeter to the test points, and I got 4 mV on the L, and 8 mV on the R. In the manual it says should be 40 mV.....(!). 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.
--
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. I'm wondering, will I damage anything doing this, should I put them back to where they were?
The amp does seem to actually sound better, less distortion, though it still distorts at moderate to high volume. I felt the chips, and they weren't getting hot.
Another thing I noticed is that when it starts distorting, the BIAS voltage drops to near zero. Would this indicate the power trasistors, or the BIAS supply?
If I were to replace the output transistors, what would you recommend as substitutes? They are 2 each of NEC 2sb618 and 2sd588.
--
I've attached the service manual and owner's manuals as RAR files (rename them from zip to rar). The owner's manual actually has a better schematic than the shop manual, all on one page. I've also included some pictures. They're not my actual unit, but mine is exactly the same, just less dusty.....
Thanks for reading this, hope it wasn't too long. Many thanks in advance, looking forward to posting here in the future!
An externally hosted image should be here but it was not working when we last tested it.
All the best,
Bellarmine
Attachments
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KenwoodKA-3500100_2747.JPG98.3 KB · Views: 759
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Pictures.zip709.7 KB · Views: 84
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Kenwood KA-3500 Service Manual.part1.zip732.4 KB · Views: 133
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Kenwood KA-3500 Service Manual.part2.zip343 KB · Views: 86
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Kenwood KA-3500 Owners Manual.part1.zip976.1 KB · Views: 51
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Kenwood KA-3500 Owners Manual.part2.zip976.1 KB · Views: 54
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Kenwood KA-3500 Owners Manual.part3.zip976.1 KB · Views: 46
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Kenwood KA-3500 Owners Manual.part4.zip976.1 KB · Views: 54
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Kenwood KA-3500 Owners Manual.part5.zip976.1 KB · Views: 44
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Kenwood KA-3500 Owners Manual.part6.zip834.9 KB · Views: 60