if the picture is what you bought it does not have a loudness tap. I have seen a couple of these that came from ebay and they were not potentiometers, they were stepped attenuators and they were not real ALPS devices.
Sansui AU-9500 – Distortion in Right Channel (Need Advice)
- Thread starter Photoshark88
- Start date
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- distorion issue sansui au-9500
Glad you found the problem. I didn't know the signal was good up to the volume pot. Thought it could be someplace before the pot.
Photoshark88
New Member
Yep, unfortunately this pot has 3 pin for each side, so probably I'll reorder for the 4 pins.
Photoshark88
New Member
Update:
Not sure if I mentioned this before, but I replaced all the caps on every board and still have the same issue.
I disassembled the volume pots, cleaned them thoroughly with Deoxit and polished with Brasso. That reduced the scratching a bit, but they’re still not perfect. I also resoldered the wires on the Main In RCA.
From testing through the Main In, the signal goes straight to the power amp board. So the problem isn’t there—it’s likely in the tuner board, switches, or volume pot. The only board I haven’t updated yet has 4 big cement 0.47Ω resistors and 2 emitter resistors (150Ω). According to the multimeter, they test fine, but maybe they’ve got micro-cracks or something similar.
I’m waiting on replacement parts and will see how it goes. Just a reminder: at the very beginning, one cap on the power amp board blew out, and the 7A fuse burned. The resistors aren’t expensive to replace, but the result is still uncertain.
Not sure if I mentioned this before, but I replaced all the caps on every board and still have the same issue.
I disassembled the volume pots, cleaned them thoroughly with Deoxit and polished with Brasso. That reduced the scratching a bit, but they’re still not perfect. I also resoldered the wires on the Main In RCA.
From testing through the Main In, the signal goes straight to the power amp board. So the problem isn’t there—it’s likely in the tuner board, switches, or volume pot. The only board I haven’t updated yet has 4 big cement 0.47Ω resistors and 2 emitter resistors (150Ω). According to the multimeter, they test fine, but maybe they’ve got micro-cracks or something similar.
I’m waiting on replacement parts and will see how it goes. Just a reminder: at the very beginning, one cap on the power amp board blew out, and the 7A fuse burned. The resistors aren’t expensive to replace, but the result is still uncertain.
If the power amp is working and sounding good then the .47 ohm cement jobs are OK. FYI those are the emitter resistors for the output transistors.
The 150 ohms are part of the overload sensing circuit
Photoshark88
New Member
Ok, so what else could be reason of the bad right channel? The sine wave on the oscilloscope doesn't look perfect at the peaks, I don’t know how to explain it. Was something like that
The top and bottom of the waveform are clipped, very evenly I might add. Is this at the speaker output of the amplifier?
Are you sure the input to the scope was not overloaded, voltage range set too low?
Photoshark88
New Member
SOLVED!!!
Hello everyone,
Finally, I brought the amp back to life last weekend.
One thing that still didn’t let me relax was the output transistors. The original 2SC1079 and 2SA679 were replaced with MJ15004G/03G, but they probably weren’t good enough by spec. So, I swapped them for MJ21194G/93G—the ones I had used when restoring a Yamaha CA-800 (that’s another story)—and everything started working fine. I adjusted the DC offset and bias, and now it’s ready to go. The bass is back, the sine wave looks good, and there’s no distortion or other noise.
Hello everyone,
Finally, I brought the amp back to life last weekend.
One thing that still didn’t let me relax was the output transistors. The original 2SC1079 and 2SA679 were replaced with MJ15004G/03G, but they probably weren’t good enough by spec. So, I swapped them for MJ21194G/93G—the ones I had used when restoring a Yamaha CA-800 (that’s another story)—and everything started working fine. I adjusted the DC offset and bias, and now it’s ready to go. The bass is back, the sine wave looks good, and there’s no distortion or other noise.