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Sansui Au-9500 shhh noise from preamp

vuman

vuman

New Member
Hello, I have an Sansui au-9500 recently upgrade all capacitors, transistors ksa992 and some Diode 1N4148 on preamp F-2019 and driver board F-2029. I neglected to replace 2asc1313 transistors. All working fine, except there is shhh noise from preamp section. From the speaker, I can hear the noise 6" from the tweeter very slightly on both channel. Plug in headphone, the noise is there steady and no change when volume turn louder but audible.

My question is, is the au-9500 absolutely quiet or the shhh noise suppose to be there. Will replace 2asc1313 on preamp section quiet down the noise? note: my iphone is completely quiet when using headphone.
 
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Did you mean replace 2sa726 with ksa992? If so then you can proactively replace 2sc1313 with ksc1845. And the two transistors have a reputation diverging standards over time.
 
1. Are both channels the same?
2. Did it do this before you did the work?
3. It is independent of the volume control so it's in the power amp, not the preamp. Probably if you replace the differential pair of transistors it will quiet down.
 
Did you mean replace 2sa726 with ksa992? If so then you can proactively replace 2sc1313 with ksc1845. And the two transistors have a reputation diverging standards over time.

Yes I replace all 2sa726 with ksa992 on different boards, but I did not replace any 2sc1313 with ksc1845 yet. I may try to replace it tonight.

1. Are both channels the same?
Yes, both channel the same.

2. Did it do this before you did the work?
I am not sure the shhh sound before the work. I did not pay attention to it before, so I don't know

3. It is independent of the volume control so it's in the power amp, not the preamp. Probably if you replace the differential pair of transistors it will quiet down.
Poweramp, you mean on the driver boards? I did replace the pair with ksa992
 
It's probably normal for this amp, but it may be possible to improve it. I'll look into it.
 
Thanks Moe, I did replace the relay as proactive during the upgrade. This type of noise may be described as white noise similar to a tube amplifier.
 
It's been my experience, that practically all low level noises that come from the driver board/power amp, like intermittent static, the sound you describe, and others have their source in the differential pair, those first two transistors on the driver board. I recommend changing them out whenever a recap is done. It seems that other transistors will just fail or thermal runaway themselves, where as the differential pair since they flow hardly any current, just make noises.

A leaky capacitor near the beginning of the amp could conceivably make noise, but we usually find it is the differential pair.
 
I just want to circle back to the post. I have time to plugin my AU-9900 today and found the low level shhh sound are there also. I think it is acceptable with the old design.
Thanks every AK's for your responses.
 
Trnsfmr said:
It's been my experience, that practically all low level noises that come from the driver board/power amp, like intermittent static, the sound you describe, and others have their source in the differential pair, those first two transistors on the driver board. I recommend changing them out whenever a recap is done. It seems that other transistors will just fail or thermal runaway themselves, where as the differential pair since they flow hardly any current, just make noises.

A leaky capacitor near the beginning of the amp could conceivably make noise, but we usually find it is the differential pair.
Click to expand...

The OP says the noise is same not matter the volume control position. If this is true, I don't think the issue is in the driver board, but more likely in the preamp as Dr*Audio suggested.

[Edit: ignore this above comment I made. I am wrong. Must have been tired ...]

OP, any update on this?
 
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Then you know it has to be after the vol control. For something like this, if you can look in and see the noise with your scope, with no signal of course, often the noise will have a signature, a certain look to it, that you can see with the scope at high sensitivity. If so, then follow through the circuit after the vol control, and see where it comes in.

That should get you close.
 
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