Weird Super Loud Static in the Left Channel of my Sansui AU-9500

Ron13a

Revolver of Vinyl
I posted at the Sansui forum, but I probably should have posted here first as this is not a problem unique to Sansui. Anyway, here's my situation: I just scored my second AU-9500. I was foolish enough to let the first one go. I'm determined not to repeat the mistake!

I get it home, hook it up and I get VERY loud trash out of the left channel, static like noise. It reminds me of what you get if you pull an RCA jack out of an active in put, but much worse.

I disconnect the left speaker.

The right channel is fine. I adjust the volume and all other pots and switches and there is no static at all. Doesn't look like a quick fix for deoxit. As you can imagine, I was immediately bummed out.

So I tried the left channel with A, B, C and headphones. Nothing but extremely loud static with the volume all the way down. That's right, the volume is all the way down, but the noise in the left channel sounds like it's all the way up.

Next, I pulled the Pre-Out Main-In jumpers out. Hooked my computer into the main in and just used the amplifier section, completely bypassing the pre amp. Slowly turned the volume up on the computer and played a song off iTunes. Both channels are nice and clear.

The issue, I figure, must be in the pre amp section. The amplifier is fine. I put the jumpers back in and hook everything back up and test it. As soon as I hear the relay click, the super loud garbage comes out of the left channel.

Anyone out there have an idea of what's going on here?
 
I would guess a noisy transistor in the preamp. Is it in both channels?
Could be a power supply issue.

Rob
 
Just the left channel. The amplifier section works great. It's something in the pre amp. I don't know what. I think I'll have to get a professional on this.
 
Had something like that once in an old Marantz.
It was a bad capacitor. One leg was rotted off.
If that has bad glue rot, you may have the same problem, bad cap.
 
It appears that you have the problem narrowed down pretty well.

1. You know the problem is on the left channel
2. You know that it is before the amplifier stage
3. You know know that is appears to be after the volume control in the preamp stage as the volume control doesn't seem to have any effect.

I would still look at a possible dirty control, button, or switch. You say you don't think DeOxit will help, have you tried it?
 
Post 2 or 4 probably nails it.

If there's a favorite or spoiler in the race, it might be glue rot.

But for me, a transistor gone noisy has been the fault causing the symptoms you describe, on more than one occasion.

Indeed caps have also been problematic, along with glue rot, fractured/dry solder joints, etc..
 
Thanks for the info guys! I'll take it to Big Bill in Charlotte. He does great work.
 
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hi

you can also try 4ch input or snr input (this bypasses the selector knob). (some inputs have pots to adjust de input level,) just turn all knobs a lot of times, this amps need this 1 time per month

anyway a thing to do with this amps is to totally clean the tone knobs,as all the signal pass through them i did it on my 2 au-9500 (1 recapped, 1 original) is not difficult you have to dissasembly them and just clean the boards with alcohol the improvement in sound was huge.
 
This happens to all 9500s, eventually. You need to replace all transistors in the pre amp, no questions asked. It'll fix your problems.
 
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