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AU555A volume potentiometer

margus_

margus_

Member
Does anyone know if sansui au555 and au555a share the same volume potentiometer? There is one for sale on ebay, but the seller also doesn't know if it fits both

https://www.ebay.com/itm/Sansui-AU-...865141?hash=item23a14a6eb5:g:8i4AAOSw4AJcYxut

Does anyone have experience with this particular product / seller?

My au555a needs new volume pot because old one seems to be unfixable. It has been cleaned properly, but wehen I turn the volume knob, at first music starts playing in the left speaker, when I turn a bit more, then also from the right speakers (this problem appears at very low sound levels). The amplifier itself is in good working order and restored.
 
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The volume controlled often gets blamed for dirty contacts elsewhere in the preamp. When you turn up the volume, you increase the voltage of the audio signal. The increased voltage can overcome resistance in dirty contacts down stream of the volume control. In the 555a the tone control board and filter switches are downstream of the volume control. Have you cleaned the tone controls? Don't replace anything until you do.

The 555a volume control carries Sansui Part number 101009, 250k ohm
The 555 volume control carries Sansui Part number 101003, 250k ohm

They have the same resistance value but different part numbers. That could mean they mount differently or have different audio tapers. No way to know without direct comparison.

- Pete
 
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Looking at the link you provided, that pot could probably be made to work.

- Pete
 
The amplifier has recently been recaped and thoroughly cleaned by professional tech. The problem was before and remained after the repair.
 
margus_ said:
The amplifier has recently been recaped and thoroughly cleaned by professional tech. The problem was before and remained after the repair.
Click to expand...
What kind of tech takes a unit in with a problem and gives it back with the same problem without an explanation. You need to discuss this with him. Who would install a replacement pot?

- Pete
 
Tech answer: This is a problem that is not related to wearout of the potmeter but something that is related to the product itself. It is possible that the NOS potmeter suffers from the same channel mismatch as potmeters during that time were not as accurate produced as they are right now. For example the Quad 33 is known for this issue.
 
Not sure if I'm buying that explanation. The AU-555 isn't that old that the two channels of the pot made in its era should track poorly (relative to each other) even - or especially - on a NOS part. That was a more common issue in the pre-1970 era and seems more likely found on tube era gear than even early solid state.

Manufacturing precision of dual (or more) channel pots was steadily improved from the early 70's onward at least until the cost cutting got excessive in the mid 80's and a lot of cheap gear made from cheap parts was being cranked out. Good quality kit still had well spec'd and manufactured pots in that era. I do see a fair number of slide (linear travel) type pots from the mid to late 80's with issues now, but not so much with rotary types.

Most SS gear I've owned or worked on with poorly tracking pots (be they volume, balance, bass or treble controls) were the result of either excessive wear or poor attempts at cleaning with improper products or technique that further damaged their condition.
 
How bad is it? Do you notice it during normal operation or just when you turn the volume to zero and then slowly increase the volume? It may not be worth worrying about.

- Pete
 
This problem appears at very quiet sound levels. I have little baby at home and I have to often listen very quietly. At normal listening levels sides seems to be balanced ok.
 
I think your tech is right. Although Sansui used quality Alps pots, they are a very basic design and are well known to not always go to zero volume. It's probably not worth fixing since any replacement part is likely to have the same issue. Just balance the two channels with the balance control. That's what it's for.

For what it's worth, the AU-555a is a great little amp. I have one that I've used as my computer audio system for about 15 years. It's on for hours almost every day and it's 100% original. Other than occasional cleaning, its as original as the day Sansui shipped it. Even the pilot light bulb is original. So enjoy your amp and don't sweat the small stuff.

- Pete
 
Thank you for the feedback. My other vintage machines don´t have this kind of problem at all.
Unfortunately, there seems to be nothing to do. Ok, I will try to live with it as it is.
 
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