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Acurus L10 problem

I guess I should've had you vary the volume pot positions while watching signal at R4. If signal was good at max volume but gets that badly mismatched at lower volume positions it says the vol pot has a problem.
 
mondialfan said:
I guess I should've had you vary the volume pot positions while watching signal at R4. If signal was good at max volume but gets that badly mismatched at lower volume positions it says the vol pot has a problem.
Click to expand...
I was about to post it.. the imbalance on R4 on the scope follows the same imbalance spottet at the output when turning the pot.
Thanks :)
 
Any of the wipers bent? You might change the position of the wipers from L to R to see if the problem changes channels.
 
mondialfan said:
Any of the wipers bent? You might change the position of the wipers from L to R to see if the problem changes channels.
Click to expand...
No, but half of them were **** dirty! I think this is it, we'll see...
I did a very light clean with a "thing for your ears-stick" (don't know the English word :)), so I didn't harm the carbon-layer. The wipers I decided it was easier to give the a good spray of cleaning solution, I use Kontakt60. All the dirt came right off the wipers without touching them, looks like new. Now it's drying, and later lubrication, kontakt61 is used for this
 
The wiper and carbon-peace posted above (those to the right on this picture). The wiper is flawless now, so fingers crossed
IMG20230117221220_copy_800x800.jpg
 
Ahhaa!! :) Didn't work :( same problem, a 40mV difference at the output half volume at 500mVpp from the generator. With 1Vrms that's 360mV difference
:boring:

But I still believe this pot is the problem. I'm gonna sleep on this, and rest my case untill tomorrow

Thanks for all
 
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AFTER A GOOD NIGHT SLEEP, AND SOME NEW THOUGHTS CAME UP:
There might be another solution: shifting the wipers from the balance pot to the vol-pot if these are the problem...? I haven't looked inside the balancepot, but I'll guess that the shaft and wipers is constructed the same way as the vol-pot, where only the carbon plate is different (this would by far be the cheapest option in production if I were to make these).
If so, and if the carbon in the vol-pot isn't damaged (I cannot see mistakes in the carbon after previous visual inspection), then I'll have a second try for free with other wipers.
If I shift wippers (and make my pre-measurments of each pot of course, to check AFTERWARDS!) then the balance pot will still function at both center and full left/right accordingly to the findings in the vol-pot so far, where only half left or right on the balance pot wouldn't be the same if we compare to the 12 o'clock difference in the volume pot measured, and the most pronounced by far:)
It's roughly a 5° turn imbalance to one or another side on the balance pot, and NOBODY WILL EVER NOTICE. The volume pot is by far more important, but balance must be center at all time if I shift wipers.

The owner of the preamp has been consulted with the findings, and fully understand the situation, so all good. The preamp is newly bought on eBay from another country, and the new owner instantly complained abort a very noisy volume pot. This has been fixed, but the imbalance on the scope!!

Of course I'll try with fixed resistance while the pots is removed, just to clarify that this really is what it looks like

I'll do some testing later or tomorrow
 
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Didn't work after switching the wipers. It's the carbon in the volume that's off.
Bypassing the volume gives a dead straight line on the scope all the way.
I rest my case.

IS THERE ANY SUTIBLE REPLACEMENT POT? Most of them are 20k, could work, but what about the fit....

If so, I'll advise the owner of this possible change of pot or I'll leave the pre as is, if he doesn't want to

Best regards
 
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Alps Blue velvet 20k ohm. However the pins will have to be lengthened to work. Mondial ordered with special longer length pins. All of the modern Alps pots I've seen have short pins.
 
Also, the last time I looked there were only a few places that had the 20k log blue velvet pots. Hificollective in the UK I believe was one of them.

One other thing,
If you put in a 50k or higher pot to replace the stock 25k then distortion will go up. Yes, measurably higher, been there done that...

It's better to go down to 20k as long as the customer is okay with a slightly lower average input impedance.
 
mondialfan said:
Also, the last time I looked there were only a few places that had the 20k log blue velvet pots. Hificollective in the UK I believe was one of them.

One other thing,
If you put in a 50k or higher pot to replace the stock 25k then distortion will go up. Yes, measurably higher, been there done that...

It's better to go down to 20k as long as the customer is okay with a slightly lower average input impedance.
Click to expand...
I've shopped at hifcollective several times when building my own A250, not cheap though, but good service.

When you say the "pins" I suspect you mean the pinout for the PCB from the pot.. If that's correct, I might just turn the housing of the pot 90° and solder it by wire to pin?

Best regards and thanks! :)
 
The pins only extend about half the length on the new pots that they do on the Alps and Noble pots that came on the Acurus and Aragon equipment.
 
mondialfan said:
The pins only extend about half the length on the new pots that they do on the Alps and Noble pots that came on the Acurus and Aragon equipment.
Click to expand...
I understand. I've informed the owner, and really surgest that we do this. Listening to an amp that shifts stereoimage from 9 o'clock and up isn't worth the build.
I'm in it for the hobby, but it HAS to work when leaving, as all other out there
 
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