Now I've heard it all

[Sokel]

We have all seen lots of gear with noises of their own,right?
Like transformers,etc.

But have you ever heard a potentiometer singing?
I mean this thing has a low level vrrrr noise which is constant and does not change with rotating it.

To be more specific,nephew never listens to the uncle so he got an ali express pre,something like 100 euro,dirt cheap one,it doesn't even matter which one,there's gazillions of them.
So it has a definitely knock-off 4-gang,10k motorized Apls controlled by an opamp and a few other components (fun fact,it has 2 smd leds to do diode inside and each one lights up when it goes at each direction )

At first I could not define the source of the noise (we're talking really low in level) ,I suspected the trafo as usual but eventually I got it.
All the above is with nothing connected.

Crazy or what?

Edit: it also outputs a nice,robust 0.8-1.3V of DC offset as level goes up.

 

[DonH56]

Power supply buzzing? Or maybe they leave the motor active even when it's not doing anything? Seems like a "fun" teardown project to find and fix, maybe mechanically isolating the pot or motor would help?

DC through pots sounds like a problem, however, making me think it's broken. I would not want to send that into the next component in the chain.

 

[AnalogSteph]

Definitely sounds like something motor-related for sure, rather than the actual pot.

And yeah, that's a scary amount of DC offset, how does one even get that much? I would check whether there's a voltage missing or something.

Have fun reverse-engineering, I say. This sounds quite broken, either by design or related to assembly. You may want to bill by the hour, otherwise they never learn...

 

[EERecordist]

You can buy small broadband RF EMF oscilloscope probes, coils, or just use a voltage contact probe and probe around in the chassis. It can also help to sketch out the schematic.

There are many great engineers in Asia, then there are companies that copy without understanding to make a quick buck. There is also a problem with counterfeit or QC-reject components.

 

[Sokel]

Power supply buzzing? Or maybe they leave the motor active even when it's not doing anything? Seems like a "fun" teardown project to find and fix, maybe mechanically isolating the pot or motor would help?

DC through pots sounds like a problem, however, making me think it's broken. I would not want to send that into the next component in the chain.

I disconnected the motor,noise is still there.

Definitely sounds like something motor-related for sure, rather than the actual pot.

And yeah, that's a scary amount of DC offset, how does one even get that much? I would check whether there's a voltage missing or something.

Have fun reverse-engineering, I say. This sounds quite broken, either by design or related to assembly. You may want to bill by the hour, otherwise they never learn...

Voltages are so all over the place that I'm tempted to desolder the whole thing apart!

You can buy small broadband RF oscilloscope probes, coils or just use a voltage contact probe and probe around in the chassis. It can also help to sketch out the schematic.

There are many great engineers in Asia, then there are companies that copy without understanding to make a quick buck. There is also a problem with counterfeit or QC-reject components.

As everywhere I guess.
Just call something by it's name,this thing was nearly electric blue color instead of the Alp's dark blue!

Nope,gave it back to him to return it and write a review about it

 

[Sokel]

Definitely sounds like something motor-related for sure, rather than the actual pot.

And yeah, that's a scary amount of DC offset, how does one even get that much? I would check whether there's a voltage missing or something.

Have fun reverse-engineering, I say. This sounds quite broken, either by design or related to assembly. You may want to bill by the hour, otherwise they never learn...

Ok,curiosity beat me to it and I got back.

And of course you were right as always,a whole 12V transformer's secondary was missing.
I mean not entirely missing,transformer had it there just fine.Is just that it's route stopped a little before the diode,they were out of copper at that point as it seems

Nephew says thanks (but it won't be that easy,lessons must be taught and learned

Edit: Seriously now it's scary how they don't even test them for DC,this thing could create havoc down the path.
(of course it will be returned,WITHOUT the fix)

 

[Roland68]

Ok,curiosity beat me to it and I got back.

And of course you were right as always,a whole 12V transformer's secondary was missing.
I mean not entirely missing,transformer had it there just fine.Is just that it's route stopped a little before the diode,they were out of copper at that point as it seems

Nephew says thanks (but it won't be that easy,lessons must be taught and learned

Edit: Seriously now it's scary how they don't even test them for DC,this thing could create havoc down the path.
(of course it will be returned,WITHOUT the fix)

Can you please say which device it is or post pictures of the inside?

 

[Sokel]

Can you please say which device it is or post pictures of the inside?

Not the exact one as it had a (kit) case too but looked a lot like it other than it was a worst knock-off,brighter blue Alps.

Hifi ALPS 27 Type Motor Potentiometer Remote Control Volume Preamp Board | eBay

Find many great new & used options and get the best deals for Hifi ALPS 27 Type Motor Potentiometer Remote Control Volume Preamp Board at the best online prices at eBay! Free shipping for many products!

www.ebay.ca

(sorry,I don't like searching ali,some things are sad)

Actual pics no,it's on it's way home

 

[Roland68]

Not the exact one as it had a (kit) case too but looked a lot like it other than it was a worst knock-off,brighter blue Alps.

Hifi ALPS 27 Type Motor Potentiometer Remote Control Volume Preamp Board | eBay

Find many great new & used options and get the best deals for Hifi ALPS 27 Type Motor Potentiometer Remote Control Volume Preamp Board at the best online prices at eBay! Free shipping for many products!

www.ebay.ca

(sorry,I don't like searching ali,some things are sad)

Actual pics no,it's on it's way home

But that's only passive and the potentiometer is probably not original Alps.

Yes, the Ali search isn't that great, to put it kindly, a lot of things aren't found or aren't displayed.
I often use the Google image search for Ali: Searchterm site:aliexpress.com

 

[Sokel]

But that's only passive and the potentiometer is probably not original Alps.

Yes, the Ali search isn't that great, to put it kindly, a lot of things aren't found or aren't displayed.
I often use the Google image search for Ali: Searchterm site:aliexpress.com

You should see the color of the "Alps" of that one that my nephew got
Also it was a 4-gang one.
That at least was leaving no room to wonder it was shouting "knock-off" from miles away.

Judging by the tremendous DC offset I would think it had some amount of gain too,these double 12V's (with the one missing and creating this DC offset) was for that,
the motor alone would not need that.
It tempted me to measure it but I was too afraid to plug it to my interface

I had another look but it's a chaos out there,I found a gazillion similar ones but not the exact one.