NAD 3020i MJ15003/MJ15004 replace MJ2995/2N3055

[bigshuggy]

Should probably start a new thread but I'll post here anyway.

Thought the volume pot might get better with use but it's not so it's time to replace.

The schematic suggests that there should be a 50k pot but it's a 20k that's fitted. A quick search for 20KAX2 brings up some Alps pots but none that look the same.

There’s an Alpha 50k that looks similar here -

Alpha 50K Type B stereo potentiometer | Hifi Collective


Any suggestions?

 

[K-amps]

Are you sure the ones you will replace with have Audio tapering rather than linear tapering? Sometimes a pot is not a pot....

 

[bigshuggy]

Are you sure the ones you will replace with have Audio tapering rather than linear tapering? Sometimes a pot is not a pot....

I'm never sure of anything! That's why I rely on you knowledgable types on forums such as this

 

[K-amps]

Please try and source pots designed for Audio. Their resistance path is logrithmic rather than linear to mimic the sensitivity model of the human ear.

 

[Mooly]

That pot looks as though it would open up and clean. Those folded tabs need to be carefully prised back to allow it to come apart.

It would need removing from the board first.

 

[bigshuggy]

Desoldered, opened and cleaned. It's still noisy at a very particular position...

 

[Mooly]

There is more to do... you need to carefully re-tension and very slightly bend the wiper so that it runs along fresh track. If the pot is amenable to having this done then it can be very successful.

 

[bigshuggy]

Can do that on one side but not the other. Think it's definitely needing replaced now

Not worth replacing with a fancy Alps pot - will try and source and Alpha 20k...

 

[bigshuggy]

Here's a 50k pot with centre detent - I guess that's just a physical bump and wont actually do anything?

2x ALPS Potentiometer 50k log Dual Pot Japan - 50KAX2 - Centre Detent - NOS | eBay

 

[Mooly]

That is probably a balance control and the log tracks will run in opposition to each other, so no good I'm afraid.

Would anything like this fit ?
POT, DUAL GANG, LOG, 22K - OMEG | CPC

 

[bigshuggy]

It has quite long legs - same dimensions as that ebay one.


Suppose I now have the long legs from previous one to solder on to.

 

[Mooly]

Tagging leads to the replacement should be easy (resistor leads are good for that kind of thing) and they can also be bent to shape to fit the PCB holes.

I can't guarantee its the same size but it looks like you have enough wiggle room in there.

 

[bigshuggy]

I'll find something that fits. Thanks again for the feedback

 

[Mooly]

OK good hunting.

 

[spandrel]

Just a note for others. The volume pot on the earlier 3020 models have a tap on the volume pot connected to the loudness control, and it's not a centre tap. The chances of finding a replacement are roughly zero, except robbing another amp, so a standard pot would leave the amp with no loudness control. No big deal really. It is best to try and clean the original if possible. Thankfully NAD gave up on the loudness switch with the 3020i.

 

[bigshuggy]

That's what had me confused initially. After reading load of forums I was assuming the loudness switch that talked about was the 'low level' switch - and therefore looking for pots that had this extra bit on it...

 

[spandrel]

I'm not keen on 'upgrades' for these amps, they're very finely tuned circuits. Different o/p trannies and emitter resistors will change the feedback loop characteristics. I've got one here, failed o/p trannies but only because there's no heatsink compound on them. Duh!

I've also had to fix a headphone socket on one of these. It was horrible, I cried. I'd recommend bypassing the speaker switches on this if you don't use headphones much. Or use the switches to operate a speaker relay like the later NAD amps.

 

[bigshuggy]

I'm not keen on 'upgrades' for these amps.

I would much rather replace with original parts but that's not really possible...

 

[spandrel]

Really? I can still get most parts. That's why I like these amps, they're great amps and
repairable.

 

[bigshuggy]

If you can find genuine original transistors - I'll buy them! (at a reasonable price)

You might get something called MJ2995/2N3055 but different manufacturing process now so not the same as original.