PL 2000 SII Preamp Issues

[SupraMan]

Hello Everyone!
I’ve searched the threads relating to this preamp and have learned a lot from reading them. However, I have not come across (or may have missed) any solutions to an issue I’m currently having.

With the preamp powered off (red LED off), I am still hearing source music coming from my speakers. Any thoughts or suggestions?

I also have a channel imbalance between the left and right speakers but I believe that may just be an issue with the switch.

*Side note: I just recapped the unit, but the issue(s) was there before and after.

Any advice is appreciated! Thanks!

 

[George S.]

Joe solved this long ago on a old thread. It's the resistor soldered across the power switch lugs passing enough voltage to keep the opamps powered. I remove that resistor.

 

[SupraMan]

George, I do remember reading that thread. I was uncertain whether our issues were related due to the fact that he had a hum with the replacement op amp but didn’t have it with the original- I still have the original in mine.

I suppose it wouldn’t hurt to remove the resistor and just try it anyway.

Thanks for the feedback.

 

[Gepetto]

George, I do remember reading that thread. I was uncertain whether our issues were related due to the fact that he had a hum with the replacement op amp but didn’t have it with the original- I still have the original in mine.

I suppose it wouldn’t hurt to remove the resistor and just try it anyway.

Thanks for the feedback.

That is because it didn't know the words

It wasn't me that had hum with the replacement op amps...

 

[George S.]

Yup, Joe solved that for one of the members who had all kinds of issues with his preamp.
Joe, do you think that was PL's attempt to limit inrush of current to tame turn on thump?
With today's higher wall voltage and a newly calculated resistor value that would keep the unit on, but not drive the opamps to a audible output level, would turn on thump be somewhat tamed?
Was wondering about that couple weeks back when I saw my $30 PL2000 S1 carcass still has the resistor.

 

[SupraMan]

That is because it didn't know the words

It wasn't me that had hum with the replacement op amps...

It took a few seconds, but I eventually picked up what you threw down .

I don’t recall who’s preamp it was, but I do recall the discussion. I suppose it won’t hurt anything to leave the resistor on, will it? I just won’t play music when it’s powered off

I am also curious now if removing the resistor would then cause a turn-on thump.

 

[George S.]

My modified PL2000 S2 preamps have brutal turn on thump. I'm going to experiment with adding a higher value resistor in the future.

 

[wattsabundant]

My modified PL2000 S2 preamps have brutal turn on thump. I'm going to experiment with adding a higher value resistor in the future.

Crowbar the output with a miniature relay powered off of the rectifier.

 

[SupraMan]

So… I fixed my channel imbalance! I couldn’t easily source a replacement balance pot so I did some digging around and found a pot with very similar internals and specs. I was able to purchase two 50k pots to rebuild the internals of the original dual-channel unit.

The original 50k pot readings were 40.9k and 58.2k- absolutely not what we want to see; almost a 20k difference between them.

In the end, I was left with a nicely rebuilt pot and two individual diy project pots. The unit sounds much better and more balanced as a result (obviously).

For those who are curious, I’ve provided the Mouser and Manufacturer part numbers below.

Mouser P/N: 774-450T328F503A1A1
Manufacturer P/N (CTS): 450T328F503A1A1

 

[George S.]

Cool! Thanks for sharing this.
Next Mouser order, I'll get the pots and do this on 3 preamps.

 

[laatsch55]

Gotta love a problem solver...

 

[GaryCooper]

My 2000II had an ambience issue so I capped it replaced Z3, Z2, and the tis97 but has a hum with original ic so put a hybrid replacement so far it's doing fine I bought unit new in 78 while in air force.