Op-amp swaps / upgrades for PL36 board ?

[gadget73]

Has anyone fooled with swapping the op-amp on a PL36 board? I have LF351 amps now, but I'd be interested to hear about any simple swaps that make a difference.

 

[laatsch55]

Anything but an LF 351 WILL oscillate....

 

[gadget73]

well that makes it easy then LOL

 

[laatsch55]

Yep...

 

[P.L.F.]

I did the swap for Burr Brown OPA134 in fully comp PL700 II model. To me it sounds much better in lows (control, punch) and gives more details in highs... No oscilations. I also plugged TL071 for testing the PL36 board under repairs (OPA chips are pricey) and it worked OK.

Still I'd follow Lee's advice not to change this IC just for the sake of swapping if your amp works fine. I had to do it as the original IC failed in one channel and LF351's are very difficult to find where I live...

 

[laatsch55]

Przem, if you don't have a scope i don't recommend it.....and this was straight from ED.

 

[laatsch55]

We were talking about the 300 in that call too, so God knows...

 

[laatsch55]

I've tried a lot of different op-amps in the 300 and nothing worked but the 351's so I could be all f*&^^/##! Up on the 36 board recommendation . Gadget...pop some in there and scope it. Let us know what ya find, there is no reason to doubt Prezm's findings as he has fixed a lot of his own PL stuff. All the PL 36 boards that have come through here get pulled...

 

[gadget73]

I've tried a lot of different op-amps in the 300 and nothing worked but the 351's so I could be all f*&^^/##! Up on the 36 board recommendation . Gadget...pop some in there and scope it. Let us know what ya find, there is no reason to doubt Prezm's findings as he has fixed a lot of his own PL stuff. All the PL 36 boards that have come through here get pulled...

Its cheap enough to try out. $6 for a pair of op-amps and a buck or something for the DIP sockets.

 

[laatsch55]

Heck yeah....we might learn something..

 

[P.L.F.]

Przem, if you don't have a scope i don't recommend it.....and this was straight from ED.

I think we know why:

LF351
Bandwidth: 4 MHz
Slew rate: 13 V/(micron)s"

versus

OPA134
Bandwidth: 8 MHz
Slew rate: min 15 - max 20 V/(micron)s

I was successful without any HF oscillations issues probably because my PL36 board was factory 'cured' against them (two extra caps added, don't recall their values) and all drivers / outputs were already MJ15024/25. So, can confirm plug&play hassle-free procedure for the BB OPA replacement with convincing sound results. Before plugging in my speakers though, I was 'burning' the amp with / without a dummy load for two days or so, checking there were no oscillations present on the scope...