SlamJam

Issue with BA512 Op-Amps (Lola)
« on: July 13, 2018, 08:03:53 AM »
Hi All,

I have recently built me a second Lola pre, and came across an issue with the Op-Amps.

There is a background distortion at anything above the very low gain settings and maybe 12 o'clock output. As you increase the gain the distortion gets worse. The distortion is not constant like a feedback but is present in the background of every sound. (when silent its subtle but there)

I was able to swap out the op amps (same BA512) from my previous build and the distortion is gone, and sound is as it should be.

What might i have done to the Op-Amps ? and is there any value in maybe ordering transistors and the other bits, swapping them out until i rectify it? (pun not intended)

Any suggestions would be greatly appreciated.

Thanks

James






scott2000

Re: Issue with BA512 Op-Amps (Lola)
« Reply #1 on: July 13, 2018, 09:00:56 AM »
The schematic is in the technical documents section

https://groupdiy.com/index.php?topic=44877.40

If you have any experience troubleshooting and replacing components it could be a good option but, I'd imagine getting a new replacement would be less painful if not...

Maybe you'll get lucky and it's something simple but, not knowing the tools you have available or the experience you have, it's hard to tell.....
"Give me a 25-stack of 9V batts, I'll monitor my truck's spark or fuel injection on the magic eye." PRR

SlamJam

Re: Issue with BA512 Op-Amps (Lola)
« Reply #2 on: July 13, 2018, 07:20:59 PM »
Just a multimeter in terms of measuring instruments. And....intermediate experience. As it's a pre-built opamp I'm sure the components would all be in the correct place, im borderline able to maybe check voltages across the transistors? Is there a check I could do to see what I should be getting? I can read schematics at a slow rate.

Sold myself well

James

SlamJam

Re: Issue with BA512 Op-Amps (Lola)
« Reply #3 on: July 14, 2018, 03:58:29 AM »
Any equivalent transistors for 2N4250a ? I can't seem to find them anywhere in the country.

James

scott2000

Re: Issue with BA512 Op-Amps (Lola)
« Reply #4 on: July 15, 2018, 09:11:52 AM »
Any equivalent transistors for 2N4250a ? I can't seem to find them anywhere in the country.

James

PN4250a? Just guessing though......
"Give me a 25-stack of 9V batts, I'll monitor my truck's spark or fuel injection on the magic eye." PRR


 

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