Re: Bias matching replacement transistor - Parasound 2250

That is what I feared, as getting replacements will be hard..2SC3520, 2SC4140 are compatible, but seems they are out of production as well. I guess running the setup as it is will cause an extra strain on the two original transistors.

I assume complimentaries should be replaced as well? Will this change cause audible difference between the channels?

Thank you for your input!

Re: Bias matching replacement transistor - Parasound 2250

Of course, that adjust everything - the replaced transistor is still roughly 1mV below the others regardless of VR1 position.

Hi guys!

I am currently working on a Parasound 2250 (class AB), which had one defective channel. Components in the signal paths have been replaced, including an output transistor (2SC3519).



According to the manufacturer, bias is adjusted by measuring 1-3mV across the output resistors. The original ones are completely fine around 1.5mV, but the replacement is not. Initially, I got a couple from eBay, assumed they were fake (they were) and was able to source a replacement locally. This exhibits similar behaviour, being around 0.6-0.8mV on its emitter resistor....

Re: New Members - please post your introductions here

Hi guys, greetings from Norway!

I am a service technician mainly focusing on audio gear and synthesizers - one of the few left in Norway doing these kind of jobs. This is more of a side gig, as servicing electronics is not a very lucrative business, due to the cost of work hours. I started off with only through hole work, but as I have progressed, I now have gear and experience to do microsoldering as well.

As my primary income, I am a software developer - primarily focused on frontend/UX and design,...