rjb5191
Well-known member
The left master output on my pm430 has some extra noise that I wanted to track down and I also wanted to play around with transistor subs in the circuit for my own learning / enjoyment. Long story short, I mixed up my NPN and PNP and accidentally ordered 2n5087 instead of of 2n5088/9. There's one pnp transistor (TR3, TR8) in each discrete section of the preamp and master circuit so I figured I would try the 2n5087 there. The 2n5087 have an hfe around 550 and the 2sa561 that I removed had an hfe around 150 as measured on my Atlas pro DCA. Their vbe measurement was also differend by about 20 mV. Anyways, subbing the 2n5087 changed the sound significantly and also increased the noise slightly. Why did a higher hfe transistor in this location cause these issues? The modified channel does not seem to be any louder in volume, it's tone just changed. It sounds like a high boost was added so it's a brighter and less full and sounds like it saturates / distors at a lower input level than the right channel. I prefer the sound of the unmodified right channel. I suppose yamaha chose a lower hfe transistor for this position; can anybody explain this? Schematic is attached.
Last edited:
