March 24, 20233 yr On 3/12/2023 at 3:27 AM, MLA said: Since you're using a GRLV, dirty power would be unlikely I think. I would replace those transistors for starters. Mpsa06/56 are in stock at least at Mouser. I've replaced all MPSW56/06 with matched using circuit from here. I've also replaced my LEDs with matched LEDs. Previously the LEDs were correct at 1.7Vf but they were rated 20mA while the new ones are only 2mA. The amp still has that intermittent rustling noise when warming up but volume was quite low. I've also realised the high pitched turn off sound is not normal after reading back like this guy. Since I'm not in a rush I spent a few days tinkering with the biasing and offset. With lower offsets between -O/+O to ground, there's no turn off high pitched noise on se output. With lower offset between -O and +O, there's no turn off high pitched noise on bal output. Lower offsets during turn on mitigates turn on thumps but it will affect readings when the amp has warmed up to temp (also the high pitched turn off noise returns on either se or bal out). All 4 VR pots on the board will affect every reading that needs to be checked. Finally settled with a setting that has soft turn on thump, no high pitched turn off noise, lowest rustling warm up noise on my very sensitive Final Audio Pandora Hope VI with 16ohm impedance and 105dB sensitivity. On HD650 and HD525 there's no noise floor. My throwaway portable Oneodio Pro-50 has a medium noise floor and very low warm up noise. The only downside about this is the +ve and -ve biasing voltages are different 750mV and -740mV. Being only 1.33% difference, I don't think I'm too worried. All in all such a great project. Maybe my next Dynahi SuSy I'll just use MPSA and see how it runs. Edited March 24, 20233 yr by penmarker
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