Home Forums GuitarPCB Build Support Dr. Phybes output buffer Reply To: Dr. Phybes output buffer

#13426
Dan
Participant

It seems that the MXR phase 90 has a similar problem, people report needing a buffered pedal after the phase 90 in their signal chain. I have a couple more pedals now (just built the Blues Breaker with an Afterblaster – awesome 🙂 and a mix of factory buffered and TB pedals, and it seems the Dr Phybes is very sensitive to placement in the signal chain. I think it would benefit from a better output buffer so that its output level is not affected by the pedals after it.

I’d like to improve the performance of the output buffer Q5 stage in the Dr Phybes, without resorting to a transistor/opamp output buffer stage as others have done to their Phase 90s.

Looking at the schematic, it seems that the mixer/buffer transistor stage output impedance could be reduced by changing R20 from 56k to a smaller value – perhaps 5-10k? Perhaps another issue limiting the output drive current from the buffer stage could be because Q5 emitter is fed from Vb , which is limited by R29 10k resistor?

I’m not totally familar with the common collector PNP buffer arrangement, so I’m struggling to think of suitable mods. Can anyone here advise how the Q5 stage output impedance can be lowered to improve the output drive without using a external booster/buffer stage?