Check if 100pF at input is correctly soldered. If it is then install two 22pF to the VAS transistors, between base and collector pins. If zobel still burns then replace them with 47pF. If it still burns then one or more transistor is dead(or too alive) and you will need to unsolder and check the input and VAS transistors.
Hope this helps.
hello, 100pf correct.
33pf vas transistor, still zobel burn.
will go 66pf tomorrow. but they 140/139. no issue, no need comp cap before.
how can vas, input transistor be dead/too alive and still make glorious sound??
and could you explain what mean by too alive?
thank you
oh.. i use 220pf instead 100pf to gnd at input. this ok?
also, if transistors all ok, can wiring cause oscillation? mine one pcb, 2 mono boards together with psu. all input output return star ground. speaker +, input +, not twisted.
33pf vas transistor, still zobel burn.
will go 66pf tomorrow. but they 140/139. no issue, no need comp cap before.
how can vas, input transistor be dead/too alive and still make glorious sound??
and could you explain what mean by too alive?
thank you
oh.. i use 220pf instead 100pf to gnd at input. this ok?
also, if transistors all ok, can wiring cause oscillation? mine one pcb, 2 mono boards together with psu. all input output return star ground. speaker +, input +, not twisted.
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Yes, as is the amp doesn't need comp cap. But if it needs a couple of them then it does for stability. In your case it is either damaged transistor or wiring that is causing the problem.
Do the VAS tranristors share a common heatsink?
dead=dead.
too alive=change of specs by overload.
A device that isn't dead but works totally abnormally is too alive.
220pF ok. Parasitic oscillation is possible with incorrect wiring with good transistor. Can you upload a few pictures?
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They seem okay. Heatsinking could be a problem if you choose to run them at or higher than 10mA, which is a requirement while driving MOSFETs. Well, in subwoofer application 5mA will be sufficient. But if you are planning to run the fullrange signal then try to get TO126 devices. They are also easy to attach a heatsink to.
All the best.
p.s. Simulation results indicate almost nothing about how a device will behave in a real world circuit, although it helps us understand how a particular circuit works.
It seems that silkscreen on post # 1 gives the wrong direction for bd139 bd140
You know me. All special amps sound the same. The Peeceebee is the best sounding 6 device amp I've heard. The PMI version has 8 devices and sounds just as good. I've built two Peeceebee's. One with TO-3 and one with 2SK1058/J162. Then I built PMI version and then JKuetemann version. Can you tell I like them?
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