BC550/560 are underspec'd for this, particularly Q33-Q35. Supply is +/-30 V, while Vceo is 45 V - it should be 60 V minimum. The original parts were fairly high voltage (high Early voltage) and low Crss, look for typical good VAS transistors. Similar characteristics are also useful for Q1/Q2.
It also looks like Q33-35 are normally running about 15 mA and are dissipating close to 400 mW each, which was doable with the original parts which were elongated TO-92 jobs rated at 0.8 W, but would be pushing it for a regular TO-92. You may have to go TO-126 or TO-223 SMD.
Yeah, this design relied heavily on transistors that have unfortunately been going the way of the dodo for years with the demise of CRT monitors. There is no proper compensation either, which might change when using other parts.
Not sure how you came up with these JFETs, no idea how good they might be for audio. About the closest thing to the originally spec'd parts would be pairs of LSK170 + LSJ74.
EDIT: At +/-20 V you'd be OK voltage and dissipation wise, BC550/560 still have kinda low Va though. There was a thread here fairly recently that looked at Early voltage across a range of devices.
It also looks like Q33-35 are normally running about 15 mA and are dissipating close to 400 mW each, which was doable with the original parts which were elongated TO-92 jobs rated at 0.8 W, but would be pushing it for a regular TO-92. You may have to go TO-126 or TO-223 SMD.
Yeah, this design relied heavily on transistors that have unfortunately been going the way of the dodo for years with the demise of CRT monitors. There is no proper compensation either, which might change when using other parts.
Not sure how you came up with these JFETs, no idea how good they might be for audio. About the closest thing to the originally spec'd parts would be pairs of LSK170 + LSJ74.
EDIT: At +/-20 V you'd be OK voltage and dissipation wise, BC550/560 still have kinda low Va though. There was a thread here fairly recently that looked at Early voltage across a range of devices.
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Kevin,
Thanks for the awesome amps!
MPSW05/06/55/56 - right? Kind of disappearing now... Can you recommend anything that is not marked as obsolete? I'm curious, why do you prefer MJE1503x to KCS2590/KSA1220?
Sgrossklass,
This is another reason why I decided to not go higher than +/-20V rails
Thanks for the awesome amps!
MPSW05/06/55/56 - right? Kind of disappearing now... Can you recommend anything that is not marked as obsolete? I'm curious, why do you prefer MJE1503x to KCS2590/KSA1220?
Sgrossklass,
This is another reason why I decided to not go higher than +/-20V rails
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With +/-20V rails, power output to even 4R loads will be quite modest. At around 20W/8R, you won't need so many parallel output devices.
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