Equin single rail power amp, with modified Quad303 triple cascade , came in Elektor January 1976
Parts PCB foil were sitting around in some box for almost 40 years.
LTSpice sim comes almost too good to be true. Perfect harmonics spectrum.
Result shown with sim of two way speaker at 200 Hz, the frequency where most music with acoustical instruments has max amplitudes. The speaker has exactly at 200 Hz impedance minimum. comfortable 4 ohms. More simulation required to test emf feed from speaker , and thermal distortion. Harmonics spectrum remains unchanged with frequency like a tube amp. Thd at 42 watts is 0.012905%
Power BJT TIP3055 is same as 2N3055 but higher thermal junction to case res. Single diffused. Faster BJT are not as rugged especially epitaxial base would require SOAR protection. The diodes D2..D6 serving output short protection are possibly not enough to protect 2SC5200
2AC5200 would allow for higher open loop cutoff , with TIP3055 it is about 10 kHz.
Parts PCB foil were sitting around in some box for almost 40 years.
LTSpice sim comes almost too good to be true. Perfect harmonics spectrum.
Result shown with sim of two way speaker at 200 Hz, the frequency where most music with acoustical instruments has max amplitudes. The speaker has exactly at 200 Hz impedance minimum. comfortable 4 ohms. More simulation required to test emf feed from speaker , and thermal distortion. Harmonics spectrum remains unchanged with frequency like a tube amp. Thd at 42 watts is 0.012905%
Power BJT TIP3055 is same as 2N3055 but higher thermal junction to case res. Single diffused. Faster BJT are not as rugged especially epitaxial base would require SOAR protection. The diodes D2..D6 serving output short protection are possibly not enough to protect 2SC5200
2AC5200 would allow for higher open loop cutoff , with TIP3055 it is about 10 kHz.
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I've started to follow Giovanni Stochino's lead, and I'm now using 1N4448 diodes as swing-clampers. Bob Cordell suggests the 1N4149 which I've also used successfully in the past, but I'm moving over to the 1N4448.
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I've used BAV21 for higher voltages. A little slower, but seems to work as a clamp for 70-100W amps.
I was also considering moving to 1N4448 but my last lot of 1N4148's had just as good forward voltage. Future, 1N4448's for voltages below 70.
I was also considering moving to 1N4448 but my last lot of 1N4148's had just as good forward voltage. Future, 1N4448's for voltages below 70.
Wow. I built the ‘brother’ of this amp called the Elektor ‘Equa’ amp in about ‘76/77 IIRC - might have been a year or so later though.
Worked well and by friends were impressed that I could draw the whole circuit out with values from memory!
Looking forward to seeing the finished amp!
Worked well and by friends were impressed that I could draw the whole circuit out with values from memory!
Looking forward to seeing the finished amp!
correct ! matters not for simulation but i'll find enough BC546-556 to build - eventually
EQUA is quite another amp that only shares two things with EQUIN: Both were published in the ELEKTOR magazine, and both were single supply designs. The main differences were the EQUA's CFP output stage and current limiters (that don't work reliably, tbh.).
Here's the EQUA circuitry for comparison: https://www.diyaudio.com/forums/att...70-elektor-equa-amplifier-circuit-diagram.png
Best regards!
From a quick glance at both Equin and Equa schematics or pcbs, it appears that the bias transistor is not in direct contact nor near the outputs heatsinks. Is it correct?
I can verify this for the EQUA. Due to it's CFP output stage thermocoupling the Vbe spreader with the power devices indeed isn't necessary. One might couple it to the drivers, though, but that's not that easy with the given PCB design.
I don't have the EQUIN PCB layout handy, hence can't comment on this one.
Best regards!
I don't have the EQUIN PCB layout handy, hence can't comment on this one.
Best regards!
the bias transistor is for compensating ambient temp . Simulation LTSpice assuming that the temp variable refers to junction temp the dc current power bjts varies from 60 mA at 20° to just 100 mA at 120 ° that is just the trick with the feedback in the triple cascade. And that without time lag. However the feedback is also ac and that should be a problem with the rather slow TIP3055
EQUIN has "solved" that with low impedance drive of the triple cascade with emitter follower . 2SC5200 could be the perfect choice but Toshiba only !
There are pros and cons using transistors with higher fT. Maybe MJL21194 with lower fT (4Mhz) would be more optimal?
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Well, the author was discussing the original 2N3055 (RCA hometaxial) versus earlier epitaxial devices, I suspect. Many of those older epi devices did indeed have a worse second breakdown (e.g. MJ481 0.2A @60V) but today's devices generally have better SOA than even that older 2N3055. Even the high frequency devices like the 2SC5200 is very close (about 1.9A @60V), but is on the second breakdown limit which is less robust than other devices at higher voltages. So for Equin/Equa amps running at ~60V should not be a problem.
Regarding CFP and triples, then I've always thermally coupled the bias to the first driver pair, and got very good stability of the quiescent current. Even using low speed (4MHz) epi devices, I've needed to add suppression capacitors to stop oscillations, and if I were to use high speed devices in a triplet I'd suggest using a CFD configuration (complementary feedback Darlington) which may be easier to stabilise.
Regarding CFP and triples, then I've always thermally coupled the bias to the first driver pair, and got very good stability of the quiescent current. Even using low speed (4MHz) epi devices, I've needed to add suppression capacitors to stop oscillations, and if I were to use high speed devices in a triplet I'd suggest using a CFD configuration (complementary feedback Darlington) which may be easier to stabilise.