This opinion is entirely personal. I apologize in advance.
However, from personal design and cobbling together all nature of amplifiers, I can say this with some authority: 6SN7 front ends are awesome, and so are J301 FET front ends. They're different, but acoustically sweet in their own way. Probably because they're unrelentingly linear, but also with a slight power-law curve to their response. Just enough.
I can also get behind the "hard-to-read" non-obvious schematics. The use of both triodes and pentodes (small signal) in all nature of VAS (voltage amplification stage) sections is benefitted by having good "old fashioned" tubes working the job. Again, somewhat apologetically, its also the case that Good Old BJTs do a fine job with modest-gain, highly linear middle-of-the-design stages. I definitely prefer valves, in the general case, but you know, I'm happily competent deploying fine crystalized sand devices as well. They are not the antichrist. They're just needing treatment that capitalizes on their strengths, and allows a LOT more margin that most designers usually give them.
OK, enough for my soapbox.
I think it is OK to have good hybrid designs.
PS: I built an amplifier about 18 years ago that used big power MOSFETs in the place of 6550 type tubes, as finals. With 500 volt B+, with very nice hand-wound finals transformers, with every 'cept the tubes. And it was a beast. A sweet, clean, awesome beast.
Why it worked so well? My theory is because of the stored electromagnetic energy of the output transformer combined with its quiescent current. I have no proof other than it was outrageously sweet… and powerful… and tolerant for my friends cobbled-together many-way speakers, but it sang.
And I'd do it again.
GoatGuy
However, from personal design and cobbling together all nature of amplifiers, I can say this with some authority: 6SN7 front ends are awesome, and so are J301 FET front ends. They're different, but acoustically sweet in their own way. Probably because they're unrelentingly linear, but also with a slight power-law curve to their response. Just enough.
I can also get behind the "hard-to-read" non-obvious schematics. The use of both triodes and pentodes (small signal) in all nature of VAS (voltage amplification stage) sections is benefitted by having good "old fashioned" tubes working the job. Again, somewhat apologetically, its also the case that Good Old BJTs do a fine job with modest-gain, highly linear middle-of-the-design stages. I definitely prefer valves, in the general case, but you know, I'm happily competent deploying fine crystalized sand devices as well. They are not the antichrist. They're just needing treatment that capitalizes on their strengths, and allows a LOT more margin that most designers usually give them.
OK, enough for my soapbox.
I think it is OK to have good hybrid designs.
PS: I built an amplifier about 18 years ago that used big power MOSFETs in the place of 6550 type tubes, as finals. With 500 volt B+, with very nice hand-wound finals transformers, with every 'cept the tubes. And it was a beast. A sweet, clean, awesome beast.
Why it worked so well? My theory is because of the stored electromagnetic energy of the output transformer combined with its quiescent current. I have no proof other than it was outrageously sweet… and powerful… and tolerant for my friends cobbled-together many-way speakers, but it sang.
And I'd do it again.
GoatGuy
Goatguy wrote:
can you tell me what mosfets? and what idle currents did you run them?
i am also wanting to do what you did years ago, but i would not want too much details from you as that will spoil the fun...
let me guess B+ of 500 volts implies 1000 volt mosfets am i correct?
the higher transconductance of mosfets compared to tubes makes them desirable as output devices.....3 to 6 Siemens as compared to 0.005S for tubes.....
can you tell me what mosfets? and what idle currents did you run them?
i am also wanting to do what you did years ago, but i would not want too much details from you as that will spoil the fun...
let me guess B+ of 500 volts implies 1000 volt mosfets am i correct?
the higher transconductance of mosfets compared to tubes makes them desirable as output devices.....3 to 6 Siemens as compared to 0.005S for tubes.....
Member
Joined 2009
Paid Member
the answer is Impasse (or other) tube preamplifier with an F4 (mosfet based) power buffer. check out the Pass forum. you can even use a flea 2A3 amp instead of the preamp to drive the power buffer which only adds current.
p.s. I have F4 as the output stage in BA3b (Burning Amp 3 balanced) which is all fet based but F4 was originally meant for hybrid amps.
p.s. I have F4 as the output stage in BA3b (Burning Amp 3 balanced) which is all fet based but F4 was originally meant for hybrid amps.
I have designed and built a few hybrids.
A few transistor and valve amps.
TDA7294 and valve amp.
I got caught out with the TDA7294 as I reduced its gain to match the valves gain.
It oscillated like a pig and got red hot.
I read the datasheet and it needs at least gain of 22 and I had 8.
So i just added a 1000pf between inv and non inv inputs on the tda and it worked fine.
My general view of hybrids is they didn't sound sufficiently different to a normal SS amp.
A few transistor and valve amps.
TDA7294 and valve amp.
I got caught out with the TDA7294 as I reduced its gain to match the valves gain.
It oscillated like a pig and got red hot.
I read the datasheet and it needs at least gain of 22 and I had 8.
So i just added a 1000pf between inv and non inv inputs on the tda and it worked fine.
My general view of hybrids is they didn't sound sufficiently different to a normal SS amp.
Have you seen the Silbatone link I posted? Those are hybrids with SE Mosfet follower to an output transformer, designed by JC Morrison.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.