The BA-3 front end with +/- 32V power supply seems to have just enough voltage output for 50W.
From https://www.firstwatt.com/pdf/art_ba_3.pdf
From https://www.firstwatt.com/pdf/art_ba_3.pdf
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BA-3 front end will work - see post #145 above.
Also see:
https://www.firstwatt.com/pdf/art_ba_3.pdf
BA-2 front end does not have enough voltage out with a 25V power supply but maybe enough with a 32V power supply as with BA-3?
https://www.firstwatt.com/pdf/art_ba2.pdf
Also see:
https://www.firstwatt.com/pdf/art_ba_3.pdf
BA-2 front end does not have enough voltage out with a 25V power supply but maybe enough with a 32V power supply as with BA-3?
https://www.firstwatt.com/pdf/art_ba2.pdf
I once made an EF91 pentode super-strapped as triode , it reached 160V peak peak, with say 100K anode. Low distortion. Needs a hefty source follower. Say 15 mA. Then it can drive the 1 - 1.5 nF gate charge of the SIT easily.
Because the SIT is running in source follower, the charge is not pumped up enormously by the way.
[My common source output Ch'Amp shows the SIT gate charges asymmetric, with a different rise time - fast- from fall time - slow - I use the standard 2SK170/2SJ74 buffer, and I see it on the scope.]
Jean Hiraga once made a driver stage with a 2SK170 strapped by a high voltage BJT, allowing over 160V pp. This cascode was biased at about 2 volt. Only second harmonics if I remember. His design was a a long tailed pair.
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so what is your currently preamp for this power amp?
I guess should be another sit preamp.
i am thinking about.the Mike's SIT preamp
Of course it is a SIT preamp 
. It's a Luminaria.
I have very sensitive speakers (102dB) so I do not need the full 50W. The Luminaria outputs enough voltage for about 40W from the amp, but that is with about 5% THD from the preamp/power amp combination, with the Luminaria adding quite a bit of distortion at its maximum output. But I don't need that much power, probably using less than 1W most of the time so the THD is probably much less than 0.5% at that power level.
The amp with a clean input will probably do 50W with about 2% THD. You can check my previous posts for various distortion measurements.
If I need more input voltage, and I don't, I would add a voltage gain stage between the Luminaria and amplifier. I think the BA-3 FE would be a very good candidate. Since I have more than one common drain amplifier, I would build it standalone so that it can be used with all of the amplifiers.
Another option is to use the BA-3 FE as the preamp, eliminating the Luminaria. It's just a matter of preference - a bit more or a bit less distortion.
There are other voltage gain stages that can be used. Many amplifiers use transformer based gain stages and there are also many other active electronic circuits too. There are also other high gain preamps.
. It's a Luminaria.I have very sensitive speakers (102dB) so I do not need the full 50W. The Luminaria outputs enough voltage for about 40W from the amp, but that is with about 5% THD from the preamp/power amp combination, with the Luminaria adding quite a bit of distortion at its maximum output. But I don't need that much power, probably using less than 1W most of the time so the THD is probably much less than 0.5% at that power level.
The amp with a clean input will probably do 50W with about 2% THD. You can check my previous posts for various distortion measurements.
If I need more input voltage, and I don't, I would add a voltage gain stage between the Luminaria and amplifier. I think the BA-3 FE would be a very good candidate. Since I have more than one common drain amplifier, I would build it standalone so that it can be used with all of the amplifiers.
Another option is to use the BA-3 FE as the preamp, eliminating the Luminaria. It's just a matter of preference - a bit more or a bit less distortion.
There are other voltage gain stages that can be used. Many amplifiers use transformer based gain stages and there are also many other active electronic circuits too. There are also other high gain preamps.
Has anyone considered replacing the active current source by a choke?
I am asking because I was looking at the LuFo, and especially its super-symmetric incarnation SuSyLu. I like those very much, but I believe they need a special kind of LU1014 with rather unusual Vgs ratings (these will be scarce!), or a very low-DCR and expensive choke (expensive!). See here and here for details.
If there is no good way out, a THF51 amp in a SuSyLu configuration might be something to consider. And I have a box full of THFs.
I am asking because I was looking at the LuFo, and especially its super-symmetric incarnation SuSyLu. I like those very much, but I believe they need a special kind of LU1014 with rather unusual Vgs ratings (these will be scarce!), or a very low-DCR and expensive choke (expensive!). See here and here for details.
If there is no good way out, a THF51 amp in a SuSyLu configuration might be something to consider. And I have a box full of THFs.
I did a choke loaded 2SK180 follower. I also have one channel of a choke loaded 2SJ28 follower completed. My THF-51S is CCS Mu follower (this thread).
But there is no problem with a choke loaded THF-51S. The Vds and Iq would probably be in the same ballpark, with some FFT investigation for fine tuning. And Zen Mod is working on a fool proof front end biasing version.
But there is no problem with a choke loaded THF-51S. The Vds and Iq would probably be in the same ballpark, with some FFT investigation for fine tuning. And Zen Mod is working on a fool proof front end biasing version.
Cody, thanks for the Singing Bush hint. Yet another Choky choke (joke?) ZMingerish thread to absorb.
Ben, thanks for mentioning your 2SK180 follower! Following the SuSyLu idea, a Fokin SuSy would get rid of the DC blocking caps in the output, and cancel some of the harmonic distortion. Hmmmmm, my THF51s are getting bored, so I should probably give them some work.
Ben, thanks for mentioning your 2SK180 follower! Following the SuSyLu idea, a Fokin SuSy would get rid of the DC blocking caps in the output, and cancel some of the harmonic distortion. Hmmmmm, my THF51s are getting bored, so I should probably give them some work.
I think I found it (here). As far as I can tell, that amp is not a source follower, as the choke and the loudspeaker output are at the drain of the output device.