Hi everyone,
I've been looking at single ended solid state designs, and Michael Rothacher's FAOW Variation #2 caught my attention: http://www.firstwatt.com/pdf/art_faow_v2.pdf
I think it's a beautifully simple design and I like the idea of a transformer coupled output to give it a more tube like sound.
Unfortunately, even with my small listening space and modest volume levels, 1 watt won't be enough. Could the bias current be raised to give more clean output power? Assuming of course the power supply can handle it. I've looked at the data sheet for the IXTH6N50D2, and it looks to me like 70 ma bias current is pretty conservative.
I assume higher bias current would also demand a bigger output transformer, like Edcor's CXSE25-3K.
Am I thinking on the right track or is more power too much to ask for this circuit?
I've been looking at single ended solid state designs, and Michael Rothacher's FAOW Variation #2 caught my attention: http://www.firstwatt.com/pdf/art_faow_v2.pdf
I think it's a beautifully simple design and I like the idea of a transformer coupled output to give it a more tube like sound.
Unfortunately, even with my small listening space and modest volume levels, 1 watt won't be enough. Could the bias current be raised to give more clean output power? Assuming of course the power supply can handle it. I've looked at the data sheet for the IXTH6N50D2, and it looks to me like 70 ma bias current is pretty conservative.
I assume higher bias current would also demand a bigger output transformer, like Edcor's CXSE25-3K.
Am I thinking on the right track or is more power too much to ask for this circuit?
Thanks juanitox, I hadn't thought of a cathode bypass (drain bypass?) capacitor.
Pushing the bias up to 140 ma would certainly increase output power, but I'm concerned that the MOSFET's distortion may increase too much with it.
but then it will sound less "tubey" my ACA doesn't sound like my single ended VFet or even my Aleph mini .
Right, it might be easier to start from scratch rather than trying to modify this design.
it's rather easy doing whatever (scaling up) , but first one need to define goals ...
For the same load impedance: you must increase both current and voltage!
Alternatively you could change load impedance, but selection of available transformers is narrow.
Yes, yes, yes, yes. WHAT do you want? 2 Watts? 200 Watts?
A first-crack at "design" is to look at available tube transformers and how they are used with tubes.
But another issue. The proposed device has a 500V limit. A common 5W 5K transformer might use a 6V6 working with 250V-300V. However in operation the plate kicks to nearly *twice* the supply voltage. 500V-600V. (More when over-driven.) A tube will stand this on peaks. A semiconductor goes FZZZT! very very quickly. You could "design" with this in mind. Or you could pick a different device, but that probably means a different bias scheme or further complication. And you may not be ready for that.
Alternatively you could change load impedance, but selection of available transformers is narrow.
Yes, yes, yes, yes. WHAT do you want? 2 Watts? 200 Watts?
A first-crack at "design" is to look at available tube transformers and how they are used with tubes.
But another issue. The proposed device has a 500V limit. A common 5W 5K transformer might use a 6V6 working with 250V-300V. However in operation the plate kicks to nearly *twice* the supply voltage. 500V-600V. (More when over-driven.) A tube will stand this on peaks. A semiconductor goes FZZZT! very very quickly. You could "design" with this in mind. Or you could pick a different device, but that probably means a different bias scheme or further complication. And you may not be ready for that.
Ideally, I'm looking to make 5 watts of clean power. My desire is a simple single ended solid state power amp of at least 5 watts that my battery powered tube preamp can drive directly.
To take this design to 5 watts would probably require increasing the voltage with the current, which sounds like that could be too much for this MOSFET. It would also bring the design very close to a single ended tube amp, of which there are many proven designs already available.
5X the current alone would be 350 ma or so, pushing the dissipation to nearly 50 watts a side. I think that would require a much lower impedance output transformer, or have I got that backwards? Either way, probably one that doesn't exist.
Where might one find genuine THF51S components? 2SK82's seem to be unobtainium now. That's a really neat amp design though and super simple.
I've looked at the MoFo many times, but my tube preamp only puts out 3.5v RMS. Might be enough power to push the MoFo to 5 watts, but ideally I want to drive the power amp to near full power.
Ouch, that's not a lot of power.
Hard to tell whats fake and whats not on ebay. I'll check out Pras1170 and see what he's got. The IronAmp looks like an even better option, but its a matter of getting the parts.
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to confuse you a little more, i will add if you ll buy any of these big Vfets don't waste it for a sissy 5W amplifer . go directly to the Nelson 2SK77B type amplifier (burning amp 2015) it is a killing machine at 1W /5W or as high as your heatsink and power supply can go. .
a freak
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