Korg NuTube + transistor 1x buffer + Edcor transformer. Works fine from the existing (+36, GND) inside the VFET amp chassis.
Nelson Pass is unashamed of using an Edcor transformer, maybe you can become unashamed too.
Transistor 1x buffer can be an opamp, or an emitter follower, or a 4T "diamond follower", or a dedicated 1x buffer IC like HA-5002 or BUF634A or LT1010. These are M2x designs Tucson, MountainView, Austin, Norwood respectively.
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Nelson Pass is unashamed of using an Edcor transformer, maybe you can become unashamed too.
Transistor 1x buffer can be an opamp, or an emitter follower, or a 4T "diamond follower", or a dedicated 1x buffer IC like HA-5002 or BUF634A or LT1010. These are M2x designs Tucson, MountainView, Austin, Norwood respectively.
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Nothing to be ashamed of. Edcor makes good products and the quality of their magnetic laminations is top notch. As good as it can be with FeSi laminations.
The nominal gain of 10 dB is for the VFET output stage, I suppose. Is this correct?
Not correct, read Pass document again and consult post #52 this thread.
Not easy to drive an edcor with a preamp tube and
what would be the point?
transistors do that very well
For me the base preamp designed by Pa is as good as it gets
If i want a tube preamp i just want a tube that does it all, most probably a high mu high gm pentode in triode mode
what would be the point?
transistors do that very well
For me the base preamp designed by Pa is as good as it gets
If i want a tube preamp i just want a tube that does it all, most probably a high mu high gm pentode in triode mode
The point would be to get the Korg NuTube sound ("tube sound") PLUS the Edcor transformer sound. Today, with the audio projects available in the Store, you can buy one or the other but not both at the same time.
OK then the latter request of 15Vrms at 7.5 gain is totally unnecessary...unless one wants to re-design the amplifier but the output stage.
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I love the idea of a traditional tube but a NuTube front end seems way more reasonable. NuTube circuits have not seen a great deal of development outside of default parameters, a front end for this vfet architecture would be great.
So 3 Vrms at the input of the VFET amp is the output of a preamplifier if one does not have high output source. It is not the driver stage for the VFET.
In that case, because of the JFET input the 330K load on the preamp should not change that much with frequency (low capacitance) and the 3S4 or 3V4 as preamplifiers delivering 3 Vrms for full power are suitable at low voltage too.
In that case, because of the JFET input the 330K load on the preamp should not change that much with frequency (low capacitance) and the 3S4 or 3V4 as preamplifiers delivering 3 Vrms for full power are suitable at low voltage too.
But you can't use low voltage. The problem is that you want to drive 5K which is quite low for any preamp tube (with gain).
If you want a two stage amp with tube driving the VFET then the best thing to do is re-design the power supply for the tube and use higher voltage. In that case, as said earlier you have a lot of choice. PMILLET did a lot of testing with high-gm pentodes. As you can see in triode mode driving 4-8K they are quite capable of 10Vrms with low distortion.
High Gm driver pentodes
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Korg NuTube combined with Edcor has not been to my liking (tried that for Mofo)
I shall (hopefully) listen one day to the VFET as designed by Pa. I guess that the base pre is a very good companion for the power follower.
I shall certainly compare with the tube preamps i have. Everything is open at this stage...
I shall (hopefully) listen one day to the VFET as designed by Pa. I guess that the base pre is a very good companion for the power follower.
I shall certainly compare with the tube preamps i have. Everything is open at this stage...
The NuTube is a fun toy, but it would need a lot of extra buffering and pampering to do what we need. I wouldn't call this a proper tube input stage. 😀
While there are many ideas and tube types thrown into the discussion, I'd like to clarify the limits for B+ voltage. What is the max. DC voltage that would be considered "safe enough" for novice builders? We can probably go higher than 50 VDC, but I feel 500 VDC is clearly too much. Any thoughts on this?
While there are many ideas and tube types thrown into the discussion, I'd like to clarify the limits for B+ voltage. What is the max. DC voltage that would be considered "safe enough" for novice builders? We can probably go higher than 50 VDC, but I feel 500 VDC is clearly too much. Any thoughts on this?
What is the max DC voltage that off the shelf DC-to-DC converters (of suitable size) can produce?
What is the max DC voltage that thru-hole mounted, roll your own DC-to-DC converter, controller ICs can produce (with external HV transistors)?
What is the max DC voltage that thru-hole mounted, roll your own DC-to-DC converter, controller ICs can produce (with external HV transistors)?
As of today there are five "base pre" boards (Nelson Pass calls them "Front End" boards) 100% released, plus one more in limited, friends and family only, sampling for prototype review & listening evaluation.
He mentions these five "Front End" boards several times in the VFET amp design document, attached to post #55 of this thread. Check pages 2, 5, 17, and perhaps other places too.
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I would certainly go for the JEFT + VFET and drive it with a tube preamp with 5x gain delivering 3 Vrms, although this is the contrary of what I normally do. Low level signal (Digital source, phono preamp and line preamp, if any) I prefer solid state and power amp with tubes.
The one from Pete Millet goes up to 400VDC
I have also three Chinese ones that go up to 350 and 400VDC
The small modules I found at Mouser etc. (example) seem to go up to 48 VDC or +/-15 VDC (=30 VDC). Their isolated outputs could be connected in series with the 36 VDC input, resulting in up to 36 + 48 = 84 VDC. Using multiple modules would allow higher voltages.
I am pretty clueless with these... my gut feeling is that several hundred volts might be feasible. I hope that others will provide better insights.
Where is the limit for "novice compatibility"?
Yeah the NuTube seems to be love or hate, personal taste or technical disdain. Still it makes the most sense in this application with this PS. Also B+T+NuTube sounds like a path which should be explored. In 2 month when the wider architecture is released and people build and run other power supplies, the conversion changes.
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