I'd like to chime in to Bob's questions (especially "What do you think is the biggest reason they have such superior distortion characteristics to vertical MOSFETs?").... albeit some aspects seem to covered already in the datasheets and appnotes, like:
Only N-Channel, thus quasi-comps or circlotrons.
175deg is a package limitation.
The gate diode is a parasitic, the devices are true voltage controlled.
- Klaus
Only N-Channel, thus quasi-comps or circlotrons.
175deg is a package limitation.
The gate diode is a parasitic, the devices are true voltage controlled.
- Klaus
audioman54 said:
Hi Mark;
it will be indeed very interesting experience to see and listen results of your work during a Burning Amp!
But currently, we are species of different Universes, despite I've started from the same one; my career started in Tomsk Institute of Semiconductor Devices, it was (and is) one of flagmans of Russian Semiconductor Industry.
At the same time I had a voluntary laboratory of electronic music where I was experimenting a lot deliberately creating distortions designing analog synthesizers and guitar effects. I did not think then that it is so hard to design and build a nice sounding power amp.
I had several design then following fashions, some of them were fully complementary. But I was very surprised when people were saying that my class A+C amp sounded better than all complementary amps, I did not believe that! It had fair class A amp and couple of unbiased complementary transistors working in parallel. Class A amp supplied an output current through resistor, and drove bases of class C output stage. The whole thingy had a complex feedback, so switching from class A to class C was very smooth, and I used as fast as I could find then opamp in an inverting mode then. Anyway, I was thinking that I was cheating approximating a transfer function, and kept believing that properly biased class AB fully complementary amp is the best.
Later I've discovered from Wireless World article that similar approach was patented and called Current Dumping, and the amp that used it was regarded well, even though I did not like that design, it was ugly, according to my preferences.
Switching my career to software design, then to design of networked systems, I still followed audio design as a hobby, and was curious why tube amps are still though out, even though their measurements were worse.
Thanks to Dr. Richard Bandler, the real Master of practical psychology in the field of subconscious perceptions, I finally realized what it is all about. And now I don't believe that complementary topologies can beat asymmetrical tube amps with class A semiconductor output stages, in terms of fooling imagination as if the sound is real.
However, I would like to hear your amps, and get converted back.
See you and your creations on BAF!
Sincerely,
Anatoliy Lisovskiy
Bob Cordell said:
N channel, that's all there is, and I don't expect a P channel in
my lifetime
But of course that still leaves lots of possibilities.I think enhancement mode JFETs is the accurate description. I
haven't seen significant gate current, but I haven't run them past
10 amps or so.
I have a simple Class AB design with a little feedback, and I was
very pleased with it. I plan to kick that out as a DIY project.
Part of the lower distortion you see there is load line cancellation
on that circuit - you'll notice that the dependence on Vds extends
to a higher voltage range than the Mosfets we play with.
Also there is the high transconductance of the part, which is
on the order of 10S or so at the currents I run (<2A), so it responds
well to a little degeneration.
The temperature coefficient is a bit better than vertical Mosfets,
and they bias up at about 1.4 V Vgs at a couple amps or so.
Worst case improvements are about 1/2 the distortion of their
Mosfet counterparts, and the linearity of the capacitance seems
better, with flatter thd vs frequency curves.
All in all, a significantly better part IMHO.
Bob Cordell said:
Hey Bob. That's my (personal) question. As I posted at the outset, it would have to be a quasi-comp. design. And I haven't ever attempted to design (or even simulate) one of those. I've only fixed a few in my day.
So it would seem one of the key questions is do the SiC JFET advantages outweigh the disandvantage of having to use them in quasi-comp. for push-pull? You (or Nelson) are probably better able to answer that question than I am!
They are obviously not targeting the linear market. For linear applications, limiting these devices at 175 C is absurd, SiC can easily take 250 C junction temperature before even thinking about increasing the leakages.
For that, they need to choose another packaging technology. TO3 would be nice, but unfortunately copper and the SiC chip would not (thermally expansion wise) match. A special mounting preform is required, and that would be very expensive, adding to an already huge cost to process those SiC wafers.
Nice devices, but I wouldn't hold my breath for something optimized for linear applications. Great for DIY enthusiast, but little hope for a slew of new, improved performance, designs. I'll check if I can get some, I can see them in a Pass type class A monster amp. Can you feel my HiFi oven singing and cooking french toast at the same time?
For that, they need to choose another packaging technology. TO3 would be nice, but unfortunately copper and the SiC chip would not (thermally expansion wise) match. A special mounting preform is required, and that would be very expensive, adding to an already huge cost to process those SiC wafers.
Nice devices, but I wouldn't hold my breath for something optimized for linear applications. Great for DIY enthusiast, but little hope for a slew of new, improved performance, designs. I'll check if I can get some, I can see them in a Pass type class A monster amp. Can you feel my HiFi oven singing and cooking french toast at the same time?
syn08 said:
Given your MOSFET YAP (and other) excellent amp designs, I'd be very interested to hear more of your thoughts about using the currently available SiC devices in a quasi-complimentary push-pull design? As I posted earlier, I'm especially intrigued by what could perhaps be accomplished with a single pair of these avoiding all the multi-pair issues.
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In a previous life I was looking at SiC for image sensors and high power microwave devices. It's funny stuff, very similar to diamond (people are also making devices from diamond), with huge high field electron mobility (but not so good at low fields), high thermal conductivity and a wide band gap so it's good to high temperatures. In fact you can have an operating transistor that is glowing brightly red-hot at over 600degC !!!
You don't add heatsinks to SiC, you use SiC to make heatsinks
Nelson, I would be very curious as to how they sound - the nature of SiC over the past few years is anything but aimed at the subtleties of audio.
You don't add heatsinks to SiC, you use SiC to make heatsinks
Nelson, I would be very curious as to how they sound - the nature of SiC over the past few years is anything but aimed at the subtleties of audio.
The group of DIYers I hosted last weekend liked both examples,
both the little current source represented by the curve I posted
earlier, and the more sophisticated 25 watt SE with feedback.
As you know, I like really simple Class A amplifiers, but at the same
time I want to minimize distortion, so better parts fill a real need.
both the little current source represented by the curve I posted
earlier, and the more sophisticated 25 watt SE with feedback.
As you know, I like really simple Class A amplifiers, but at the same
time I want to minimize distortion, so better parts fill a real need.
As you know, I like really simple Class A amplifiers, but at the same
time I want to minimize distortion, ...
Nice to read
Well, how can we get them at any price? Discussion otherwise is merely academic, except for papa-type patriarchs. (Not dirting on papa by any stretch of the imagination, but how do us peons get some of these?) If poeple are willing to drop mad money on 300Bs, surely the same can be done here, assuming some sort of distribution channel. What do the Soviets do with these things? They would work very well in oil wells and other nasty places.
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I have built four different amplifiers with these parts, and they are
quite superior to Mosfets.
Here is an example with one place in an F2 circuit, which is a simple
Common-Source stage with no feedback.
Nelson,
Looking at the data sheet they spec quite low resistance for the gate and quite high gate current. How do I interprete that, it that just the resistance/current to charge up the gate or what? Doesn't look like it. Am I missing something?
jd
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