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In Reply to: RE: Solid State Power: MOSFET vs. Bipolar? posted by Duster on October 4, 2010 at 13:26:32
has been all bipolar, input, VA, driver with Hitachi Lateral MOSFET outputs.
Go figure.
Never attribute to malice that which can be adequately explained by stupidity.
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Like I said, ironic.
I've heard jfet/mosfet/bipolar that I thought were outstanding as well.
Speaking generally, I can't say I care for all bipolar, too shrill or all FET, too veiled.
Never attribute to malice that which can be adequately explained by stupidity.
I never heard one either. They were supposed to be pretty good for a $495 kit amp back in 1980. I can't imagine they'd be competitive today, but who knows? What was the amp you liked so much?
It's losely based on a Hitachi application note from '77, and then I believe the Maplin 150 shared elements of it. I believe Erno Borbely used elements of this when at Hafler.
An article appeared in Electronics World in August, 2001 that has a modified and updated schematic. I have substituted some parts and use heavily biased vertical MOSFETs.
I am wanting to try lateral MOSFETs as these are supposed to sound even better and would allow me to get rid of the bias circuit and replace it with one fixed resistor.
I'll see if I can dig it up.
Never attribute to malice that which can be adequately explained by stupidity.
I still have the original Hitachi databook from 1977 with the suggested schematic, so I know it quite well. The circuit is very ordinary -- nothing unusual at all except for the MOSFETs.
The Hafler DH-200 is fairly similar although with one large difference. The Hitachi circuit is a conventional circuit, with the only complementary stage being the output stage. The Hafler circuit is fully complementary from input to output, as first exemplified by the Ampzilla (James Bongiorno) and later "the Leach amp" (as a construction article in Audio magazine by GIT professor Marshall Leach was popularly known as).
I'm sure that you can find used DH-200's for less than $200, and they would make a fine platform for modification. I think that the XL-280 would be even better, but they are much less common, probably more expensive, and have a JFET input stage that violates your "magic formula".
If you like the vertical MOSFETs, you may or may not like the lateral ones better. The lateral ones are much more linear and even lower in measured distortion. (You may need to parallel additional output devices to compensate for the lower transconductance.) The vertical devices are quite colored (due to their nonlinearities), but some people apparently like that sound. You may or may not be one of them.
there is no magic formula. I just mentioned one particular topology I liked.
I'm familar with all those circuits you mentioned. The circuit I'm using has added CCS to the input long tailed pair and a complementary CCS to the VA stage. The bias generator is much better than the one in the Hitachi design. It's simple, basic and has good sound, kinda like Nelson's F5 is simple yet sounds soooo good.
Vertical MOSFETs biased high(er) do much better in practice than their reputation would suggest. I agree laterals sound much better. I had some IRF640 and IRF9640s on hand at the time, what can I say. Next build I'll use some 2sk1058/2SJ162 or equiv.
I like the McCormack DNA-1 Deluxe alot (the real McCormack, not the CJ era stuff). I beleive that's jfet/mosfet/bipolar, so there you go, there is no one solution to everyeone's problem.
Never attribute to malice that which can be adequately explained by stupidity.
BTW, Mosfets don't sound veiled when run in Class A and without feedback. In this respect they are quite tubelike.
There is nothing wrong with negative feedback.
IMO tubes sound veiled, that, among other reasons is why I prefer SS.
I have posted on this.
Never attribute to malice that which can be adequately explained by stupidity.
"IMO tubes sound veiled, that, among other reasons is why I prefer SS."
You obviously haven't heard good tubes, both with output tranny and without output tranny. The clarity of a good tube design makes all the SS I have heard sound, well, wrong.
Go hear a well designed OTL amp and you will realize that all the amps you have had before were very veiled.
I've never cared for the MOS-FET output amps sound. Every one that I've heard sounded a bit metallic, and there was no doubt that it was MOS-FET.
Now there could some great sounding units out there I have not heard, like Pass Labs current amp line, should sound great.
My preferred amps are Nelson Pass STASIS units, or Yamaha M series. To me, they are the best bang for the buck.
As always, YMMV.
"What this country needs is a good 5 watt amplifier!" (Paul Klipsch)
I recommend that you try a true Class A design (or at least heavily biased A A/B) with little or no feedback. Hybrids in particular work well with a Mosfet output stage with nary a veil or metallic sound in site.
Some examples:
Sphinx Project 16 (100 watt Class A hybrid with Mosfet output)
Sphinx Project 14 (180 watt Class A A/B hybrid (20 watts Class A)with mosfet output)
Monarchy Audio SE160 (160 watt Class A A/B hybrid (50 watts Class A) monos with Mosfet output)
Acoustic Plan Santor (50 watt Class A A/B hybrid (20 watts Class A) with mosfet output)
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