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Old 11th February 2012, 05:58 PM   #1
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Default Vintage V-FET Amps - Why So Little Interest These Days?

I've been wondering this for quite a while now and I'm hoping someone can help me with an answer. Why is there such little interest these days in these amps? I have a Yamaha B-2 and I'm always amazed at how wonderful it sounds; such depth and detail in the sonics.

V-FET's make so much sense as audio amplifying devices and except for Nelson Pass no one else seems to be too interested in them. Can anybody tell me why that is please?.

Last edited by Yamahear; 12th February 2012 at 08:05 AM.
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Old 11th February 2012, 06:33 PM   #2
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Not true.

If you have a reliable source for these devices which still functions, please let us know.

3 years ago I bought 20 of them from a reliable supplier in Germany, NOS unused.
I measured all of them, and they no longer adhered to their ranking specs.
Luckily the vendor was willing to take them back.

So even if you can still get them now as NOS, there is no guarantee that they are as new.


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Old 11th February 2012, 06:46 PM   #3
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Lack of complementary symmetry devices. Safety, as the schematic of B2 shows a power supply = 200 V plus the +/- 80V supply of the output stage. The B2 is more complex than the run of the mill power amp. It has additional circuitry to sequence its turn-so as to protect the V-FETs. At the end of the day it boils down to cost-performance.

DIYers acting as or on behalf of Audiophiles may spur demand. Most probably you've read parts 1 and 2 of L'Amp SIT Amplifier by Michael Rothacher.
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Old 11th February 2012, 07:04 PM   #4
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V-FETs are pretty much made out of unobtainium. If a vintage V-FET amp blows up (Sony TA-5650s are particularly notorious for this when the rail bypassing 'lytics are dead, and they commonly are after 35+ years), repair requires reworking the circuitry to accept other parts. Needless to say, major drama ensues.

There are so many ways of building amps with excellent performance these days, so why bother with extinct technology?

The most exotic technology ever brought back has to be magnetostatic headphone drivers. But even those weren't totally extinct, their equivalent of Nautilus is named Fostex T-50RP.
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Old 11th February 2012, 08:07 PM   #5
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Quote:
Originally Posted by Antoinel View Post
Lack of complementary symmetry devices. Safety, as the schematic of B2 shows a power supply = 200 V plus the +/- 80V supply of the output stage. The B2 is more complex than the run of the mill power amp. It has additional circuitry to sequence its turn-so as to protect the V-FETs. At the end of the day it boils down to cost-performance.
From what you bring up I doubt if you actually know the B2.
I do know the amp; had one which got all electrolytics replaced, sounding great then.
The input/driver stage has a regulated +/- 80V supply; the output stage runs on +/- 55V unregulated supplies.
When you look into the schematics, it looks more complicated than it actually is.
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Old 11th February 2012, 08:36 PM   #6
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I agree with you pieter t regarding my ignorance of B-2. It was due to a momentary lapse of good recall!. Sorry for my misquote. I do not have the amplifier like you; but I have the service manual of its father the B-1. The B-1 is a brute. It delivers 360 W continuous RMS power per channel into 4 or 8 Ohm loads. I also misquoted above the power rails of the output stage of the B-1 which were/are equal to +/-85 V instead of +/-80 V. Regards.
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Old 12th February 2012, 02:00 AM   #7
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Does the Digital Do Main B-1a amp uses the same class of transistors ?

6moons audio reviews: RoadTour Digital Do Main
Digital Do Main B-1a review | from TechRadar's expert reviews of Amplifiers
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Old 12th February 2012, 08:55 AM   #8
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Quote:
Originally Posted by Antoinel View Post
Lack of complementary symmetry devices. Safety, as the schematic of B2 shows a power supply = 200 V plus the +/- 80V supply of the output stage. The B2 is more complex than the run of the mill power amp. It has additional circuitry to sequence its turn-so as to protect the V-FETs. At the end of the day it boils down to cost-performance.
Agreed, to build an amp like the B-2 from the ground up today might not make much sense as far as cost vs performance goes but there are enough of them out there that can be picked up fairly cheaply and with a little DIY restoration like new caps and protection relays these amps sound spectacular and will likely continue to perform magically well into the future at relatively low cost as compared to the cost of a more modern amp.

Quote:
Most probably you've read parts 1 and 2 of L'Amp SIT Amplifier by Michael Rothacher.
Yes, a very enjoyable read to be sure!
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Old 12th February 2012, 09:24 AM   #9
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Quote:
Originally Posted by pieter t View Post
When you look into the schematics, it looks more complicated than it actually is.
Yes indeed!

Click the image to open in full size.
Attached Images
File Type: jpg B2 Block Diagram.jpg (150.0 KB, 411 views)
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Old 12th February 2012, 10:08 AM   #10
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Quote:
Originally Posted by Yamahear View Post
why that is ?
What better proof that logistics drives a market, manufacturers value continuity over technology.
The P can afford to get into the V, due to his marketing talent and status in the geographical area where the real money is at.
(plus sell a lot of VW's, before losing cash on making a Bugatti)
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