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Old 9th April 2014, 01:41 AM   #201
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Quote:
Originally Posted by Jon Lord View Post
I have an internal SONY technical report at hand, which shows THD spectra of a TAN-8550 with and without overall feedback applied. The open loop THD was less than 0.1%, far below the claimed 2% of the Pass design using the switch V-FETs. You can be sure, that three pairs 2SK60/2SJ18 pair at rank 58 was much better matched (at least at that time), than you could do with the last remaining stock of 2SK82/2SJ28 (which were made for switching applications !)
While making a sally, I didn't remember a certain detail accurately of this very technical report from SONY about the TAN-8550. It was not 0.1%, but 1% THD, certainly H2 dominated in open loop, but at 75dB open loop gain and 100W into 8 Ohms.

What is very interesting is the fact that open loop THD is identical at 1kHz and 20kHz and also constant between 1 and 100W. The small signal open loop bandwidth was 35kHz, dominated by compensation. If these BW and gain figures are correct (they sound almost too good to be true), the GBP would therefore be 140 MHz at 35kHz. Very impressive in 1974 and still also nowadays ...

The first functional protos of the SONY V-FET amp were btw. already running in 1969 (At that time in housings looking like a TA-3120). It needed until 1974 to make the V-FET device or the LSI process fab they were produced in (almost) mass production proof.
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Old 9th April 2014, 03:02 AM   #202
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It would be nice if you would be so kind as to post the very technical report as an attachment or a link. Rgds
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Old 9th April 2014, 05:13 PM   #203
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Quote:
Originally Posted by Jon Lord View Post
That disadvantage, which already exists for non bridged PP V-FET amps in a more mild form is btw. greatly reduced by running the V-FETs in cascode with bipolars (like SONY TA-N7B), as you also can read in official technical SONY literature. But this then wouldn't be an amp with a "pure" V-FET output stage anymore ...
You seem to be operating from some mis-information.

I will address some of your points later, but here is a schematic of the TA-N7
amplifier, showing that in fact the VFETs are being used to cascode the
Bipolar outputs, not the reverse. This is a bipolar amplifier in my opinion,
and any part would have served as the cascode - here it is simply convenient
that the VFETs are self biasing.

Attached Images
File Type: jpg TAN7os.jpg (98.9 KB, 299 views)
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Old 9th April 2014, 06:20 PM   #204
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Quote:
Originally Posted by Jon Lord View Post
.... We don't have a schematics of it so far ... and that's good, that nobody tries to clone it, burning even more V-FETs for a horrible 2% of distortion afte matching a hundred ...
You are conflating the performance of two entirely different amplifiers.

One, the published DIY project is a common-source amplifier in which the
VFETs are expected to provide both voltage and current gain.

The other, which was made for Sony and is more in keeping with Sony's
particular needs, is a Common Drain (follower) design.

As you should know, followers inherently contain their own feedback in the
form of degeneration with the load. They tend to measure a lot better
for that reason, and don't make for an apples-to-apples comparison.

The amplifier made specifically for Sony's 4 ohm AR1's does 0.6% thd at
100 watts into that load with 6 dB of feedback and has a bandwidth of -3dB
at 100 KHz. I believe that this is comparable to the measured performance
you quote. Attached is a curve.

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File Type: gif SONY DAMP 4.gif (7.6 KB, 274 views)
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Old 9th April 2014, 06:24 PM   #205
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Quote:
Originally Posted by Jon Lord View Post
Complementary+bridge symmetry certainly helps canceling second order nonlinear effects of junction caps, but doesn't help a lot for the remaining symmetrical modulation of the group delay and such an effect can often be heard easily, even if no widely accepted easy measurement routines (or a large promoting group of people) exists for that.
This would be the kind of argument that would be more popular over in the Blowtorch thread.

I don't get excited by the symmetrical modulation of group delay in an
amplifier with 100 KHz bandwidth and little or no feedback.

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Old 9th April 2014, 06:26 PM   #206
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Pa , you forgot to confirm that OS VFets in PapaSonyAmp are driven in a rather sluggish way ........



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Old 9th April 2014, 06:45 PM   #207
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Quote:
Originally Posted by Jon Lord View Post
Declaring the 0.5A idle current in e.g. a TA-8650 as being Class B strictly follows the definition of Douglas Self, that Class B is where the minimal (static) crossover distortion is. Above the associated bias point you get gm rise (often called gm doubling), below you get gm droop close to zero.
I do not accept a 0.5A bias as being Class B. I regard it as AB.

I recall that Douglas Self (who is a great bloke, BTW) is talking about bipolars.

When it comes to THD measurement, he is totally correct on the matter of
"optimal bias" as well as the proper ballast resistors to use to get the effect.

As to sound, there is a little more controversy - I have noted that higher
bias in bipolars still sounds better than "optimal" and this was how I biased
the Threshold "Stasis" amplifiers - they measured better at lower bias, but
they sounded better at higher bias.

With FETs, it is my considered opinion that (within rational limits) the higher
bias the better. All you have to do is build an output stage and measure
the distortion vs bias current and you will clearly see what I mean.

I attach some graphics of distortion vs bias for a push-pull follower FET
output stage:

Attached Images
File Type: jpg FIG 3.jpg (80.2 KB, 270 views)
File Type: jpg FIG 4A.jpg (182.6 KB, 268 views)
File Type: jpg FIG 4B.jpg (170.3 KB, 265 views)
File Type: jpg FIG 4C.jpg (168.8 KB, 81 views)
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Old 9th April 2014, 06:49 PM   #208
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Quote:
Originally Posted by Jon Lord View Post
And I expected to get all kinds of negative criticism of almost all people here. Just like stirring up a hornet's nest and that's exactly, what I wanted to provoke The massive reaction also showed to me, that some people were deeply hit in their unreflected believes.
It has been my friendly intention to respond to your provocative comments.

I appreciate the opportunity to get up on my soapbox and trot my erudition
out for the benefit of all.

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Old 9th April 2014, 10:45 PM   #209
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Quote:
Originally Posted by Nelson Pass View Post
Operated Common-Source with 18 dB of gain, I get about 3 nF effective input
capacitance.

Some passive preamps (maybe a few actives too) will be very unhappy...
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Old 10th April 2014, 12:17 AM   #210
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Quote:
Originally Posted by Nelson Pass View Post
It has been my friendly intention to respond to your provocative comments.

I appreciate the opportunity to get up on my soapbox and trot my erudition
out for the benefit of all.


Thank you Papa…..you have removed most opportunity for confusion amongst even we lesser mortals!

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