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Old 13th August 2014, 06:53 PM   #371
Zen Mod is offline Zen Mod  Serbia
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Default Here they are , What's the Buzz , parts I and II

tnx to Mr. M.

non-shrinked :

Part I

Part II
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Old 16th August 2014, 04:48 PM   #372
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Thank you Dr. Mazzola for your reply and clarifications in Post #365. I am glad/proud to say that you have a successful college course [for Spring 2015] entitled "What's the Buzz?; which bridges the objective transfer function of semiconductors with their subjective sound. Mr. Pass may wish to lecture this future class about his complementary point of view. Like others, I look forward to Part III.

I hope that you include in Part III:

1. Additional detail on the basis, application and especially the benefit/sonic value of Schade Feedback in semiconductor circuits; which to me is a mysterious phenomenon.

2. Simulating the performance of power SIT like that described by DIYer wrenchone in his thread entitled "L'Fake .. " in the Pass Labs Forum.

N.B. The shortcoming of BJTs that you highlighted in post #365 maybe alleviated by using LM395 K/T as a well-behaved BJT model; which was called in 1976 [or earlier by National] an "Ultra Reliable Power Transistor".

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Old 16th August 2014, 05:35 PM   #373
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O. H. Schade …… Beam Power Tubes , article about special feedback , 1938 | Zen Mod Blog

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Old 16th August 2014, 05:43 PM   #374
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Hello Zen Mod. Thank you for the pdf on your blog site regarding Schade.
Best regards.
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Old 16th August 2014, 09:17 PM   #375
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My continuing study of "What's the Buzz? Part II" led me to propose this hypothesis regarding the superb performance of THRESHOLD power amps. Their NPN and PNP transistors of the output stage which operate using the famous "STASIS" mode, operate at their Sweet Spots in Candy Land; like that described by Dr. Mazzola.
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Old 17th August 2014, 09:46 PM   #376
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Thanks for the great ideas. I've been scoping the article in my mind. As Bob Seger's song Against the Wind goes, "what to leave in, what to leave out..."

I looked up the part you mentioned. Here's a concise description from a datasheet:

"The LM195/LM395 are fast, monolithic power integrated circuits with complete overload protection. These devices, which act as high gain power transistors, have included on the chip, current limiting, power limiting, and thermal overload protection making them virtually impossible to destroy from any type of overload."

Interesting trick and I agree it could fix both the thermal stability and the base current issue. But, without any experience at all with such a gain device (notice I don't call it a transistor), I would express caution about all that protective stuff. Could it introduce unexpected features during audio reproduction? What sort of unexpected features? Well, the overload monitoring circuitry works by influencing the transfer characteristics. In other words, I suspect the protective circuitry could create distortion in the signal being amplified. Looking at the output curves in the datasheet you can see the power limiting explicitly in the output curves. That is something to be wary about. Maybe you can give one a spin and let us know?

But the little application circuits shown in the datasheet are sooo 1976. What a great time to be a teenage DIY circuit builder! Popular Electronics, Forrest M. Mims III, Radio Shacks with stuff worth buying, beer, girls

Quote:
Originally Posted by Antoinel View Post
Thank you Dr. Mazzola for your reply and clarifications in Post #365. I am glad/proud to say that you have a successful college course [for Spring 2015] entitled "What's the Buzz?; which bridges the objective transfer function of semiconductors with their subjective sound. Mr. Pass may wish to lecture this future class about his complementary point of view. Like others, I look forward to Part III.

I hope that you include in Part III:

1. Additional detail on the basis, application and especially the benefit/sonic value of Schade Feedback in semiconductor circuits; which to me is a mysterious phenomenon.

2. Simulating the performance of power SIT like that described by DIYer wrenchone in his thread entitled "L'Fake .. " in the Pass Labs Forum.

N.B. The shortcoming of BJTs that you highlighted in post #365 maybe alleviated by using LM395 K/T as a well-behaved BJT model; which was called in 1976 [or earlier by National] an "Ultra Reliable Power Transistor".

Best regards.
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Old 18th August 2014, 12:35 AM   #377
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100% Schade feedback applied to a SJEP120R100 JFET on a curve tracer with an eight ohm load line superimposed. Other than the curves are upside down due to the need to trick the curve tracer, they look similar to those in O.H. Schade's original article, especially to what can be seen in Fig. 34. Definitely going to talk about this in Part III...

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File Type: jpg Schade_Figure 34.jpg (54.8 KB, 229 views)
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Old 18th August 2014, 01:29 AM   #378
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Quote:
Originally Posted by Semisouthfan View Post
. Maybe you can give one a spin and let us know?

What a great time to be a teenage DIY circuit builder! Popular Electronics, Forrest M. Mims III, Radio Shacks with stuff worth buying, beer, girls
Thank you for your comments. I hope to practice your 7 step procedure on LM395T which I have; so as to extend, and generalize the scope of this application.

During the period of 1975-1979, I was at the Champaign/Urbana campus of the University of Illinois; which was the birthplace of the Parachuting Streakers. I remember on a bright sunny day a chance encounter with possibly Mr. Pass in its auditorium for concerts; demo'ing with other competitors powerful amps driving loudspeakers with low frequencies which caused me to literally run away from their intense sound pressure. This concert auditorium hosted The Carpenters, Tom Jones and Elvis [his final performance] in addition to others which I attended. Those were the days.

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Old 18th August 2014, 01:33 AM   #379
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Ha ha. We probably both listen to the 70's on 7.

Quote:
Originally Posted by Antoinel View Post
Thank you for your comments. I hope to practice your 7 step procedure on LM395T which I have; so as to extend, and generalize the scope of this application.

During the period of 1975-1979, I was at the Champaign/Urbana campus of the University of Illinois; which was the birthplace of the Parachuting Streakers. I remember on a bright sunny day a chance encounter with possibly Mr. Pass in its auditorium for concerts; demo'ing with other competitors powerful amps driving loudspeakers with low frequencies which caused me to literally run away from their intense sound pressure. This concert auditorium hosted The Carpenters, Tom Jones and Elvis [his final performance] in addition to others which I attended. Those were the days.

Best regards.
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Old 19th August 2014, 02:52 PM   #380
poynt99 is offline poynt99  Canada
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Quote:
Originally Posted by Antoinel View Post
1. Additional detail on the basis, application and especially the benefit/sonic value of Schade Feedback in semiconductor circuits; which to me is a mysterious phenomenon.
Antoinel,

In today's terms, Schade feedback is called "Parallel Voltage Feedback" (PVF), and is not uncommon. Check out Nelson's Zen amp for a clear example of how it is used with semiconductor amplifiers.

The application of PVF reduces distortion caused by gain changes that result from changes in the load being driven. However, my simulation tests indicate that the difference in distortion between a MOSFET with and without PVF is negligible when the device is driving no load, other than RD.

The distortion-reducing (actually output resistance reducing) mechanism of PVF is quite simple;

1) The SS device output current becomes partially dependent on the output voltage due to the application of PVF.
2) Vin and PVF are average-summed at the input of the device which lowers the device's mu and gm.
3) If Vout is reduced by loading and not by a change in Vin, then this results in a proportionate increase in Vin (due to PVF), and the correct level of Vout is re-established, essentially mimicking a device with lower inherent Ro.
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