John Curl's Blowtorch preamplifier part II

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VladimirK

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Joined 2007
john curl said:
For everyone to know and understand, this paper from a Russian Scientist is virtually what I have been trying to put up here for almost 10 years, in my own limited way. It is a KEY to understanding why circuits that Charles Hansen, Nelson Pass, and I make are so 'successful'.
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What is interesting, attention to this paper has been drawn by one strong supporter of NFB at one russian forum. But he was trying to simulate and to measure with all possible details just a transfer function of his amps. And he has catched it very fast, that if we look at the TF from dynamical point of view (their is nothing infinitely fast), then even GNFB can cause a kind ot TF jitter. I would add, after-action of electrolytic caps can also add. So we may deal with "thickening" of TF line, and it cause some loss of signal microdetais.
What everybody always note with deep GNFB designs.
Chumakov speaks not about pure kinds of noise generated by parts, but about "effective noise" due to all kinds of imperfections of dynamical origine.
In SE tube designs we have no zeners, no bad electrolytics, no transistor distortions due to chip temperature variation under signal, no or short feed back path - vuala, good pure sound, plenty of microdetails.
In a russian forum, they have reported listening impressions from three designs
1) tube SE amp by Makarov (russian tube guru, makes amps of 500kg weight)
2) deep GNFB SS amp by Sergei Ageev (russian SS guru, improving implementation of the same schematics for the last 20 years, not to confuse with Ageev-academician and his theorem)
3) low power but very fast SS amp, with very short and fast current NFB path (something like 500V/uS in the FB loop)
Main claim to the amp 2) - loss of microdetails (of cause, in comparison with the amp 1), amp 3) was closer to amp 1) )

Other system's components were
CDP Mark Levinson, near 30 000 USD price tag
speakers Montana, near 80 000USD price tag
Before claiming about microdetails, they have listen also during a night time, at very silence
 
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ThorstenL

ThorstenL

Previously: Kuei Yang Wang
Joined 2002
linkedin.com/in/thorsten-loesch-studio-raumklangg/
Hi,

PMA said:
But tube preamplifiers and amplifiers are very noisy :)
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They are? That is news to me! How come I never noticed?

Let's be realistic.

Tube Amplifiers and Preamp's can be very quiet. But they need to be designed to be quiet. I believe the same holds true for solid state amplifiers...

Ciao T
 
ThorstenL

ThorstenL

Previously: Kuei Yang Wang
Joined 2002
linkedin.com/in/thorsten-loesch-studio-raumklangg/
Hi,

VladimirK said:
Without external PS, in tube designs it is usually difficult to get rig from 100Hz tone. But I am not sure that they produce a lot of white noise.
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Well, a MC sensitive Phonostage I designed and which has two big transformers and two chokes on-board, manage around -80dB re 0.5mV for 50 & 100Hz and are only a few dB above the general noisefloor at LF. John Atkinson measured SNR as around 80dBA as well.

As MC Phono Stages are usually the toughest to get low noise any other item should manage better.

Ciao T
 
ThorstenL

ThorstenL

Previously: Kuei Yang Wang
Joined 2002
linkedin.com/in/thorsten-loesch-studio-raumklangg/
Hi,

PMA said:
How would you design a tube preamplifier for 1-2 nV/rtHz input eq. noise? MC stage without input transformer, e.g., would be my question.
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I can tell you how I did it, if that helps?

E88CC parallel cascoded, run at loads of current. Probably around 2nV|/Hz A Weighted... The WE 437A also comes clsoe to those noise figures, arguably tubes need to be selected.

If we can use more exotic tubes we can do better. The E810F run at zero bias and around 40V Anode voltage (cascoded) gives similar trasconductance and noise as a 2SK170...

Ciao T
 
vuki

vuki

Member
Joined 2002
drzlab.com/
VladimirK said:
Other system's components were
CDP Mark Levinson, near 30 000 USD price tag
speakers Montana, near 80 000USD price tag
Click to expand...

In picture...
 

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Joao@AltheaMusica

Member
Joined 2009
altheamusica.com
john curl said:
Joao, you are asking a difficult question and the answer should become obvious from my design history over the last 45 years or so.
In the beginning of solid state, there were only single gender solid state devices for the most part. PNP Ge transistors, and NPN silicon transistors. Attempts to mix them did work, but not well.

By 1967, Motorola came out with a range of devices from small signal to complementary power transistors that allowed true complementary operation. This is when I started designing in earnest on a 'super' solid state power amp. Jfets were available for special applications, BUT they were very noisy and had low gain. Selected parts 'could' work fairly well, even then, and in 1968, while at Ampex, I made my first jfet (selected) input analog tape reproduce stage. It was a little noisy, but not much different, (except in noise sonic character) from what we normally used. I knew that it was only a matter of time when jfets would get much quieter, on average, and that it was only processing problems that kept it relatively high at the time. Still, there were only Nchannel jfets that were reasonably quiet, until the early 1970's, when Siliconix came out with a whole series of jfets, some complementary, and some that were VERY low noise, about 1nV/rt Hz at mid frequencies. This became my source of new designs, but before this, I made dozens of prototypes of amps from 15W-2000W, line drivers, etc, etc. for pro audio, all from complementary bipolar transistors, with some success. Still, the jfets held a lot of attraction to me, because by mathematical definition, they were more linear.

At first, I only changed my input stages to jfets, instead of bipolar. The circuits were faster, and tended to have lower order distortion. This was good. Then, for the Levinson JC-2 phono stage, I used complementary devices for the output followers, as well. This worked well, also. Please remember that I count on 'listener feedback' of my designs by other interested parties, to make a real determination of progress. I was then getting famous with what these circuits did in the consumer audio world with Mark Levinson's products, and in the pro world with my work for the Grateful Dead. If the 'public' did NOT like my designs, they would have made it obvious.

Still, during the 1970's, it was almost impossible to replace complementary output transistors, until the advent of Vfets, Vmos, and power mos, in the mid to late 70's. Then I could make my entire circuit with fets, and I made many examples like this. Still, I found that bipolar devices worked very well for many applications, including output devices, and I use them today, that way. That is about it.
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John, eery time it's nice to read your progress overthe years and your experience - thanks.

Yes, the JFets might be like tubes, when we look to the tubes designed in the full bloom of their time (espected powertriodes) because the curves of the FETs are like tubes like EL8etc.

To my experience FETs sound more groundy and with more clearity compared to the more "airy" sound of BJT. Is combining FET/BJT in a cascode the linear application, and what about the differences from a single cascode compared to a cascoded dierential input?
 
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