John Curl's Blowtorch preamplifier part II - Page 2324

john curl · 21st May 2012, 05:26 AM

I really don't know. I designed that circuit in 1974, as a horn tweeter (T-350) amplifier for a 3 way all-horn loudspeaker system with John Meyer, in Switzerland. It worked quite well, at the time.
Mark Levinson wanted a slightly 'improved' version in 1975, for a small amplifier, which he built.
What is important is that: The amplifier is very fast considering the lowish Ft bipolar transistors available at the time, about 100V/us.
The design followed Otala's recommendation of reducing the open loop gain and increasing the open loop bandwidth.
As the original circuit was operated in Class A, heroic efforts for output stage linearity were not too important.
It was a successful experiment, as it worked very well for the task, sounding better than any other commercial solid state amp that we could find to compare it with. We could use commercial amps up to about 5,000Hz without too much trouble, but above 5KHz, they all sounded lousy, until the Otala prototype arrived within the year, and I bought it immediately, especially for electrostatic headphones. One of the best purchases that I ever made.
Now what does this all mean?
Does it really matter IF the open loop bandwidth is 20KHz? I think so, but it is difficult to get it without compromising the distortion level at near full output. It is just a matter of how much global negative feedback is available. Today, NO Parasound power amp has internal feedback resistors that reduce the open loop gain, it just is not practical.
So where is the argument? I compromise, like just about everybody else, to get 'specs'. I just don't 'sell out' to make a 'spec' at the lowest cost possible, trading any potential sound quality for it.
The CTC Blowtorch is the ONLY product that I have yet produced, that is not 'compromised' by commercial concerns, and I have not made one for at least 5 years and never expect to make another. Yet, I will say, it is the best piece of electronics I have ever made, and I expect it to last me my lifetime. Everything else is a compromise that I would replace, if I had the time and money to do so.

john curl · 22nd May 2012, 03:41 PM

Well, I guess I scared everyone away! Sorry about that. I hope it is understood that I simply attempted to describe the design philosophy behind the JC-3. It was not a 'tour-de-force' of advanced mathematics, but a mating of a successful line driver with an output stage, to make a small power amplifier. It worked.

morinix · 23rd May 2012, 02:23 AM

Quote:

Originally Posted by john curl

Well, I guess I scared everyone away! Sorry about that. I hope it is understood that I simply attempted to describe the design philosophy behind the JC-3. It was not a 'tour-de-force' of advanced mathematics, but a mating of a successful line driver with an output stage, to make a small power amplifier. It worked.

You didn't scare me away. I'm just busy building my preamps right now

Chris Hornbeck · 23rd May 2012, 02:51 AM

We're *all* guilty of hubris, of believing that the map is the world (our map! and not somebody else's), of believing our linear models of a non-linear world, and of curve-fitting from the safe mechanical known to the dark perceptual unknown. What else can we do? We're a modeling species - it may not even be possible for there to be any other kind of intelligent species.

But sometimes it's also valuable to accept that we don't really know *everything*, and that in the remaining twilight areas the "lore" of experienced trackers is most valuable. That's why I read this thread, for the lore. Thank you for keeping it going.

There's a Tarkovski movie whose title is translated poorly into English as _Stalker_ that comes to mind somehow.

Ruminations, sorry. But thanks for the thread,
Chris

iko · 23rd May 2012, 02:57 AM

Quote:

Originally Posted by john curl

The CTC Blowtorch is the ONLY product that I have yet produced, that is not 'compromised' by commercial concerns, and I have not made one for at least 5 years and never expect to make another. Yet, I will say, it is the best piece of electronics I have ever made, and I expect it to last me my lifetime. Everything else is a compromise that I would replace, if I had the time and money to do so.

If you can do a better one, why not do it? You will be remembered by what you do. And if jfets are not good enough any longer, why not do tubes?

PMA · 23rd May 2012, 04:46 AM

I wanted to ask the same. When speaking about 'not compromised product' (preamplifier), tubes are even better parts than JFETs. Why not 6H30, e.g.

hitsware · 23rd May 2012, 05:30 AM

No compliments. BIG part of Johns approach.

john curl · 23rd May 2012, 06:04 AM

My forte is jfets. I have a lifetime supply. I will leave tubes to people more skilled in that effort, like JC Morrison. I do KNOW that some tubes are really more linear than any jfet can be.

morinix · 23rd May 2012, 12:55 PM

Quote:

Originally Posted by john curl

My forte is jfets. I have a lifetime supply. I will leave tubes to people more skilled in that effort, like JC Morrison. I do KNOW that some tubes are really more linear than any jfet can be.

The best tubes are not made anymore just like the best jfets

wayne · 23rd May 2012, 09:03 PM

Well John with your Jfet's you won't have to worry about them breaking in or burning out.

23rd May 2012, 04:46 AM	#23236
PMA diyAudio Member Join Date: Apr 2002 Location: Prague, Kitakyushu, Fukuoka	I wanted to ask the same. When speaking about 'not compromised product' (preamplifier), tubes are even better parts than JFETs. Why not 6H30, e.g. __________________ Pavel Macura http://www.linkedin.com/pub/pavel-macura/4/783/637 http://web.telecom.cz/macura/audiopage.html

23rd May 2012, 05:30 AM	#23237
hitsware diyAudio Member Join Date: Mar 2002	No compliments. BIG part of Johns approach. __________________ http://www.youtube.com/watch?v=xZmfCYr8mwA

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21st May 2012, 05:26 AM	#23231
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	I really don't know. I designed that circuit in 1974, as a horn tweeter (T-350) amplifier for a 3 way all-horn loudspeaker system with John Meyer, in Switzerland. It worked quite well, at the time. Mark Levinson wanted a slightly 'improved' version in 1975, for a small amplifier, which he built. What is important is that: The amplifier is very fast considering the lowish Ft bipolar transistors available at the time, about 100V/us. The design followed Otala's recommendation of reducing the open loop gain and increasing the open loop bandwidth. As the original circuit was operated in Class A, heroic efforts for output stage linearity were not too important. It was a successful experiment, as it worked very well for the task, sounding better than any other commercial solid state amp that we could find to compare it with. We could use commercial amps up to about 5,000Hz without too much trouble, but above 5KHz, they all sounded lousy, until the Otala prototype arrived within the year, and I bought it immediately, especially for electrostatic headphones. One of the best purchases that I ever made. Now what does this all mean? Does it really matter IF the open loop bandwidth is 20KHz? I think so, but it is difficult to get it without compromising the distortion level at near full output. It is just a matter of how much global negative feedback is available. Today, NO Parasound power amp has internal feedback resistors that reduce the open loop gain, it just is not practical. So where is the argument? I compromise, like just about everybody else, to get 'specs'. I just don't 'sell out' to make a 'spec' at the lowest cost possible, trading any potential sound quality for it. The CTC Blowtorch is the ONLY product that I have yet produced, that is not 'compromised' by commercial concerns, and I have not made one for at least 5 years and never expect to make another. Yet, I will say, it is the best piece of electronics I have ever made, and I expect it to last me my lifetime. Everything else is a compromise that I would replace, if I had the time and money to do so.

22nd May 2012, 03:41 PM	#23232
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	Well, I guess I scared everyone away! Sorry about that. I hope it is understood that I simply attempted to describe the design philosophy behind the JC-3. It was not a 'tour-de-force' of advanced mathematics, but a mating of a successful line driver with an output stage, to make a small power amplifier. It worked.

23rd May 2012, 02:51 AM	#23234
Chris Hornbeck diyAudio Member Join Date: May 2011 Location: Little Rock	We're all guilty of hubris, of believing that the map is the world (our map! and not somebody else's), of believing our linear models of a non-linear world, and of curve-fitting from the safe mechanical known to the dark perceptual unknown. What else can we do? We're a modeling species - it may not even be possible for there to be any other kind of intelligent species. But sometimes it's also valuable to accept that we don't really know everything, and that in the remaining twilight areas the "lore" of experienced trackers is most valuable. That's why I read this thread, for the lore. Thank you for keeping it going. There's a Tarkovski movie whose title is translated poorly into English as _Stalker_ that comes to mind somehow. Ruminations, sorry. But thanks for the thread, Chris

23rd May 2012, 06:04 AM	#23238
john curl diyAudio Member Join Date: Jul 2003 Location: berkeley ca	My forte is jfets. I have a lifetime supply. I will leave tubes to people more skilled in that effort, like JC Morrison. I do KNOW that some tubes are really more linear than any jfet can be.

23rd May 2012, 09:03 PM	#23240
wayne In the hills diyAudio Member Join Date: Jan 2002 Location: Northern California	Well John with your Jfet's you won't have to worry about them breaking in or burning out.