John Curl's Blowtorch preamplifier

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#8,542
Charles Hansen said:


The KX-R has a very similar input stage to the Blowtorch. However, I have changed to current mirrors instead of the folded cascode.

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Charles,

You mentioned the use of mirrors also in the MXR instead of folded
cascodes. Folded cascodes can be made (slightly) more linear than
mirrors, is there any reason you went away from FC?



Also the KX-R has a variable gain stage, eliminating the need for a attenuator-based volume control. The KX-R has a FET buffer output stage, while the Blowtorch runs as a transimpedance amplifier.
Click to expand...

I asked the question some time ago in this thread, why don't
blowtorch and similar open loop designs use an 'active' vol control
at the IP jfet source degeneration? It seems the most obvious
way with least in signal path.

cheers

Terry
 
#8,543
Terry Demol said:

.........
I asked the question some time ago in this thread, why don't
blowtorch and similar open loop designs use an 'active' vol control
at the IP jfet source degeneration? It seems the most obvious
way with least in signal path.
Click to expand...

Terry, are you talking about something like my "proposal", many post ago:

http://www.diyaudio.com/forums/showthread.php?postid=1556535#post1556535
Post: 7371

Yes, the question is still open....

Tino
 
#8,544
pmkap said:


Anatoliy,

Apologies for my previous lack of clarity. My question is how exactly do you define optimal? If it is based on measurements, do you use more than one measurement and how do you weight them?
I'm leaving out subjective measures as one man's optimal, is another man's mush...... but ultimately, from my perspective, my subjective ascessment determines whether I want to listen to it in my system.
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Paul;
I mean the simplest way to satisfy all criteria, no matter are they measured by tools or by human ears. However, available set of active and passive elements limit a lot, as Carl Sagan said, in order to make an omelet from scratch we have to invent the Universe, so active and passive elements have to be selected according to end results, together with their combination. How? I can't explain the algorithm of creative thinking, though I learned DHE from Dr. R. Bandler and J. LaValle.

Edit: I can give you an example.
Suboptimal way to screw the bulb is to take a stool, stand on it, ask 4 people to lift the stool and rotate it clockwise, then ask 4 more to go around to prevent dizziness. An optimal one is to take a stool, to stand on it, and to screw the bulb rotating it.
 
#8,545
As far as feedback volume control is concerned. We used it, 35 years ago, with pro equipment. However, it is more difficult, and even more expensive (I should think) than just using a conventional volume control.
Charles is even more unconventional than even I tend to be.
 
#8,546
john curl said:
As far as feedback volume control is concerned. We used it, 35 years ago, with pro equipment. However, it is more difficult, and even more expensive (I should think) than just using a conventional volume control.
Charles is even more unconventional than even I tend to be.
Click to expand...

The usual way to control sensitivity of microphone preamps is a pot between emitters of differential input stage.
 
#8,547
Steve Eddy said:
It's never made any sense to me to have a gain stage ahead of an attenuator.
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There is at least one manufactuarer that claims otherwise: http://www.ba-labo.com/balabo/f_page/fe_win-bc1.htm

A traditional control amplifier has been employing the pre attenuation method that the input signals are made to decline with attenuaters at the first stage of an amplifier, after that the signals are amplified. This method, however, degrades the sound quality, as low level signals once attenuated are buried into the thermal noises and fluctuations. No matter how excellent amplifier after that the signal made to decline once, the original signal quality can't be restored again. For example, the contents on a paper which were made by size reduction copy once can't be 100% restored by means of a copying machine with a size expanding copy, as detailed information have been lost at the first size reduction and the reproduced copy is felt rough outlined and isn't vivid on the expanded copy. BC-1 uses "Post Attenuation Method" to avoid these degradation. The input signals are amplified at the input stage of BC-1 before attenuation, then made to decline at the later stage of the amplifier to the necessary level to the output. It becomes possible at the next generation high end control amplifier, BC-1, of the dynamic range as well hardly to make it deteriorate and keeping the high purity as to.  The high voltage power supply in BC-1 enables "Post Attenuation Method" without loosing dynamic range and low level linearity.
 

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#8,548
Terry,
You asked about using an atten between the sources/emmitters of a diff pair as again control mechanism.

We did it on our tube line stage of our RTP3 prototype preamp, for about three months.

Sounded great, but had problems that we couldn't solve so we went back to a conventional switched resistive attenuator.

Main problem was shifting DC offsets, which gave huge bangs through the system with a gain control change. You could trim it up but a week later it was banging again.

Second problem was that to get enough gain change, that R had to go from zero to 100k, then the fequency response was really screwed, as the stray capacitances gave far less atten at 100kHz and up - than at lower freqs.

The problems may have been much lower with a solid state gain block, but we tend to not use them...

Our hybrid mic pre does use this sytem, between the emitters of a MAT02 bipolar in diff, but the users are warned that gain changing during recording is not recommended...

Regards, Allen (Vacuum State)
 
#8,551
I would like to say that I am pretty sure that many here who "battered" Moamps for building his amp the way he prefers, envy him for his achievements. I would not be surprised that these same people have already downloaded all the information from his website for their own benefit. Only not bold enough to mention it here.

I'm also surprised by the level of admiration for some designers here which is close to worshipping. Soon more hymns of praise wil follow, but ............ ONLY if they keep getting what they are looking for. And remember... the members will always protect their object of worship, even by "force".

Franklin
 
#8,554
Are not Nelson's, Curl's, Krell's and God knows who's other designs cloned here on an almost if not daily basis?

I consider something a clone when it is a copy of the original. Reverse engineering a design to get a better understanding of a topology is NOT cloning to me.

Did I accidentally hit your or someone else's shrine passing by?

Franklin
 
#8,558
PMA said:


Try good Telarc recordings of classical music, with pure DSD chain. They usually name all the equipment used, from mikes to edit.

I can see that many here have not much experience with good recordings.
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It seems many would rather go to McDonald's and try to make a big mac taste like a steak, rather than going to another restaurant and buying a steak to begin with.
 
#8,559
courage said:
What "value system" are we talking about if you and I are negotiating peace and meanwhile waving with our flags of belief, ideology, politics, violence, etc. ??

Do you see any value anywhere??
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The problem is; if I learn something useful from John Curl I would openly say and write that I am grateful. But when somebody after asking lot of questions presents own "improved" version of his preamp without mentioning his help it looks not very good... The worse case is, when somebody asking questions in e-mail quickly files for patent... Or when somebody on another forum writes bad things about my condenser microphone calling it weird and me stupid organizes manufacturing of exactly what he criticized publicly... You know, it is painful!
 
#8,560
Franklin,

You seem to be going off the deep end here.................all we are saying is that moamps should have acknowleged Mr.Curl's work (polite thing to do), we have no problem with him cloning a Blowtorch.........Yes he did good work but when you publish something you should also include a list of credits unless the work is original. His attempt at copywriting the schematic, welll.......................you draw your own conclusions.

Time to get back to more important issues in the thread.

Regards,

Jam
 
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