John Curl's Blowtorch preamplifier

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#8,001
We can always speculate that sanity is relative. 10 years ago I wouldn't spend more than $20 on a potentiometer, these days I wouldn't mind spending $800, and not because I'm after perfect sound forever, but mainly because I'm curious how close I could get.

Another thing, there is not much risk in buying expensive parts, you can always sell them back with little loss, if any😉

http://www.diyaudio.com/forums/showthread.php?s=&threadid=122538&highlight=
 
#8,002
john curl said:
Now, some can understand why the Blowtorch cost so much. We didn't compromise and used these TKD pots. They got so expensive, later, that this made us not want to make any more units, as well as the extra cost of the cases over time. This is why the CTC is not made anymore.
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John,

My apologies if this has been covered already - would not the best
vol control for BT type, open loop, full bal topology be simply
switching different values of Rg (connected between IP jfet
sources)?

cheers

Terry
 
#8,004
hermanv said:
It's a hobby, sanity stops wherever you want it too.
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Sure. Beauty industry alone makes billions on deception. If it makes you feel good, money well spent, by all means.
I'm more interested in subjectivism free discussions, if at all possible. I do understand though that interpretation of 'subjective' can be subjective too 😀
 
#8,007
Electronic switches are convenient. Do you know anything about them? I have perhaps 100 various types in a drawer. Anyone want to buy any? I did a research on them about 20 years ago, but perhaps they have improved in some way.
Usually, this is what I have found:
Silver on silver, clunky, hard to turn, expensive, usually open frame, and wonderful sounding IF you use the switch once in a while to clean or 'clear' it.
Relays, hermetic or just plastic, good, moderately expensive, usually gold over silver contacts in nitrogen or some other neutral gas. Sound darn good, next best for sound and excellent for remote control. JC-80 and Para JC-2 preamps use this.
Solid state, easy for computer control, high residual distortion, limited dynamic range.
Anyone else with an opinion?
 
#8,008
john curl said:
Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.
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Now what should anyone do that ? High quality design, precision machining and clever ideas do and should pay well. Noone is questioning that. I'm not going to argue if a Rolex or a Rolls is priced fairly or not.
I'm just arguing it is fair that for a particular AUDIO device (like preamp) to be judged on objective merits, which includes measurements and (you are going to hate it, I know) a DBT. So if one can't hear a difference between a Dyna and Levinson, maybe the things that matter aren't audio after all ?
Which really is fine, we are subjective species after all and cannot really switch some of the senses on or off at will. Lets just call things their proper names, shall we.
 
#8,009
john curl said:
Electronic switches are convenient. Do you know anything about them?
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Yes I do. I'm an electronics engineer first and foremost (that is what my Uni degree says anyway).
I just seem (perhaps erroneously?) to remember you talking fondly about using an AP to test your electronics. It sounds strange to me that one would resort to an inferior testing device, knowing it would skew the results.
 
#8,010
Are you talking about solid state switches from personal experience, or because someone, somewhere uses them in some fashion? Are you talking about Cmos or jfet switches? Video quality? How do you reduce the distortion to virtually nothing, and would it be better than a typical relay?
 
#8,014
Why would you reduce distortion to "virtually nothing" ? There are complete branches in audio world that thrive on exactly opposite (triodes, horns, turntables). Digression, sorry.

My experience in active switching is perhaps irrelevant to audio, but it is related to low (to extremely low) level signal, often to a single electron level. But people who presumably know a lot about audio (shall we mention AudioPrecision again?) seem to use them without fear. Maybe ask someone there ?
 
#8,015
Analog switches are a practical and cheap way to make audio connections. They have a significant amount of noise and distortion. So far, I have designed 3 full preamps with analog switches. First, was Lineage, with Saul Marantz as president. We were trying to replace the Marantz 7C preamp of the '50's-60's and a darn good preamp. This is when I did my fundamental work with analog switches. The are OK, but the good ones are expensive, or at least, they were. Cmos is OK, but ... The other 2 preamps were made by Parasound and used integrated switching assemblies by Toshiba. They were OK for an inexpensive preamp, but I could certainly measure their limitations.
Later, with the HCA-2000 and the Parasound JC-2, we reverted to relays that are really measurably and probably sonically better. Better isolation too!
However, silver on silver is really the best.
 
#8,017
Peter Daniel said:
And who cares what some might do?

There's no such thing as perfect pot, and if you find one for $800 it's still a bargain.

I went cheap way and was simply hand switching shunt resistors for a while, didn't need many of them as I'm not too fussy about listening levels 😉
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Oh yes, I can see how that 5 ct DIL header block beats any 800 $ pot 😉

Jan Didden
 

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#8,018
john curl said:
Do something really well. See how much time it takes. It might be a product, a work of art, who knows? Then give it away cheaply, just because you feel that it should not cost so much, even if it took a lot of time and expensive materials to make it.
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JHohn,

I think this is an important observation. Things are often very expensive because they are one-of works of love.
If I set up a one-man company to build one great amplifier every six week and had to live off it, it would have to net me at least 10k$, even if the parts and case came free!

OTOH, if I could interest a company to build 50 per month, they could probably sell it at 1000$ with huge margin.

The important thing here is that both amps would be equally well performers. Price often has little or no relation to quality, except as perceived by the buyer.

Jan Didden
 
#8,019
john curl said:
Are you talking about solid state switches from personal experience, or because someone, somewhere uses them in some fashion? Are you talking about Cmos or jfet switches? Video quality? How do you reduce the distortion to virtually nothing, and would it be better than a typical relay?
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John,

That is not difficult. I have published a SS level control in Electronics World at least 25 years ago that just did that. The trick is in arranging it in such a way that the signal across the switch is zero, that makes the distortion zero.

These days you can have SS switches with sub-ohm on-resistance and virtually unmeasurable distortion of their own anyway.

This scene changes so fast you really need a subscription on EDN or something to keep following it.

Jan Didden
 
#8,020
That is a bit negatively put.

Mankind has for a long time been searching for the perfect. Some cultures more than others. Some people more than others.
We strive forwards - and if we would have stopped anytime,
we would not be where we are today.

I read some science magazines and try to keep up date, and the future shows no sign of mankind stopping.


Sigurd

Bratislav said:
There is no such thing as perfect anything.
The question really is where the sanity stops.
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