John Curl's Blowtorch preamplifier part II

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I've always assumed forward biased LED's are very quiet.

They are. Several of us have measured them, and in the His Master's Noise preamp, a forward biased LED is effectively in series with the input signal. And it manages to be the quietest tube phono stage I'm aware of.

Taking engineering guidance from a loon is not my idea of competent design, but to be fair, I don't make my money from fashion and superstition.
 
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There is extensive literature in using LED's for medical devices. Those SPO2 finger clips use RED and IR pulsed at very high peak current. I have found 1/f and popcorn noise in the optical output. Don't fool yourself the medicos use the cheapest stuff they can find, I have stories.

This one has useful data... http://www.researchgate.net/profile...ing_diodes/links/54bcea0f0cf29e0cb04c55e3.pdf

EDIT - This paper is available for free but now my link points to the one the company pays for.
The pulse oximeters build the one-time-use things for three bucks and sell them for eighty. Another example of the screwed up med markets.
 
diyAudio Member RIP
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They are. Several of us have measured them, and in the His Master's Noise preamp, a forward biased LED is effectively in series with the input signal. And it manages to be the quietest tube phono stage I'm aware of.

Taking engineering guidance from a loon is not my idea of competent design, but to be fair, I don't make my money from fashion and superstition.
What's the input tube?
 
it made Gordon Ramsay spontaneously boot on camera.

Aargh, why haven't I seen that video ages ago ?
I should have known there are Four Knobqueteers, not 3 !
Abfab, downloaded it for therapeutic purposes (only).

Hick question, but is accelerated aging not applicable to/for LED's ?

(had to look up the pronunciation of Icelandic sheep head : svith)
 
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I gave up on 'fun' after I built my first Heathkits in the early 60's. IF you want to live, one has to do something to pay the rent. The CTC Blowtorch was our best effort in a compromising audio environment. We wanted to see what we could do BEST within using fets, rather than tubes. We made them for ourselves, primarily, but paid for our units by building building more for other people. I could never have been able to afford a CTC Blowtorch, if I did not do it this way. However, we put the same care and effort into other people's units as our own. In the end, we wound up not making enough on each unit to even make it worthwhile to make them anymore to compensate for the time and COST it took to build them. When our bare boards essentially ran out (100 for about $5000) we decided not to make another batch, and Bob wanted to give away the schematic and BOM to everyone, so they could build one, if they wanted. Unfortunately, Bob Crump, the primary BUILDER of the Blowtorch passed away suddenly, leaving me with about 8 units to finish, because they were prepaid. I was stuck finishing them (#40 is one of these I believe) the best that I could, but I had to compromise on the internal wiring (copper instead of silver) and there was a small, but noticeable difference, but I had to do that or else pay back the $50,000 dollars that Bob had received earlier for 5 units destined for Japan. I don't think my finished units quite matched what Bob had done for himself, me, and about 39 other customers, but it took me many months to finish them. While doing this, I decided to hold back the schematics, rather than give them away, and that is what started this thread.
 
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