John Curl's Blowtorch preamplifier

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PMA

PMA

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Terry Demol said:


Pavel,

What are some reference CD's you use
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Terry - some of them:

1) Maurice Ravel, Suite No. 2 from Daphnis et Chloé. Paavo Jarvi, Cincinnati Symphony Orchestra. TELARC SACD-60601

2) JOHN WILLIAMS: Concerto for Cello and Orchestra Yo-Yo Ma, cello/Recording Arts Orchestra of Los Angeles/John Williams - Sony Classical multichannel SACD-only SS 89670

3) STEELY DAN/EVERYTHING MUST GO DVD-A, Reprise records
 
john curl

john curl

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Two cents? Tell me where to buy them! ;) Relays? Sure, how much do you want to spend? Is ANY relay as good as a good switch? Shallco is great, but expensive and hard to turn. Takes BIG knobs to smooth it out. I would stick to TKD. Good pots, already made to work. A bit expensive, but my time is worth more than the hassle of making up my own attenuators, especially for other people. One bad solder joint and you are compromised.
 
anatech

anatech

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Hi Milan,
Then again, a piece of equipment going for $xx,xxx just might be worth the hassle and expense.
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I'm just going to go out on a limb here with a wild guess. Anthing that increases manufacturing cost will be reflected (multiplied) in the selling price. The very most expensive thing would be labour.

My house cost $xxx,xxx.xx and doesn't have a lot of things. If I paid more, it would. Just as an example.

-Chris
 
Ultima Thule

Ultima Thule

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Relays, yeah, I know it's actually an old topic covered long time ago in current thread and you gave worthwhile insight to why which I find understandable, my thought was that relays are much more closer in quality to a switch than a pot, and besides that it's easy to implement a remote controll if so required, at least that is my believe.

JC, bringing up a question I throw in for couple of days about plastic conductive shielded cables/wiring, what's your take on it for internal wiring as well as for external use?

Cheers Michael
 
courage

courage

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Joined 2006
John,

Apart from the specifications on the TG Audio Lab website there have been several reviews of the Blowtorch, which of course rave about the sound, but none of these are supported by actual measurement graphs. I know that ultimately it matters how it sounds, but would factual measurement graphs brake the mystical spell?

There seems to be some sort of code surrounding very high-priced audio gear which supports the spreading of vague subjective claims which are rarely supported by detailed specifications and solid measurement graphs.

What is your opinion on this in general and specifically on the Blowtorch?
 
S

Sigurd Ruschkow

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Joined 2004
John Curl,
I have designed and had made solid brass BIG knobs for just this purpose. Weight is about 2kg and due to the weight I use a ball bearing in the front panel that takes up the weight of the knob. I use it with the Swiss made ELMA rotary switches.

Yes, it is a pain in the butt to assemble a stepped ladder stereo attenuator with 90 resistors! If there was someone that made them assembled with good resistors, I would definitively buy those instead of assembling them myself!



Here is my dual double output stereo headphone amp.
An externally hosted image should be here but it was not working when we last tested it.



Best
Sigurd


john curl said:
Shallco is great, but expensive and hard to turn. Takes BIG knobs to smooth it out. I would stick to TKD. Good pots, already made to work. A bit expensive, but my time is worth more than the hassle of making up my own attenuators, especially for other people. One bad solder joint and you are compromised.
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Sigurd Ruschkow

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Joined 2004
I think that the volume attenuator is the most important component in a preamp. I started using stepped pots in the mid 80s and never regretted that. My next attenuator will be realy controlled but back then it was good enough with a manual rotary switch stepped attenuator.



Best
Sigurd


john curl said:
Folks, I might say something about pots.
Back in the '60's we usually used Allen-Bradley baked carbon pots. We used them exclusively at Ampex and for virtually every pro audio application. When I met with Mark Levinson in 1973, he was using a very expensive dual pot (for the time) $20.00, because it TRACKED better than any other dual pot, at the time. To improve tracking further, Mark used a linear taper pot (100K) with a 50K load resistor as a load to make it into a sort of log taper. This idea was given to him by Dick Burwen (sp), and it worked very well.
I got my Levinson JC-2 in 1974 and I put it into our professional sound system that we were developing at our lab in Switzerland. At one point, in one listening test, my associate, John Meyer and my other associate Bob Minor, (his father used to be my audio mentor) both told me that something was wrong with the sound of my JC-2 preamp.
WHAT? My preamp is virtually perfect! I exclaimed, but they were insistent about it
So, I said "Don't touch anything!" and I carefully took the preamp to my test bench, WITHOUT changing the controls. Well, guess what I found? DISTORTION! and lots of it. It was in the POT, but only at certain positions on the pot. Full on, or over most of the range of the pot was OK.
Flying back to the States, I tried to tell Mark Levinson about my finding. He was very resistant, so I rubbed his nose in it by taking a pot off his assembly line and measured it with his test equipment in front of him. Mark was converted.
I started to measure all kinds of different pots, and I found that many of the Allen-Bradley pots that I had stocked my lab with, failed! They had significant distortion at certain positions of the pot. I also tried some Bourns pots, that looked almost exactly like the A-B pots and they were OK. What is going on here?
Later, Alps pots became available and they measured great! Yet, over the years, I found that they did not sound right, for my best efforts. Still, they are practical, track OK, and have very low distortion. Personally, I think that it is the substrate that they use that makes the difference, for some reason. I have much more experience about this, but you should understand that something can even measure OK and still not sound exactly right. Go figure!
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jcarr

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PMA said:
probably expensive exotic passive components, high-Q wood :)D :D ) etc. make the final price of the "HighEnd" component much higher - which is of course positive for the seller - would not it be the case?
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Not necessarily positive, even from a purely business perspective. The goal should be to maximize the total return on investment without forcing your manufacturing facilities to operate at beyond capacity, and this is manifestly not the same thing as trying to maximize the price and profit per unit. Simplistically, one should do a projection of price per unit vs. likely sales volume (said volume tends to decrease as the price goes up). The next step is to map that expected sales volume against the production capacity of the manufacturing facilities that are at your disposal. Eventually you should arrive at a good balance which optimizes the return on investment within the limits of your manufacturing facilities.

In any case, however, my experience is that the annual operating profit for an audio company is absurdly low compared to what similar efforts could yield in other industries - at least in developed countries where labor costs are high.

regards, jonathan carr
 
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