John Curl's Blowtorch preamplifier part II

[RNMarsh]

Originally Posted by john curl

Yes, one SMALL value resistor did it all.

It was another give away - like dc servo control. I published it and so anyone could use it. If others here missed it, try it. Thx - RNM

[marce]

Lucky

[john curl]

Good input, Richard.

[RNMarsh]

Originally Posted by john curl

Good input, Richard.

I had forgotten all about it... must have a copy here somewhere.... it was actually part of an article on a low feedback power amp design with very low thd. And, I threw that into it. I have been reacting/recalling from things people bring up here... it triggers something I did which I can contribute or throw into the mix.

BTW-- speaking of Ambisonic -- A multi-part series by W.Sommerwerek is in TAA... starts with part #1 in issue 3/84. The last part (1985-86?) is to have the schematic for diy building. That can be the basis of a revival with new descrete or opa circuits to go along with the microphone talked about here. To me, I have not seen in my life time any better way and it deserves to be kept alive until it catches fire. Lower cost can do that. Thx-RNMarsh

[Esperado]

Originally Posted by RNMarsh

it triggers something I did which I can contribute or throw into the mix.

So, you too had played with kind of servo for Loudspeakers ?
Did-you still use it nowadays, or gave-it up, like me ?
For the same reasons, if you gave-it up ?

[bcarso]

Originally Posted by RNMarsh

I
BTW-- speaking of Ambisonic -- A multi-part series by W.Sommerwerek is in TAA... starts with part #1 in issue 3/84. The last part (1985-86?) is to have the schematic for diy building.

That's a very good series of articles by Sommerwerck, 3, 4, and 5/84. I haven't seen the later one yet but I must have it somewhere.

[kgrlee]

Originally Posted by RNMarsh

I doubt that the appalling cable actually was very low Ls. Did you measure it? And what is the Ls of the "winning" cable? What are the numbers of each?
Never-the-less, low Ls is better than high Ls for dynamic tweeters if you dont want attenuation. But it is interesting that you did hear differences between speaker cables. Thx-RNM

You have to read the paper though IIRC, we didn't publish the parameters of the cables tested cos it was only an interesting side issue to the main speaker listening tests.

In dem days, 'Low Ls' was done by introducing loadsa evil C and these had adverse audible effects at HF, especially with Golden Pinnae amps. Dunno how 'Low Ls' is done this century.

The cynical might conclude that you just have to get the x-section of Cu high enough to beat the zillion $/ft cables A more useful recommendation might be to have the PAs at or built into the speaker & run evil balanced line level instead but that has its own problems.

Much later, 90's, we lent the cables to a well known UK HiFi mag for a mass review. The editor told us they easily beat all the Golden Pinnae cables but didn't feel it was appropriate to report in the mag.

BTW, the techniques in Absolute Listening Tests - Further Progress are quite simple and one wonders why no one had done anything similar before. The results when you REALLY investigate obvious stuff with Blind Listening Tests are often surprising.

Blind Listening Tests don't actually pooh pooh the differences in cables etc. They just show that the most accurate, best sounding, bla bla cables, preamps, PAs, speakers are often NOT the ones the Golden Pinnae brigade claim.

[kgrlee]

Originally Posted by john curl

After all, the CTC BLOWTORCH ended production, about 6 years ago, and will never be started again, so why have I been talking about how we built the Blowtorch preamp on this thread, over about as many years?
My reason was to pass on what we found WORKED in making the Blowtorch, and to fend off petty criticism of our approach to this project that we did when money was not so tight, and some customers just wanted the 'best' without regard to price.
Some might say that the Blowtorch was OVERBUILT and it could have been made much more cheaply. I say, go for it! If you or anyone can build something much less expensively that truly sounds just as good in their listening system over an extended period of time, then go out there and sell it to the public, with my blessing.

JC, as Blowtorch is no longer sold, why not publish the schematic? I'm sure many people have stuck with this huge thread(s) in the hope that you might lighten all mankind with this pearl of wisdom. No irony or sh*t stirring meant. It's just my lack of facility with English as she is spoken

Publishing the schematic is unlikely to affect your present or future finances.

Unlike putting it in a Blind Listening Test .. which I fully understand though I bemoan the chance to sample a 1st cru Burgundy again before my demise.
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If I may ask another 2 questions .. again without any sh*t-stirring motive.

How long does it take for a Golden Pinnae or even a member of the unwashed masses like us to distinguish Blowtorch from lesser designs and appreciate its unique strengths? In sighted, no stress listening as specified by the designer of course.

Which 1980's Mark Levinson power amps were you involved with?

[Chris Hornbeck]

Originally Posted by kgrlee

JC, as Blowtorch is no longer sold, why not publish the schematic? I'm sure many people have stuck with this huge threads in the hope that you might lighten all mankind with this pearl of wisdom. No irony or sh*t stirring meant. It's just my lack of facility with English as she is spoken

Those who have bothered to read through the thread know that this has been answered several times already. Those who haven't, regular as clockwork, appear every couple of months, attack John Curl, then lose interest. Gets old sometimes.

Chris

[kgrlee]

Originally Posted by gpapag

Two forums discussing ACE-BASS
STAHL - 'Acebass' Synthesis of Loudspeaker Mechanical Parameters by Electrical Means

ACE-bass amplifier design

Who are the “Dynamic Duo “?

Thanks for this George. Good to see people have been busy while I've been in the bush Rythmik seemed to have picked up my point about temp. affecting DC resistance but I think David Birt's solution is more elegant.

I'll get my lawyers to see Yamaha et al for infringing my Powered Integrated Super Sub patents.

The Dynamic Duo are Stan Lipsh*tz & John Vanderkooy, the High Priests of ABX and other good stuff. But their ABX team also have at least one of the best ears in the business.
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Originally Posted by RNMarsh

An easy way to get the bass thd lowered in a driver is to return the neg speaker wire thru (in series) with the resistor which goes to ground in the gain setting R's of the power amplifier. Works well, cheap and even extends the bass lower at the same time. Just one resistor is added. [published in TAA and showed before and after results]

Mr. Marsh, I tried this in the 70's and it was old then. There was a very old Wharfedale Engineering Memo with test results too. As you say, 1 resistor.

Anyone got a copy of TAA article?

It's the great grandfather of the supa dupa ACE stuff.

I'm not sure you get bass extension though you get other good stuff.