John Curl's Blowtorch preamplifier part II - Page 2436 - diyAudio
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Old 11th July 2012, 05:52 PM   #24351
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Quote:
Originally Posted by RNMarsh View Post
LP? Thats the reference now?

Guess I am not a normal person.... have a large living room. Now use 4 -15 inch cerwin vega bass drivers and adding a pair of TC Sounds Ultra 5400 18 inch drivers for subs sitting in the garage waiting for time to get it done. Not much compression and lots of dynamic range.
My current living room is not small, but I am satisfied by couple of 12" woofers in concrete boxes, and one concrete horn subwoofer under the floor that uses also a pair of 12" drivers. The reference is DVD and blue ray movies. Running horses and earthquakes feels quite real. What else to wish? However I can put few 18" drivers under the floor, but what about walls and ceiling, what are their resonant frequencies? Do I need to follow realism of destruction of houses in the movies I watch?
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Old 11th July 2012, 06:24 PM   #24352
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In any case, I find that servos work, are reliable, can sound good enough to give me A ratings in the audio press, take very little space, and can be quite inexpensive, compared to an AUDIO GRADE film cap like the ones that Dick Marsh designed for Rel. IF I had to use a 1uF coupling cap, I would recommend RTX 1uf, 100V @ $18.25 ea, or the TFT 1uf, 100V @ $218.50 ea, and might even try the PCU 1uf, 200V @ $170.50 ea.
For Parasound, maybe I could get away with PPFX 1uf,200V @ $16.50 ea.
I hope that Richard Marsh will suggest which of my choices would be best, or offer another alternative. What do you recommend, Dick?
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Old 11th July 2012, 08:12 PM   #24353
morinix is offline morinix  United States
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Well, for the audiophile world the answer is easy; The most expensive one.
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Old 11th July 2012, 08:18 PM   #24354
morinix is offline morinix  United States
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What do you heavies think about this servo? And how does a short across the R9-C10-C12 network work?
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Old 11th July 2012, 08:19 PM   #24355
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by Wavebourn View Post
My current living room is not small, but I am satisfied by couple of 12" woofers in concrete boxes, and one concrete horn subwoofer under the floor that uses also a pair of 12" drivers. The reference is DVD and blue ray movies. Running horses and earthquakes feels quite real. What else to wish? However I can put few 18" drivers under the floor, but what about walls and ceiling, what are their resonant frequencies? Do I need to follow realism of destruction of houses in the movies I watch?
Nice to know others are here which go the extra mile to have full blown system without compressed dynamics. We have all this dynamic range available now but many never hear it because the typical speaker system is anemic in this regard. My ceiling is about 20 feet up... sloping to 13 feet. Over 30 feet long room so it takes some serious power output to blow this roof off. But I'm trying. :-)
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Old 11th July 2012, 08:27 PM   #24356
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Servo too complex.
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Old 11th July 2012, 08:31 PM   #24357
RNMarsh is offline RNMarsh  United States
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Quote:
Originally Posted by john curl View Post
In any case, I find that servos work, are reliable, can sound good enough to give me A ratings in the audio press, take very little space, and can be quite inexpensive, compared to an AUDIO GRADE film cap like the ones that Dick Marsh designed for Rel. IF I had to use a 1uF coupling cap, I would recommend RTX 1uf, 100V @ $18.25 ea, or the TFT 1uf, 100V @ $218.50 ea, and might even try the PCU 1uf, 200V @ $170.50 ea.
For Parasound, maybe I could get away with PPFX 1uf,200V @ $16.50 ea.
I hope that Richard Marsh will suggest which of my choices would be best, or offer another alternative. What do you recommend, Dick?
Jeeeezus are they charging that much for the best caps on the planet? Wish the patent hadnt expired so I could get royalties. A film cap to get a patent for improved performance (higher self resonance) in decades. No cap sold for audio use is patented/unique, as far as I know..... just rehash of what has been done before so the cost should be low for them. The REL cap to be made under the patent required buying a customised (new) cap winding machine.... but that cost has long been paid off. Now it is just low volume causing the price to be high.... btw - the styrene from REL is the best quality available.

I wouldnt pay that much and would find some way around using them, if I could.... But the best would be an annealed styrene film and foil and a Teflon film and foil (tin foil) with copper leads with gold plating and made under the patent (stock REL are not the same as the MultiCap but use same materials).

Last edited by RNMarsh; 11th July 2012 at 08:42 PM.
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Old 11th July 2012, 08:38 PM   #24358
bcarso is offline bcarso  United States
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What do you heavies think about this servo? And how does a short across the R9-C10-C12 network work?
I think I could lose a few pounds. Well, make that a solid twenty.

Five caps instead of one or two. Stability issues if the servo has too much gain.

A differential integrator that probably is not needed, as the simulated power amp is single-ended. But one is equipped for a bridge-tied load I suppose.

The second stage is a d.c.-offset-free three-pole lowpass. It has some advantages (no offset voltage or current, no opamp input common-mode swing) and some disadvantages (sensitive to loading, as the output impedance is not low, as it would be from a conventional active filter's opamp output). Kendall Castor-Perry showed some filters based on the topology fairly recently (sorry don't have the ref.) although it is quite old --- I recall puzzling over it in an Ideas For Design many years ago, and having the same reaction as you to what looked like a "short".

Brad
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Old 11th July 2012, 08:53 PM   #24359
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Extra filtering MAY help, 'subtle improvements in performance' but it adds to cost, complexity, space used, and MAY promote instability, if done wrong, due to added phase shift.
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Old 11th July 2012, 09:02 PM   #24360
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What amazes me is that I put up a SIMPLE, cheap servo that really works well, and I get 'shouted down' that it is too complex, expensive, or whatever.
Then a servo, 3 times more complicated, is put up, and no complaints. Go figure!
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