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Old 13th September 2012, 08:47 PM   #921
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Quote:
Originally Posted by RNMarsh View Post
The non-IC discrete here should do that and more, if possible -- Key to design for: be very simple -- use the fewest transistors. Low cost, easy to find parts. Drive low Z. No dc servo. wide OL bandwidth. THD and noise < -100db ref 1v. Gain at a range of 4-10X etal. Others can decide what more can be done by their design. -Thx RNM

You said it not me , " it must be able to also do lower Z at low thd than IC opamp/IC buffer combo. Or what's the point -- just use an IC. -RNM " I just pointed out that there are single IC's that do all of the above (and they even look like op-amps).

Yes, an ADSL driver won't make a good phono pre-amp.

I choose not to particpate in your challenge, do you mind?
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Last edited by scott wurcer; 13th September 2012 at 08:54 PM.
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Old 13th September 2012, 08:56 PM   #922
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John,
I think that I have some of your earlier amplifier designs from Parasound that are about that vintage. One has been sitting for quite some time with all the output devices fried. My fault with an unstable crossover that went into oscillation and the amp was running in bridged mode, couldn't turn it off fast enough. Still want to fix that though. Needs all new NPN and PNP devices though.
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Old 13th September 2012, 08:57 PM   #923
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What is the model #?
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Old 13th September 2012, 08:58 PM   #924
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by scott wurcer View Post
You said it not me , " it must be able to also do lower Z at low thd than IC opamp/IC buffer combo. Or what's the point -- just use an IC. -RNM " I just pointed out that there are single IC's that do all of the above (and they even look like op-amps).

Yes, an ADSL driver won't make a good phono pre-amp.
Ok - you get one point for that.

It was thought up to do a best effort in a discrete form.
My question or challenge was -can the limitations/conditions I gave be all met and still do as well or better than an IC opamp? Maybe.

No. Of course, I dont mind, Scott. Just keep doing what it is you are doing is fine. -Dick

Last edited by RNMarsh; 13th September 2012 at 09:08 PM.
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Old 13th September 2012, 09:11 PM   #925
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John,
I have to find it. I also have the smaller amp from the same time that is the HCA 800 ll but that was a smaller 100 watt amp. The one I am thinking of had 200 watts per channel. I have two of those around here somewhere. One still working and one dead.
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Old 13th September 2012, 09:14 PM   #926
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The 800 is not a product that I am directly identified with, but I might be able to help, if I have more info as to your problem.
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Old 13th September 2012, 09:42 PM   #927
coluke is online now coluke  Italy
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Breadboarded a slightly modified version of the circuit in #271 - more or less a JC2 with a diamond out: *** unselected *** J113/J175 in the front-end, BC550/560 in the gain/driver stages, MJE243/253 in the output stage. Even with randomly choosen devices, it rocks - THD < 0.001% @ 1kHz, 0dBV into 30 ohm, only low order.

More to follow.

Ciao,

L.
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Old 13th September 2012, 10:58 PM   #928
RNMarsh is online now RNMarsh  United States
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Quote:
Originally Posted by coluke View Post
Breadboarded a slightly modified version of the circuit in #271 - more or less a JC2 with a diamond out: *** unselected *** J113/J175 in the front-end, BC550/560 in the gain/driver stages, MJE243/253 in the output stage. Even with randomly choosen devices, it rocks - THD < 0.001% @ 1kHz, 0dBV into 30 ohm, only low order.

More to follow.

Ciao,

L.
Very nice -- esp. unselected and not a sim of ideal perfectly matched parts. :-)
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Old 13th September 2012, 11:36 PM   #929
RNMarsh is online now RNMarsh  United States
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Coluke -- what is the schematic, pls?

I am tinkering with boot-strapping a whole circuit and see if it stays together. Just adds two more transistors. Thx - RNM
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Old 13th September 2012, 11:53 PM   #930
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Rumbling around back here in the pantry... minimum parts count is certainly something that minimalists will like... and of course anything that has low parts count may also be elegant which is always good.

But equaling the JE990? Is that a valid goal today? I would think exceeding it? No?

Wonder if things like rise time, settling time, overshoot show up in the distortion figures? (I really do not know if there is a direct relationship that can be drawn) If there is not a direct correlation, should these factors be considered as well?

Are all these designs Class B output stages?
Should Class A output stages be under consideration?
At a thermal and power cost, will they yield a better spec (and sounding) op amp?

And, is the claim being made that from a listener's point of view that any device with sufficiently low distortion is audibly not different than the next? Personally, I have yet to find that to be the case. In some instances I have been rather surprised by this.



I'd say the winner is the one that sounds the best, measures the best and not only looks the best on sims and specs... and do we *need a single "winner"?* (rhetorical question)



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