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Old 22nd January 2005, 09:08 PM   #11
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I'm sure that the headroom is bigger than regular opamps because of the high voltage you can operate it from,
but I wonder how does it compare in sound quality...
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Old 22nd January 2005, 10:04 PM   #12
sss is offline sss  Israel
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Quote:
Originally posted by udip
It looks so simple...I wonder how does it compare to a good
IC opamp like AD825 or OPA627....
did u compare ad825 with opa627 and heared a difference?
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Old 22nd January 2005, 10:22 PM   #13
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Quote:
Originally posted by sss

did u compare ad825 with opa627 and heared a difference?
Yes, I think the opa627 sounds better...
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Old 23rd January 2005, 07:45 PM   #14
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Consider one of the discretes from Borbely Audio...
Quite excellent - you can package the design tighter like the 990 or API modules if you need compactness...

I built up some 990s years back - they were very good in their day, but don't have the performance available today.

The main deal was the supermatched bipolars for super low noise at the input and the little inductors on the legs of the diff input pair... the whole thing is written up in JAES.

Is there a schematic for the 992?

Deane Jensen was ahead of the pack in his day.

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Old 23rd January 2005, 08:43 PM   #15
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Borbely Audio designs are to complicated for me....
I think I'll try the ELEKTOR magazine design..I'v heard it's a
good one..

Haven't seen schematics for the 992 or 2520.

Udi.
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Old 26th January 2005, 12:35 AM   #16
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Quote:
Originally posted by udip
Borbely Audio designs are to complicated for me....
I think I'll try the ELEKTOR magazine design..I'v heard it's a
good one..

Haven't seen schematics for the 992 or 2520.

Udi.
I'm kind of confused by this... what are you trying to get done?
Is this just for messing around or is there a particular application?

If you want superior sound & studio output level capability then a design like the Borbely stuff is hard to beat.

If you don't need studio output levels, then it's hard to beat some of the newer monolithic opamps. Darn near impossible actually.

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Old 26th January 2005, 08:33 AM   #17
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[QUOTE]Originally posted by bear
[B]

I'm kind of confused by this... what are you trying to get done?
Is this just for messing around or is there a particular application?

If you want superior sound & studio output level capability then a design like the Borbely stuff is hard to beat.

If you don't need studio output levels, then it's hard to beat some of the newer monolithic opamps. Darn near impossible actually.


Hi,

I'm trying to get a very good sounding opamp, for
professional recording, and I think that a good discrete
opamp design will outperform any monolithic opamp,
even the OPA627, LT1115 or AD's.


Also, I haven't seen a discrete opamp on borbely's website.


Udi.
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Old 27th January 2005, 12:14 AM   #18
PRR is offline PRR  United States
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> I think that a good discrete opamp design will outperform any monolithic opamp

Why?

The modern chip processes make essentially the same transistors as we buy individually. The sad old days of lateral PNPs are still here, but we can also get perfectly good PNPs on some processes.

Chip designers are sometimes clueless about real audio quality, but some are good and some are very-good.

Thermal feedback used to be an issue but today it is probably less than PCB trace resistance coupling.

If you are driving 10V 10K levels, the only real issue is that chip Class AB outputs are sometimes underbiased. This looks "better" to chip makers, but is usually bad news for sound.

If you are driving 10V into honest 600 ohms (very rare today), then you are at the upper limit of common small chips. Even there, either the old 5534 or some of the new kids will beat +18dBm with ease.

What Jensen's original 990 did, aside from quite low noise voltage, is give GOBS of output so you could use massive fan-out and low-Z feedback without strain. 14V RMS across 75 ohms is not a real problem, and that is over 2.5 WATTs.

I respect Mr Curl's view, and sure agree that there are many places where the sonic advantage of "soft" FETs are better than "naked junction" BJTs. On the other hand, sometimes you want to go with the serious gain and drive that comes easiest with BJTs.

The Jensen 990 is still a gold-standard in the recording industry, especially in heavy work. Jensen did lay out all the problems of a good audio op-amp, and solved them in best 1970s style. Fads come and go, and we have better FETs now than then, and Deane himself might have worked on an FET amp (if he had lived). But it would not be better in all ways, just in some ways.

You can get Jensen's AES paper from his company, VERY good reading. (They can't post it for copyright, but are happy to paper-mail upon request.)

John Hardy is using (essentially) the original Jensen 990 design. See John's paper http://www.johnhardyco.com/pdf/990.pdf

JLM has a 990-pinout module, called JLM99V, http://www.jlmaudio.com/JLM99V.htm that is FET input, and is not zero DC offset. This seems to be very sweet in many applications that don't need the extreme low noise voltage or output drive (or DC coupling) of a full 990. It can eat +/-34V, and will drive 600 ohms. Some sticklers would object that a 0.6V offset defies the "op-amp" concept; but in audio, we can often overlook DC error.

> I think that a good discrete opamp design will outperform any monolithic opamp

I don't think you can let yourself off the hook that easy. You can find perfectly good chips and perfectly awful modules. (You should see some of the Burr-Brown antiques the mikepre nuts find on eBay.) A lot depends on what you are doing with them: a gold-plated Deane-blessed 990 would be useless as a condenser mike head-amp, just as the 627 is not the bee's-knees for transformerless operation from 50-ohm ribbon mikes on harpsichord.
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Old 13th February 2009, 12:00 AM   #19
mlloyd1 is offline mlloyd1  United States
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studiotech:
if you're still around, did you ever post pics of your preamp based on the jfet 992 modules? i'd still like to see them.

thx,
mlloyd1

Quote:
Originally posted by studiotech
the 992 to be exact.
I could post some pictures maybe tomorrow of my design.
Greg
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