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Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Discrete OP-Amp vs. Integrated OP-Amp include discret Buffer - e. g. AD797/844+IRF610
Discrete OP-Amp vs. Integrated OP-Amp include discret Buffer - e. g. AD797/844+IRF610
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Old 17th September 2017, 09:18 PM   #11
MarcelvdG is offline MarcelvdG  Netherlands
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Quote:
Originally Posted by tiefbassuebertr View Post
The main question for me is in the moment as follow:
Is there any justify for the use of a discrete OP-Amp, if I implemet to a good integrated OP-Amp an additional output buffer (e. g. a single ended source follower or emitter darlington follower, either with CCS or simple resistor, either inside or outside of the NFB loop) for using both in a line preamp stages and in phono RIAA input and output stages ??

Maybe one of the members have this check out by listening tests with various op amp and buffer versions.
Thank you very much for advices.
Well, this forum is about DIY audio, that is, about audio circuits that people build because they like to build them. If someone likes building discrete circuitry more than using integrated op-amps, that in itself is a perfectly valid justification for using discrete circuitry.

By the way, there are some feedback configurations that you can make with discrete transistors or valves but not with op-amps (unless you add floating supplies). This includes a nice configuration for RIAA amplifiers invented by Hoeffelman and Meys in the late 1970's, and an interesting but not very well-known tone control designed in the late 1940's by L. V. Viddeleer.
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Old 29th November 2017, 10:38 AM   #12
tiefbassuebertr is offline tiefbassuebertr  Germany
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Quote:
Originally Posted by DPH View Post
Tief -- you'll get plenty of nonsensical answers like the latter, but it's really important to have a goal in mind and work backwards to a schematic that fulfills those objectives.

How much do you want to invent is the other question?


Line-level stuff, especially if you're not driving long cables is going to not load down any number of modern opamps any more than setting up their feedback networks for low noise will. Composites are cool, but definitely tricky to keep stable, and really of questionable necessity in audio (except for their pursuit just for the fun of it).

RIAA has a definite place for hybrid/composite discrete/IC setups as you may want more voltage swing along the way (for overload) than your typical +/- 15V can provide. Then again, with something like the 44V LME49860 (same exact thing as a 49720 except 44V validation vs 36V), how much do you really need? We so rarely need high gain in audio, and line-level is very much in the wheelhouse of IC's.

Jim Williams wrote dozens of articles/datasheets (Linear Technology) on discrete + IC hybrids as did Walt Jung. Really worth your while looking through them and gleaning wisdom.
On a very wide range of performed listening tests over the years I still note a great lack in sound quality in all line stages and riaa stages with opamps, because the quiescent current respective the idle current of the integrated output stage inside of the OP-Amp chip is too low, even on devices like NE5534 or AD797. Discrete OP-Amps provide better results mainly through only reason: Higher value of idle current in the output stage. Therefore the question in post #1.

The question does not refer to a special amplifier project, but generally to RIAA and LINE stages in pre-amplifiers and active crossover networks.
P.S.: My name is Andreas and the member name is based on my old, no longer exist web address - go to webarchive under
A. Kirschner, individuelle Basslautsprechersysteme

Last edited by tiefbassuebertr; 29th November 2017 at 10:42 AM.
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Old 30th November 2017, 09:53 PM   #13
xrk971 is offline xrk971  United States
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Discrete OP-Amp vs. Integrated OP-Amp include discret Buffer - e. g. AD797/844+IRF610
I built this hybrid by Wayne Kirkwood and it works exceedingly well. One of the lowest district amps I have measured. Very simple and no global feedback. Feedback internal to THAT balanced line driver (used here in unique mode to provide Class A bias current control).

Click the image to open in full size.

I have extra PCBs if anyone wants to try. Just send PM me, you pay shipping.

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Last edited by xrk971; 30th November 2017 at 09:58 PM.
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Old 30th November 2017, 10:05 PM   #14
MarcelvdG is offline MarcelvdG  Netherlands
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Join Date: Mar 2003
Location: Haarlem, the Netherlands
Quote:
Originally Posted by tiefbassuebertr View Post
On a very wide range of performed listening tests over the years I still note a great lack in sound quality in all line stages and riaa stages with opamps, because the quiescent current respective the idle current of the integrated output stage inside of the OP-Amp chip is too low, even on devices like NE5534 or AD797. Discrete OP-Amps provide better results mainly through only reason: Higher value of idle current in the output stage. Therefore the question in post #1.

The question does not refer to a special amplifier project, but generally to RIAA and LINE stages in pre-amplifiers and active crossover networks.
P.S.: My name is Andreas and the member name is based on my old, no longer exist web address - go to webarchive under
A. Kirschner, individuelle Basslautsprechersysteme
How about forcing an op-amp into single-ended class A by simply adding a current source, or even simply a resistor to a supply rail? That way you can even make an LM324 work without crossover distortion (not that I would recommend using an LM324 for high-quality audio, of course).
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