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

How about this line preamp ?
How about this line preamp ?
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Old 20th February 2020, 08:14 AM   #1
gaetan8888 is offline gaetan8888  Canada
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Default How about this line preamp ?


How about this line preamp ?

Anyone try this type of topology ?



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Old 20th February 2020, 08:34 AM   #2
ubergeeknz is offline ubergeeknz  New Zealand
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The original BB application note I'm guessing is the one on p273 in this compilation. Worth a read. But is it necessary? Depends what you're driving, I suppose.

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Old 20th February 2020, 08:35 AM   #3
bimo is offline bimo  Indonesia
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I tried this for headphone amplifier. It is good, depend on the quality of the op-amp.
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Old 20th February 2020, 08:38 AM   #4
analog_sa is offline analog_sa  Europe
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How about this line preamp ?
I cannot see this making a difference in a line stage where there is hardly any current passing through the load.
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Old 21st February 2020, 09:05 AM   #5
sgrossklass is offline sgrossklass  Germany
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Has been used in headphone amplifiers for ages, see "apheared-47" amp.

Pros: Doubled output current, low output impedance.
Cons: Needs a noise gain of at least about 3 to be stable. (A small cap from "master" opamp out to -in may be beneficial in this regard.) Only moderate benefit in distortion as "master" opamp still sees significant output loading. (Circuit shown in first post "cheats" by employing output Class A biasing as well.) If memory serves you can trade off output current / distortion / stability by varying splitter resistor values... will have to drag out my sim.

It's basically the "el cheapo" version of using a proper high-speed power buffer (either discrete follower or BUF634 and the like).

I could see it potentially being useful when you're trying to wring out the best dynamic range from some inexpensive low-noise opamps with so-so output driving like NJM2068, which normally are not too happy driving feedback network impedances below ~2 kOhm at high levels. But as stated, if you can afford going full power buffer that'll probably be better.

Also see Technics "Class AA" circuit.

Last edited by sgrossklass; 21st February 2020 at 09:16 AM.
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