Admittedly I haven't tried it, but I have to think that for driving headphones, adding a couple buffer transistors after the op-amp is a good idea in general.
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Yes – opamps swapping may make a measurable difference in a preamp
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audio_tony
Addicted to Fun and Learning
I completely agree with this - back in the 80's I built a very simple headphone amp with two buffer transistors and it worked really well with the ~100 ohm headphones I was using at the time. I seem to recall the design was from a National Semiconductors databook, and was intended as a 600 ohm line driver.
audio_tony
Addicted to Fun and Learning
Very interesting - I was surprised that the 5532 had stability issues though! Ironically in my tests, I had stability issues with the LM4562, and I've had issues implementing that opamp in other designs too. Apparently later versions have improved stability.Opamps that are used to directly drive headphones can bring some surprises that can be audible.
I testes some (less suited) opamps 10 years ago in a typical 'C'Moy' amp with rail splitter.
Portable op-amp headphone amplifier test
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Speedskater
Major Contributor
Most op-amps are designed to drive a high impedance load. Say about 1 kilo-Ohm or so.
Though op-amps designed to drive a low impedance load (under 100 Oms or so) are a different ball-game.
Though op-amps designed to drive a low impedance load (under 100 Oms or so) are a different ball-game.
audio_tony
Addicted to Fun and Learning
A lot of the so called 'jellybean' types (NE5532/LM4562/OPA134 etc.) are typically designed to drive 600 ohms, as many of these are intended for use in the professional field which typically operates into 600 ohms.
Many of them will happily drive slightly lower loads (as my tests mentioned previously demonstrates).
You can also put them in parallel to increase the load driving ability - Douglas Self has made (low powered) amplifiers driving 8 ohms with several 5532's in parallel.
They can get hot very quickly though!
solderdude
Grand Contributor
I designed this one 12 years ago. Still in use (lightly modified)
Also build this speaker amp (balanced outputs).
It used a whole bunch of 1A capable L272M opamps in parallel (with small resistors) about 40 years ago.
Worked like a charm till one of the opamps blew and took along a bunch with it.
The Schiit Heresy/Heretic also uses parallel opamps to increase output power. (also known to blow some opamps)
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