Hi, while searching for information on current loading op-amp outputs I stumbled upon this info on the Keith Snook.
https://keith-snook.info/op-amp-class-a-current-dumping.html
Basically, putting an extra resistor between the output (pin-8) and driver output (comp, Pin-5).
Resistor values between 68 and 150 ohm seem OK if one is to believe the web-page.
Did anyone try this trick? Do anyone have some measurements or feedback on sonic results?
https://keith-snook.info/op-amp-class-a-current-dumping.html
Basically, putting an extra resistor between the output (pin-8) and driver output (comp, Pin-5).
Resistor values between 68 and 150 ohm seem OK if one is to believe the web-page.
Did anyone try this trick? Do anyone have some measurements or feedback on sonic results?
Hi,
Already tried on breadboard. It sound nice but the chip runned hot. If you want to drive low z load a buffer might be needed ( either discrete or a chip like a buf634 or lme49600).
I was inspired by this:
https://tangentsoft.com/audio/opamp-bias.html
https://www.audioasylum.com/audio/tweaks/messages/31186.html
Already tried on breadboard. It sound nice but the chip runned hot. If you want to drive low z load a buffer might be needed ( either discrete or a chip like a buf634 or lme49600).
I was inspired by this:
https://tangentsoft.com/audio/opamp-bias.html
https://www.audioasylum.com/audio/tweaks/messages/31186.html
My bad. I was doing multiple things together, and read 5534 in class A and extra resistor... apologize to LJT.
This technique was called “pull-down” of the output into class A. I tried it 35 years ago for my Phillips Cd3040 and Cd 650 players following articles in Audio Amateur magazine. They were part of series on pooging Phillips CD players, written by Walt Jung. But as I recall, Gary Gallo also referred to the pull down technique as well in articles on upgrading other output stages.
That's a bit confusing, because pull down sounds like it is a resistor or current source from the output to the negative supply, which it isn't.
With a resistor to the negative supply, you would only increase the quiescent current through the pushing side of the output stage, and (unfortunately) lower the load impedance the op-amp has to drive. With this resistor from pin 6 to pin 5, you increase the quiescent current through both the pushing and the pulling side. As the voltages on both sides of the resistor more or less track, the load impedance the op-amp has to drive does not decrease much. Besides, it acts as feedforward compensation to some extent, although it only bypasses a bias spreader and an emitter follower.
With a resistor to the negative supply, you would only increase the quiescent current through the pushing side of the output stage, and (unfortunately) lower the load impedance the op-amp has to drive. With this resistor from pin 6 to pin 5, you increase the quiescent current through both the pushing and the pulling side. As the voltages on both sides of the resistor more or less track, the load impedance the op-amp has to drive does not decrease much. Besides, it acts as feedforward compensation to some extent, although it only bypasses a bias spreader and an emitter follower.
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One should not jump too quickly to conclusions regarding the effect of bias current, loading, etc. on the linearity. Sometimes, a completely unexpected behaviour shows up:
https://www.diyaudio.com/community/threads/a-good-unbalancer-suggestion.374539/post-6726034
https://www.diyaudio.com/community/threads/a-good-unbalancer-suggestion.374539/post-6726034
Stability for driving capacitance loads at high frequency?
likely modern equivalents that do it
with already provided internal circuits
likely modern equivalents that do it
with already provided internal circuits