That's a huge inductor! Good luck trying to fit that on the PCB. Do you have any references for this tweak/modification?
This amp is very similar:
https://cxem.net/sound/amps/amp249.phphttps://cxem.net/ckfinder/userfiles/comments/82832_KT21_IMPORT.jpgPCB:
https://cxem.net/sound/amps/images/amp249-20.jpg
Amorphous metal nanocrystalline core, m=20000
https://cxem.net/sound/amps/amp249.phphttps://cxem.net/ckfinder/userfiles/comments/82832_KT21_IMPORT.jpgPCB:
https://cxem.net/sound/amps/images/amp249-20.jpg
Amorphous metal nanocrystalline core, m=20000
Attachments
I was thinking air-core since there was no core shown on the schematic. Anyhow, I'm pretty unimpressed by this mod. It's just defeating the emitter degeneration at low frequencies so the input stage will be less linear as a result.
100 micro-H at a few mA is not big.
This looks-like Dean Jensen's 990 trick to reduce input audio hiss while keeping supersonic (>40kHz) stability. Which makes sense at a microphone interface, not a power amp input (which works at least 20dB higher level).
With an increase in the overall gain of the open-loop amplifier, the difference signal of the input differential stage decreases and, at the same time, the linearity of the input and the entire amplifier will be several times better.
Emitter resistors for high frequency interference will work and will reduce intermodulation distortion.
Emitter resistors for high frequency interference will work and will reduce intermodulation distortion.
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Like I said, you're defeating emitter degeneration, which will give you higher gain, but at the cost of linearity and increased distortion at higher power levels.
Kramtweeter, You convinced me 🙂. From the coil in this circuit, the effect is only 1.5 times.
If in other circuits the emitter resistors are larger (470-750) ohms, I believe that the effect of the coil will be 10-15 times greater.
