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op-amp questions

Actually 1000 and 4. I originally had only one stage, but I needed a little more gain so I was playing around with the other half of the mcp6022. I'm back to just one amplification stage again using a 1M feedback resistor and 10K adjustable for the input resistor. I've also got a second 6022 acting as a band pass filter. fun stuff :-)

BTW, I got my IGBT thingy working. So far, the transistor, SCR and coil hold up nicely at >300V discharges. I guess that microchip gate drivers is doing a good job for me. Now I'm looking for some better caps and planning out a less inductive setup for use at higher voltages. I'll also be putting the caps into some kind of container in case of explosion.

Reply to
Anthony Fremont
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And what was the matter with the 741 and 555 combo-only 100uV required to flip that thing. Too much for you?

Reply to
Fred Bloggs

When you use a loudspeaker as a mike, besides from the very low impedance of maybe 6 ohms, it has a resonance in the lower frequency range . This will always be a "boomy" sound with the resonance frequency being responsible for the decay time and -behaviour. Your envelope will be dominated by this effect and you throw away resolution which you could have with a 1$ electret mike. If you now put a even bigger resistor on the input. the whole thing only becomes more noisy. Throw out this resistor and let the current of the speaker, not the voltage across it, drive your amp, which now will function as a I-V-converter. With a feedback resistor of only 10k you will now have a transimpedance of 1.5V/mA, which is probably high enough. The electrolytic cap on the input needs to be much bigger(150uF for f-low=180Hz), and should roll off above the before mentioned resonance. An R-L-C combination across the speaker leads can dampen this resonance even further. You should plot the impedance of your speaker and mount it on a small open baffle but not in a box, to not raise this resonance to higher frequencies. From this plot you can determine the values of The RLC combination. The required coil and cap will be big and costing much more than a decent electret mike. BTW that is the reason nobody sane uses this method.

--
ciao Ban
Apricale, Italy
Reply to
Ban

"Fred Bloggs"

a

also

The 741 only has one channel, doesn't have enough gain for me at 5V, and it doesn't have rail-rail outputs. I couldn't find a 555 in my junk box either and I had already had the MMV on hand.

BTW, what do you mean by "too much for me"?

Reply to
Anthony Fremont

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