"Slick Trick" Rectifiers for Level Detection

[Guest]

[quote author="mediatechnology"]

(I use log conversion before rectification).

Sort of like the one posted above your reply. (Which you probably didn't see because we posted at the same time.)[/quote]

Yep, very similar approach. I use an opamp with diodes in feedbeck, then opamp with hi-V transistor with common base plus an emitter follower as a half-wave rectifier (however, a current mirror plus one more transistor will give full-wave rectification, but I am happy with that since I have also LEDs in screen grid current sensors of output toobs to indicate clipping (peaks of screen grid current is the best indicator).

One capacitor connected to emitter of that hi-V emitter follower is for peak rectifications; 10 times bigger cap with resistor in series averages rectified signal. Why hi-V transistors? Because it drives directly grid of EM-80 magic eye (I don't use a triode from it, it would need too high voltage swing from opamp.)

 

[JohnRoberts]

Responding to the log first or rectify first discussion, one tidbit that may not have been pointed out about my TS-1 rectifier, the actual voltage output of the opamp doing the rectification is a crude AC log as it represents the Vb-e of the current output. This crude AC log waveform is used to feed the frequency counter as it extends the sensitivity down well below the uncompressed linear input.

JR

 

[mr coffee]

This is another precision rectifier. Not super low component count, but novel and not one I have seen too often. It seems to sort of fit with the flow of the thread, if not the title. FWIW.

Sorry, I just don't seem to get the hang of posting images yet.

 

[JohnRoberts]

For any having trouble following the schematic, try to ignore the mislabeled opamp pins. (pin 2=-, pin 3=+) :roll:

JR