back-to-back diodes for gating

[jdub]

Came across this in an older post (http://www.diystompboxes.com/smfforum/index.php?topic=74359.0)

3) Squelching/gating: Crossover distortion can be your friend here.  Remember that when a diode pair are in series with the signal path, nothing gets through that isn't over the minimum signal-level threshold.  So a back-to-back pair of Ge diodes prior to and after a more typical TS-type clipping stage may be able to keep any "misleading" signals safely away from your fundamental detector.

This may be a blockheaded question, but by "back to back", are we talking literally, as in anode of one to cathode of the other connected in series, or does this refer to a parallel pair with opposite orientation (as in clippers) but inserted in series with the signal?  I'm assuming the latter, but I've seen "back to back" used in both contexts...

Thanks

[Quackzed]

I believe your assumptions are correct, sir! parallel pair, opposite orientation, in series with signal. 

[earthtonesaudio]

Your assumptions are correct, but the term is totally incorrect and oft-abused. 

What they're talking about is the anode of diode 1 connects to the cathode of diode 2, while the cathode of diode 1 connects to the anode of diode 2.

There's absolutely no logical way of interpreting this as "back to back" but for some reason (i.e. not thinking about it) people use this term all the time.


I prefer the term "antiparallel" which tells you the diodes are in parallel (rather than series) and pointing in opposite directions.  "Cross coupled" is more vague but still correct, in my opinion.  Even "back to front" would be more correct than "back to back."



For the discussion in the quotation, they're talking about 2 diodes, in parallel with each other, of opposing directions, and in series with the signal.

[jdub]

Thanks for the clarification, guys.  I, too, find the phrase to be misleading- I think something along the lines of Alex's "antiparallel" is much more appropriate. The idea of two diodes in series with opposite orientations didn't make much sense anyway...

[earthtonesaudio]

The idea of two diodes in series with opposite orientations didn't make much sense anyway...

...Unless you're building a "no-pass" filter. 

[jdub]