I know this has been beaten to death - but I need help, in order to get my circuit working right.
In the archives someone (Brett?) suggested a scotchy 1N5819 as an alternative to GE-diodes. My local store don't stock 1N5819 - but have 1N5817, 1N5818 and 1N5820.
Will any af these do the job?

I also wonder, will the amount of compression (subttle as it is) vary with the DC supply - 9 vs 12V?

Erik

googled "1N5819.pdf" and hit "I'm feeling lucky"

result; http://www.fairchildsemi.com/ds/1N%2F1N5817.pdf

The main thing that you would notice from this datasheet is that the forward voltage drop is different for all three.

Given that you're after a sub for a Ge diode, you'll probably want the lowest forward voltage drop you can get; 1N5817.

However, having ALSO googled up the datasheet for the 1N100, it has a forward voltage drop MAX of 1V!!!  Sheesh, that's high for a Ge!

RG should chime in soon with a definitive answer!

The 1N5820 is a higher current device and again has a slightly different forward voltage characteristic.

Scotchy describes me on Saturday night...  :wink:  Schottky is the one you're after!  

Scotchy.... hmmm, I don't know what I was thinking, sorry.

niftydog - thanks for the advise. I'll buy a few  1N5817-18's next time i pass my local shop.

IIRC I've read somewhere that it's possible to use a germanium transistor (collector and base I guess?) as a sub for a ge-diode. I have some AC128's - anyone know how this would work as a sub for the original 1N100 diode.

Again - would 9 vs 12V supply have any influence on the compression characteristics/threshold?

Erik

I have no clue about the compression thing. Make a topic about it. As for the diodes, what ar you using them for, Signal (clipping) or Voltage Regulation. If it's signal, get some 1N34A's as they're more common, and sound good. If you need that exact diode, go for the 18 as they have the closest specs.

Schottky diodes and Germanium diodes have low voltage drop, somewhat lower than Silicon diodes. The low voltage drop is the main motivation for the substitution - they are not identical diodes in general.  The type of Schottky is not important, any of those small types will do since they all provide the low voltage drop approximation to the Germanium.  The ones you mentioned are fine.

QuoteI also wonder, will the amount of compression (subttle as it is) vary with the DC supply - 9 vs 12V?

The circuit is largely unaffected by the supply rail and the compression is mainly to do with the diode and the JFET.  However with these feedback type compression circuits it is possible to overload the opamp for a short while during the attack part of the compression.  When opamp overload occurs the higher voltage rail can decrease the attack time-since it charges the attack cap quicker.  The higher voltage rail also prevents clipping in the first place.  I suspect this would be a fairly subtle effect on that design.

When looking at foward voltage drop data, note the current that it is measured at. A power diode might have spoecs of 1.5v drop at 1 amp, but actually be as low (or lower) than a small signal diode when they are both at 1ma current.
Of course, using your multimeter (if it has diode setting) then yo9u have everything tested at the same current.