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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  Low Vf Diodes: Ge Vs. Schottky 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: Low Vf Diodes: Ge Vs. Schottky  (Read 3515 times)
Earthscum
Posts: 1932


David Edgar


Low Vf Diodes: Ge Vs. Schottky
« on: February 17, 2011, 09:46:18 PM »

So, I was curious... can you sub schottky barrier diodes in place of Ge diodes where you are shooting for a low Vf? Places I'm talking about are in certain compressors, and envelope followers. Also, I guess, other octave ups, etc (assuming, basically, that the Ge isn't used solely for it's tonal qualities).
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CynicalMan
Posts: 1613


Alex L. - Canada


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Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #1 on: February 17, 2011, 10:34:18 PM »

IIRC, schottky and germanium diodes have forward voltages of 0.3, but germaniums have a more gradual transition to conduction, a 'soft knee'. So, schottkys are better when you want as low a vf as possible. You might be able to emulate a germanium diode using a schottky with a resistor in series, but I don't really see the point given the availability of germanium diodes. Also, I'm sure there are many applications where schottkys would work as fine subs on their own.
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R.G.
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Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #2 on: February 17, 2011, 11:34:57 PM »

CM is about right.

Silicon Schottky diodes are a little highver Vf than Ge, leakier than normal silicon junctions, and able to carry large currents with lower internal resistance. They leak less than Ge. They're less temperature sensitive than Ge.

If you want a good envelope detector (including in a compressor) use a precision rectifier circuit. This will get you down to a Vf of a couple of millivolts. If you want quick and cheap, use either Ge, or Schottky. If you don't have either one, use a silicon.  Better, try it all these ways and see what you like.

Most good octave circuits (Superfuzz, Blender, Tone Machine, others) use biasing tricks to balance out most of the Vf from the silicon junctions they use.
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R.G.

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Hides-His-Eyes
Posts: 1422


Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #3 on: February 18, 2011, 03:53:23 AM »

IIRC, schottky and germanium diodes have forward voltages of 0.3, but germaniums have a more gradual transition to conduction, a 'soft knee'. So, schottkys are better when you want as low a vf as possible. You might be able to emulate a germanium diode using a schottky with a resistor in series, but I don't really see the point given the availability of germanium diodes. Also, I'm sure there are many applications where schottkys would work as fine subs on their own.

Wait, what?

At least from my POV availability is pretty poor. 40p each upwards per diode when you can get them.
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ralley
Posts: 125


Rob A. Auckland, NZ.


Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #4 on: February 18, 2011, 04:07:49 AM »

Wait, what?

At least from my POV availability is pretty poor. 40p each upwards per diode when you can get them.

$0.52 Au for 10 from Futurlec (http://futurlec.com.au/price1.jsp?part_no=1N34A) and it gets even cheaper the more you buy.  Shipping is cheap too.  Just beware that the last ones I got from them were actually 1n60 instead on 1n34, made no difference to me.

Rob.
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Perrow
Posts: 1779


Pelle T


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Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #5 on: February 18, 2011, 05:55:10 AM »

$0.52 Au for 10 from Futurlec (http://futurlec.com.au/price1.jsp?part_no=1N34A) and it gets even cheaper the more you buy.  Shipping is cheap too.  Just beware that the last ones I got from them were actually 1n60 instead on 1n34, made no difference to me.

Rob.

LOL, I thought that price was for one. I'm still waiting for my order, let's just say I'll be stocked for 1N34A's for a while  icon_eek I thought I'd get 6, guess I'll start a production line for fuzzes Smiley
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Hides-His-Eyes
Posts: 1422


Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #6 on: February 18, 2011, 06:44:10 AM »

I too thought that price was for one.  Shocked
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Earthscum
Posts: 1932


David Edgar


Re: Low Vf Diodes: Ge Vs. Schottky
« Reply #7 on: February 18, 2011, 04:33:01 PM »

I just remembered (and double checked) that I got a crapload of 1N60P's. These are shottky's, though... not the germanium. They look like your typical Si package, little brown glass, like 1N4148, 1N914. I've been digging on the sounds I get from these. I also have a ton of 1N5158's, which is why I was wondering about the Ge vs. Schottky. I gotta use 'em up so I can buy more! lol... actually, more like I have so many that I don't wanna add to my collection with another couple hundred diodes. Maybe just a handfull of Ge's for those times I need them for their sonic qualities.
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