Tube Amps / Music Electronics
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|8/27/1997 12:32 PM|
|R.G.||Clipping Diodes, Levels, and "distortion theory"|
Responding to and expounding on some of the items from the DOD preamp/distortion item:
Mark Hammer sez:
"my choice(and recommendation) to use a toggle switch to select between diode types is simply that, with a higher clipping threshold, your basic 1N914 will deliver about 250-300mv more potential signal at the output than a 1N34A or 1N270 will."
I use a second or third pair of Ge's in series to get the clipping threshold up to about on par with silicon diodes when I use germaniums in most cases.
It's pretty easy to install a surplus rotary switch that will give you eight or more selections of clipping diodes, and a wealth of options.
I find that installation of a variable resistor in series with the diodes can make MAJOR differences in how the clipping sounds. The venerable Distortion Plus becomes a good blues sound pedal with a 10K pot in series with the clipping diodes.
Mark Hammer sez:
"I've always liked the sound of a guitar that
accumulates litle bits of distortion along the way, rather than everything coming from one box/source. The 1N914's let me crank up the gain of the Dist + without clipping too hard, and let the higher output generate distortion in the amp itself."
I like this approach too. Russell Hamm's paper on Tubes vs Transistors hits this a bit when he notes that the big distinction in tubes and transistors seems to be in the first 12 db of overdrive where the tube distortion is perceived as compression, not distortion.
I've wanted to make a distortion device using an active device, probably inverter sections ala the Tube Sound Fuzz, or N channel jfets, and set them up so they ...just... overdrive, then put a resistive attenuator between sections to cut the gain back so that the next stage ...just... overdrives, too. After a couple (or ten or twenty) iterative stages, you'd pick up much more of the flavor of that particular clipping device, as the distortion should accumulate gradually.
So many ideas, so little time...
|Jack Orman You might be interested in the test... -- 8/27/1997 3:29 PM|