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2nd Harmonic

10/28/2004 11:39 AM
Dave James
2nd Harmonic
Hi All,  
Any of you ever design your circuits to specifically maximize the 2nd harmonic content of the guitar's signal?  
If so, how?  
10/28/2004 1:26 PM
Use single ended output stage w/cathode bias. Lots of 2nds produced.
10/28/2004 4:09 PM
Dave James

Thanks! Any other techniques?  
10/28/2004 5:42 PM
Carl Gigun

Bypass said cathode resistor well, play with bias point looking for a widening on one half of the wave and a narrowing on the other? (ie. a larger than leo cathode resistor)  
10/28/2004 7:31 PM
anything that whacks half the signal is generating even harmonics. A single diode to ground.. biasing a tube really cold (ala Soldano..)  
IMHO just even harmonics don't sound that great all by themselves, you do need a mix IME.
10/31/2004 12:24 PM
R.G., well, there's the tube version of my JFET thingie, the Mu Doubler.  
Take a tube. 12AX7 works nicely. Connect both plates to a single 100K plate resistor, both cathodes to a single 680 ohm cathode resistor bypassed by a 47uF capacitor to ground, tie each grid separately to ground through two 1M resistors. Feed the grids out-of-phase signal from a good phase inverter.  
Each tube-half amplifies what it gets, in the process causing even-order distortion. When the signals get to the joined plates, the out-of-phase amplified signal cancells out, leaving only the even order distortion **which reinforces**.  
What you get is only the even order distortion if the tube (halves) are well matched and the feed signals are mirror images. Small imbalances allow the original signal to be not-quite-cancelled, which means you get signal plus a lot more even order distortion than would otherwise be there.  
11/1/2004 12:51 AM
Carl Gigun

Neat idea, a diff amp and mixer in one efficient package. How come the cathode resistor is so small? Seems a bigger one would bias the tube into a more nonlinear region and possibly improve the differential action?  
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