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Old 16th November 2012, 09:28 PM   #11
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Originally Posted by DF96 View Post
Single-ended Class B will give you lots of 2nd.
I think you want single-ended Class A. Class B implies that the output device shuts off for half of the cycle, which would create massive distortion of all kinds.


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Old 16th November 2012, 10:16 PM   #12
DF96 is offline DF96  England
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My suggestion of single-ended Class B was slightly tongue-in-cheek, as was (I assume) the Class C suggestion from jcx. However, SE Class B still produces mainly fundamental and 2nd.

Single-ended Class A can give very little distortion.
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Old 17th November 2012, 01:25 AM   #13
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Hi lineup,

In this book there is a simple circuit with two jfets wich generates your second harmonic. I don't remember the page. Maybe someone here in this forum have it. I have one but unfortunately it is so far way from me at this moment.

Field-effect transistors (Texas Instruments electronics series): Leonce J Sevin: Books


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Old 17th November 2012, 01:29 AM   #14
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Use full wave rectifier to get 2'nd order harmonic and above.
The Devil is not so terrible as his math model is!
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Old 17th November 2012, 01:41 AM   #15
Bigun is offline Bigun  Canada
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You can do it easily with almost any feedback push-pull amplifier like this:

TGM amp goes 'tubey'

I've looked at other options before too:

Bigun's Bootstrap

And Hugh Dean of AKSA fame is probably the best at tuning amps for a good harmonic profile, usually favouring H2.

Danielwritesback talks about putting a diode in parallel with a resistor in the +ve supply rail for the same result, here (post 62):

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Last edited by Bigun; 17th November 2012 at 02:10 AM.
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Old 17th November 2012, 02:20 AM   #16
GregH2 is offline GregH2  Australia
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Perhaps a highly asymmetrical output stage - quasi maybe? Also a singleton input stage and single ended vas.

This configuration is the basis of the design I am currently working on and it is looking very promising!
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Old 17th November 2012, 02:59 AM   #17
wahab is offline wahab  Algeria
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Another radical solution...

Click the image to open in full size.
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Old 17th November 2012, 06:09 AM   #18
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Don't be too focused on just H2 distortion. The most desired distortion is said to be low order; i.e. H2,H3,H4,H5 in declining magnitude.
AFAIK, that's like Jerluwoo's graph in post #7 or your #5. It's probably easier to generate that desirable type of distortion "profile"
than any single harmonic.

Last edited by Ian Finch; 17th November 2012 at 06:14 AM.
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Old 17th November 2012, 08:29 AM   #19
RJM1 is offline RJM1  United States
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Originally designed as a guitar distortion preamp I added R17 so the input is +-1V instead of +-10mV. Just mix Vout and Vin to get as much distortion as you want.
Schematic, FFT 1Khz, Vin-Vout 1Khz, distortion 1Khz, distortion 100hz
Attached Images
File Type: jpg Schematic.JPG (115.7 KB, 199 views)
File Type: jpg Vout-FFT.JPG (89.0 KB, 174 views)
File Type: jpg Vin-Vout.JPG (111.9 KB, 148 views)
File Type: jpg distortion.JPG (118.9 KB, 142 views)
File Type: jpg distortion100hz.JPG (154.8 KB, 30 views)

Last edited by RJM1; 17th November 2012 at 08:32 AM.
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Old 17th November 2012, 08:55 AM   #20
RJM1 is offline RJM1  United States
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However the distortion does vary with input amplitude, but it is still predominately 2nd harmonic.
100mV Vin 1Khz
Attached Images
File Type: jpg distortion1Khz100mV.JPG (187.4 KB, 33 views)
File Type: jpg Vout-FFT-1Khx100mV.JPG (74.0 KB, 47 views)

Last edited by RJM1; 17th November 2012 at 08:59 AM.
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