Pass H2 Harmonic Generator

[watchnerd]

"If, as DIY audiophiles we want to break the rules and play with some 2nd harmonic, we want some cheap and practical way of doing it. The first option is to buy some Triodes (for example low voltage 6922's) and some other parts plus the equipment to build and calibrate a single-ended gain stage with just the right amount of 2nd harmonic. This is a very rewarding approach whose only drawback is the time and money.

Alternatively, the musical instrument company Korg, working with Noritake, has developed a Nutube, which is a tiny dual Triode about the size of a computer chip that runs on a tiny amount of power and delivers 2nd harmonic on demand. An excellent solution, it was the subject of my 2017 talk at Burning Amp Festival, and my write-up of that can be found in the Articles section at www.FirstWatt.com

But here we are going to explore this effect with a common inexpensive Jfet on a little circuit board powered by a small wall-wart. I don't think it can get any simpler or cheaper."

https://positive-feedback.com/audio-discourse/the-pass-h2-harmonic-generator/

 

[cjfrbw]

Nelson Pass gave these out as door prizes at the last Burning Amp, and I gather they were scooped up like pork rinds at Super Bowl.

He also has a DIY design including the Korg triode in his (previously) passive line stage to add second order harmonics on purpose.

 

[andreasmaaan]

Does anyone know if it also kind of soft clips in the way an SET would? Or does it just add a fixed amount of 2nd harmonic until the point at which it overloads (same question applies to the other two alternatives he mentions)?

 

[cjfrbw]

http://www.firstwatt.com/pdf/art_h2.pdf

You can read about it.

 

[milosz]

I have auditioned a well-regarded Class-A solid state amp (Forte 4a with the Soderburg mods) on a pair of quite revealing small 2-way speakers (DIY version of Selah Anniversario) against an AMC CVT-2030 class-A MOSFET/EL-34 hybrid amp.

Both of the amps sound very clean.

The solid state amp had better bass control / extension. Not a LOT better, but you can hear a difference.

The AMC hybrid MOSFET/EL-34 amp has a LOT more "depth" in the stereo. VERY noticeable, even by non-audiophiles who listened to the comparison.

The solid state amp and the hybrid amp all had the same good left/right stereo lateralization- but the hybrid amp gave much more depth impression.

Everyone who listened preferred the AMC amp's sound. This depth thing is very beguiling.

I strongly suspect that the AMC hybrid amp is adding just a smidge of 2nd harmonic, which the ear+brain perceives as a depth cue (this is what Nelson Pass says a little 2nd harmonic adds, anyway.)

Or maybe it's changing phase shift vs frequency in the hybrid amp that is not shown by the solid state amp? I do not know.

I ran speaker frequency response plots with both amps and they were as identical as I've ever seen, especially through the mids and treble- less than half a dB of difference there, which is within my measurement accuracy. So I don't think I was hearing some kind of Ohms-law frequency response effect created by the speaker impedance load interacting with the different source impedance of the two amplifiers output stages. (Which reminds me, I'll have to measure the AMC amp's output source impedance some day when I drink enough coffee to motivate me to do so...)

The AMC CVT 2030 is a pretty wonderful little amp, by the way, and you can get them really inexpensively when they turn up on the used market. Highly under-rated.

 

[PierreV]

The AMC CVT 2030 is a pretty wonderful little amp, by the way, and you can get them really inexpensively when they turn up on the used market. Highly under-rated.

I own a AMC CVT 3030 - it isn't reliable, it is relatively noisy by modern amplifiers standards, its frequency response is amazingly non-textbook but yes, it is a fun amplifier with a lot of character

 

[milosz]

I have a CVT-2030. It's a power amp. The CVT-3030 is an integrated amp. Different product. The CVT-3030 has no PRE OUT/MAIN AMP IN jacks, unfortunately.

I've had my CVT-2030 for 7 years or so. Never had any reliability issues with it. Doesn't seem noisy to me, I can hear nothing out of the speakers when the amp is on but there's no signal. I wonder if your experience of noise is coming from the preamp section.

I also had a CVT-2100, which is a hybrid tube power amp using KT88's instead of the EL-34's of the CVT-2030. I did not like the sound of the CVT-2100. I sold the CVT-2100.

 

[kaka89]

@WolfX-700 did a measurement in here https://l7audiolab.com/f/来一点谐波失真！pass-h2-harmonic-generator-介绍

 

[RayDunzl]

For anyone wondering where even harmonics originate, generally speaking, I think it is asymmetry in the signal.

In the above waveform, the negative excursion is reduced.

Positive excursion flipped and overlaid on the negative:

The analysis includes odd harmonics, so, I guess my thinking is damp.

http://www.neumann-kh-line.com/neumann-kh/glossary.nsf/root/F77C48111116FFBDC12578B20039968C?Open&term=THD+N#:~:text=Total harmonic distortion (THD) is,+ fourth + fifth + etc.&text=Second-order harmonic distortion is,by asymmetries in the system.

 

[milosz]

I own a AMC CVT 3030 - it isn't reliable, it is relatively noisy by modern amplifiers standards, its frequency response is amazingly non-textbook but yes, it is a fun amplifier with a lot of character

I wonder if the noise is coming from the tube preamp stage....? The CVT-3030 is an integrated amp, the CVT-2030 is a basic amp. Stereophile did some measurements of a CVT-3030 => https://www.stereophile.com/content/amc-cvt-3030-integrated-amplifier-measurements

 

[DualTriode]

Hello All,

I have been checking out H2 Version 2 of this device. So far I am missing the required trim pot to adjust the operating voltage that adjusts the amount of H2.

The output voltage is at 1 Volt RMS as instructed.

Thanks DT

See attached.