Anyone see Nelson Pass's new 2nd harmonic generator on Positive Feedback? Anyone tried it?

[morricab]

It is interesting that Nelson has come up with something like this; however, I doubts that this goes to the heart of addressing the difference between SET designs and Push/pull designs. It makes two assumptions: 1) That the injection of 2nd order harmonic all by itself is the answer to systems with "warmth" issues and 2) It assumes that his device makes only 2nd order harmonic and not other, higher order harmonics.

Let's look first at assumption 1. IMO, this idea of just adding some second order harmonic is a gross oversimplification to a very complex perceptual experience. If you inject just a bit, it will be inaudible due to masking and if you add a lot it will warm up or golden up or something the sound but it won't make it necessarily sound like a good SET OR like real life. Real life instruments and sounds are (mostly) mechanical in nature and as such make monotonic distortion patterns (except for chaotic instruments like cymbals). SETs also make a similar pattern (more or less following the pattern depending on the quality of the design). The point is that it is not just one harmonic that shapes perception but the pattern of the harmonics as a function of SPL. Injecting a lot of 2nd order will not just give you the right pattern and will have a different impact depending on the level you listen as this new harmonic injection is overlaid with whatever your source, preamp and amp make at a given output level.


Assumption 2 does not hold as the data Mr. Pass shows clearly has 2nd, 3rd, 4th and likely beyond (not shown); however, the pattern is monotonic, which suggests it might mimic an ideal distortion pattern that our ear brain finds essentially invisible at lower distortion levels. If this pattern is higher level than the one it is overlaid onto but still low overall would this then trick the ear/brain into being less audible or are the effects additive and it will be like trying to smear lipstick on a pig??


OR is this kind of like what a designer might attempt to do with a hybrid design, where the input/driver stages are triode tube and have a roughly monotonic pattern (in Class A without feedback at least) and then use a high bias AB or A MOSFET stage to be as transparent as possible (According to Boyk and Sussmann's simulations a Class A PP MOSFET stage would have essentially no harmonic distortion...of course that is with a perfect transistor and perfect power supply...both of which do not exist). I have heard some pretty successful (and not so successful) designs of this type. The more successful were significantly more musical and less artificial sounding than comparable all transistor types. Perhaps Pass's device is close enough to a triode mimic that it can achieve something similar?


I throw this open to debate... curious for your opinions.

 

[cjfrbw]

I guess NP gave these away as door prizes of sorts at the last Burning Amp festival in San Francisco.

However, I don't think I have ever heard him state that he thought second order harmonics made solid state devices sound like tubes or SET. Although others sometimes compare his circuits with tubes, he seldom if ever does and seems to consider such comparisons beside the point. He is acutely aware of the way second order and third order harmonics tend to add a certain quality to the sound of amplifiers. Some of the First Watt emphasize second order harmonics (described as 'warm') and some third order harmonics (described as 'lively'), but other harmonics are avoided or not honored in any particular manner.

NP seems to honor solid state devices the way tube-o-philes honor certain tubes: he studies them carefully, matches them painstakingly, listens to them with some kind of star chamber of buddies to see if they sound good or not, and attempts to optimize them creatively with his circuit genius.

I rotate two Pass related amplification devices into and out of my system at various times, along with my vintage VFET amps. I have a First Watt M2 and the Pass based VFET DIY knock off. Driving these with Allnic DHT, Manley Neo300b preamp, or 26 based preamps is about as exotic and pleasing a sound as I have ever heard anywhere, much less my own ribbons. The sound is so nice across the board, they indeed make me think the issues of tubes or SS are moot. I am currently using the Pass DIY VFET as a Stax headphone amp without any tube driver, and it is the best headphone sound I have heard from either tube or solid state, including my 50 watt WAVAC SET.

I agree, though, that SET continues to have a wonderful and ineffable character that only SET is able to duplicate.

At the last CAS, I heard the Destination Audio stuff ( big horns, lots of transformers and flea powered amps) with the big horns and a 1.8 watt 45 SET driving in a large room, and I thought the sound was amazing. Likewise at the CAS the year before, my favorite sound was the Pure Audio Project Voxativ open baffle speakers with a 3 watt 2A3 Whammerdyne. I can see where the insane devotion to flea power and high efficiency comes from and I can't argue with it.

The Whammerdyne/Voxativ had some very stiff competition in other rooms, including many big electrostats i.e. Soundlabs, Martin Logans which tend to be amongst my favorite sounds.

(On second thought, I just read NP's article on the H2 second harmonic generator, and he does discuss comparisons with tubes and second order harmonics and the role they play in SET sound. I don't know that he actually says he thinks it's the ONLY thing that makes tubes sound different, but second order harmonics do contribute warmth. He does think of triode tubes (as well as triode-like transistors like VFET and JFET) as second order harmonic generators, and pentodes (as well as pentode-like transistors) as third order harmonic generators. He has been fiddling with the Korg NuTube, which uses a florescent cathode and is a legitimate triode. Its a pretty compact dual tube that tucks nicely into his B1 preamp and selectively adds second order harmonic character, but NuTube is a real triode tube, not a transistor.)

 

[ack]

Interesting, but Pass's circuits already play with the 2nd harmonic so this should not be much of a surprise

The lesson of the Xs and SIT amplifiers was that a small amount of second harmonic of a particular phase character gives a desirable sonic result. To get that effect, we altered the arrangement of the constant-current sources in the output stage to better duplicate the sound of the Xs output stage. While the .8 amplifiers still have low distortion, they do not suppress second harmonic as much as the .5 series, giving a mostly second-harmonic character at ordinary listening levels and segueing into third harmonic at higher power.
Read more at https://www.stereophile.com/content...monoblock-power-amplifier#s1lUID1Pihlv7KiO.99

I have always thought Pass amps sound tubey-colored and I guess this is why.

 

[morricab]

I guess NP gave these away as door prizes of sorts at the last Burning Amp festival in San Francisco.

However, I don't think I have ever heard him state that he thought second order harmonics made solid state devices sound like tubes or SET. Although others sometimes compare his circuits with tubes, he seldom if ever does and seems to consider such comparisons beside the point. He is acutely aware of the way second order and third order harmonics tend to add a certain quality to the sound of amplifiers. Some of the First Watt emphasize second order harmonics (described as 'warm') and some third order harmonics (described as 'lively'), but other harmonics are avoided or not honored in any particular manner.

NP seems to honor solid state devices the way tube-o-philes honor certain tubes: he studies them carefully, matches them painstakingly, listens to them with some kind of star chamber of buddies to see if they sound good or not, and attempts to optimize them creatively with his circuit genius.

I rotate two Pass related amplification devices into and out of my system at various times, along with my vintage VFET amps. I have a First Watt M2 and the Pass based VFET DIY knock off. Driving these with Allnic DHT, Manley Neo300b preamp, or 26 based preamps is about as exotic and pleasing a sound as I have ever heard anywhere, much less my own ribbons. The sound is so nice across the board, they indeed make me think the issues of tubes or SS are moot. I am currently using the Pass DIY VFET as a Stax headphone amp without any tube driver, and it is the best headphone sound I have heard from either tube or solid state, including my 50 watt WAVAC SET.

I agree, though, that SET continues to have a wonderful and ineffable character that only SET is able to duplicate.

At the last CAS, I heard the Destination Audio stuff ( big horns, lots of transformers and flea powered amps) with the big horns and a 1.8 watt 45 SET driving in a large room, and I thought the sound was amazing. Likewise at the CAS the year before, my favorite sound was the Pure Audio Project Voxativ open baffle speakers with a 3 watt 2A3 Whammerdyne. I can see where the insane devotion to flea power and high efficiency comes from and I can't argue with it.

The Whammerdyne/Voxativ had some very stiff competition in other rooms, including many big electrostats i.e. Soundlabs, Martin Logans which tend to be amongst my favorite sounds.

(On second thought, I just read NP's article on the H2 second harmonic generator, and he does discuss comparisons with tubes and second order harmonics and the role they play in SET sound. I don't know that he actually says he thinks it's the ONLY thing that makes tubes sound different, but second order harmonics do contribute warmth. He does think of triode tubes (as well as triode-like transistors like VFET and JFET) as second order harmonic generators, and pentodes (as well as pentode-like transistors) as third order harmonic generators. He has been fiddling with the Korg NuTube, which uses a florescent cathode and is a legitimate triode. Its a pretty compact dual tube that tucks nicely into his B1 preamp and selectively adds second order harmonic character, but NuTube is a real triode tube, not a transistor.)

First question and maybe I have asked before...what WAVAC 50 watt SET do you have?

I don't use flea powered SETs because my horns are not quite sensitive enough to take full advantage of them...so I used "muscle SETs". Truth be told I don't think the flea powered ones are inherently sonically superior, what matters I think more is the linearity of the tube, how you drive it, the stability of the power supply and the all important output transformers.

I have mixed feelings about the single driver speakers I have heard (and even own). They still often sound too thin and, well, papery. Better a good compression tweeter and use them as a mid only (like Horning) and then put a good bass system together with it. Some co-ax design (like Dynamikks, which I sell) are very good too.

As you know I am coming from the planar world and until I heard some horns that didn't sound obviously colored I didn't want to change to gain that last bit of dynamics and umph. I have owned 8 different brands/models of planars (5 electrostat and 3 planar magnetic) and none did dynamics like my horns (although the Acoustat Spectra 4400 were not far off and the Infinity IRS Betas could scale wonderfully to big music...big bass bins helps...but not so good small music.). Microdynamics were similar though, with the STAX ELS-F81s perhaps doing even better...although my DecWare HDTs do the low level and subtlty thing very well indeed.

Based on your second thought: 2nd harmonic only contributes to warmth when it is excessive. At normal listening levels with a SET/horn combo the distortion, which scales with the power for a no feedback design, will be quite low (well under 1%) in a good design and should be completely inaudible. IMO, he makes several overly simplistic statements but he does not give any absolutes per se.

I have a small amp from MasterSound, the Dueundici (means 2 11), which is a single ended pentode amp with a small bit of feedback (seems to be need for pentode amps). I use this on my attic system and it drives the HDTs, which are 96db sensitive and play very loud with little power. The DAC is an old (but good sounding) PS Audio Ultradac II (this has the UltraAnalog R2R 20 bit module). That Mastersound does sound close to a SET but not quite. It is a little bit sharper and doesn't have quite the 3d imaging and soundstage of my SETs in house (Aries Cerat Genus on the big rig and JJ-322 on the downstairs rig) but it is lively and fun. Doesn't make me curious though to try a big SEP...if one exists.

A SIT would interest me because I would like to hear if it really has SET qualities without the drawbacks of at least the lesser quality SETs (top SETs have little to be desired from what I have heard so far). The word on the street is that they don't sound like SET despite mimicing many traits. In fact my NAT did not sound like a SET really...tonailty wise, yes, the rest no.

 

[morricab]

Interesting, but Pass's circuits already play with the 2nd harmonic so this should not be much of a surprise



I have always thought Pass amps sound tubey-colored and I guess this is why.

Actually, they might sound warmish (not all of them though the normal X series sounds not terribly warm at all) but not in the way of a good tube amplifier.

 

[ack]

Actually, they might sound warmish (not all of them though the normal X series sounds not terribly warm at all) but not in the way of a good tube amplifier.

Yes, great tube amps are very neutral

 

[cjfrbw]

I think that observers glom on second order harmonics, because it is something in SET that can easily be measured and to some extent controlled by design.

I think there are attributes not so easily measured which contribute to SET ability to portray space and tonality. What they are, I wouldn't know exactly, except that the sense of fluidity and dynamic ease can be audibly apparent.

Some DHT also have a kind of beguiling 'raw' sound that seems to place no barrier between the signal and the ears. Good SET amps also seem to act as dynamic range expanders (just my feeble attempt at describing the effect, not intended to be accurate), especially in the upper midrange.

Comparing VFET or SIT with SET is kind of beside the point. I would say, however, that a directly heated triode driver in front of a good VFET has made me largely forget about pursuing SET.

I think most blindfolded audiophiles would think that a DHT driving a VFET sounded like tubes, albeit very quick dynamic tubes with sweet but abbreviated(by comparison) deep tonality. Lots of dimensionality and tonal specificity coming out of a black background. However, the 'tube-i-ness' would probably be more toward the OTL side than the SET side. Whether one actually thought one or the other were 'better' or sounded more authentic would probably be to taste.

When I heard the Destination Audio stuff (big horns, lots of transformers, flea powered amps), I was charmed. I went home and played the same Dire Straits vinyl on my system. I was surprised that the similarities in sound exceeded the differences, even though my system uses vintage VFET with DHT preamp/tube drivers on ribbons.

 

[morricab]

I think that observers glom on second order harmonics, because it is something in SET that can easily be measured and to some extent controlled by design.

I think there are attributes not so easily measured which contribute to SET ability to portray space and tonality. What they are, I wouldn't know exactly, except that the sense of fluidity and dynamic ease can be audibly apparent.

Some DHT also have a kind of beguiling 'raw' sound that seems to place no barrier between the signal and the ears. Good SET amps also seem to act as dynamic range expanders (just my feeble attempt at describing the effect, not intended to be accurate), especially in the upper midrange.

Comparing VFET or SIT with SET is kind of beside the point. I would say, however, that a directly heated triode driver in front of a good VFET has made me largely forget about pursuing SET.

I think most blindfolded audiophiles would think that a DHT driving a VFET sounded like tubes, albeit very quick dynamic tubes with sweet but abbreviated(by comparison) deep tonality. Lots of dimensionality and tonal specificity coming out of a black background. However, the 'tube-i-ness' would probably be more toward the OTL side than the SET side. Whether one actually thought one or the other were 'better' or sounded more authentic would probably be to taste.

When I heard the Destination Audio stuff (big horns, lots of transformers, flea powered amps), I was charmed. I went home and played the same Dire Straits vinyl on my system. I was surprised that the similarities in sound exceeded the differences, even though my system uses vintage VFET with DHT preamp/tube drivers on ribbons.

The one thing I have yet to try at home is a single ended OTL. I was kind of hoping the NAT Symbiosis SE would be like that...sadly it was not, although it was a SE(Transistor) hybrid with no output transformer. Having owned a world Class OTL (Silvaweld OTL monos) and heard several others (Atmasphere, Joule Electra and Tenor) that spooky transparency wasn't there with the NAT nor with any single ended transistor design I have heard (like the Pass Aleph series).

This leaves, AFAIK, two companies that make a true SET OTL. One is cheap from Transcendent Sound and makes 12 watts in monoblock form (4 watts in stereo). These are kits and would take probably take 20 hours or so. The other is expensive, huge and hot running with 20 watts and it comes from Aries Cerat. There is no comparison on power supply, drive etc. but it might be fun to build the Transcendents to see if that is the right direction for ultimate transparency AND SET coherence (the PP OTLs I have heard are not completely coherent and tonally a bit bleached...except the Joule Electras, which are richer in tone).

I doubt this will replace my Genus (love this amp) but it might find a good spot in a secondary system (at least for the Transcendent...if I go there).

 

[bonzo75]

I bought the old Berning zh270 integrated and atmasphere ma60 mk3.2 and compared them both to various sets on horns universum as well as horns fp10. I preferred sets to both. That said, I love the bigger Berning quads, and tenor 75 otl continues to be my favorite amp though never heard it on a horn

 

[Stacore]

Lynn Olson used a similar logic in his Karma amplifier. He advocated for an intentional mismatch of a PP pair to generate even order harmonics, not just the 2nd, and gaping the OPT (by the way linearizing the core). It does appeal to me, although purely intellectually as I've never heard his amp. IIRC our hearing mechanism produces even order harmonics, as well as odd order ones, following roughly the 1/n rule where n is the order of the harmonic.

Cheers,

 

[morricab]

I bought the old Berning zh270 integrated and atmasphere ma60 mk3.2 and compared them both to various sets on horns universum as well as horns fp10. I preferred sets to both. That said, I love the bigger Berning quads, and tenor 75 otl continues to be my favorite amp though never heard it on a horn

I heard the Tenors on a pair of Dynamikks 3.1 horns several years ago. It was phenomenal. I too ultimately preferred SETs but the initial response to a good OTL is WOW.

 

[morricab]

https://www.innerfidelity.com/content/katzs-corner-episode-25-adventures-distortion

Seems someone else did nearly the same thing but with a Nuvistor tube. The results are interesting to say the least. Also, they reflect a lot of what I have been telling you guys on this forum for awhile now.

 

[alfa100]

I have the H2 in my system between MSB DAC with built in volume control and Pass Labs. Xa100.8. H2 has anout 90 hours and still improving. 1. Adds body to the mids and smooths out the tops. Low bass is lessened. 2 . Adds musicality . 3. Accuracy slightly diminished. 4. Good up to about 72 dB after which second harmonics overpower accuracy. Serves my need ; having moved to an apartment I can enjoy music between 60 to 70 dB. It adds second harmonics which accentuates the mids and lessens the bass. Now I enjoy the music without bass travelling to the neighbour. Not ideal at higher volumes hence I’m working on moving to a stand alone house where my music will not affect the neighbours.

 

[Amir]

Small-Signal Distortion in Feedback Amplifiers for Audio

James Boyk and Gerald Jay Sussman

April 22, 2003

 

[alfa100]

Thank you

 

[cjfrbw]

I have been listening for nine months or so my Pass DIY OS2 single ended amp based on the ancient Sony 2SK60 VFET, that I built into an old, defunct Sony TA 4650 chassis as a kind of tribute.

It seems to be a ‘current amplifier’ spin on the commercial SIT 1 and SIT 2 amps, since those had both voltage and current gain in the single SIT device while the OS2 has only current amplification and requires voltage amplification from a preamp stage. Every voltage amp I have tried, both tube and SS, sound great with it.

It’s probably about as transparent as anything I have heard, while still maintaining analog characteristics. I think it sounds a bit better than the SIT 1 and SIT 2 I heard at shows, (I don’t like to say that too loud) which were amazing, but one could say a skosh on the dry side if you were hunting for criticism. The SK60 version is liquid and analog sounding


It’s the first transistor device that I think can challenge the might fleas (45, 2A3, 300b etc.). It has their transparency, tonal and spatial characteristics, but also has surprising dynamic thrust. The traditional fleas seem to give a pleasing rendition of sharp dynamics and transients, but the 2SK60 has real energy on things like trumpet blasts and sax, that bely its modest power ratings.

I didn’t see any harmonic spectra for it, but I would imagine it has a reasonable harmonic content of H2. I guess the only down side is you would have to source the VFETs and build one to find out.