Post by Owen Y on Jul 26, 2018 14:52:04 GMT 12
Nelson Pass's FIRST WATT offers the latest 3rd incarnation of his a new amplifier based on the out-of-production SIT (Static Induction Transistor aka VFET) transistor - with greater linearity, lower distortion, greater damping factor. Reviewed by Part Time Audiophile. Only 18 watts per channel but.... " In the right system, I believe the new SIT-3 can provide a nearly perfect balance of open, dimensional, enjoyable harmonic beauty coupled with sufficient extension and control to keep matters well in hand at the frequency extremes. " US$4,000 
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Post by Owen Y on Sept 22, 2018 15:25:26 GMT 12
" The best sound I've heard from any Nelson Pass amp, on those speakers. " " I'm just blown away by the SIT-3....It just does something...magical! " " It just makes music sound more like music! " 18 watts into 8 ohms. 30 watts into 4 ohms. US$4,000 (production limited to only 250 amps).
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Post by colinf on Sept 23, 2018 7:50:45 GMT 12
Very interesting. Nelson Pass uses a transformer to step up the voltage gain to the SIT source follower output stage, instead of an active gain stage. Transformer voltage gain step up is something I fiddled with a few years back and was impressed with what it did for the sound. I have some suitable transformers in the cupboard, and some Sony Vfets, experimenting is not far away!
AMR-iFi R&D
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Member
Post by SONDEK on Feb 13, 2019 16:31:42 GMT 12
I'm fairly certain that Mr. Pass already trod that path - transformer used for voltage gain - with his earlier FIRST WATT M2.
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Post by Owen Y on Feb 13, 2019 21:15:36 GMT 12
And everybody used to do it in the 1930s, before high mu/amplification valves & then transistors.
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Post by Owen Y on Apr 3, 2019 9:07:48 GMT 12
The Absolute Sound weighs in with Dick Olsher's review of the First Watt SIT-3.... 18Wpc into 8 ohms; 30Wpc into 4 ohms " ... brings the listener a tad closer to the tube amplification experience with a far more incisive bass range than tubes can offer... It is clearly a remarkable, deliciously organic-sounding low-power amplifier, a contender for best in class, and is surely destined to become a classic. " 
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New Member
Post by rochlevoff on Apr 28, 2020 5:04:58 GMT 12
Hi...a friend of mine, using First Watt schematics, built one of their SIT amps and it is a very good solid state amp. That amp, and others I've heard from First Watt, are so much better than most other solid state amps if you have the right kind of speakers (I do, and my friend runs 105 db/w speakers). medical pcb assembly
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Post by Owen Y on Apr 28, 2020 10:58:07 GMT 12
Greetings rochlevoff & welcome - can you describe a bit more, the sound of these amps please. One of the members here has a SIT-3 (perhaps the same person), but I have yet to hear it myself.
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Post by Citroen on Apr 28, 2020 20:58:07 GMT 12
Hi...a friend of mine, using First Watt schematics, built one of their SIT amps and it is a very good solid state amp. That amp, and others I've heard from First Watt, are so much better than most other solid state amps if you have the right kind of speakers (I do, and my friend runs 105 db/w speakers).
Do tell us more. What speakers?
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Pundit
Post by peter0c on May 27, 2020 17:15:36 GMT 12
Lock down seemed a good time to settle in and give my SIT-3 an extended listen. Too often we flick from one miracle amp or speakers to another and notice the difference rather more I think than we notice the music. It is close to axiomatic that if we listen to and compare two state-of-the-art amplifiers costing north of $50k the differences between them are surprisingly large. This is surprising because amplifiers like this have a vanishingly low distortion (TIM distortion is most often not quoted), heroic regulated multiple power supplies and a dampening factor with three zeros after the numeral. Are there comparable differences between say a Ferrari or Maserati? Probably not. Then we get to speakers where the differences between them are more evident for more understandable reasons. At first blush these differences might suggest that one speaker is more detailed in a particular frequency range (peaks are more obvious than troughs) but after a while your ears bleed and we move onto the next one or a change of interconnects or cables to solve our problems. The next issue is matching the amplifier to the speaker which is where many audiophiles get it wrong. A generally nice sounding amplifier on one speaker might indeed sound wonderful whilst on the next speaker sounds dreadful. The reasons for this are often fairly obvious - e.g. impedance mismatch say with a valve amp or an overly complex crossover - whilst at other times it is suck it and see. The most common error is using an amp such as described above with a highly damped (usually IB) and necessarily inefficient speaker resulting in a dry sound and no bass or at least a bass that doesn't decay naturally like instruments do. These speakers (e.g. Yamaha NS1000, B and W Nautulis and derivatives) certainly need a vast amount of current to actually work but think about it. Speakers need to respond quickly to a signal and changes to it. Now if we were to design a sports car we would be unlikely to start with a Mack truck chassis because this would require 12 litres of turbo charged V8 diesel and a 16 speed Eaton gearbox to actually move, let alone be agile around a track. Yet this is what we do with speakers! To get a flat frequency response a complex crossover is required with its attendant problems of inductor and capacitor insertion loss and even more significantly, phase changes. Not commonly understood is that fact that if you put a signal though a capacitor the current leads the voltage (a negative phase swing) whilst with in inductor the voltage leads the current (a positive phase swing). As well as having two or more filter poles (12db or more slope per octave) most crossovers include one or more zobel circuits to smooth the impedance and therefore frequency response. Add to this that even with very steep crossover slopes at and about the crossover point, the signal (music!) is propagated through two transducers (e.g. woofer and midrange or midrange and tweeter) which are unlikely to be phase or time aligned. The result is an incoherent mess which we mostly live with, even with the revered Quad 57s. (You might have noticed that many high end speaker manufacturers have recently seen the error of their ways - e.g. B and W, Wilson Audio and Legacy - and have reverted to simple crossovers and higher efficiency designs).
You can see where I am heading - towards high efficiency and single driver - but ones which do the job are few and far between. Some of the old drivers e.g. Goodmans 201 and 301 come very close but roll off at about 10khz so need a super tweeter. (As an aside I recommend 12db per octave rather than a single capacitor for super-tweeters this to minimize comb-effect lobing. It also might be apparent from the above that a single capacitor also results in a 90 degree phase change to the point that it doesn't really matter whether you wire it in phase or out of phase! 12db crossovers change the phase by 180 degrees so it is a simple matter to reverse the poles). One of the features of the old drivers is that even if they have a a low Qt (The Goodmans 301 and Tannoy MGs for example have a total Q of about .27 which discouragingly doesn't allow the use of Thiele Small alignment parameters whilst the 201 has a Q of about .7 which is too high) they have a relatively high Qms or mechanical Q. The low Qt is brought about by they having a low (i.e. highly damped) electrical Q or Qes. You can pick the high Qm (i.e. under-damped speakers) by gently tapping on the cone. If they sound lively (good) they are under-damped but you are rewarded by a dull thudish noise (for example with bextrene cones from the 1980s) and this is bad. My choice of speaker for the SIT 3 therefore is the Alnico SEAS Exotic F8 (US$869 so don't all rush out) run full range (but with a .47mH foil choke paralleled with a 4ohm resistor both run in series with the driver to drop the rising response which is typical of full rangers with whizzer cones) and a Hiquphon OW2 tweeter crossing (12 db of course) over at 15khz in a 2 cubic foot IB Baltic birch cabinet al la Audio Note.
Now back to the SIT-3. An earlier online reviewer commented that it doesn't sound like any other amp. (You can find reviews on Stereophile, 6Moons, Steve Guttenburg and Absolute Sound). Too true it doesn't, but maybe not for the reason - i.e. that it sounded better than any other amp that at least one reviewer had listened to - that was exculpated. (Why are nearly all reviewers 'he' and why do they listen almost exclusively to classical music?) Quite simply (through an appropriate choice of speaker of course) the SIT-3 doesn't have a signature sound. Music just sounds better though it and I'll come onto this eventually. Some of my other amps - mostly tube - have a 'house' sound. For example the AN 300B has a signature euphonic sound (romantic and gorgeous!), the Ecofan SE6A3 (which incidentally bettered a Yamamoto Type 45 amp) has an almost etherial top end (sublime!) whilst the First Watt F7 and Transcendent Audio SE-OTL monoblocks were so clean and incisive etc etc. The SIT-3 has none of this and I will simply conclude that every note and every sound seems denser, the layering of musical instruments and distinguishing between them is more obvious, the bass is articulate and bottomless, and the sound of each individual instrument and voice is much more like the real thing than anything that I have heard before. It is that good. I don't think that the word neutral suffices and indeed Nelson Pass suggests that he has tweeked the second order distortion (the knob on the SIT-1 monoblocks changes this from negative to null to positive phase) based on consumer feedback. He has quite deliberately added a touch of 2nd order distortion (about -40 db down) to the negative phase swing (only) and of 3rd order distortion by 15db (i.e. about -55db down), the latter in proportion to an increase in gain in the SIT-3. All very mysterious. The SIT device (Static Induction Transistor) is a development of the Sony / Yamaha V-FET (Vertical Field Effect Transistor) of the late 1970s which has a transfer curve very much like a triode valve. When used in common source mode it is capable of amplifying both current and voltage as in the SIT-1 and SIT-2. In the SIT-3 which is agreed to be the better sounding of the three amps it is used in common drain mode and the voltage amplification is through a transformer. Transformers are not all bad - they are better than solid state devices when used for example in moving coil head amps - added to which moving coil and moving magnets cartridges are of course transformer based! So with the SIT-3 you have a single stage single-ended amp (or more correctly sort of p-p without a phase splitter as the SIT device is linked to a Mosfet) that is most comfortable with efficient speakers between 4 to 8 ohms. It doesn't have much gain (11.5db with 3.2 volts input) so you need to drive it with a good preamp - I use either an Ecofan 12 tube or a Transcendent Audio Grounded Grid preamp. Simple is indeed good.
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