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).
Take good care of that amp because I don't think that replacement transistors will be easy to come by now and in the future.
There is a kit version. Sort of.
the kit version is very nice as they can use the tokin transistors from japan.
Those transistors are actual V-fets, from the last batches of high current RF use design criteria.
Tokin used the original process for making V-fets, IIRC. Japanese made and in the last run of Japanese V-Fets.
I’d have to check, but I suspect the Tokin transistors have a better spec than the First Watt SIT transistors. As in higher frequency capacity, greater current capacity and possibly more linear. Or at least individually tested and quality spec’ed, sorted and QT’d for release to the public (like all high end expensive transistors).
To clarify, the SIT transistor that Nelson had made up, came from an offer to do so, from Semi-south, a smaller transistor manufacturer. Nelson had the proto batch made up, and then Semi-south was bought up by another manufacturer. The end...( of that ride). The Tokin, is another matter. It came from a decades long run of making the best in V-fets for extremely demanding applications of extreme voltage swing and extreme current loading (think radar power amplifier). That run had a chance to be perfected over decades of iteration.
Thus, a Tokin version, might be capable of having a higher voltage and higher current rail, for a notably higher wattage and impedance handling range than the SIT-3.
The operative word being ’might’.
Importantly, the (very) few who’ve had the chance to make the comparison say the Tokin version outperforms (according to them) the SIT-3.
I am not a DIY. You'd think I could as I can rewire a house from weather head to outlet, but I have never worked with transistors. A question becomes - could you switch out the Semi-south SITs to the Tokin SITs on a SIT-3 itself? Or are there other parts that would need to be changed.
I read about people upgrading their caps, etc and have no idea how or how to know what an upgraded capacitor vs original is. All stuff I could track down. Perhaps when my life is less hectic.
V-FETs are finicky! The amp could be changed over but there would be more than just replacing the output transistors.
Even the old V-FETs are hard to find. BTW the kit that was offered makes about 25 watts. IMO the V-FET was the solid state solution to end the tubes/transistors debate, but Sony never saw fit to also offer driver and small signal devices, so the technology didn't go anywhere, like many of Sony's ideas... But that kit amp is one of the very best solid state amps I've heard.
I have one coming to me, serial number 3937 ordered this week. Not sure how that relates to your number 107.
Amplifiers are typically manufactured in "batches", therefore, your amp could be one from the last production run/batch
The Pass Labs XA25 costs about the same as the SIT-3 and doesn’t seem to be tied to a Transistor Anachronism...both amps are well regarded nearly to the point of astonished worshipful reverence, but I want an XA25. Why? Just because it’s there, although I doubt my single ended tube amp is going to explode any time soon which would be my only reason to drop the coin on a Pass. Still...it’s there...haunting me...now if they'd just put a meter on the front...
Those considering purchase of a SIT-3 should keep in mind that its gain is only 11.5 db, which is extremely low for a power amp. Consequently it requires a single-ended input of about 3.2 volts to be driven to its rated maximum power capability of 18 watts into 8 ohms.
That is particularly likely to be a problem in applications where it would be driven directly from a DAC, or in vinyl-based applications if an active preamp providing something like 15 db or more of gain is not being used, and of course in just about any application in which a passive preamp is used.
The XA25, in contrast, provides 20 db of gain, which is still below average but should be ok in most applications.
Almarg brings up some very good points. There is more than just the efficiency of your speakers involved if you want to get the most out of this amp. I am fortunate to have one and it is a beautiful sounding amp but even if you match up everything perfectly you will might find some albums that because of the way they were recorded just won’t have enough volume. The amp sounds so good that I am willing to accept this but others might not.
Al, the xa25 is also an amp that hit my radar, perhaps for a future purchase. It would be appreciated, I think by more than a couple of us, if it wouldn’t be inconvenient, if from time to time you might provide progression reports of how it acquits itself in your system. Thanks, George
Lwin, thanks for providing the additional perspective.
George (Jetter), I've owned my XA25 for about five months now, and the early impressions you've probably seen me mention in other threads continue to apply. Basically, I've found Teajay's review
to be absolutely spot-on, and for that matter to be more accurately focused than Herb Reichert's comparably positive review in Stereophile
The bottom line IME is that I don't miss the 300B-based VAC Renaissance 70/70 MkIII I had been using during the previous several years at all. The XA25
comes remarkably close to the VAC with respect to dimensionality,
imaging, liquidity, and other traditional fortes of high quality tube
amps. It’s a bit less rich sounding than the VAC, but I interpret that
as an increase in accuracy, which is fine as far as I am concerned.
I should add, though, as you're probably aware, that my speakers (Daedalus Ulysses) are extremely easy to drive, having an unusually flat and benign impedance curve as well as high sensitivity (rated at 97.5 db/1W/1m). Also, in case it matters (which it probably doesn't), most of my listening is to classical music.
Finally, I'll mention that as it happened I didn't have an opportunity to do much critical listening during the week I gave the XA25 the 120 hour breakin that was recommended by Mark at Reno HiFi (from whom I purchased the amp; he was wonderful to deal with, btw). So I can't comment on how its sonics might have changed during that period.
You should ask Mark if he has any SIT-3 amps left. Your speakers would be a good match with the amp, if your preamp has enough gain. He is great to deal with.
It sounds wonderful with my Horning Eufrodite Ellipses and I have no desire so far of putting back my Frankenstein 300b mono's. It almost sounds like an SET amp with much better defined bass and more extension in frequency response.
Thanks, Joe (Snopro). But the SIT-3 wouldn't work for me, as the DEQX HDP-5 I use as my preamp provides essentially zero gain from its analog inputs to its analog outputs. (And in fact the default positions of some internal jumpers result in negative gain). Basically, it can be thought of as driving an amp directly from the output of a volume-controlled DAC circuit, with no intervening preamp.
And in any event, as I indicated I'm very satisfied with the XA25.
The SIT-3 just got reviewed by Herb Reichert in the new Stereophile, so I’m sure they’re now all sold. Some of the First Watt designs get cloned, which Nelson Pass has no problem with, as long as it’s for personal use. If a schematic can be acquired, a clone can be built.
Thank you Al, from your description and also all I have read the XA25 is a strong candidate for a future purchase. My speakers are reported as 89 dB 6 ohms nominal so based on the speakers many have reported pairing the XA25 with I don’t think there should be a problem driving them.
Actually, it seems like your speakers are among the highest efficient speakers and that most of the reviews or users reported no problems driving less efficient speakers. I don’t recall anyone having problems regarding the XA25 not adequately driving their speakers to adequate volumes.
Sorry dseltz for taking your thread on a tangent.
No problem, I am learning the HiFi world and your questions/comments and Al's excellent input is valuable to me in my pursuit of knowledge.
As to your situation, I agree with Al. Your speaker efficiency pf 89 might not pair the best with the SIT-3. I have 99 dB Rethm Maarga that pair up well, along with an Audio Hungary APR 204 tube amp with a gain of +12 dB (+52 dB for its Phono setting)
Actually, it seems like your speakers are among the highest efficient
speakers and that most of the reviews or users reported no problems
driving less efficient speakers. I don’t recall anyone having problems
regarding the XA25 not adequately driving their speakers to adequate
?? My speakers are 3 dB more efficient than Al's. And there are speakers that are a good 8 or 9dB more efficient than mine...
I was not aware there was such a world of high efficiency speakers. I haven't been in the market for speakers in years so its all kind of flew under my radar.
My first post here dseltz. Some First Watt thoughts. I recently got to demo a First Watt F7 for one week in my home system, from my local dealer. I have a pair of Focal 807 V W Prestige bookshelves. The amp it replaced for the week was an Emotiva A 300 (150w). The Emotiva is approximately a 28db gain amp vs the F7’s 14db I’d gain. Class A vs AB. All I can say is WOW. I was impressed. The synergy with the First Watt and the Focals produced a smoother,almost tube like tone. I found myself enjoying longer and non-fatiguing listening sessions.I struggled with the idea of giving back the First Watt to my dealer. 3k vs $400. The Emotiva is OK for a 150w stand alone amplifier. A bit forward sounding for the Al/Mag tweets. I did have to disconnect and remove the two noisy, cheap and unnecessary heat sink fans. The amp runs very cool. The First Watt? Um- a nice added source of heat for the man-cave, the week I enjoyed it. Enjoy the new amp and hope to join the First Watt/Pass club soon!
So where do you get this "sort of kit"?
I also have just taken delivery of a SIT-3. I think this must be from the second production batch.
Halfway through the break-in now and sounds great.
Although I'm largely skeptical of Stereophile reviews, it would be worth looking at the recent SIT-3 review, which also includes comments on the XA25.
There is no reason to be skeptical of Stereophile reviews.
You hear some of the stuff they hear... and using this, you can correlate what the reviewer says... to what you feel you have heard.
That is all the review is for. They tell you this repeatedly, in print, at every opportunity.
the next rule is that there can be no bad reviews in print, for any magazine, be it paper or web based.
To do so is to go out of business. So they look to only review gear they know they will like. Negative reviews cannot be tolerated by the magazine or the entire collective group of all audio manufacturers.
Any scenario which is opposite to this, would end much of the audio business that exists today. A lot of your choice in gear...would disappear. End. Nothing would move forward and no one would be making anything.
It’s a simple obvious logic.
Due to this problem, Stereophile additionally goes out of their way to say that ’just because it has not been reviewed, does not mean it is a bad choice’.