Vfet / SIT Amplifiers

First Watt SIT-3 owner checking in. Well, it has limited power but it sounds bigger than suggested by its spec sheet. It sounds more like a tube amp than a SS one, with a lot of dimensionality, super staging and air. Overall balance is warm and full. 

If you pair this with the right speaker, I can imagine that it will make the owner very very happy. I have the AGD Audion monoblock on dealer loan at the moment. It has very similar characteristics, except much better authority and power in the bass. 

Pass Labs SIT amps are very appealing.
@ericteh  thanks for posting your impressions! 

The warm and full sound seem to be consistent across most vfet amps and the resemblance to the "tube sound" is not by coincidence since the SIT I-V curve characteristics are similar to those of a triode.

I cherish my vintage SIT amplifiers and C-1, the only Vfet preamplifier, and put them through rotation in my listening space. I have most of the SIT amps ever made by the five Japanese manufactures from Japan (except the newer B-1a from Digital Do Main)

One of these days I will look to build a Pass design SIT amplifier, as I have a few transistors that can be put to better use than to rest comfortably in my storage bins.

The list of my curent SIT Amps collection:

Yamaha B1, B2, B3 (C1 preamp)

Sony TA-N7, TA-N8550, TA-5650

Victor (JVC) JM-S7

Sansui BA-1000

Lo-D (Hitachi) HA-500F

@ericteh ,

I now have a First Watt SIT-3 in my room right next to the other Vfet amps :)
I concur that it has great finesse and yes, it is a low gain amplifier.
The low gain is not a problem if you ran the SIT-3 with the proper preamp and efficient speakers.
I have the SIT-3 hooked up to a Yamaha C-1 that can push out like 3v, For speakers I am using Yamaha NS-2000 that are 90dB+ .
The all vfet sound of the preamp and the amp is addictive. An excellent match for the Beryllium drivers of the NS-2k..

I recently acquired a First Watt SIT-3 and I like my F2-J much better. I know I am in the minority in not loving the SIT-3.

It may be that the SIT-3 doesn’t like the impedance swings of my particular speakers.  Not saying it’s not a good amp, just not good synergy in my system.

In my system, the SIT-3 sounds like a computer simulation of an SET amp.

Yes, SIT-3 likes linear and higher efficiency speakers. More important is what you use to drive it with, since SIT-3 has relatively low gain.
There is lot of synergy between the SIT-3 and the Yamaha C-1 I drive it with. 

It sounds sublime in my setup and fits well with the pack of classic Vfet amps.

I have a FW SIT-3 amp, which I really like. It has plenty of power for my Horning Eufrodite Elipse Speakers. They have 98db efficency with a 4 ohm flat load, which is in the SIT-3 sweet zone.
The sound is detailed, smooth, airy, with beautiful tonal colors and has no electronic signature whatsoever.
I also run 300b mono's, which have a little more texture but, the FW comes very close.
It will be a classic in years to come!

You guys are making me jealous I can't get more out of the SIT-3 in my system!

My speakers are 95db efficient and are 8 ohms. I tried dropping resistors in parallel to reduce the impedance down to 4 ohms but honestly didn't notice much of a difference.

The main issue I'm having is that I listen at low to modest volume most of the time and I can't get enough out of the SIT-3 at low volumes.  It sings at higher volumes but usually I don't want to listen that loud. 

This might be an issue with my preamp's gain, which is only 10.3dB.  Combined with the SIT-3's low gain, maybe this is a recipe for failure.  I haven't tried it with another preamp yet.

@snopro , I share the same experience.  "Detailed, smooth, airy" is how SIT-3 sounds to me too, with  most emphasis on "airy". The "depth" of its sound image was most noticeable to me.

@zm , the preamp could be the culprit. I have not tried anything else other than the Yamaha C-1, but I probably should, to see how much influence the vfet preamp has on the "SIT-3 sound".

I have a SIT-3, which is paired with a Supratek pre and Klipsch Forte III speakers. The Supratek has high gain, which I dial back about 40% via the gain pot and still have plenty of drive and wonderful sound. 

I mostly listen at reasonable volumes (70 db to 80 db range) and find the music doesn't have to be loud to sound good. 

I also have a Rogers EHF 200 Mk. 2 integrated, it has 5 x the power,  more body--and also sounds awesome--but can't match the finesse and intimacy of the SIT-3/Supratek combo. 

Which is "better" would be a matter of a coin toss. 

@jayrossi13 ,
thanks for sharing!
re: " I mostly listen at reasonable volumes (70 db to 80 db range) and find the music doesn’t have to be loud to sound good. "
and
re: " Which is "better" would be a matter of a coin toss. "

I personally prefer finesse and quality over brute force. However, I am spoiled to have both with either one of the classic vfet amps...The finesse and airy sound of SIT-3, plus the "whoomph" to shake things when required.

I have not tried anything else other than the Yamaha C-1, but I probably should

@sonetduo Yes. Your Yamaha is outclassed by the amplifier. You might try a tube preamp; I think you'll hear a transformation.

@atmasphere curious what you think about the idea that a preamp with relatively modest 10db of gain (Microzotl MZ2) paired with the SIT-3, itself a low gain amp, might be contributing to the issues I’m having with the SIT-3. Is that likely to be a "problem’, so to speak, or is it more likely that my speaker’s impedance swings would be the defining issue here? (If I had another preamp just sitting around to try, I would - but wondering if I should invest in a higher gain preamp.)

Basically, in my system the SIT-3 sounds a little dark, limp, anemic, and closed down, especially at the volumes I listen: ~65db.

My F2-J on the other hand - pure heaven. Literally designed for the single driver, crossoverless speakers I use.

@atmasphere
Thanks for your feedback on trying a tube preamp. A luxman tube pre has been on my crosshairs for a long time and will probably bring one in soon.

As far as the C-1, I am not sure what you mean by: " Your Yamaha is outclassed by the amplifier" ?? would you define "outclassed"??

The SIT-3 needs a preamp with sufficient gain to come alive. The C-1 provides that plus C-1 is the only vfet preamp ever build. The synergy between the vfet preamp and the vfet amp, is something to be heard. You should try that combo if you have a chance.
I have not tried other preamp yet because the C-1/SIT-3 combo sounds superb. If I want "more" I can switch out the SIT-3 with one of the B amps from Yamaha, which have the similar airy sound and distinct vfet warmth, but much more headroom and authority.
BTW, my C-1 and other vfet gear is fully restored and sounds the way Yamaha intended it to sound ;)

@sonetduo I love the idea of a SIT-based preamp! The problem here is the Yamaha is far too complex. When you're dealing with purist amps and speakers (and let's be clear here- people these days that insist on crossover-less single-driver speaker tend to be on the purist side of things) the least circuitry you can get away with (without making it **too** simple) usually the better. That Yamaha has its heart in the right place, but it has a lot of encumbrance. It would be really interesting to find out how it sounds with no tone controls or tone control switching, just done in a simple no-nonsense approach. 


Now as a designer, the idea that an amplifier needs to hit a certain power level to 'come alive' is disturbing. I have a VFET amp that was designed by Nelson Pass and it certainly does not behave that way. This makes me think that its the Yamaha that is why you are saying what you are. In looking at the preamp and its signal flow, apparently its equipped with a loudness control in addition to a volume control. Your description matches that of the loudness being improperly set. If this was my preamp I'd be cutting all that extraneous stuff out of it. Since that would ruin whatever collector value it has, it seems prudent to me to just go to the type of circuit that the SITs behave as anyway- triodes.

I love the idea of signal-level SITs; I wish they were commonly available.

@atmasphere 
I see some assumptions on your part which could probably come from a misunderstanding.

First off, I love the SIT-3 amp. Low volume, high volume, I love the amp all the way. What C-1 does, it allows SIT-3 to play louder (if and when needed), but SIT-3 does extremely well at even the lower levels. 
In short: at no point I voiced any dissatisfaction with SIT-3, but emphasized the synergy between the vfet pre and vfet amp.

About C-1: my unit is fully restored and with SIT-3 I use it with all tone controls defeated (including loudness). If you have not heard the line stage of a C-1, I wish you have the opportunity to do one day. I am also thinking that if you like tube preamps, you will be in for a pleasant surprise listening to a vfet preamp :) 
Tone controls in the C-1 come in handy with certain amplifiers, or to tune in the room. I did not find it necessary to use any of the tome controls with SIT-3.

About the simplicity of design: The simplicity of design can be argued back and forth. Designers have learned since the 70s and are able to simplify modern designs. Also, certain components are built better today then were built in the 70'. All that is true but also many things done in the 70' have been forgotten. 
In the case of Yamaha, most of the complexity comes in the form of circuit protection of sorts...quite crazy in the case of the B-1 for example, or tons of features in the C-1 pre, which at first glance is the anthesis of "wire-with'-gain".  Some features of the 70's amplifiers are probably there just because the marketing department wanted them to be there. Some of these features can be defeated or carefully bypassed. Additionally, after 40+ years of use, some of the original ancillary components are at the end of their functional life and can be substituted for better components built today, and one can use the 70's vfet amps the proper way ;) and ensure that it would ran for many more years to come.

Making a side note here: complex or not, these 70's amps run for 40+ years already. I giggle when I hear some manufacturers marketing claims related to 20 years warranty as if that would be of any relevance....yet you see many consumers basing their opinion of brand preference based on such irrelevance.

What is important in the end is what the amp sounds like and will the amp be around long enough for the owner to enjoy it. That is simply the ultimate test, right?

One could argue for instance, that SIT-3 has relatively high THD, right?
But if most of the harmonics are of the even kind and if overall the amp sound as good as it does, how important are the technicalities?
Same goes for the Yamaha or Sony amps...yes more stages, NFB, etc...but if the amp sounds good, why do technicalities matter?

As far as I know, there is no scientific proof or empirical evidence that just for being simple, it must also sound best. Since we are talking about Yamaha, one of their other statement pieces, the MX-10000, is one of the most revered amps of all times. Yet, it is one of the most complex designs I am aware of, has stupid low THD, but in the end, it sounds phenomenal and can pretty much drive any load speaker. 

I hope I was able to clear any misunderstanding. I am a fan of anything that sounds good to my ears, agnostic of how complex or simple it was built, in technical terms :) 





 

I hope I was able to clear any misunderstanding.

@sonetduo  You did- I realized reading this that I had conflated some of your comments with that of another poster. I was addressing his comments, not yours, but with the idea that he was running the Yamaha. In a nutshell, I blew it. Sorry about that.

That explains it!  I was confused.  It seemed like @atmasphere might be talking to me, but I wasn't sure.  I was jealous of the answer @sonetduo was getting!

No worries at all.
I am happy to see there is still so much interest in SIT/vfet amps.

@zm if you do not feel a "woow" factor from SIT-3, you are either too sophisticated comparing to my modest standards :) or maybe there is lack of synergy in your system??
In any case, I wish you find a way to enjoy that jewel of an amp.

@sonetduo haha, it's definitely a synergy thing... I am a big believer in the genius of Mr. Pass!  

@zm Me too. You might take some of my comments that were previously misdirected, and scrutinize your preamp. It should not be a volume thing that make an amp 'wake up', unless it has a malfunction (which, to do that, would probably be bias-related). But if the amp seems OK, really take a hard look at the preamp.

So yesterday I ended up pulling the trigger on a Don Sachs model 2 - going to try that with the SIT-3 and see how it does!

Well, I guess I'll resurrect this thread. I've recently bought Victor JM-S7 and two Yamaha B-3s. I found this forum looking for some info about Victor's amp for my review. Unfortunately, it's practically impossible to find any.
I've recently reviewed the Yamaha B-3 amps and it was a delight. Sure, I haven't heard all the amps in the world, but I can say one thing, Yamaha B-3 is the best sounding amp so far (at least to my ears).

Both, the B-3 and the JM-S7, are fantastic amps. I can't agree more about the sound signature of the B-3.
Unfortunately for you, now you are tainted by the vfet virus and I have a prediction to make that your vfet collection will gradually grow :)

I have most of all Vfet amps ever made and I never get tires of listening to them. B-3s are special indeed and besides the Sansui BA-1000s, they are the only vfet amps that could be used in BTL mode, albeit, if you have hungry speakers, the B-3 or the BA-1000s are not the best choice, while using them in BTL mode.

You will also enjoy the Victor but the sound signature of the NEC vfets is different than that of the Yamaha.
Note that all three of your amps will need restoration soon.

If that's the virus, I'll gladly stay unvaccinated :) That's why I bought third B-3 to make sure I've got a backup in case of some fatal failure, they are on 24/7 :)
And Sansui BA-1000 is on its way and I'm looking for Sony TA-N7.

OH YEAH, that Sony is wicked too. A marvel of audio circuit design. It is actually part vfet part bjt.

And if you like the B-3 so much, wait until you hear the B-2 and the B-1  :)

I should have mentioned, the Sansui is nice but is no giant killer. It uses the same type of NEC vfets as the JM-S7 you have, but of different rank. You would enjoy it for sure but I am thinking you would enjoy the B-3s a bit more.

Do you actually reckon, that the B-2 or the B-1 is better than the B-3? I've read quite the opposite, that's why I went for the B-3 in the first place.

yeah, I read some different opinions and I will not try to justify why anyone would state that, other that they had units of different conditions, or did not perform true A/B listening. 
In my system where the amp would be the only variable, a properly restored B-2 or B-1 will sound same or better in most situation than a B-3 or B-3 duo.

The problem with the B-2 or the B-1 is that they require lots more work and some simplification to bring them back to prime. The simplification part would actually allow for by-passing some of the selector functions and streamline the signal path. This brings them to a simpler signal path level, similar to that of the B-3 (or TA-N7, JM-S7, TA-8550, BA-1000, SIT-3, for that matter).

I spend countless hours of A/B listening to most V-fet amps ever made. 
One thing I can say is that ALL of them are very engaging, where some would sound different than others or have more authority, but the differences are subtle. Another out-right statement I can make based on my listening impressions is that none of the other amps matches the B-1 in terms of sound stage and 3D of depth. The low-end of the B-1 could be blurry if the wrong type bulk caps are used. This is true for all the others, but it is more noticeable with the B-1.

An important callout is that during the restoration, if the wrong replacement parts are used, that WILL impact the sound signature of the unit and not in a good way.
For my restorations, I keep a well preserved and mildly refreshed original unit of each model as frame of reference for the other units I am restoring.  During the restoration process I do not introduce any components that would negatively impact the sound signature of the original. Sadly, replacing components just for the sake of replacement, is a practice wildly popular which in most cases would actually cause a "rebuilt" unit to sound worse than the original.

Now you've done it! I have to go now and get the B-1 and the B-2 to make sure I am not missing on anything :)

What do you think of TA-N7 and TA-N88?

The TA-N7 is the one to have. It sounds excellent. Very clean and transparent. Different signature than the TA-N8550 which has a lot warmer sound.
I did have a N88, but did not keep it because it had issues and I did not want to spend the time to fix it at the time, so I sent it back. Eventually I will get another one.
My friends who have both, the N-7 and N-88, give the N-7 the edge in versatility and overall sound performance. My understanding is that the N88 could sound good too, but it requires more thought on system matching.

Hi, i'm new...
It's really nice to see people who like V-fet😊
I com from France and the V-fet are not popular, people prefer hegel or rega sound, they never listened to it...
I don't like that sound...
I have a Sony ta-5650 amp (i use the power part) and a "lampizator subminiature" preamp, built by "the polish guru" Lukasz Fikus (SRPP circuit, 6h16b russian valve nos and a 6c4p-ev rectifier valve).
I have a preamp Sony ta-E88, too clear for me, and lack of density, the preamp lampizator is much better, the sound is more realistic!
Lukas Fikus compared it to a Verdier preamp at 20.000€, almost impossible to differentiate!!!

Does the N-7 suffer from the diode issue as the Sony's intergateds did?

Hello PR,
Actually there are a few vfet connoisseurs in France....but I agree that  vfet units are so exotic and very much extinct...unless you find a vintage unit and have it properly restored.
Nelson Pass has some newer offerings, but those are becoming rare as well. 

I agree with you about the using a different preamp and not the one in the ta-5650. The Lampizator is in a different class and I am not surprised you like it so much. I am aware of Lukasz and his creations, but I do not own any yet.
About the ta-n88: I agree it could be a bit too transparent but it is a good preamp, nonetheless for those that like that level of transparency. If you have not had it serviced yet, that could also be a reason why it might sound "dry/sterile". Also, if not serviced, your unit could experience PSU failure (some zener diodes in there are ill-fated) that could take out the transformers.

@kitr,
Yes, the TA-N7 has the veractor "diodes" / death diodes, but it also suffers of problems with fusible resistors. The thermal runaway of those fusible resistors is horrible and over time they drift substantially from the original value. When they drift past a certain point, they will take out a vfet or two.
Also, the BJTs in the final stage need to be replaced as they are also known to fail.
Net, Net, while the TA-N7 does not have the death rate of the n4650/n5650, it needs to be restored nonetheless. The problem is that there are very few techs that fully understand vfet units and even fewer who would take vfet units for service or restoration. This is valid for all vfet units.
Depending of where you are located (I mean on which continent) I could point you to someone qualified to service your units. 

Yes, my Sony V-fet is full restaured with nichicon and VD1221 have been changed by 1N4148😉

The "bias" must be lowered to 45mv for the ta-4650 and 55mv for the ta-5650.

You meant the ta-E88, not the N88 ?
I speak the preamp E88, i preferred my old 700c, that's a question of preference...
But i prefer again the valve preamp with Sony V-fet, this combo is fantastic!

Enjoying the SIT3 with my Daedalus Athena 95.5DB sensitive speakers. Currently using the Pass XP22 preamp which is kept at the upper range of the volume. I have no issues with low level listening and can crank it up with volume to spare.
Still always listening below unity gain

@sonetduo,

Cheers for that, but I have a bloke who serviced my B-3s and he seems very capable. He's going to enjoy working on the Sansui as well :)

BTW, there is also Yamaha C-1 on my wishlist, do you have any experience with that?

It seems to me the C-1 is the only V-fet preamp, it's exact?

It looks like it. I used to reckon, that Victor JP-S7 is also V-FET, but after I bought one, I found out it's not :)

Find a victor jm-s7, it's a V-fet amp 😉

The victor jm-s7 amp have V-fet transistors Nec, not sony or yamaha

Yes,
Victor JM-S7 is a Vfet amp (sse above)
Victor JP-S7 It is not a Vfet pre-amp

Sony TA-5650 has a vfet in the pre-amp section, but I can't really call that a vfet preamp

@kitr,
The Yamaha C-1 is the only vfet preamp ever made, all the way to unique vfets made for, used only in the C-1 and nothing else.

The C-1 it is also an absolute statement piece in terms of sound and it is my ultimate preamp and the frame of reference I use, when I compare anything else I get to listen to. While I did not try every preamp on the face of the earth, I did try a few...and to date, none gave me more pleasure of listening to, than the C-1. IMHO, the C-1 is really in a class of its own and even at 40+ years old, there are very few amps (new or vintage) that can equal its sound performance. 

Side note:  I have restored more C-1s than very much anyone else except the Yamaha centers and one tech in France.
The restoration process is an adventure of its-own. Extremely intense from an effort perspective and there is ZERO room for error.
Most of the units I restored were fully working even after 40+ years which is a statement on its own, considering the C-1 is a complex beast in terms of the many options it has....all working just fine, if you ever need them, or bypass if you are a wire-with-gain seeker. Some units needed repair and some were of the worse case scenario, but all C-1s I restored are now singing like new, or better :)
 
The C-1 is built like a tank, but some of the ancillary components are ill-fated and when they fail, they could take out a vfet or more. That said, any piece of audio equipment would need restoration after 40+ years and while the failure rate of the C-1 or other Yamaha vfet units is actually very low comparing to that of any manufacturer, it is still a good idea to provide preventive maintenance. 

It is amusing to see how some manufacturers use something like a 20-years warranty as a sale's pitch and also sad that many consumers fail for it. Maybe for newer equipment that is full of digital stuff is a valid pitch, but for the analog stuff that is alive and kicking after 40+ years, what good would a 20-year warranty do?

The C-1 preamp is an institution on its own🙏

Has anyone compared a V-fet amp with a Luxman L-505ux or L-590ax ?

Well, I've played about with the Victor for couple of days now and I need to share my findings. Since it's a V-FET, it sounds very similar to Yamaha's B-3. Very detailed, perfect imaging, deep bass, but it's not exactly on par with the B-3. Something was a little bit off. I don't know how to describe it, but the Victor sounds a bit dry and not so "musical". Still better than almost anything on the market today, though.

Still better than almost anything on the market today, though.

Ha! Not buying that for a second. Not saying its not nice though.