Vfet / SIT Amplifiers


Are there Vfet amplifier owners on this forum?

If yes, what do you own and what are your impressions?

sonetduo
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!