Mosfet amps A true compromise betw. tubes and SS?

I heard from several people that Mosfet SS amps are a nice compromise between tubes and SS amps.
There is one manufacturer in particular I am interested,s croll down to Fusion 700 (its a German made amp, but he has an English web page) who calls his hybrid amp a Mono tube mosfet amp.
I would really appreciate if someone who has more insight would tell me a bit more of advantages and shortcomings of this design and if the claim: "sound of tubes with power of SS" is true or not. Also I would like to know if these are fast amps, as I plan to maybe use them with my ML Prodigy, should the Wolcott amps, I bought recently, not work satisfactorily.
Mosfet is solid state. It is a type of transistor.

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Even tube is not tube. The sound you get depends on what tubes you use. Their is no direct correlation between Mosfet transistors and tube like sound.

For example; the current crop of Conrad Johnson solid state amplifiers that replaced the MF2100 (and others) use Bi-Polar output transistors instead of Mosfets. They also use Field Effect transitors because they handle voltage in a way similar to tubes.

So just buy an amplifier that you like the sound of; and forget the buzz words.

You may want to try a tube preamp with a solid state power amp. It is a good way to get the best of both worlds.

Yeah...what they all said. I ended up buying a used Counterpoint SA-100 amp (a hybrid tube/mosfet design). It sounded pretty nice in stock form, but those particular mosfets had a history of failure. I had mine completely rebuilt by the original designer and he has since switched to something other than mosfets (you can check it all out at on his newer designs and rebuilds. Some people love their characteristics, but like the above people all depends on the designer. There are good and bad designs using all technologies. Still...I do prefer some tubes in the system. I have gone in the direction of hybrid amps and preamps, but you can always mix tube and SS like Sugarbrie mentioned above.
Interesting question - from my own listening (and there are a lot more experienced listeners in this forum), very bad MOSFET designs have similarities to very bad tube designs ("mist") and very good MOSFET designs can sound remotely similar in character to pretty good tube designs as can some other SS approaches. Understand that I am definitely a tube fan, so my response is biased by that perspective.

When combined with a tube input stage (one of the possibilities for "hybrids"), MOSFETs often sound better (to a tube enthusiast like me). As support, I would point to the LAMM M1.1, though I have heard some of the Counterpoint gear sound great in synergistic systems.

That having been said, I have spent a great deal of time lately looking for SS amplification that could make a tube fan like me content to listen... I have yet to find a completely satisfying compromise, though a recent thread gave me a number of good leads (the suggestions I've followed so far have been among the most musical SS I have heard).

Overall, I have to agree with everyone else here that, while I understand where the reputation arises, there is no clean correlation in my experience between "tube-like" and "MOSFET" so you've unfortunately just got to listen in your system.

Good luck in your search. Incidentally, I have not heard the Fusion 700, so can't comment directly. Hope my rambling somehow helps...

Isee now that the Brinkman offers a optional onboard DAC. So its not a hybrid. It's like a amp-dac??? But i do like the fact they don't try to hide anything. The unit comes with a glass top!! Thats cool.
Of course Tweeterman will take exception with me on this, but I don't believe that anyone can look at a web page, see what type of technology is employed in a piece of gear, and think they have even an inkling of what it will sound like - either in an absolute sense (if that even exists), or particularly in their system (the only place that it ultimately matters). By all means, audition some MOSFET gear if you are curious, but don't expect any more uniformity of sound between different amplifiers of this type than there is between amplifiers of the tube type. If that sort of thing were actually the case, then there would only be a handful of distinguishable amplifier "sounds" - one for each type of active device employed in amp circuits, and we all know that is not true. That's because everything matters, not just one thing, and the way the overall circuit is designed and implemented is generally regarded as being even more important than what type of active devices are used. If I were interested in trying out something new based on an idea about its technology, I sure wouldn't make it a "sound-unheard" purchase, off of a website, of foreign gear that no one in my country sells or services, much less has even heard of. Sure, the stuff *might* be great, but what would I be able to do with it if I wound up not liking it so well? (FWIW, the MOSFET amp I used to own sounded nothing like [and not as good as] my present tube amp.)

P.S. BTW Tekunda, mightn't you be jumping the gun just a little bit, plotting your next amplifier change before you even know if, in your words, your "recently" bought amps will "work satisfactorily"? Why not give 'em a chance - they certainly weren't cheap! You have my sympathy if Audiophilia Nervousa is really that advanced!
Hey Zaikes, very great answer. You've answered my question from your many years of experience. I'm for tubes all the way. I own a "100" watt ss Rotel amp which i can not listen to for more than ..oh like say 5 minutes and then fatigue sets in. Now with my "40" watt tube amp i can listen to for hours happily. And the 40 watter is their entry level model so future upgrades will make the speakers sparkle even more. So as you say there is "tube sound" and there is "ss sound" , and in both categories not all labs are equal..more so when it comes to tube design.
Zaikesman, thank you for caring. You are absolutely right. Its kind of crazy to worry about new amps without even having auditioned the new ones I have bought.
The reason is not an advanced stage of Audiophilia Nervousa though.
I am in Germany right now for a short visit and the guy who makes the Mosfet amps, tries to convince me that his amps are really worth taking a shot. The only problem with this is, that my system is in Florida. Before I go through the trouble and ship the German made amps over to the US for an audition, I hoped to find out what people in general have to say about such a design.
If most people would have agreed that a Mosfet is nothing I should look into, I wouldn't have bothered even thinking about having these amps shipped. But from what I read here, I planned my startegy now, which is to audition the Wolcott first and only if I am absolutely not happy, have the German amps shipped for a further audition.
So, will you audition these amps in Germany, and if you do, let us know what you think? Good luck, Z.

P.S. Tweek, I must admit that in this thread as well as our previous encounter, I have had the darnedest time trying to follow you. Is it me? Or are you crediting me with saying things I don't think I said? (Or maybe you're just having me on - er, "Tweek"-ing me!) Oh well, I've got to admire your enthusiasm - say, maybe while he's in Germany, Tekunda can give a listen to those speakers you saw on that website (now, what were they called again?)!
Personally I'll take a mosfet design over bipolar or glassware any & every day: I just love the mosfet sound & everytime that I try out something else I've always eventually gone back to mosfet's. I've gone through a lot of equipment over the years, but mosfet has always turned out to be my common demoninator. You get the typical bass control & high speed transient response of solid state with some of the warmth of a tube based design, but without the heat inefficiency, microphonics, noise, & unreliability of tubes.
I will totaly agree with Bob Bundus. Bipolar amps sound dull in comparison to Mosfet amps .Mosfets characteristics give high thermal stability and very high output current and voltage with reliable operation. Power Mosfets are sonically superior to the Bipolar transister, but have the sweeter qualities found in tube equipment.
I agree with Bob bundus, as well. Good mosfet amplifiers do NOT sound like tube amps. I use mosfet amps in both my HT system and my 2-channel system and would not find them satisfactory if they sounded like tubes. I've tried a number of tube amps from the cheep to the way expensive and none of them gave me the clarity, precision, speed, dynamics, and detail that I get from good SS gear.

That being said, I'm first and foremost a musician and only secondarily an audiophile. My objective is to hear the music with as little sonic degradation as I can manage. The warm, euphonious distortion introduced by tubes is seductive but ultimately--for me--it gets in the way of the music.

Different strokes and all that.


Hi Will

I would be interested in your list of good tube amps that fall short of ss in the areas of clarity, speed and dynamics and even detail, my you have me curious. You might want to hear a good OTL design with a proper load to put that assumption to further test. This aside from your preference of ss over the warm, even ordered distortion characteristics of tube circuits. btw, the Atmas-pheres have among the fastest slew rates of any amp, period.

I am a big fan of the Counterpoint hybrids amps from the 80's. Mike Elliott truly got the best out of those designs other than their tendency towards premature failure (mosfets). The SA-100 was the best 1K amp that I can recall in its day.
Yes Tubegroover, I too was a big fan of the old Counterpoint sound, with their tube/mosfet hybrid amp design. Tried some other mosfet-output SS amps in recent years like Gamut, Belles, Pass. I think the mosfet amps really do give a certain "dimensionality" to the music, and a palpable midrange. Most recently I discovered the Llano Design Trinity amps (small-signal tubes for voltage gain stage, mosfets for output current stage). To me this is the best-sounding design so far. They are fast, clean, and reliable amps (and no mosfet mist!). Plus, not nearly as expensive as Lamm!
Mosfets & Hybrid amps = not equal. On one hand Mosfets are actually "pentodes" when it comes to the transfer curve. So, to that extent they are "tubish." They also tend to have a soft saturation, meaning that they tend to clip gracefully, not as soft as tubes, but not hard and sudden like BJTs.

No amp is any "faster" than the source that it has to reproduce - which in our case is fairly pathetic these days, being bandwidth limited like a brick wall at 20kHz. Having said that, there is some benefit to a bandwidth on the order of 250-500kHz. and the resulting slew rate that comes along with that.

The sound of "fast" amps, IMHO, has little to do with the nominal specs - it has more to do with the distortion products and how it handles things like leading edge damping in the realm of real world loads. The power supply design and size plays a great role in the way a given amp will sound - all other things being about equal and the circuit being well executed and reasonably designed (not always the case...)

Hybrid amps, perhaps the original being the Moscode, usually have a tube in the front end. The *only* purpose for this is to provide some degree of euphonic coloration. Which, it can. So, if you *want* that slightly "tubey" coloration (not a bad thing in many cases) for your system, one way to get that PLUS a reasonable DF, and power is to use a Mosfet output stage. The only caveat is that the Mosfets want a fair amount of drive power, so there should be something between the tube and the mosfet to drive the output stage. Usually there is...

Personally, I'd get a rock stable, solid, low distortion, high current, high bias class AB FET input Mosfet output amp and "adjust" any desired coloration in a line stage, if that is what I wanted to acheive. My Symphony No.1 amplifier is an example of such a design... you can hear the effect of whatever you put in front of it, very nicely. Makes it easy to set up a system, not having to worry about the "color" of an amplifier in the equation. (IMHO)

As far as OTLs, nice, if you get them to be stable, if you can control the leading edge, and IF you have *enough* output tubes to provide a sufficiently low output Z and high enough current *for the load you have to drive.* But they have nothing to do with Mosfets...
Very intersting points of view here. I predict, however, that you will like the Wolcott/Prodigy combination. I borrowed a friend's Wolcotts and they were superb running the CLS's in my Mini-Statement system. I understand that the Atmasphere's are even more sympatico with big esl's.
If MOS FETs are so superior, why would AYRE, who used them in their earlier amps, now prefer bipolars for their latest design? Which sound pretty good, at least in a store audition.

MOS-FETS, bipolars -- listen to each amp and judge it on its own merits. The circuit design and parts make the biggest difference. I certainly wouldn't buy a MOS FET amp based on how much the designer brags about his own creation.

For my taste, tubes are where it's at.......As far as being colored and slow -- NO WAY, JOSE. I hear more detail and realness from my tubes than I hear from any solid state amp.
Nelson Pass Amps .Try this link you can get answers directly from Nelson Pass himself and even build your own Pass designed amp .
Listen to Chaz. Speaking of Pass, I enjoy both tube and Mosfet worlds the economical way. This is how: First get a solid state amp with the least signature. My choice is the Pass X. The guys at Pass Labs told me the X amps are on the lean side (and so they came up with the class A XA). I humbly disagree. The X amp is so transparent to the incoming signal (check the Pass Labs site to see why), that you can taylor the music any way you want with your front end. I use a cd player with a tube power stage. After a bit of tube rolling, I have landed the sweetest (tube) sound with all the black back ground, world class dynamics and bass control of a Mosfet powered amp.
I have to disagree with Muralman1 about Pass X. I think these amps are indeed relatively lean in the midrange compared to some other amps, certainly to certain tube amps or hybrid amps. I'm talking "body" in vocals, "wood" in cellos, "resonance" in piano middle registers, and so on, especially when the reference sound is the real thing. The Pass X series is a very clean and well-made amp, but is leaner than the Aleph. I've noticed its lean midrange character even when using tube preamps and tubed CD players to feed it.
You may be right, Ral, and very soon I will be trying class A mono blocks. I do not agree about the need for tubes in the amp. The Pass X takes what it is fed and simply amplifies while not adding any character of its own.

I am very familiar with the Llano Trinity hybrid, and it mystifies me. No electrical engineer I know believes the Trinity is a class A amp. Not with it's diminutive heat sinks and cool running temperatures. I'm trying to get one over to my place for an audition anyway. A friend of mine is using Telefunken tubes with his. Hearing it at his place, I can't come to any certain conclusion of it's overall worth.

My Apogee Duetta Signature speakers have a rich sound on their own. I've found straight tube amps to be too slow and sticky with the Duetta. The Pass X is the cleanest sounding solid state bar none. It has no character. Coupled with my ribbon speakers and great tubes, the combination is as real as it gets.... With cd material.

I have run straight tubes on slightly brash Apogee Stage speakers, and that had the same synergy in the mids as my Pass plus Duettas. What I want is all the liquid mids of the tubes without the syrup. Mating a tube signal to a sonically passive amp has worked well for me.
Lateral MOSFETs have a negative temperature coefficient and so will basically protect themselves (and your speakers) from over current due to improper sharing or high load demand. They are also faster than BJTs since they aren't minority carrier devices and don't need perfect biasing for good crossover distortion characteristics (if class B). However, MOSFETs are not as linear as BJTs and there is no engineering connection with tubes in term of their sound. Arthur
Muralman1 - Yes I can see how tube pre + Pass might work well on Apogees. That combo didn't quite do it for me with my Maggies (3.6/R), but of course different systems, cables, listeners, etc. Not just midrange aspects, but a tube preamp seems to ripen up the bass too much for me. I agree that pure tube amps on magnetic planars can sometimes sound slow. (One exception is the Wolcott 200W monoblocks I once home-auditioned....nice but a bit pricey).

I actively biamp my Maggies in order to optimize the bass versus mid/high performance separately. Experimented a lot with various SS amps, and some SS/tube combos for the two amps. Finally settled on using 2 Llano Trinity amps because of (1) their control of the panels, (2) their sonic "tuneability" by rolling the input tubes, (3) just fewer tubes to replace than pure tube amp, and (4) overall reasonable cost of the Trinity amps. (The choice of the 2 input tubes makes such a huge sonic difference with Llano that one must be careful in auditioning one of these amps.) E.g. I like 6DJ8 in the mid/high amp (for detail, imaging) along with 12AT7 in the bass amp (for full yet tight bass). All NOS of course (Maggies are too revealing for anything less).

I'm not sure whether the Trinity is pure class-A either. I use the Trinity 300W for bass and the 200W for mid/highs. They both run too hot to rest your hand on, though. (Definitely not "cool-running" amps). But seems like a 300W class-A amp should get even hotter than this....
oops, Ral, I gave you the wrong idea. I tried a tube pre (Sonic Frontiers) but found the solid state Aleph P more to my liking. Like it's brethren, the X amp, it has a relatively benign sonic stamp. I'm controlling the character of what I am listening to with a Jolida JD-100. With the correct NOS tubes installed, Telefunken, RCA, Siemens, Syvania, this is an inexpensive musical wonder. Ral, I wonder if you have found, like me, Mullards are poor sounding in a revealing system.

By the way, Maggies are great. Biamping is the norm for Apogee users as well.

Muralman1: O.K. now I see your system setup. As for the tubes, I did like some 1960's Mullard 6DJ8 I put in an ARC LS25 preamp I owned a while back. (Currently I skip a preamp, by using a Wadia CD player only). But in the Llano amp, such Mullards don't seem quite as grainless and refined in the treble as some other classics like Amperex. I'm still experimenting with different types of NOS tubes, and not quite satisfied yet. The Llano's input tube stage provides all the voltage gain in my system, so the tube choice is everything. E.g. 7025/12AX7 are quite musical but lack focus, 5751 have more focus but sound a little muddy, and 6922/6DJ8 character varies wildly with manufacturer. I'm looking for a liquid and grainless midrange with dimensionality, super-sweet treble (to tame the Maggie ribbons), and tight bass. Of course, I guess that's what most people want. I haven't yet tried some of the ones you listed like Siemens, Telefunken, and Sylvania, though. BTW, is your Jolida an integrated amp?
The Jolida JD-100 is a cd player. I hate to harp on amps again, but according to experts I trust in the field, the Pass X amps are the cleanest amp built due to it's DC circuitry throughout, accomplished by not using the usual amp builder's crutches, like detail robbing feedback and step up capacitors. Nelson's ingenious utilization of his super symmetry finishes the job. With the help of the tube cd player, I enjoy all the points on our collective wish list, except perhaps Krell like bass slam. That's not something I miss.

Given the Pass amp is colorless, I can control the sound with my cd player tubes. Like you, I find tube selection critical for my listening enjoyment. The 12ATX7 Mullards CV4004 tubes were not grainy, and were quite musical. The trouble I had with them was they starved my system of micro detail. Mullard tubes are visually flimsy. JAN Phillip tubes gave better detail. I am using 1950s Sylvania 5751 tubes which are purposely built to defeat microphonics. At $45 apiece, (if you can find them) they are a bargain Telefunken, full liquid mids, sweet highs, and a seductive bass.
Muralman1 - what is a "step-up capacitor"?

BAT also has a very neutral sound MOSFET amp in their VK-200 (now replaced by the VK-250). Two gain stages and no global feedback. A very "Passish" design philosophy. If one is looking for some inexpensive but well built MOSFET amps they might want to try the last of Sony's ES amps. Especially the TAN90ES. Not a BAT or Pass, but quite inexpensive and at least their equal in quality, if not quite there to the nth degree in sound. Also fairly "Passish" in design philosophy.
Nearly all multi stage amps need a capacitor in line to facilitate the bridge between the two. The trouble is, any capacitor or resistor in line with the signal is going to add it's own degradation of the signal.

It isn't easy to create a circuit with no resistors or capacitors in line with the signal. The Pass X and XA series not only do without, any bit of distortion getting through is canceled at the output through Supersymmetry.

Think I will jump in with a thought on the Llano Trinity. I'm using mine with a BAT VK3i amp and Vandy 3ASigs. I have tried various tubes in the 12A?7 series and typically found the 12AT7s and AX7s to be a little forward in the upper vocal registers. Since I listen to a lot of female vocalists, that was a problem. Was not impressed with the RCA 7025s or 5751s. If anyone wants to try some of these, send me a private email. So far, the best in my system has been some Amperex Holland 12AU7s. BTW, this amp was much better with the BAT than a CAT SL1 Sig I tried (also now available).
Muralman1, are you certain that the Pass amps contain no resistors in the signal path? Also, I thought the 'Super-Symmetry' topology was implemented prior to the output stage. (I too have not heard of interstage coupling capacitors being referred to as "step-up" capacitors - though I believe they are sometimes called DC-blocking capacitors.)
Zaikesman, sorry, that was something I got off of a review a long time ago, and I never bothered to look it up. There are resistors, a few, in line. Resistors are passive.

The two stages of Pass X amps are direct coupled.
Yes, resistors are passive, and so are capacitors (plus of course transformers, and wire). And both color the signal that passes through them (as do active devices like transistors), but both are necessary to construct circuits. Since an amp's power supply is actually in the signal path (the input signal to each amplification stage serves only as a 'template' to modulate a new larger one for the output, taken from the power supply), and since all conventional amplifiers contain capacitors in the power supply, we can't really say that direct-coupled amps contain no capacitors in the signal path - only that they contain no coupling capacitors.