Full-sounding SS amps (besides Pass)

@pbnaudio - Hi Peter - I remember Marty DeWulf, whom I wrote for a number of years, was a big fan of your designs. They look amazing... if only you had something a little smaller, or better yet, my apartment were bigger. :-D

@mitch2 I think MOSFET "mist" or softness is a thing of the past in a proper design. I've heard a number of more recent designs that have none of that and are indistinguishable from a good bipolar amp in speed and clarity. April Music Ai500 when properly biased (they had some QC issues) was one example, a few others I've heard but can't recall off the top of my head. 

@bobheinatz I just contacted Stéphane Even @ Neodio to see if he is seeking a US review. Really intrigued by his designs.

taww, I believe Pass uses MOSFETs in his output stages.  The two most recent MOSFET amps I have owned were Lamm's M1.2 Reference monos and the BAT VK500.  The Lamm amps were the best of those two but still sounded a bit soft/rounded in comparison to the three other amps I owned at the time (2 bi-polar amps and a set of NCore monos).  This may have been due to the hybrid design with a 6922 tube or the lower power of 110 wpc compared to the other amps that all provided at least 300 wpc.  You are correct, I should hear some of the newer MOSFET designs for comparison.

I would also like to hear the Gamut M250i (250 wpc) mono amps that use only a single NPN high powered MOSFET per phase (i.e., two per channel).  I am curious whether a single output device would improve clarity and naturalness over having banks of transistors that will never be exactly matched with each other.  However, I am sure there are other trade-offs (pluses and minuses) as with any design, which is why we need to hear the gear rather than purchase based on topology or reviews by others.

Mitch,

Pass use Hexfet in the output stages, namely the IRF240/9240 (TO247) these are more of an industrial transistor then one designed specifically for Audio. If one pairs many of them in parallel in an output stage it becomes necessary to use source resistors to make them share current properly, if not one device will hog all the current and self destruct.

In our entry-level Liberty Audio B2B-100 I too use HexFet, the IRF630/9630 (TO220) industrial devices too and they need Source Resistors too to play well together as well.
http://www.libertyaudio.com/products/b2b-100-all-mos-fet-stereo-power-amplifier

These types of HexFet need a lot of Bias current to sound good.

Toshiba and Hitachi/Renseas make some Mosfet specifically designed for Audio, in our earlier series of Amplifiers I used the Toshiba J200/K1529 in the current series of amplifiers I use the modern day equivalent of the J50/K135 lateral MosFets made by Exicon 10N20/10P20 (TO3) these are made specifically for Audio - Renesas makes the same type MOSFET J162/K1058 (TO3P)

These have a softer sound than the Industrial type Mosfet mentioned above, you don’t have to run quite as much bias current to make them sing, and if you match them close there no need for Source Resistors to make the share current.

I prefer the sound of MOSFET output stages - to my ears Bipolar always produce a "lisp" "s" kind of sound.

As with anything its in the execution of the design - Pass makes excellent amplifiers with the HexFet’s

Good Listening


Peter

Taww,
I owned Neodio top of the line integrated and if you get a chance to get your hands on one go for it.  His two cdp’s are the most musical available.

Hi Peter and thank-you for the detailed reply.

I prefer the sound of MOSFET output stages - to my ears Bipolar always produce a "lisp" "s" kind of sound.

I know both design and parts selection are important and I have heard the "lisp" type sound with a couple of amps, including Cary's newer 500.1 SS amps (that I simply couldn't live with) but I never had that problem with their older 500MB SS amps that I found to be quite musical and liked much better.  The older 500MBs used Sanken 50 ampere, high current, wide bandwidth bipolar output devices.  My Class A Claytons, which use Motorola bipolar transistors do not have any signs of "lisp" or haze or any other artifact but I am sure the Class A operation bias and large power supply contribute to the sound.

I prefer the conveniences of having monoblocks and I am curious about your choice of really large stereo amplifiers vs. dedicated monoblocks, and whether the sound is affected (or not) by bridging a pair of your stereo amps (such as the mini-Olympia) as a monoblock implementation.  Do the amps provide fundamentally the same sound quality whether they are operated as a single stereo amp or a bridged mono pair?  Are there differences in addition to power output, such as input or output impedance, frequency or distortion characteristics, or other differences between the amps run in stereo or mono?