I listened with interest to the interview with Bascom King about his latest hybrid tube-mosfet amp design for PS Audio. In it he explained that using a tube as an input stage instead of SS resulted in a huge increase in believability of the sound. 
I’ve been making hybrid amps for decades and my second amp design when I was 16 was hybrid class A. Bascom uses a 12au7 balanced at medium gain for the input stage and the output amp is SS with a gain of 4. That makes sense to get lower distortion than with a pure tube input stage.
My late friend Peter in Nelson always preferred to use a valve preamp and a SS poweramp as having a valve in the system warms it up a bit over pure SS. And you have the power and control to drive inefficient speakers with a solid state poweramp.
But I sense there has always been a slight resistance from audiophiles to having a hybrid amp like a Counterpoint, or Audio Research's efforts from the 90s. I suspect people generally prefer the design when it is either pure SS or pure valve.
So my question is, is there any love for hybrid amplifiers out there?

AMR-iFi R&D

I have a Copland CSA14 which I‘ve had for close to 25 years now and while it is no longer in my main system it still gets used regularly, and so it will continue until one of us dies!

Nice, did you choose it because it was something a bit different with the hybrid thing or because it is a nice amp from a respectable maker, or both? Or did it choose you?

AMR-iFi R&D

A bit of all three really. It was one of those lucky buys that come your way occasionally, as soon as it was in my system I knew it was staying.

Jun 24, 2018 19:55:49 GMT 12 colinf said:

My late friend Peter in Nelson always preferred to use a valve preamp and a SS poweramp as having a valve in the system warms it up a bit over pure SS. And you have the power and control to drive inefficient speakers with a solid state poweramp.
But I sense there has always been a slight resistance from audiophiles to having a hybrid amp like a Counterpoint, or Audio Research's efforts from the 90s. I suspect people generally prefer the design when it is either pure SS or pure valve.
So my question is, is there any love for hybrid amplifiers out there?

many did indeed used to believe in using a tube to warm things up but as systems got more transparent, the warming was revealed as nothing more than another distortion.

no love now but 20 years ago it would have been arc sp14 + classic 60

In my first real system, had a Sonic Frontiers SFL1 preamp. It partnered firstly a Plinius SA50 then a SA100, and kept it for many years.
The SFL1 was a hyrbrid design, with one tube and mosfets. Chose it as I wanted a tubed front end. Tried a cheaper VTL all tube first, but it didn’t fit. Really wanted an all tube Audio Research, but I didnt have the funds. Then the old EHF shop on Broadway in Newmarket started importing Sonic Frontier, and I could afford the SFL1. The SFL2 was an all tube model, but that was way expensive.
The SFL1 was very neutral, and combined well with my Plinius Jarrah phono Pre - seemed to tame the exuberance of the Jarrah that others found “bloated”.
Would still like tubes in the front end, but living off grid with electricity stored in batteries and generated by solar, that is not an option due to the high power demands of a tubed amp.

'Warmth' was not what attracted me to valves, it was 'transparency' & 'life'.

My first valve amp & the one that turned me onto valves was an unassuming DIY EL84 amp made by Alan Seccombe (Spendor/Luxman importer at the time).
Wow - my Plinius SS set was on-sold not long after.

Then came a Leak Stereo 20 amp (valve push-pull, Ultralinear feedback)
Counterpoint & their hybrid SA80 then took my fancy, however, the Leak Stereo 20 still sounded more like real music to me & the Counterpoint went.
The Leak is one of the most 'musical' amps I've ever heard & is one I'll probably never sell.

Later an Audio Research SP8 tube preamp + D70II power amp resided here for quite a few years.
I went on to audition various hybrid ARC preamps (SP8II, SP9, SP14), but to me, the addition of MOSFET transistors ruined the sound (despite improved S/N ratio etc).
The ARC Classic 60 power amp sounded similar to me - grainy, un-relaxed.

Then I came to realise that the heavily SS-regulated PSU of the ARC designs, imparted a sound that I did not care for.

So, I ended up not a SS fan & my experience with SS-tube hybrids has not been to my liking either, however.... YMMV!

DarkLantern blog - darklanternforowen.wordpress.com

i quite liked the classic era arcs...

unlike their all-tube brethren the hybrids took forever to warm up and if you ever turned them off it was back to square one.

i'm pretty sure the opaque nature of many of the speakers (eg. shahinians, maggies et al) used with the arc's masked a lot of the graininess.

Count me as a fan of the classic ARC gear too. I had an SP9/D7011 combo, sounded great with the ML's or Prozacs I was running at the time. Wish I hadnt have sold them....

Also had the Copland CSA14, and wish I hadnt sold that either....

However, worst amplifier I ever heard was a CJ PV10a with a Plinius SA100. Combination didnt work at all, worst of both worlds really, whereas the SP9 worked quite happily with SS power amps the CJ just made the Plinius sound soft and mushy. Just horrible. And thats probably the issue with hybrid pre power combos: getting each bit to match the other, especially if they come from different manufacturers..

Ok great, that’s interesting. I guess like anything in audio, it’s all about synergy and matching. So it's becoming clearer that people don’t have an issue with hybrid per se, or whether the pre is tube or SS or the other way around, ditto for the poweramp. It's all about the sound.
Does the way they look count for anything? Is it personal preference?

AMR-iFi R&D

Reduced Tolerance and I were having this conversation last week... For me personally, when I'm listening to SS I sometimes wish I was listening to valves, but when I'm listening to valves I'm never wishing I was listening to SS. But yes I could pretty much live with either. Also note that my power requirements are not large....

For me the look had quite an influence. See photos below. Not only did the SFL1 look good, but was very thoughtfully designed and presented.

The front had three knobs evenly spaced for source, balance and volume. Then a row of rocker switches for source direct, tape, mono, mute and on/off.

On the back the rca inputs and outputs were spaced wide apart, unlike the crammed set ups of many amps.

The packing was a delight, separate box - no a cradle - for the tube, a screwdriver and a pair of white cotton gloves for handling the tube.

Good point there Ian. When I’m listening to SS I do often wonder what the valves would do to the same music. However when the valves are in the system I don’t really wonder about what the transistors would do. But I am aware that output valves put out lots of heat and I feel almost obliged to be doing all my listening in an efficient space of time to avoid wearing them out prematurely. That’s ok to do with valves because they seem to need not much time to warm up.
MichaelW makes a good point in that SS does need to take ages to warm up and in an Audio Research Classic 60 the output tubes are on and ready while the SS input stage takes ages to sound good. My Sansui sounds harsh and splashy when it's cold but warms up in about 2 hours to sound open and clear.
It's a reason I made my big hybrid class A because that mode of operation seems to need less time to sound good than class AB or class B.

AMR-iFi R&D

Sub, yes the practicality is also a big issue and I've been guilty of making the connectors on the back too close together too!

AMR-iFi R&D

Jun 25, 2018 19:41:58 GMT 12 cartridgeguyonline said:

Reduced Tolerance and I were having this conversation last week... For me personally, when I'm listening to SS I sometimes wish I was listening to valves, but when I'm listening to valves I'm never wishing I was listening to SS. But yes I could pretty much live with either. Also note that my power requirements are not large....

oh i have...

medium powered valves on maggies.

painful to listen to.

Absolare is a true hybrid and with 200w of grunt it has plenty of power!

It looks like there are two schools of thought here.
One is the high powered amps over 100w to drive inefficient speakers like the Maggies, for which solid state serves well.
The other would be the low to medium powered amps of, say, 5 to 25w that can drive efficient speakers well, for which you can enjoy using a small to medium valve amp.
So there wouldn't seem to be much satisfaction to be had from a lowish powered hybrid amp, only high powered ones.
Do you think that would be the case?

AMR-iFi R&D

The Absolare integrated looks interesting, a high powered hybrid of 200w into 8ohms. Absolare are using all valves for their medium powered amps.

AMR-iFi R&D

This AES paper is quite old, but still a decent basic explanation probably, when it comes to comparing differences between vac tube & solid state amps:

(Excerpts...)

DarkLantern blog - darklanternforowen.wordpress.com

and a classic piece from harry pearson of the absolute sound (tas #14 1979) on the mystery of the 60w amplifier

Nothing too mysterious really about a 60 watt tube amplifier - thats what you get from 2 x 6550 or EL34 tubes in push-pull, fixed biased.

ie Just 2 tubes, no paralleled multiple output devices to potentially degrade signal fidelity, as in higher powered amps, tube or SS.

DarkLantern blog - darklanternforowen.wordpress.com

Audio Research D110, a solid state amp from history. The D76 and it’s ilk live on and are revered even today as they are valve amps.
That brings up another point. Are valve amps more acceptable than SS over time because the valves are readily replaceable and upgradeable? Transistor amps have the transistors soldered in and seem to be a victim of their manufacture date. By contrast 12ax7s and EL34s etc have been made since the 1940s and are still current!
I made my headphone amp with sockets for the discrete transistors so they can be changed without resorting to a soldering iron, and you can listen to the differences in each suitable transistor. To me that makes it more timeless as current or past manufacture transistors can be used and changed over by the owner.
That's great about listening to an amp at higher levels where occasionally the clipping region is reached. A small valve amp such as most SET ones would overload more gracefully than a similarly powered transistor one.
But what about listening at normal volume, where the clipping level of the amp is never reached?

AMR-iFi R&D

Jun 26, 2018 19:29:11 GMT 12 Owen Y said:

Nothing too mysterious really about a 60 watt tube amplifier - thats what you get from 2 x 6550 or EL34 tubes in push-pull, fixed biased.

ie Just 2 tubes, no paralleled multiple output devices to potentially degrade signal fidelity, as in higher powered amps, tube or SS.

simplicity rules

it's always been said a smaller amp will sound sweeter and more musical than it's higher powered brothers.

Moscode 402 AU from 2009. 200w pc.
Here's a section from Doug Schroeder's review of it from 2009. The George he refers to is George Kaye, who is its designer and who worked with Harvey Rosenberg in the 80s.
”Ok, so it’s a hybrid amp – so what? One must remember that this was pretty radical thinking nearly 25 years ago in 1984! We don’t even look twice at hybrid cars, as they have become so common. A hybrid amp was anything but ordinary back then; it’s had incredible longevity and sonic merit to be implemented a quarter century later!

George is adamant about the fact that the Moscode 402Au is not just a tube gain stage slapped onto a solid-state power amplifier; rather, it is a tube amplifier with a MOSFET output stage. It’s obvious from the depth of the discussion in the Owner’s Manual that he wants people to appreciate the thoroughness of the design of the amp, not just its sound. For the three pages which comprise the discussion of the circuit the manual uses technical nomenclature, extolling the amp’s topology. Discussed is the fact that the tube driver stage and the MOSFET output stage are complimentary as both are high impedance devices. Further, the use of MOSFETs eliminate the need for Output Transformers, which George insists add unnecessary inductance and capacitance, “…and that,” states George, “interferes with the transfer function of the output transformer at high frequencies. They exhibit phase shift within the limits of the audio band.” This hinders them from revealing the maximum musical detail. MOSFETs, while not perfect, have power-related (harmonic distortion) as opposed to frequency response errors. George uses feedback to control for THD. His design rule, his “Rule of Ten”, is to, “Make the circuit work well to 10 times the highest or lowest frequencies it will handle…” A little overkill is a good thing!”

AMR-iFi R&D

did the moscodes come with Audio Pampers ?

Nappies? Probably! Tell your friends!😚

AMR-iFi R&D

the story goes that upon listening to his amplifiers, the listener would be so caught up in the sheer musicality that they could lose control of their bodily functions.

They do do things a bit differently over there in NYC 🙃

AMR-iFi R&D

Radford SC22 preamp. Could this be one of the first hybrids? It had a transistor-valve MM phono stage. I repaired one last week and it sounded quite nice!





ammonium sulfate properties

AMR-iFi R&D

Hi Colin - what was the design purpose of the solitary BC107 transistor at the input of this preamp?

DarkLantern blog - darklanternforowen.wordpress.com