I wonder if anyone make, commercially or otherwise, any (good sounding?) a two-stages classe “A” hybrid running 100-200W into 8Ohm, with no feedback?  AcousticPlan looks like tried to do something but their amp is just 50W and it looks they have no good driver for the first stage. Lamm did M1.1, good class A hybrid, quite powerful but with 4533 unnecessary stages. Hawk Audio does a little 50 watter with SRPP driving MOSFETs… I wonder why there is not a lot two-stages class “A” powerful amps out there?

I have my interest to ask, as Dima and I are very slowly working on a concept of a Super Zarathustra - a powerful 200-250W, pure class A, super-small size (!), two-stages amp with no feedback. I would like to learn what practice out there exists regarding the packaging of those type amplifiers. I have seen a few solutions but I violently do not like any of them. I wonder of anyone else might propose something else inspiring….

Rgs,
Romy the caT

Chirag wrote:

Well..my first question would be regarding the application.  The big Melq tube is already doing the bass towers...is it not enough current?

Chirag, I’m not planning to use this power amp in my system.  The Melq LF section does perfectly enough for my room. The Zarathustra prototype that I mentioned before:

http://www.goodsoundclub.com/TreeItem.aspx?postID=1029#1029

did something quite good but there were also the areas where it did not do good (driving high sensitivity for instance). I attribute it to the class AB operation. Also, we have some interest to see how it will perform if the very same amp will be biased class A and made with no cheating of any kind (unfortunately it means expansive). We really do not know how it will sound in comparing to the Melq LF section. I think the only one way to learn is to try. I assume that if everything will be done properly then it might be a very good full range amp, as I have seen how the class A amps (M1.1 for instance) do drive high sensitivity with good results. In the end I will hate if the amps will sound good, as I will have no use for it. Well, at least it will give me some self-confidence and reasons to call names the other guys who do SS amps.  :-)

Chirag wrote:

In addition to the Aria guy, the tubecad.com guy has several circuits up using his "aikido" circuit as a driver and several mosfet and transistor outputs.  It looks on the surface like a complicated SRPP setup, but I am not capable of commenting on the design.  Most of his suggested amp diagrams focus on lower outputs of 10-20w, but using more current capable tubes, you may be able to drive a bank of solid state outputs to get you what you need.  I generally like his approaches and I'm not basing this on any experience with this particular design.

Thanks, I will look at his lately. Although we do not need any circuits, we have the one but rather some interesting packaging ideas, though I did not see any high-power-low-size class “A” design with bold objectives.  Well, over the last few days we have come up with a solution that do look attractive so far… will see…..

Chirag wrote:

The other option I would suggest are the non-hybrid feedback based Pass Labs aleph amp circuits.  They remind me of the artificial sweetener Splenda...they taste kind of like sugar, but the overly sweet and chemical attitude does come through in the higher frequencies.  The Aleph 30 I tried for a few months did not screw up the midbass with my little Tannoys any more than my PP tube amps.  I am wondering how well his newer 30w "J" version could work on my 15" pro tannoys.

Thanks, Chirag, we all set with the topologies and circuit design. We are not in Kansas anymore and the whatever Mr. Pass does  Sonically is good only to be use as a ballast for ships…

Chirag wrote:

I think the italian Pathos company has a products that might fit the bill.  From the smaller integrated amp I heard, it may not cut the musical muscle you require.  This amp has a lot of fluffly names around it, but they do claim tube driver and class A output.

Actually I did hear this amp in Belgium I believe. It was driving Danlavy V and it was very pleasant.  I do not think they were powerful though….

Chirag wrote:

Regarding the Lamms, is it possible to cut away some of the odder opamp type middle stages and use a higher current tube to push the outputs?  The output setup and case is already there.

Not really, I would like the Super Zarathustra be twice smaller then Lamm 1.1, twice or trice more powerful and be at least 10 time more advancely made and sound, not to mention way better engineered. If I remember correctly Lamm 1.1 had cheap consumer-type PSs, the first stage was around some kind of integral buffers, then it had SS stages, then tube-based SRPP, then another SS stage and then the MOSFED output. There is negative feedback around the stages and a lot of other things… The Zarathustra will be completely different amplifier with completely different design objectives, so even the box of the M1.1 will not be reusable.

Chirag wrote:

If you're as intense as I believe, can your little 6E5P tube in the Melq configuration drive a bank of mosfets or transistors?

It will be very simple: no expansive and properly (sonically) made PS, super effective heat dissipation mechanism, Melquiades’ input stage in SRPP configuration driving the SS stage, no feedback, and the Dima’s own “kinky” output stage. I can hardly comment what is in the Dima’s output stage but Dima climes that it has some his own inventions that make it “different”. I prefer do not know what it is as I know absolutely nothing about SS.

jamesrm618 wrote:

The Vincent SP-T100 looks close "The SP-T100 is a hybrid mono block with tubes in the input stage where voltage is amplified. The power output Amplifier circuitry works without feedback." Nominal output power Class-A 8 Ohm: 10 Watt Nominal output power RMS 8 Ohm: 100 Watt Nominal output power RMS 4 Ohm: 200 Watt vincent-tac.de/en/design/dl3/spt100.php

“A vacuum tube-based 'Class A' input stage configuration complements the solid state output stage, which operates in pure 'Class A' for the ultimate in rich detail and imaging for the first ten watts. Above ten watts, the Vincent automatically switches to 'Class AB' to deliver over 200 watts of power for effortless transients and drive capabilities.”

How damn smart! To be proud that the input stages ruin in Class A is defiantly a big compliment for an amplifier for TV sets!

Rgs,
Romy the Cat

Hi Romy,

I did the review on the AcousticPlan amp, called the "Santor".  It is indeed a two-stage amp using 4 6922 tubes in parallel to drive a high Bias Mosfet output stage (it is class A to approximately 15 watts and runs very hot).  It is rated at 50 watts 8 ohms and 100 watts 4 ohms.  The first stage is simply a grounded cathode arrangement, thus the need for multiple triode sections in parallel. 

Sonically, I found this amp to be of a very high caliber.  In many ways it was superior to my own 3 stage hybrid (Sphinx Project 14MkIII...also no feedback and Class A to about 20 watts).  I think for relatively sensitive speakers (90db or greater) the Acousticplan amp has more than ample power.  It drove both my Apogees (3 ohms) and Acoustats (3 ohms in the bass and high treble plus quite reactive) with no problems and it drove a friend's Apogee Divas with no problem. 

I am now in the process of reviewing the Acousticplan Sarod preamp that has only 1 dual triode for both channels in the linestage.  It is a simple grounded cathode that is transformer coupled to the output.  So that's it 1 triode stage per channel for the line stage.  Output impedance is 200 ohms.  The power supply is an all tube affair with shunt regulation.   The sound from the line stage is phenomenally good.   One of the best I have heard.   The phono stage is more complex and uses all transformer coupling between the two active stages and then transformer coupling between phono and line sections.  Also, excellent sound.  The phono section I feel is not the equal of the line section.  Another top preamp I have on hand that you should seriously consider is the latest creation from Allen Wright of Vacuumstate, the RTP-3D.  The phono is the best I have so far had the privelege of hearing.  The linestage is also at the top.

I know of one other amp on the market that is just as simple and it comes from Monarchy Audio.  This amp is using 1 tube per monoblock (in an SRPP configuration I believe) coupled to a Mosfet output.  It has no feedback, is rated Class A to 50 watts with power available up to either 160 watts or 250 watts (depending on the model).   It is also a very good sounding amp.   The best news about the Monarchy is that it only costs about $2500 for the PAIR.  www.monarchyaudio.com

Another interesting thing: why not a lot of people make the single ended hybrids? I understand that single ended output has very low efficiency but still: it is only about the heat dissipation. I have seen some single ended SS amp. There was a strange 20W Italian hybrid. The Czechoslovakian KR amp does some kind 20W-30W hybrid. Brazilian Eduardo de Lima (the guy that I like) does 30-40 single ended SS amp…. Still, if it is juts about heat dissipation… then come on. It is 21 century! I can see a nice 2 stages hybrid where first stage driver 150W-200W solid-state assembly.  I wonder what can I head something like this? A very high efficiency forced cooling, or even water-cooling… Nowadays it is really not an issue… Even if that amp would have 20% efficiency and for 200W it would burn 1kW then what would be a big deal!? We Yankees are gloater anyway. An efficient and smartly built forces cooler with 4”” flexible pipe running outside, similar what we use for laundry dryers, would be quite simple to implement.

The Cat

behhl wrote:

Hi Romy, but I am simply curious that your Designed-&-Made-Yourself have always had the flavour of the names and places from A Hundred Years of Solitude ... Macondo the village, Melquiades the gypsy ... so why the departue now to Zarathustra? Perhaps you will reconsider to name it Segundo?  [tongue in left cheek] Perhaps even the title AHYoS may clue us as to the point of this DMY equipment? [tongue in right cheek]

Interesting that naming of an amp could be ridiculously important. Let leave the metaphors aside. The amps name is the way in which the amp might be referred.  Ironical some people convert those reference names into absurd. It is customary that I keep bitching about Lamm electronics but Lamm is a great example how naming of product could become ridicules. Many people, including me and including Lamm business associates, with whom I spoke over the phone about Lamm’s electronics were confused in the endless tang twisting:ML1, ML2, M1.1, ML1.2, ML2.1, M1.2, M2.1, ML1.1, M2.2 and so on and so on…  I do not know why Lamm did not provide more distinctive names. Perhaps he was saving money on front panel paint or was trying to make this customers and dealers be confused in the infinite colloquialisms of upgrades and models... Who knows….

Rgs,
Romy the Cat

guy sergeant wrote:

If you are a manufacturer with a range of products you have to export and sell to distributors all over the world (many of whom don't speak english), it is far easier to give your products numbers rather than names. It is also far easier for those distributors to then order them if they are listed in this way. It simplifies communication. If you are making one or two amplifiers at home (not for resale) then, of course, you can call them whatever you like!

I do not think that all of it has anything to do with “Two-stages, hybrid, small, powerful class “A” but who do not like early morning bitching”

The Cat

guy sergeant wrote:

I found the DG Privilege (70's reissue) gatefold double LP of the 1961 Mravinsky 4-5 & 6 yesterday. How many LP's were in the box set you mentioned? Presumably these symphonies were also available individually? Anyway, as you suggested, the performances are astonishing making every other version I have sound feeble. The sound quality (even squashed onto two LPs) is pretty fine aswell.

The Mravinsky set you got is very bad, trash it, you should get off CD better sound.  DG Privilege was DG’s budget line, unfortunately produced. All Privilege LPs were horribly pressed, severally compressed, have no LF and actually the entire sound of the “Privilege” is not recognizable.  I literally threw the Privilege LP away is I accidentally get them. The best Mravinsky 1961 was available as 3LP box set, pressed in Italy. It is a very common set and it cost nothing: ~7$ everywhere. There were huge among of then pressed, they all sound very slightly deterrent but still they all better then their competitors. There are also the original DG pressing with the ring of Tulips. They are savable as the individual Records, one per symphony. Unfortunately the Tulipsed sonically are not as interesting as the Italians. The Mravinsky 1961 Tulipsed have problems with side imaging; have larger surface noise and a lot of other issues.  They also much less available and much more expansive, Only God knows why the morons pay extra for inferior pressing of the Mravinsky 1961. Perhaps the audiophiles stupid label adoration takes over their sense of Reality… Anyhow, in the future try to stay on the subject of the thread, as there is a dedicated thread bout the Mravinsky 1961 in the music section of the site.

The Cat

Bud wrote:

Perhaps this link and the information trumpeted within will help on this project. Certainly the leader of this pack has solid credentials in HF switching power supplies, though this particular link is actually about roasting transistors in an Audio Amp... http://ridleyaudio.com/Technology.htm

Very interesting, Bud! I neither heard about this company nor hear their products. They do not say a lot what the Ridley Effect™ is all about. I have no expertise to assess how real it might be but I know that generally there is some sonic “kink” at high temperatures. Perhaps it is what makes tubes to sound sometimes interesting – the fact that we BBQ the electrons…. The “overheated electricity” usually sounds more “civilized” and less mechanical…

With Zarathustra everything is not known yet. I mildly fight with Dima regarding how much we should heat the Zarathustra output stage. He accustomed to the “SS that operates warm” as he mostly design AB-operating amplifiers. I keep arguing that 70-75 Celsius is perfectly normal oration temperature, particularly for the type of the heat dissipation that we use. Anyhow, he knows what he is doing and I am sure that in the end he will put the Zarathustra in the optimum operation temperature with respect to the sonic yield for the transistors we use. Still, the question is wide open how different the amp will sound at different temperature and what would be the sonic difference if would be change the stabilized operation temperature for 10 Celsius up or down. It will be very interesting to hear, I personally do not know who has this knowledge, as particularly regarding the different SS devises… I spoke with few people I know but I do not know if their experience would benefit Zarathustra as Dima uses his own ”different” ways to control temperature and bias.

BTW, do you know where is possible to hear the Ridley Audio power amp?

Rgs,
Romy

Bud,

thanks, perhaps I will get in touch with him but I do not know what I might doe with his AB amp…

Still, I generally have difficulty to talk with audio people and to extend any credibility to what they said if I did not experience personally the reference points that people have in their minds. You see, the technical people do deal most of the time with actual Sonic results but rather with development of the own algorithms to control events and to manage own egos. A person might be perfectly reasonable and intelligent in his/her realm of expertise but his research might have explicitly theoretical application only with the restricted context of “none applied theory”. Being applied the “research” might become a different way of doing….  Absolutely nothing. I’m sure that this guy is able to run transistor at 150 degree but the question is not how he does it but what result he is getting. I would need to hear “what I need to hear” and then a person might have a credit to claim how that Sound was done. Without the actual familiarity with Sound that those people are talking about all of them consider themselves geniuses and great inventors. I certainly do not mean the Ridley Audio guy but I dealt a lot with pro audio folk and with high-end specialists who consider themselves  “fancy” but after familiarizing with their Sound, or with Sound that they consider “acceptable” I realized that I wasted my time extending to them any trustworthiness.

Rgs,
Romy the Cat

I would like to extend my last previous post a little. First off all, I would like to remind that I am very much not an expert in usage of transistor and second - I would like do not convert this thread into those DIY desecration: as you all know I hate DIY people.

Still, the Ridley Audio guy smudges that he found a way to runs his transistors at 150 degree C.  With raise of temperature the current carrying capabilities decrease significantly.

So, driving Zarathustra in pure Class A, with no tricks or biasing abracadabras, I wonder how mach “save current” (power) we would be loosing is we go over 100 C. It looks like the Ridley Audio guy uses custom made MOSFETs and suggest that they do better at high temperature. He might be very correct but would it affect only HIS MOSFETs? Zarathustra does not use MOSFET, does not operate in AB and meant, quietly wise be good enough even to drive horns (!), which is very bold requirement that I do not know if we would be able to meet. The Ridley suggest the Kevlar-ribbon loudspeakers… If my definition of success were to make a playback to sound good for  jazz then it would be enough….

The Cat

I keep thinking about the temperature. Whatever the best I heard in Class A was running very very very hot. However, what is the association between sound, heat dissipation design and temperature.  It is obviously that any amplifier designers would like to get more power within smaller package size. More power = more bias current and more parallel transistors, which means more heat during idle operation. Let now to pretend that we have a super high efficiency heat dissipation mechanism that can absorb unlimited amount of heat and that make temperature not a factor. Now we can select a desirable power or output stage without regards to the heating problems. Or let me rephrase: now we can select the power we would like to have and then select the temperature we would like the output stage to operate. Now is the question: what would be with sound if we maintain the same idle current but change the effectiveness of the cooling, from up 30 degree C. to 50 degree C? How about 80 degree C? 100 degree C? How about the different transistors? We limit our views with size and dissipateable temperature but what is it is not a factor and if we have some kinds hypostatical cryogenic coolant cooling down the output stage? The transistors data shits give to us data what happen with transistor at different temperature but it said nothing about it’s sound.  I wonder if anyone had experience to assess this moment and at the same time be able to evaluate sound musically objectively. I obviously have no such experience and I do know anyone who does.

I personally still have a very strong inclination to higher temperature but I have no tangible rational for it. It would be fun to run Zarathustra at different temperature and to see what it will be doing sonically….

The caT