Balanced Low Power Tube Monoblocks?

I'm interested in suggestions for balanced, low power (let's say 60 wpc or less) tube monoblocks.

For example, the Atma-Sphere M-60.

Power tubes other than 300B are preferred (due to the high cost of NOS 300B tubes)

Well, since you are familiar with the the Lamm equipment, (having owned their preamps), the obvious recommendation would be the renowned 18wpc SET ML2.1, (athough while it accepts XLR inputs, I do believe that it is not a true balanced amp).

You've given us your maximum power requirement, but what is you minimum power requirement?

What is your budget?

Do you want to bias it yourself, via a separate meter, or do you want auto-biasing?

Good Luck in your search!
Thanks Kurt_tank.

I had forgotten about the Lamms. They'd be stunning, and I'd love to own a

Frankly, they're considerably more than I want to spend. While I don't have a
firm price in mind, under $5k would be preferred, and less if possible. Price
will be a moving target.

I don't have a minimum power requirement, but not much is required. They'd
be used with 100+db speakers.

It's all "what if" list compiling at the moment. Nothing definite.
Well Tvad, I am trying to think which tube amp companies make low output monoblock tube amps, that are also very well thought of. (I know that you have tried many very good amps, and so I descarded many of the middle of the road brands.)

I first thought of VAC, but they don't make a low powered monoblock amp, but only make either high powered monoblocks, or low powered stereo amps.

My next thought was Air Tight (I am not sure if their equipment is run balanced though). The ATM-211 (22wpc SET) is one unit that might work (new they run about $10K, and so used they should be around $5K), another is the push pull ATM-3, which is 55 wpc if run in triode mode (110 normally). Used the ATM-3 is just a little above your budget though, and here is a link to one pair for sale here on Audiogon.

>Air Tight ATM-3's

Another company that I thought about was Jadis. Their JA-50 is set up for balanced operation. The JA-15 replaced the JA-50, (I think), so the JA-50 is now out of production. Here is a link the one pair for sale here on Audiogon, which are also slightly above your budget.

Jadis JA-50's

Well, that is all I can think of now.

Good Luck in your search!

Question: What speakers are you going to be using them with?
Question: What speakers are you going to be using them with?
Kurt_tank (Threads | Answers)

Since nothing is definite, I'm not going to get into specifics, but the idea is high sensitivity. There are a few manufacturers under consideration: Audiokinesis, Daedalus, Zu Audio, among others.

Again, it's a moving target.

I may end up staying with what I have.
TVAD -- I don't know much about them, but the Einstein MK60 and MK23 appear to fit your requirements, other than price. There is an MK60 listed here now for $13.5K (the listing shows msrp of $32K). I'd assume that the MK23 is considerably less expensive. Here is the sales brochure on them:

-- Al
Gee, looking further at the Einstein brochure, they claim damping factors for the two amplifiers of 90 and 45 relative to 8 and 4 ohms, respectively, even though they are OTL. Pretty remarkable, assuming it is true.

-- Al
Tvad- Let's see, balanced mono-block 60 wpc max. Three recommendations come to mind, in no particular order:
1. Atma-sphere M-60
2. Atma-sphere M-60
3. Atma-sphere M-60.
Power tubes are pretty cheap, service is extraordinary, used price is WAY less than $5k. Reported to work well w Audiokinesis.
09-02-09: Swampwalker
Tvad- Let's see, balanced mono-block 60 wpc max.

I should have left this open ended.

You guys are taking the max power rating too literally, and I failed to mention
in the initial post that my intention was to use the monoblocks with high
sensitivity loudspeakers.

With high sensitivity loudspeakers, more than 60 wpc would be overkill.

If leaving the max power rating open ended produces more suggestions, then
let's assume no max power rating requirement.
Another choice might be the EAR 861. Not easy to find used but it might be just the ticket. The circuit is fully-balanced input to output (and has balanced inputs, after all that's where designer Tim de Paravicini's roots are), and direct-coupled. It uses an interesting method to get triode out of a pentode tube (ties Grid 1 to Cathode, Grid 2 is signal, Grid 3 is floating) and the result is highly linear. It uses an EL519 tube reasonably low in its operating range, and the tube naturally has long life. Barring accident or bad luck, one set of tubes should last you a very long time (operating life of the tubes is something like 15,000 hours I think, so 3hrs a day for 15 years?).

One stereo amp ouputs 32W but they can be bridged, so you could start with one, and add a second later when you found it. The EL519 Enhanced Triode Mode circuit sounds really wonderful. I am frankly surprised it hasn't gotten more press over the years. I have an 859 but would love a pair of 861s if I could ever find them used.
Thanks, T_bone. That is right in the wheelhouse. Any idea of the approximate cost for a single unit (used)?
I would take Duke's advice. I always have.

Whatever, buy something you can get serviced relatively easily. I would stay away from foreign companies that don't have US repair support.
The big Cary SET monoblocs (845/211 output tubes) are the first that jump to mind. 300b tubes are used in these amps as drivers, but they should have a long life in that application.

Good Luck

I live around the world from you (or so I'm betting). In Japan, the integrated amp version of the amp called the 859 won a StereoSound "Best Component" award about 12-13 years ago I think and they sold a bunch of 859s here. The 861 came not long afterward I believe, and I have seen them around but they are somewhat rare. If I went looking for a pair, I would find them separately and probably have to pay $3-3.5k each. I would expect they would be easiest to find in the UK. This is more of a deal where you buy one if it comes up at the right price, but you might not try to hold your breath...

Travis (the other one) has a point - anything you buy you'd better know how it is going to be serviced if something goes. My gut is that these could be serviced by someone outside the EAR family - they are, after all, a reasonably simple tube amp I believe. However, if you are a person who needs brand servicing, you'd need to figure out if it was available to you. They have a couple of dealers in the US but that's it.
Quicksilver used to make a Triode Mono @ 50 watts / 8 ohms that could have balanced imputs. Not sure if it is made any longer but still shown on Galen Carols website.
Quicksilver is a brand that interests me. Their products are well regarded, and their pricing is reasonable, IMO.
I looked at them hard before purchasing a pair of VAC PA90 (45 watts triode & 90 watts ultralinear). Sent them to Kevin for service and upgraded to their D series with balanced imputs.
Not to long ago i was looking for amps along the same lines you are, I ended up buying the Manley Snappers. Might want to put them on your list.
Tvad those Audio Valve 60 watt monoblocks might work for you;I think they are a balanced design but not 100% sure;might be worth checking out.
I have the Challanger 180 monos and they are just fantastic
driving my soundlab M2's.
Auto bias circuit that lets you run el34's,6550's and kt88's ;you can even mix then up it you want but I have not tried that as of yet.
Presently using JJ kt88's with very nice results.
Tvad -sorry but I just noticed the 60 watt mono's are only RCA's;the challanger line is fully balanced but high power;sorry for the error.
I remembered years ago Avant Garde demo their big Trio in San Francisco Stereophile show with BAT 150SE and it was mighty impressive, in fact I voted that room as the best sound of the show. if you don't need that much power, 75SE will do fine and under your budget though it's not mono block.
Balanced ... Hummmm ... (scratching my chin). If you can live without balanced, I can suggest the VAC Renaissance 70/70 (Mk. III or Signature). I started with a 70/70, then ran the monoblock "140/140" version for six years, and now I'm back to the 70/70 (Mk. III) which I alternate with a darTZeel. The 70/70 is one chassis, but completely dual mono, all the way down to two power cords and two on/off switches. A very potent 65 watts per channel (excellent output transformers and power supplies). Real quality - $14k in 1999 dollars - unlike VAC's Phi products, the Renaissance amps are all point-to-point wired. The amp autobiases the 300B's and there's a tube shut-down feature which automatically kills power to any output tube that fails - it's a zero maintenance tube amp (there aren't many of those).

I run mine from a fully balanced preamp and a 25 ft. balanced interconnect with Neutrix XLR-to-RCA adapters - sounds super. I'm using Sylvania 6SN7 GTB chrome tops for drivers and phase splitters, and the original 300B's that came with the amp.

Most people don't know what these amps are - you can pick one up for $4k/$5k.
Raquel, the VAC 70/70 is certainly a fine amp, but it has three things that do
not fit the profile of what I'm seeking, which is monoblock configuration,
balanced operation, and no 300B tubes (cost prohibitive to maintain...IMO).

I used a pair of VAC 160 MusicBloc amps with my present speakers (Silverline
Sonata III), and frankly the match was not optimal. Of course, I realize the
70/70 is a different animal.

What speakers are you driving with the VAC amp?

How loudly do you listen, and what type of music do you primarily enjoy?
Hi Tvad:

I have used a number of different speakers with my 70/70 and 140/140's. With the 70/70, I have used Dunlavy SC-III's, very briefly Vienna Acoustics Mahlers, Escalante Fremonts, and currently, Eben X-3's. With the 140/140's, I used the Mahlers, Ultimate Monitors, and very briefly, the Esclanates, but most of the time (4 years), Revel Salons. Roughly 75% of the music I listen to is symphonic (tending toward big symphonic), with the balance being a mix of acoustic jazz (with lots of bossa nova - the wife is Brazilian), blues/rock and French and Brazilian pop.

The Renaissance amps are a cut above the current Phi offerings, having been designed and manufactured at the height of the two-channel boom in the mid/late 90's when people were spending big money on state-of-the-art two channel gear (they were designed by Kevin Carter, incidentally). No boards - only expensive point-to-point wiring and generally outrageous parts quality. Regarding the 300B's, you are right that they are much more expensive than power pentodes. In addition, 300B's used in the Renaissance circuit have to be carefully selected, as it is a hotrodded Class A design that runs the output tubes at 95% of the WeCo 300B spec maximum voltage. That said, good 300B's are extremely hearty little beasts and have far more life than pentodes. I bought only one set for the 140's, and I went back to the original octet that came with my 70/70 when I went back to the 70/70 (I had my 140's converted into two stereo 70/70's, having sold one and kept the other). The stock VAC 300B's, which are rebadged Golden Dragons or Shunguang factory 300B's, are quite good and work very well in the amp - I've got at least 10,000 hours on this original set. Having corresponded with other owners, the amp evidently sounds best with Sofia carbon plates, which is where I will go when the current octet dies.

The 70/70 has really stiff power supplies and superb output transformers - it has 2 Ohm taps and can drive virtually any speaker (Sound by Singer was unable to drive the big Pipedreams with the VTL Brunhilde - they used a 70/70 instead - the amp is a beast). It would not be ideal on an 86 db. speaker with big orchestral in big rooms, but I understand that you will use a highly efficient speaker? If that is the case, then I would suggest the 30/30, which is generally considered to be the "honey" of the Renaissance line. It's only 32 watts/channel, but a real 32 watts - one of the shops in Manhattan (Innovative? I can't remember) hooked it up to the B&W 801N, of all speakers, just for laughs, and it drove it - not very loud, but nothing blew up.

Regarding balanced operation, my opinion is that, by the time the signal gets to the amp, most of the advantages of balanced operation have been achieved. The truly differential balanced tube amps like AtmaSphere and BAT mentioned by others in this thread are certainly well built and great sounding products, but as I have written, at the amp end, I do not believe a balanced amp is necessary. If I were going to use highly efficient speakers, I'd look at a low powered push/pull amp like to 30/30 or the Cary that uses a pair of 845's, or perhaps a high-powered single ended amp like the Lamm or Zanden. Of course, room size, musical preferences and equipment synergies are crucial.

Not sure I understand why you need monoblocks - do you have a lot of money tied up in short speaker cables made for monoblocks? I have a 1 meter pair of Jena Symphonies on ice in the closet for that reason - I bit the bullet and bought 8 ft. runs for my amps, each of which is single chassis. If monoblock operation is desired simply due to design advantages, dual mono designs are generally the same thing (again, nothing is shared in the 70/70 other than the chassis).

Hope this helps.
Thanks Raquel.

My equipment rack is along a side wall and near the back of the room, so I run 30 foot interconnects (rather than 30 foot speaker cables). Therefore, monoblocks are preferred.
Understood. To make a final pitch for VAC's Renaissance amps, there is a monoblock version of the 30/30, called the "30/70", which is 65 watts per monoblock channel. They come up for sale on Audiogon from time to time, and the 30/30 can be rewired by VAC into 30/70 monoblocks for roughly $500 per amp. I find the cosmetics on the 30/30 || 30/70 to be a bit loud, but, like all of the Renaissance amps, they sound superb, being incredibly transparent, open and alive (assuming they're run with zero feedback).
Tvad anything interested you yet?
Rleff, there are several good ideas!
I have Quicksilver Triode (6C33C) Monoblocs and they are not balanced. They are terrific though.

Not sure I understand why it has to be monoblocks. Can't you just as easily place a stereo amp between the speakers with short speaker cables, and run the long interconnect around the room to your rack containing the pre and sources? Regardless, most monos are best way to go.

Why does it have to be balanced? I've run balanced preamps into single-ended amps and visa-versa. You can get long runs of Mogami custom-terminated with XLR on one end and RCA on the others. This avoids adaptor connection points.

If "you go 2 out of 3"(i.e. not balanced)then the VAC rens, the Quicksilver Triodes(badboss427 also can tell you alot about these in his rig), or the Dehavilland Aries 845G all make sense, as well as the Atma M60s that you suggested yourself.

The Aries 845G are class A, zero feedback, single-ended, and quite powerful for SET amps. They are designed to drive a wide variety of speakers unlike most SETs. They provide much of the magic that good OTLs possess, without the issue of impedance matching problems. The use the Electoprint trannies, which are supposed to be some of the best available(I'm no techie), perhaps someone else could comment on that. Kara Chafee at Dehavilland has been super in terms of making sure that I get the best performance out of my amps.

If you must stick w/balanced, I'd stay with Atma-Spheres, and make sure you match with speakers that don't dip much below 8ohms at any frequency. IMHO, autoformers degrade the sound too much. Ralph can point you towards many compatible speakers if you need ideas on that. Cheers,
09-05-09: Sbank
Can't you just as easily place a stereo amp between the speakers with short
speaker cables, and run the long interconnect around the room to your rack
containing the pre and sources?
Yes, I can, but it's not the installation that we prefer from a standpoint of

You can get long runs of Mogami custom-terminated with XLR on one end and RCA on the others.

I've made these myself in the past. Yes, it's a possibility. Frankly, though, I hear little difference between XLR>RCA interconnects, and XLR>XLR cables using adapters. I have never detected the sound degradation that so many others comment on. Sometimes I wonder if the so-called sound degradation when using adapters has grown into a myth through a version of "telephone" where readers simply repeat what they've read without actually trying it for themselves.

In any case, I believe there's a benefit to running balanced if it's possible to do so.

... the VAC rens, the Quicksilver Triodes, or the
Dehavilland Aries 845G all make sense, as well as the Atma
Yes, these are all heavy contenders. I'm also considering Rogue M-150

My present speakers dip to about 4.5 ohms. The Atma-Sphere M-60 do not
work with these, and the Dehavilland are probably underpowered.

Ultimately, different speakers are in the future, but how far into the future is
unclear. In fact, the amplifier purchase might be deferred until the new
speakers are acquired, but I was thinking that I might be able to find an amp
that I could use with my present speakers until new speakers are purchased.

I realize I may be asking too much.
There's always autoformers. On the M-60s the Speltz Zeros are not entirely sonically neutral (a bit more neutral on the higher wattage A-S amps) but the small trade off might be an alternate route. On the other hand, I've always liked Mike Sanders gear (still have a pair of the original 8417 monos).

I tried Speltz Zeroformers with the M-60 amps. I didn't care for the sound.

Thanks everyone for some excellent suggestions.

At this point, I'm going to wait a few months and revisit a speaker change
before purchasing a different amp.
Tvad, You might be surprised at how apparently powerful the Dehavillands are. My Alon V's supposedly recommend 200w/channel according to the manual, but I was impressed hearing Nolas & Dehavillands @ CES a few years ago, called Kara, who agreed that it was a great match. I don't listen at ear-splitting levels, but they go pretty loud >95db without running out of gas. These are 4ohm loads we are talking about, too. I think you would be fine, certainly on an interim basis. You might consider calling Kara Chafee; very helpful and not at all salesy. Good luck and keep us posted,
Tvad, FWIW, a 'dip' to 4 ohms is not a problem for the M-60! OTOH, having the bass frequencies be 4 ohms (while the mids and highs are 8) is, and is a problem for **any** zero feedback tube amplifier.

When you see speakers that are 4 ohms in the bass and 8 ohms in the mids and highs, quite often the speaker designer is using woofers that are 3 db less efficient, and expecting that the amplifier will double power with the 4 ohm load. This brings the woofer output up to the level that the mids and highs operate at, but you need transistors to do that properly.

No tube amp will sound right with a load like that since no tube amp can double power as you cut the impedance in half! You can make a speaker like that work (sort of) if the tube amp has lots of feedback in its design. The problem is that the negative feedback will foreshorten the soundstage and impart a sheen to the mids and highs- IOW it will not sound natural.

That is why our amps have little or no feedback- why bother try to drive a speaker that will always sound electronic? I agree it has limited our market, but limited to the speakers that can sound like music (work properly with tubes), and that is not a bad thing :)
When you see speakers that are 4 ohms in the bass and 8 ohms in the mids and highs, quite often the speaker designer is using woofers that are 3 db less efficient, and expecting that the amplifier will double power with the 4 ohm load. This brings the woofer output up to the level that the mids and highs operate at, but you need transistors to do that properly.


This may seem like a matter of semantics, but I want to raise an issue in connection with this statement because I think it has been a point of confusion in some other recent threads.

A speaker that has say a 4 ohm impedance in the lows, and an 8 ohm impedance in the mids and highs, and that may have woofers that are 3db less efficient than the other elements, will, as you say, generally be best suited for a solid state amplifier that can double power into 4 ohms.

BUT, as long as the amplifier has an output impedance which is negligibly small in relation to 4 ohms, and as long as the volume levels it is called upon to deliver are within the limitations of both its voltage swing capability and its ability to deliver current, then a flat frequency response will result. It is not the ability to double power into 4 ohms per se which results in flat frequency response into such a speaker, but rather it is the ability of the amp to act essentially as a voltage source, up to some maximum volume level.

In other words, to cite an example, a solid state amp having low output impedance, which is capable of 200W into 8 ohms but only 300W into 4 ohms, will deliver just as flat a frequency response into such a speaker as an amp which is capable of 200W into 8 ohms and 400W into 4 ohms, IF it is not called upon to generate more volume than its relatively limited current capability can support.

Do you agree?

-- Al
Almarg, can you point to a solid state amplifier model that mentions output impedance in the specifications?

I've done only a quick search, but neither Pass Labs nor Bryston publish this information.
TVAD -- What is most commonly specified is damping factor, which is almost always defined as output impedance divided into 8 ohms.

So assuming that the specifications do not indicate that damping factor is defined relative to an impedance other than 8 ohms, just divide the specified damping factor into 8 ohms and that is the output impedance.

Example: Damping factor = 40; output impedance = 8/40 = 0.2 ohms.

-- Al
Consider Audio Mirror. Best bargain I've ever seen.
The Audio Mirror amps do seem like a good deal. Thanks for pointing them

I decided to break the rules and buy a pair of single ended George Wright
Signature AU-15 monoblocks.

George made great, underrated stuff. I owned a WPP200C phono preamp,
and spoke with George on a few occasions. It was a bit of a sentimental
Tvad, "It was a bit of a sentimental purchase."

Those are ALWAYS the best kind. Somehow, the music and enjoyment seems to transcend the equipment in these instances. Best of luck with the new babies Grant!
Thanks, Joe. Now, for the 2A3 tube vetting...
Grant -- Best of luck with the new amps.

Some approaches to consider if you want to try to find VINTAGE 2A3's, aside from the usual dealers who will of course charge very high prices when and if they have any for sale:

1)Take out a subscription to Antique Radio Classified, and run a free want ad there each month.

2)They were used in the power amplifier/power supply chassis of several very high end multi-chassis "radios" ca. 1935. Most notably, those made by E. H. Scott (no relation to H. H. Scott, the hifi manufacturer who came later). During the intervening 75 years, the power amp/power supply chassis have often become separated from the rest of the set, and sometimes appear for sale in ARC or on-line auctions. I found one via a local classified ad for $35 some years ago, complete with 4 good 2A3's. There were undoubtedly a lot of people in your particular neck of the woods who owned these sets, and some may still be sitting in basements, or become available through local auctions, tag sales, classifieds, etc.

The particular Scott sets which used 2A3's were the Allwave 15 and the Allwave 23, also known as the Allwave Imperial or Allwave High Fidelity.

3)The Brook amplifiers of the early 1950's (designed by Lincoln Walsh) commonly used 2A3's (sometimes 300B's), although they appear infrequently and usually command high prices.

-- Al
Almarg, No, I don't seem to agree. The issue is that tube amplifiers are not always going to act like a true voltage source (that is the domain of transistors). You *can* get tubes to *start* to behave like a voltage source if you add enough feedback, but then IMO/IME, by doing so you obviate the main reason to go with tubes, which is linearity without feedback.

The problem with feedback is that it will *increase* the odd-ordered harmonics that the human ear uses to determine the volume of a sound. Since these harmonics are considerably higher in frequency (5th, 7th and 9th harmonics specifically) they also add an electronic brightness that everyone on this forum is very familiar with. Nelson Pass wrote a great article about this:

pay particular attention to the graph showing the odd orders.

So IOW we as audiophiles are always having to decide between sound that might not be perfectly flat but otherwise sounds natural *or* sound that measures flat but sounds hard and bright! Either way there is a coloration and either way neither one sounds like the frequency response is flat.

I for one prefer highs that are natural as opposed to bright. I don't like boomy bass or anemic bass either, so I choose speakers wherein the designer knew that the amplifier driving that speaker was not going to be a perfect 'voltage source'. see

for what that is all about.
Ralph -- Thanks very much for your good response, with which I am in complete agreement.

But please note that my post (the one dated Sept. 8) was not dealing with tube amplifiers, or with amplifiers or speakers designed based on the power paradigm. It was addressing the narrow situation in which a speaker having a low impedance in the bass (e.g., 4 ohms), and a higher impedance in the mids and treble (e.g. 8 ohms), is being driven by an amplifier (typically a solid state amplifier) having an output impedance which is negligibly small in relation to the speaker impedance at any frequency.

And the question was whether or not such an amplifier driving such a speaker would produce an excessively bright response as a consequence of the amplifier not being able to double power into 4 ohms (relative to 8 ohms). And my contention is that it will not, as long as the volume levels are such that the amplifier is not called upon to deliver more current than it is capable of (and as long as the amp does not produce an excessively bright sound for other reasons).

-- Al
Shop around for a used Rocket-88R.
Thanks for the suggestions, Al.
Almarg- OK, I see your point, but in practice such an amplifier will in fact 'produce an excessively bright response' not due to frequency response variation but due to generation of odd-ordered harmonics.

I apologize for repeating myself often, but the simple fact is that that audio industry is ignoring 45 years of research into how humans perceive sound! Were that research taken into account, I would agree that your statement is correct as today's amplifiers would be different. What amazes me about all this is how the audio industry has stuck steadfastly to design rules that, even while they were being implemented during the 1960s, were already being proven wrong by said research.

What I am talking about is the typical amplifier that you are describing violates the most fundamental rule of how we perceive volume, by exaggerating odd-ordered harmonics. Another way of putting this is that you can be convinced that a sound is a lot louder than it really is if the 5th, 7th and 9th harmonics are tampered with. These harmonics are not only cues to the human ear brain system, they also contribute to brightness- quite literally our ears are more sensitive to these harmonics than they are even to vocal frequencies! So there is almost no way an amplifier like that will not appear to have excessive highs.

This is the fundamental reason why tubes are still around after being declared 'obsolete'...
Excellent points, Ralph, and I think we are now fully converged on this. Thanks!

I would add, though, in relation to the particular issue I raised initially, that a "voltage paradigm" amplifier with very low output impedance that is capable of doubling power into 4 ohms (relative to the power it can deliver into 8 ohms) would not NECESSARILY be either better or worse with respect to odd-order harmonic generation than another voltage paradigm amplifier with similarly low output impedance that is not capable of doubling power into 4 ohms.

Best regards,
-- Al
Almarg, I agree completely. As you have probably figured out by now, I regard the quality of the amplifier by its ability to not enhance these harmonics more than anything else.