You're better off not using electrostatics or ribbons with your amp. Besides wattage, this type of speaker needs an amp with high current delivery capabilities into difficult loads. You ought ot look elsewhere. Proac Studios is usually a good match for CJ electronics. But in my opinion your amp does not warrant a $2000+ speaker. You'll be better off with sub $1000 speakers, like Proac Tablettes, or Sound Dynamics 300i. rgds, david k.
tube amps and electrostatics
What kinds of experiences have people had mating tube amps to electrostatic speakers (full range and/or hybrids)? I love the sound of both separately, but am concerned about the reactance of electrostats with tube power. I already own the CJ CAV-50 and am looking to upgrade my speakers with something in the $2500 range. Thanx, Dave
124 responses Add your response
I recently changed from a highly rated 400 wpc @ 4 ohms solid state beast to 100 wpc (triode mode) Cary SLAM-100 monoblocks driving Martin Logan SL-3 hybrid electrostats. The sound with tubes is far superior at low, normal & loud listening levels. At VERY loud levels the SS was better. Ultimate bass extention was better with SS, but this is offset by a more realistic bass tone with the Cary's, particularly on strings. Sound stage, presence, musical realism, emotional impact - all far better with the tubes. |
Dabble, I believe your amplifier would work well with most hybrids, but not necessarily with full range electrostatics. The reason is that full range electrostatics usually have a very high impedance in the bass, often over 50 ohms, and your amp would not put out much power into this load and so would clip prematurely. Electrostatics typically have a very low impedance at high frequencies, but with the CJ this shouldn't cause a significant frequency response anomaly. And remember there is relatively little energy up around 20 kHz, so the amp is not likely to clip as a consequence. I sell Sound Lab electrostatics, and they have a couple of hybrids that would work with your amp. I think the Martin Logan and Inner Sound hybrids would work well also. Avoid used Acoustats or Martin CLS's as they will give your amps a severe pain in the output stage. Historically Connie J. EL-34 based amps work well with Quad 63's (& USA Monitors), which are full range electrostats. I have a few reservations about these Quads, however, and personally prefer the Originals. But, I have no experience driving the Originals with EL-34 based amps, so while I think it would work I don't really know. I'd like to ask some specific questions that might help me make a more educated recommendation. Don't worry, I'm not going to push my product at you. I am one of you, not one of them. Audiokinesis@home.com. |
With stats you have to be careful because the impedence curve varies a lot. You may have some trouble in the bass since some tubes cannot drive very low impedences. If you do not want to change your amp, which by the way is a very good one, you should try the Maggie 1.6. These are different from stats since they have a very flat 4 ohm impedence. I have the Maggie 3.6R and am driving them with OTL tubes with great success. The web site is www.magnepan.com. |
I do not have experience with your amp, but I run my Martin-Logan Aerius i speakers with tubes by choice. I use 130W monoblocks and they made the Plinius SA250 (and several solid state others even more so) sound sick. A well constructed tube amp can sound much more lively than solid state amps provided you do not push them too hard. Friends with more experience of Martin-Logans believe tubes are preferable. If you are thinking of spending $2,500 on electrostatics then your musical tastes do probably not include playing drum and bass at 120dB, right? So what you lose by not using solid state will not be very important. If you are buying an electrostatic its probably because you want the transparency, purity, grainlessness, lack of cabinet resonance etc that the electrostatic can offer. Why spoil this with the electronic nature of solid state sound? You will probably just love the sound of your tubes when you hear them through some 'stats (preferably a hybrid for reasons stated in previous posts). The only problems you might encounter will occur because you want to play them louder than your amps can deliver. Try it. |
Something like 80% of our MA-2 amplifier production has been for Sound Lab owners. The Quad ESl 63 as been a good match for our M-60 and MA-1 amplifiers. Martin-Logans (which have a lower impedance) usually require a set of ZEROs (http://www.zeroimpedance.com) to work with many tube amps. The CLS-1 is an exception- its impedance was set higher and so is easier for tubes (M-L really wants their stuff to work with transistors, so even though they sound better with tubes, their impedance is usually set lower so transistors will have an easier time with them). Some of the old Accoustats were an easy load for tubes and some were not, as Accoustat was trying to crack the solid state market too. If one of the higher impedance Accoustats, IME 50-60 tube watts is plenty of power. The fact of the matter though is that the nature of tubes where they do not always act like a voltage source (which is the ability to double power as impedance is cut in half) is an advantage when trying to drive the higher impedances that an ESL often has. Unlike a box speaker where the high impedance in the bass can be the result of a box resonance, the high impedance of an ESL has nothing to do with resonance and so they still need power to drive them even though the impedance is high. Tube amps do this better than transistors. As an example, a 600-watt transistor amp can't make any more power into a set of Sound Labs than you might get from a 150 watt tube amp. Put another way, a lower powered tube amp can often make as much or more power than a more powerful transistor amp when driving ESLs. In short, ESLs and tubes have been one of the better combinations in audio for the last 55 years. |
Here are just two speakers that are not a good match with tube amps the Infinity Kappa 9 and an Acoustat not shown is the phase angles which can make them even worse as seen by the amp. http://www.rageaudio.com.au/index.php?p=1_12 Note the low impedance dips (left scale) at 2ohms and down to .5ohm and at what frequency (across the bottom), this is where tube amps will have trouble. (right scale is the phase in degrees not plotted) when this goes into the minus figure with low impedance together then it can become an amp killer at that frequency. Like this graph of the the Genesis 5.2 http://www.stereophile.com/content/genesis-advanced-technologies-52-loudspeaker-measurements And this one of the magico Q5 http://www.stereophile.com/content/magico-q5-loudspeaker-measurements This one of the Sonus Faber http://www.stereophile.com/content/sonus-faber-cremona-elipsa-loudspeaker-measurements Cheers George |
I will let the more technologically astute (Atmasphere) explain the reasons why, but one of the most eye-opening and educational experiences for me happened about twenty years ago. I bought my first pair of Stax F-81 electrostatics (known to be a highly inefficient and brutal load) after hearing them sound glorious in a friend's system. My amp at the time was a NYAL Moscode 600 capable of 300w at 8ohms and 500w at 4 ohms; it is a hybrid design with ss output stage. I thought, surely the Moscode can drive the Stax with no problems. Wrong! The Moscode sounded thin, flat, and DEAD DEAD DEAD, with no dynamic verve. I tried various cables; no better. Then, for the hell of it, I tried a rusty old Dynaco ST70 (35w) that I had bought at a local TV repair shop for $50 and was my first pure tube amp. I figured, what the hell? Result: MUSIC!! The Stax's suddenly sounded the way I remembered them; sweet, refined, detailed, dimensional, and within an admittedly limited dynamic range, very ALIVE and dynamic. I drive my current Stax's with Manley tube mono's with great results. |
Hi Atmasphere, nice to have met you in person at RMAF2013. I always enjoyed listening to the Classic Audio Hartsfield & T1.4 & they were sounding very good with your amps..... I believe that Roger Sanders has also done a great job with his s.s. amps - ESL Mk2 & Magtech - to drive electrostatic speakers. I listened to his speakers in the Sanders Sound Labs room & I really liked the sonics there as well. So, the s.s. world is not totally shut.... thanks. |
Frogman hi, the Moscode 600 you mentioned not being able to drive the ESL's very well. I believe that the Moscode 600 is a hybrid employing Mosfet output stage, even though it has a lot of watts!!, mosfets don't do current like a BJT (bipolar)output can This is why it wouldn't drive the ESL's, as with ESL's the impedance curve can dive to below 1ohms at places and very capacitive as well, and for this a solid state amp should have a BJT (bipolar) output stage that is high current and be very stable into capacitive loads. Cheers George |
Bombaywalla, yes, Roger sets the impedance of his ESLs quite low, to make them more compatible with solid state. ...the Moscode 600 is a hybrid employing Mosfet output stage, even though it has a lot of watts!!, mosfets don't do current like a BJT (bipolar)output can Georgelofi, I'm pretty sure that is not the right explanation. Keep in mind that a much smaller amp with tubes, the Dynaco ST-70, was able to play the Stax, with only 35 watts. Those older Moscodes had problems (IMO) unrelated to the fact that they used MOSFETs (IMO the topology itself was an issue). We had customers play the Stax with our original MA-1s (which back in those days made about 100 watts) and they seemed to play well together. The old MA-1 was an OTL with no feedback and a fairly high output impedance, yet sounded find with the Stax. So 'current' is not the answer. Stable into capacitive loads- that makes more sense as that is something true of both the ST-70 and the MA-1. |
If you like tube amps and stats check out the virtual system of audiogon member Bruce_Weiland http://forum.audiogon.com/cgi-bin/fr.pl?vevol&1200440547 Really nice set-up he has there. |
Play yes Atmasphere, but really you and I both know they were not able to give a flat 20hz to 20000hz into those hard loads. They acted more like they had tone controls in them and made the FR look like a dogs hind leg. I have a old friend that has two pairs of Stax F81's and not even his mighty Rogue Magnum 150 monoblocks drives them as well and with flat FR with a vice like grip as a good stable BJT amp can, like the big Krells and such. Cheers George |
George and Ralph, not really interesting in starting another discussion on the differences between Voltage Paradigm amps (generally solid state amps with very low output impedances -- high power SS amps can generate high current) and Power Paradigm amps (usually tube amps with higher output impedances). Suffice to say that as Ralph and Al (Almarg) have said many times, if a speaker was designed and voiced to be driven by a Voltage Paradigm/SS amp, using a high output impedance Power Paradigm/tube amp will likely result in acoustic colorations. The reverse case also being true. But hey, not all acoustic colorations necessarily sound bad. ;-) |
I copied this from a post from Kent of ESS. He's the expert on F81s. Has them. Sells them. Rebuilds them. The Stax ELS F-81 is one of the most difficult loads one can find. From 40Hz-800Hz the impedance is well above 100 ohms. Around 180Hz the impedance peaks around 512 ohms! Amazing. Solid state does not like this sort of load. A Zoebel network is highly recommended if using solid state. OTL tube amps are ideal but can be pricey. Transformer coupled tube amps will handle this kind of load. Power output will depend on required SPL in the listening room. A smallish room with a nearfield set-up will yield SPL in the 90-92 range with a mere 60 watts. I use an ARC D-70, 65 watts, with good results except for clipping if I want to drive things. Or I have an ARC Ref300, 280 watts, that will drive them louder than I like without clipping issues. Well I can clip the Ref300 but then I am pushing the speaker close to failure, probably the transformer. Any power amp will need to have a large, robust and stable power supply. An ARC VT130, 110 watts, would be ideal with these speakers and is within your budget. The AtmaSphere M-60 would be a great match if maybe just a little under powered. |
You forgot to mention Dhcod that they also dive down to below 2ohms as well. And don't go by the Stax published impedance graph, it's fudged quite a bit, we measured it and it's far from what they pictured. Add to that it's capacitive loads and you have a speaker that is easy to drive at some frequencies and a down right pig at other frequencies. And a quad esl 57 is even worse. And other ESL's are just as bad if not worse again, look at the Martin Logan Montise crazy amp impedance load and add to that the nasty phase angle, amps with current need only to apply. http://www.avsforum.com/t/1454033/amp-for-electrostatic-speakers post number 12 http://www.stereophile.com/content/martinlogan-montis-loudspeaker-measurements For over 40 years I've only used ESL's Quads, RTR's, ML, Acustat, Stax. Sure some of my big tube amps will sound good into them, but nothing drives them like a strong current bjt output stable solid state can. Direct drive esl's can also sound good but that's getting into the deadly territory Cheers George |
Mr G- You may want to realign your blanket statement, re: MOS-FETs and current. MOS-FETs are innately self-protecting, regarding thermal runaway, unlike bi-polar transistors (http://www.onsemi.com/pub_link/Collateral/AND8199-D.PDF). I sold(mostly modded) David Hafler products, for years, which all used MOS-FETs as output devices. As a sales point: I used to demo the DH-500, measuring the amperage into a 2 ohm dummy load. I had read as high as 48 amps, without damage or overheating(and thermal protection activation). You could practically arc weld with the suckers! I, as well as a couple other customers, owned Acoustat Model III's, and had excellent results with the Hafler amps, at realistic SPLs. |
MR G- I can't recall ever seeing anyone publish specs, claiming to double output wattage, all the way to two ohms. Nor did I claim that for the amps that I sold. re: Current handling/MOS-FETs vs BJTs: Maybe that first article wasn't clear enough, or too technical. Here's something a bit easier to digest, perhaps: (http://www.ixys.com/Documents/AppNotes/IXAN0061.pdf) |
Rodman99999, this debate on MOSFET vs BJT has been duked out before many times & I do NOT want to get into it again. So, I'm writing this with a bit of trepidation - both your references for MOSFETs seem to deal with MOSFETs used in a high frequency switching application (this is the key here - switching application) where MOSFETs are deemed better power devices than BJTs simply because MOSFETs are all-majority carrier devices (unlike BJTs which are bipolar carrier devices. hence the word "Bipolar" in BJT - both charges exist in this device - majority carriers in the emitter & collector & minority carriers in the base). Today's class-D amplifiers use power MOSFETs in their final output switching stage & for good reason as this stage operates at 10X the max audio frequency & we want to minimize the losses in this stage. For traditional class-A & class-AB power amplifiers, the output stage is NOT being used as a switching output stage; it's being used a continuously-variable analog output stage with high current capacity. I.E. the output stage is a gain stage & not a switching stage. There's a big difference here. You can definitely use power MOSFETs in the output analog stage as we see with Pass Labs, Threshold & many other brands. Not saying it cannot be done.... MOSFETs make better high frequency switches because at high frequencies we worry about the AC losses (CV^2f). These are the losses that are directly proportional to frequency & the parasitic capacitances of the device. Recovery time from off-to-on & on-to-off is also a big consideration in switching application & in MOSFETs this time is less than in BJTs as one does not have to wait for the majority & minority carriers to move from & get back to home base 'coz in MOSFETs there are no minority carriers! MOSFETs are self-limiting current output-wise (higher temp means higher resistance, which means lower output current. BTW, if you did not realize this - this is negative feedback! But this negative feedback is localized to within the device) & all that is very well. Output current-wise I also believe that BJTs do a better job - for the same amount of drain (MOSFET) or collector (BJT) current, the gain of the semiconductor device is higher in the BJT than in the MOSFET. Current in a BJT is linear relationship to circuit parameters like Vbe, circuit resitances, etc. In a MOSFET, the drain current has a square-law relationship to gate-source & threshold voltages. At the very heart of it, the MOSFET is a voltage device (yes, it does convert input voltage to drain current, hence, the transconductance) but, naturally, it is a Field Effect device. And, intrinsically, the BJT is a current device. Yes, applying voltages to the terminals does create high electric fields but the applied voltages are meant to create electron flow (current) in a BJT & not setup a source-drain channel (like in a MOSFET). MOSFETs have become very good power devices off-lately but I believe that BJts do a better job of high current delivery in analog circuits. |
I am no fan of SS amps(except for driving woofers), but- when someone makes blanket statements, regarding MOS-FETs and ESLs; I have to take exception. Whatever their application; they still protect themselves against thermal runaway, unlike BJTs, and can remain stable in high-current situations. I will side with those that have used them(past and present), to great success, in their output circuits, ie: David Hafler's SS amps, Acoustat TransNova TNT 200, Van Alstine Synergy 450, Accuphase A-60, BAT VK-655SE, Goldmund Mimesis8, Jeff Rowland M-9, to name a few(all Class A or A/B). I've not heard any of those accused of being unstable, into any kind of real-world load. It's been my experience, as well as others, that MOS-FETs(in a correctly designed circuit) have no problems driving ESLs. You mentioned PASS and I'll use the following article, as my parting shot. Especially pay attention to the portion entitled, 'Stretching Those Muscles': (http://dagogo.com/pass-labs-x350-5-amplifier-review) Happy listening! |
Rodman999999 You mis-read my statement on I vs R. I said "that can almost double", the app word being "almost" you read what you wanted to see. And here is the advertised specs of an Australian amp called and ME1500 and yes it can "almost" double all the way down to 1ohm 220-8 430-4 800-2 1500-1. And thats both channels driven at the same time!! http://www.me-au.com/ME_1500_data_1.jpg http://www.me-au.com/ME_1500_data_2.jpg And even the smaller ME amps do the same amount of "almost" doubling. Show any Mosfet that can do these kind of figures, and like I said I'll show you a case for false advertising. Cheers George |
Regardless, the ability of an amp to double power as impedance is cut in half is not an advantage on an ESL. This is because the speaker really wants to see constant power regardless of its impedance at a particular frequency, as the impedance curve is based on a capacitor rather than the resonance of a driver in a box. Consequently tube amps have been the preferred choice for ESLs since the 1950s and remains that way today- if you really want to hear what the ESL does, you gotta have tubes, else you are leaving a lot of the speaker's capabilities on the table. |
I couldn't agree more. I base that strictly on what my ears tell me whenever I hear electrostatics. What I hear is that the transparency of electrostats lays bare ss amps' tendency to sound leaner and less dimensional than tube amps with a resulting sound that can can be sterile and dimensionally flat; as opposed to the dimensionality and image density that a good tube amp offers. A couple of examples of this (besides my own) that come to mind are Martin Logans run by Threshold amps at audio shows, Quads/Spectral at Lyric, and most recently a friend's InnerSounds with the InnerSound amplifier. On the very same InnerSounds, my Manley tube monos sound timbrally closer to real with full and and dimensional images; but, admittedly, not capable of as much volume or bass extension. In fairness, original Quads driven by Levinson ML2 sounded very good. |
Frogman: "original Quads driven by Levinson ML2 sounded very good." And what you would have also heard was a more defined and extended treble because those quads and these (ML's Acustats and other els's) go below 1ohm in the treble and start that impedance dip at 10khz. Tubes I aggree with these speakers still sound good but they are definately subdued in the treble compared to a GOOD s/s amp that is BJT output and that can do current into low impedances. Like you found with the ML2 which can almost keep doubling it's current down to 1ohm for each halving of impedance. Cheers George |
I can't dispute your technical assertions, but I can tell you unequivocally that the electrostats driven by good tube amps that I have heard (my own Stax, Quads/Jadis, Quads/Quicksilver, Soundlab/CJ, and others) have ALL sounded more natural in the highs, and certainly not "deficient" in the highs than even the Quads/Levinson. Your definition of "defined and extended" may not necessarily be my definition of natural. |
Frogman: You know I hope that most SS amps have a lower output impedance than most tube amps. Here is a quote from Roger Sanders of ESL fame a white paper on Solid State v Tubes for ESL's. "This impedance problem is relatively minor when dealing with conventional, magnetic speakers. But an electrostatic speaker is an entirely different animal. An ESL is a capacitor, not a resistor like a magnetic speaker. The impedance of a capacitor is inversely proportional to frequency. Therefore the impedance of an ESL typically varies from around 150 ohms in the midrange to about 1 ohm at 20 KHz. A tube amp will be able to drive the high impedance frequency bandwidth (the midrange and lower highs) of an ESL with linear frequency response. However, at higher frequencies, the impedance of the ESL will drop below the impedance of the amplifier and the amp will then roll off the highs to some degree depending on the exact impedance mismatch and the frequencies involved. I think you can now see why I prefer very high power, solid state amps without any protective circuitry for driving ESLs. This is because they can drive ESLs with linear frequency response, while tube amps roll off the highs." You can read the whole White Paper here: http://sanderssoundsystems.com/technical-white-papers/172-tubes-vs-transistors Cheers George |
Georgelofi, thanks for the link and I am glad that you found what works for you. So did I, and it's tubes with electrostats. This is an old story in our hobby and after many years enjoying it I have learned that one of the few things that I can consistently trust to tell me what's "right" is my ears. |
"Frogman: Georgelofi, thanks for the link and I am glad that you found what works for you." Like I said, I even liked the sound of tubes into ESL's, but when you hear the extension and dynamic presence that's missing with tubes once you've heard a "good" solid state BJT (bi-polar not mosfet) output stage amp into them with lots of watts and current, you will think hard about what's missing, but then maybe you like that subdued rolled off top end. It's not what works for me, it's fact, and electronic maths made up of Ohm's and Kirchoffs Laws, there is no voodoo involved. Stated by one of the masters of ESL's design Roger Sanders that I quoted from the white paper I gave the link to. Here again in case you didn't fully read it. http://sanderssoundsystems.com/technical-white-papers/172-tubes-vs-transistors Cheers George |
OK, George, you win; clearly, I don't know what live music sounds like. ****It's not what works for me, it's fact, and electronic maths made up of Ohm's and Kirchoffs Laws, there is no voodoo involved.**** I will go back to sticking pins into my tube sockets now. Interesting (appropriate?) moniker, BTW ;-) |
I have never heard quad esls have a dynamic low end like is possible with good full range dynamic speakers. I always figured that to be their inherent achilles heel, as is the case with planars generally. Have not compared with a good beefy SS amp though. I would expect some difference there I suppose, the question would be how much and what happens to all the rest. I have heard some very good results with bass dynamics using es headphones, like Stax, so I have to think such things on a larger speaker scale are possible, at least in some rooms with some amps. I tend to like tube amplification best though I would say with my Stax electret (not es) phones, FWIW. Of course, those use the custom Stax transformer box to help get things right. Maybe there is a similar transformer device possible for use with large es speakers to help address the electrical issues? Did not realize es speakers had those electronic properties. Sounds like you almost need some kind of extended bi or multi-amping to really get best results, more so than with most any other kind of speaker perhaps? OR maybe a Stax-like transformer box designed to solvethe problem, if such a thing exists? I read the key to driving ES speakers effectively is high voltage. That is an attribute of Class D Icepower amps I believe. Has anyone tried a high voltage Class D amp with ES speakers? I'm thinking it might be a good match. |
And what you would have also heard was a more defined and extended treble because those quads and these (ML's Acustats and other els's) go below 1ohm in the treble and start that impedance dip at 10khz. This is not entirely true. Quads and Soundlabs have a higher impedance at 20KHz. In the case of the ESL57 and ESL63, the 20KHz impedance is high enough that even our small M-60 (60-watt OTL) can drive the speaker easily with no loss of HF performance. In the case of ML, later Quads and Sanders ESLs, because the manufacturer is wanting to open up their market to more transistor amps, the impedance is quite low at 20KHz (some MLs are only 0.5 ohm). In cases like these, you do as Tomcy6 mentions- you get a set of ZEROs (http://www.zeroimpedance .com) which allow you to easily drive ML or whatever! We have several customers doing just that with our older MA-1s (12-tube version) that only make 100 watts/channel, and they have no problem whatsoever making high frequencies on the speaker, with proper response to 20KHz and beyond. |
12-04-13: FrogmanHopefully Frogman won't mind if I provide some perspective on his comment by stating what he is too modest to say, that he is an accomplished professional musician in the classical, jazz, and other genres. Regards, -- Al |
Just the Quad ESL57 impedance curve, my ML's and Acousats are even worse when I measured their impedances. http://www.quadesl.com/quad_main.html and add to this the highly capacitive nature of ESL's, and you can see why Roger Sander says Solid State is better than Tube or OTL Tube for ESL's The only tube amp which is great match and is not worried by these impedance drops is High Volatge direct drive tube amps (up to 5000v at the speaker terminals). For ESL's like the oringinal Acoustat X. But these are difficult and hard and make safe. As you can imagine. Cheers George |
There's no question that when driving the many ESL's that have impedances descending from high values at low frequencies to very low values at upper treble frequencies nearly all solid state amps will provide an increased emphasis of the upper treble in comparison to nearly all tube amps (assuming the amps being compared are operated within the limits of their voltage, current, power, and thermal capabilities). Which of those two kinds of amplifier/speaker interactions results in the most correct acoustic output from the speaker is a separate question, however. Regards, -- Al |
