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I finally received my direct drive amp from Roger Modjeski for my Beveridge Model 3 speakers.
This amp gets rid of all transformers to the line sources and provides the High Voltage Polarizing B+
First order filter right on the amp to operate the line source above 150hz and my stereo subs overlap and cross down from there.
I get rid of the entire HV multiplier and step up transformer in the base:
And connect direct to the line source with High Voltage silicone wire:
Very nice early experimentation; really makes the panels very dynamic and the energy on the top end is definitely airier over what I believed to be a very revealing system before.
Will report back as I continue to balance it ... definitely worth the wait from Modjeski who was probably the only person capable and willing to pull this off - hat's off to him.
definitely worth the wait from Modjeski who was probably the only person capable and willing to pull this off - hat's off to him.
Actually the real issue is operator safety. That is the main reason you don't see more direct drive amplifiers.
They do sound nice though!
"This couldn't be a commercial product unless it was caged and mono. I have no pets and the room is mine so my grown kids don't come down to fuss around and neither does my spouse"
Yes, agreed- I mentioned that in my follow up post. Current safety regulations would make it difficult for a commercial product
I got quite an unpleasant jolt from the speaker wires of my NYAL OTL3 while it was playing music once. I can't remember why I touched them, but I was sorry I had.
But perhaps a DD amplifier could have been fatal.
To work on my Beveridge DD amplifiers, I bought a special probe rated for 6kV. It looks like a short sword with an insulated "hilt", so that voltages at the sensor end cannot jump across to the handle end. On one occasion, the tips of my fingers were overhanging the hilt, just on top of its bulge, not really on the danger side. Nevertheless, while measuring (only) 1600V, I got zapped on my exposed fingertips, which later split open and required quite a while to heal. Needless to say, I was very careful thereafter about how I gripped that probe. Bill Thalmann showed me his scars from working on my unit, too; he got it much worse but also only in the fingers, fortunately. Across the chest and you're a goner for sure. The Bev amps use +/-1600V, or 3200V from + to - poles. The Sound Lab ESLs require much higher voltage, although I don't know, and SL won't say, exactly what that voltage is, probably at least 6kV.
Obviously Direct Drive amps are the correct way to drive and ESL. The Model 3 requires 750 Volt-Amps (VA) to play Miles Davis at high levels. The problems with transformers are many and the load presented to a conventional amplifier is about 1 ohm at high frequencies. The transformer I designed for the Model 3 added quite a bit to that load due to winding capacitance. Since the load is capacitive it causes transistor amps with load line limiting to clip at low volumes, this is why ESLs are best driven with transistors with no limiters, but those are rather rare. No wonder tube amps tend to drive ELS as they have no limiters but now we are going through two transformers and still not enough current. Low voltage OTLs, though some like them, are not the best choice either as they cannot supply any where near the high currents required by a 1 ohm load.
The virtue of an DD amp is its high operating voltage. At 1500 volts one needs only 1/2 amp to get the 750 VA required to play trumpet music. I only make these amplifiers for sophisticated users who are comfortable with high voltage.
On the safety factor let me remind all the high voltage DC is not the same as AC. Its not the voltage but the current that matters and it's path through the body. AC causes the heart to fibrillate and DC defibrillates (as seen on TV with the paddles). I have unintentionally taken a shock across the chest several times. Most recently with 3 KV on a Bev 2SW amp from arm to arm and more recently while packing the amp being discussed here by a similar voltage. All got was a burn the size of a pin head on my finger and a jolt. I said one bad word and moved on. If used normally the warm tubes will discharge the B+. The polarizing has to be discharged manually but it is DC in a capacitor.
One should be careful while playing music however as that is AC, but only the bass is dangerous around 60 HZ. High frequencies are not as dangerous.
There are far more dangerous things around us every day. Of course we dont want a child or pet to stick there nose in these things. You probably dont want them in near your turntable for obvious reasons.
AC has a higher propensity to interrupt conduction in the heart muscle, resulting in cardiac arrest. I am guessing that's the basis for the difference in lethality between AC and DC.
Are you saying that it is an intrinsic characteristic of ESLs to present a one-ohm load? I bow to your far superior knowledge, but it does not seem to apply to my Sound Lab 845PXs. I measure impedances in the range of 20-30 ohms, from 50Hz to 2000Hz, about 8 ohms at 5kHz, and reaching as low as 2 ohms only above 10kHz, where the energy demands are minimal. This is using a non-factory full-range audio step-up transformer with a 1:90 turns ratio. (Below about 500Hz, this transformer is in parallel with the Sound Lab bass transformer, which has a much higher turns ratio, probably 1:250, but there are no other passive parts between the amp and the paralleled primaries of the transformers except an inductor in series with the bass transformer.) Since the impedance seen on the primary side will vary as the square of the turns ratio, I concluded that the step-up is a major factor in determining what the amplifier sees and that the intrinsic Z at the panel is much higher. In my view, many modern ESLs are "ruined" for tube amplifiers by added circuitry in front of the step-up audio transformer, such as low value resistances in parallel to effect a crossover, as SL does, all of which tends to bring down Z to values that indeed are very difficult at times for tube amplifiers. (In stock form, Z was around 4-5 ohms at mid-range frequencies for my 845 PXs. There may have been a 2-ohm dip in there too, at 1-2kHz.) With a solid state amplifier, these added circuits do not present much of a problem, but I have yet to meet an SS amplifier that can come close to the musicality of an OTL driving an old school ESL, such as a KLH9 or Quad 57 or my modified Sound Labs.
But I sure do not disagree that direct-drive is Nirvana. I bought my Bev 2SWs just on a lark, to have something to listen to in my basement far from the madding crowd; now I am addicted. Did you sign every Bev DD amplifier? You signed the ones in my 2SWs and dated "1979". Thanks for your contribution to this great speaker.
I didn't mean to start a storm. The transparency of the amp speaks for its self. It really is the way to drive these speakers. Others like de Paravinci have flirted with versions of DD for Quads for example.
I have experience in electronics as an engineer in another discipline. I can handle the risk. I have built 211 amps and I'm ok.
Roger was good enough to take it on and he has provided a great opportunity to hear what was a really good speaker turn into one that is quite extraordinary. I am glad that I stumbled on to Audio Circle and realized that Roger was able to make something up Great memories of the Dayton Wrights I had and the Acoustat X Servo amps.
The Beveridges still are able to do things that are out of scope for even the modern speakers. With the DD even better.
No, the amp in my equipment rack is the Wyetech Topaz 150lb behemoth SET. This is actually what I used to drive the line sources before the Direct Drive amp arrived. It is quite special.
The pic is "before" the direct drive - my room is a bit of a mess as I have been dropping the Beveridges for the hook up and doing other work so I did not show the current state. The direct drive as shown in the pic sits on the floor right now right in front of my rack. My room is just a little over 17' wide. Thus, I have high voltage silicone wire rated for 5KV as the hook up for the polarizing voltage. I notice no bad effects. At the old Audio Circle site Roger speaks about using his set up in the same way with runs of high voltage test probe wire.
Short runs with monos is safer for sure, and looks better. It doubles the cost. I don't think I would practically notice the difference. Check the link out for the "1/2 Drive" which was an attempt by Beveridge years ago to modify the Model 3's to DD. Roger's effort with me takes a simpler purer input all tube driver approach.
This couldn't be a commercial product unless it was caged and mono. I have no pets and the room is mine so my grown kids don't come down to fuss around and neither does my spouse.
These speakers are the exact same speakers I heard over 30 years ago at a local audio nut's home. I got wind of the sale - they were passed along to someone locally for over 25yrs - and I have them now. The left an impression on me 30years ago and I wanted to try them again - I have not forgotten the first time I heard them. I am glad I have the chance to restore and enjoy them for a while.
I will have to pick up some mylar- where did you get it? My panels look really good no delamination or aluminum erosion.
It seems I actually got the special mylar from RM Labs in Santa Barbara, 3-4 years ago perhaps. This is surprising to me, because I thought I got it from some guy in Ohio. Anyway, the guy in Ohio claims or once claimed to be able to repair the panels, if necessary. I may have found him on the internet by searching on "Beveridge speaker repair" or "ESL repair".
Got it, I will send Roger a note.
There is a guy somewhere in the Midwest that claims , on his website at least, that he can repair the Bev panels. As you know, they are different beast from the other types of ESLs... so who knows. Also there is a Beveridge fanatic in Italy at the "Sound of the Valve" who, if you can read Italian, (google translate is lacking) says that he has perfected the panel repair. He is unresponsive.
Rick Beveridge is a nice guy but I am not sure he is able to do this and based on his situation may never be able to again.
I spoke to Wayne Piquet in Florida earlier this year as I had a set of Quad USA monitor panels into him for repair and he said he would be willing to try to rebuild them... but he has never done it before either.
Wayne's work on the Quad speakers is impeccable. Kent M at electrostatic solutions is unwilling to try.. so if the panels do go it will be interesting to see if they can ever be rebuilt again appropriately. Right now , knock on wood, no need.
I don't know for sure if it's the guy in Italy whom you cite here, but there is some business in Europe that has messed up a few pairs of Beveridges and/or held the vital panels hostage for years before returning them to the respective owners in nonfunctional condition. I think the business was sued. Thankfully, there are a few possible reliable sources of repair work in the USA. As noted, I think I have spoken to a guy in Ohio. It really amounts to finding a guy who can stretch the mylar onto the frame and then re-established the proper circuitry without introducing shorts. On the other hand, if your panels are all well, it's likely they will remain so. Seems most panels have been damaged by bad amplifiers or amplifiers that were hot-rodded by persons who did not understand the circuit.
Yes, I read that post sometime ago whereby a Beveridge owner was had by improper refurbishment of his panels. That outfit was in Germany. The link ,posted, I referred to, is in Italy.
I chatted with Roger briefly and he has the film available on his website for sale. He also mentioned that he "might" be prepared to refurbish panels in the future after his new home base is settled. He has moved from Santa Barbara closer to Berkely
I wonder if Roger himself would be willing if it came down to that. He told me that the Beverages are unique in that both the stator and the panels are driven. Since he has built his own ESL's, it might not be impossible to convince him.
Kent did a very good job on my Stax's, but he knew them well ahead of time. He is probably right to be cautious.
RM Labs in Santa Barbara is, of course, owned by none other than Roger Modjeski. However I think he is no longer in Santa Barbara. He makes his own ESL system now, which seems to be something like the Stax F81's but much more efficient and easier to drive.
Perhaps what you say as regards RM's current location is true; I wouldn't know. As mentioned, I purchased the mylar 3-4 years ago, and, knock wood, I have had no need for it so far. But for sure, AJ knows how to find RM, because he just did business with him, as RM built AJ's new direct-drive amplifiers. And for that same reason, I knew that AJ would know the acronym "RM" refers to Modjeski. Sorry if my response was vague to others.
Wow, congratulations. Roger recently moved up near me and has been extremely helpful. Are those 6LF6 tubes in the DD amplifier?
Some day I may try that for my Stax's, but Roger got my OT3 NYAL (Futterman design) working really well, so for now I'm super happy.
I would love to find an OTL 3 one day - I have the original Futterman H3 - the Stax are amazing.
The output are 26DQ5 TV deflection tube. More robust than the 36Dk6 on the original and cheaper and more plentiful than the 6LF6 -about $3-5.00 each.
Thanks for posting. Do you have photos of the amplifiers separated from the speakers, or can you take some? Here or privately, can you give me an idea of cost? As you know, the original direct-drive amplifiers, in use in my SW2s, used solid state input and driver stages. Thus I have been tempted to consult RM on a tube revision. Interestingly, my amplifiers are signed in magic marker on the inside wall of each chassis, "RM, 1979". I think Harold Beveridge designed the amplifier or had a major role in it, but RM obviously built them for HB.
I think you have my Email Lew. This is a stereo amp. I did not know how I would like it. I elected to minimize the investment, after all these are 30year old speakers. One bad panel and these are expensive planters.
These are robustly built and I really don't know how much better the separation et al would be in mono in this form factor. I also elected to keep the chassis a simple Bud box to minimize cost in case it did not work out.
These are completely tube input and driver.
The main advantage of mono of course - and it is a nice one- is that you can have extremely short polarizing runs to each speaker which is definitely what I'd like to do, keep things neat and gain , theoretically, better separation. Weight plays no factor in this amp so no mono advantage there. I am not missing much with the stereo.
All that said it sounds really nice now and I was running a $13K amp on them with my front end many multiples of that.
The Beveridges were a diversion and they turned out to be almost as incredible in today s advanced world as the were more than 30 years ago. They will be staying around for a little while longer
I have plans to change the caps ( already in house) and if I get time will do that this weekend. Roger offered to install what I wanted, I elected to wait and hear it before I invested $5-600 in caps for it.
I made the investment in the caps :)
I bought my 2SWs completely on a lark, just "because". I wanted only to have the experience of hearing them and then thought I would pass them on to someone else of a similar level of craziness. But now I am addicted; I would never let them go. It took some experimentation, pain, and frustration to get them just right, but now I love them. Best of all, I can stay up all night listening to them, if work obligations permit, because my wife is oblivious to them; she cannot hear them at all in our bedroom, two floors above. Whereas, my big Sound Lab speakers are in the living room right below our bedroom; they must be turned off by 11:30, most nights, or I have a domestic dispute on my hands.
Incidentally, the panels are very long-lived if not mistreated by a blowup of an amplifier, I think because they do not carry a quiescent charge. I bought a roll of aluminized mylar, which is what you need for rebuilding a panel, should the need arise. It's still available commercially, but I would advise stockpiling some, just in the rare case.
PS. Is that the (stereo) direct-drive amplifier, sitting down on the lower left in your equipment module? My only thought is not about stereo separation or any other niceties of monoblocks; it's more about the length of the speaker wires. They would need to be quite long and very well insulated.
Marantz 10B. Very very cool.
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