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I too have made the AU-90 baseplate mod to my M-1's, but I have measured far lower impedances than others have (less than two Ohms at high frequencies). I'm still puzzled about why I should be getting lower impedance readings than everyone else, but let's assume my readings are correct.
My problem is this. I have Atma-Sphere MA-1MKII Silver Ed monos that I bought off Audiogon. All the tubes lit up and they seemed to play just fine. But they won't play high frequencies: roll-off starts around 2 KHz.
Ralph referred me to the support tab in his website, which has instructions for inspecting the output tubes. It turns out that each tube has two built-in filaments that act as fuses. To my dismay, I found that 5 of the output tubes on one amp were faulty.
As I remember OTL theory, each pair of tubes halves the output impedance. If I have 2 1/2 pairs of tubes not working, does this impair the amp's ability to handle high frequencies? Would the answer to my problem be as simple as getting some replacement tubes?
Thanks.
Follow Ups:
FYI.
Credit to Brian Walsh.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
I believe the mystery is at least partially solved. The tube situation was far worse than I thought. Of the 41 total tubes sent to me by my Audiogon seller, 29 tested bad (no conduction in one or both sides of the tube) with the tube tester. I don't have enough good tubes left for even one amp.
Since the tubes were sent separately, I have no idea how many bad tubes I put randomly in each amp. I thought (by visual inspection) that I had 5 good tubes in the amp I did most of my testing on. Turns out some of these were bad also. No wonder I was having trouble.
I'll get some new tubes and try again.
Thanks for all the info...keep it coming..
I gess we now know were the highs went...the amps must have been runing on just what... 4 of the tubes....these amps are great...not minny amps would even try to work an then would just blow-up...only thing here....it to hot to run the amps.....but just knowing that i have some of the BEST amps ever made by man....it all good.....an i have other things see...
I find that now that i have my ESL runing like i new thay could an should....i feeeeeeeeeeeeel a lot better about most things......goodluck
Edits: 06/16/12
Thanks, TYU. I just thought about something else. You mentioned the heat. I'm wondering about the effect of altitude on impedance. My house is at 7,000' (Colorado); certainly the air load on the panels must be less. Lew has already theorized that humidity might make a difference (very low here). Small effects, maybe, but stuff adds up.
Just kidding, sorta, but the capacitance of your panels must be marginally lower up there in them mountains. Since the multiplier for the dielectric contant of air is 1.00054 compared to vacuum, the lower the pressure the closer you get to 1. When you get to one you will hear nothing :). I did some calculating and it turns out for the 2350 sqin area and abut 0.15 in panel to stator distance, and having the two sides of the push-pull in series, the resulting capacitance is somewhere between 1500 and 1800 pf. which is very closed to the published value. There is also an interesting side observation that if the panel was not push pull there would be an asymmetric distortion with the displacement of the diaphragm, but the push-pull cancels it out, very clever, never thought of it. looking at the panels at high volumes, they move quite a bit, the capacitance is a linear function of the distance, so moving half a distance closer doubles the capacitance, at the same time the opposite side halves, the series value of course is not constant. I have not calculated forces, but because static force on a charge has a quadratic relationship to distance the push pull is nto entirely linear either. I am sure Dr. West has a precise model of the whole thing just for satisfying ones own curiosity, or hell just listens to the damned thing and ignores the mumbo jumbo.
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Edits: 06/18/12
with your understanding of the physics.
In fact, in a few rare instances there have been reports of problems with ESLs at high altitude. Thanks for reminding me why and that it did not have so much to do with humidity as with the density of the atmosphere at high altitude. I heretofore thought Chuck was near Denver, at about 5000 feet. 7000 feet; that's high. But his speakers do work, thank goodness.
Another force in play is due to the tension on the diaphragm and its elasticity, which will tend to make it want to move back away from the stator, after being displaced by the electrostatic force, in either direction. The whole thing is quite complex.
most of it is just being able to search in google, and the very, fading, basics one learned in EE undergrad :). if i gave you the second harmonic distortion resulting from the tensors stretch forces and the quadratic force of static charges then you could be :), but just thinking about what the panel does in a dynamic environment is not very impressive thinking .
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
"the quadratic force of static charges"
I think that's just Coulomb's Law, F = K(Q1*Q2)/r^2, where K is a constant, Q1 and Q2 are the charges on two objects, and r is the distance between them. It's just an analog of the equation for the force of gravity, also called an inverse square law. I remember that from freshman physics at a good liberal arts college. But I am going only on a 45-year-old memory, not Google or Wiki.
Sound Lab is located in Park City, UT. My Google effort tells me that PC is located at 7,000'--approximately the same altitude at which I am operating my speakers.
I agree about the effects of humidity. When I lived in Northern Virginia, there were days I hated listening to my double KLH-9's because of it. They sounded, well, soggy.
I was running them with Futterman-designed 200-watt monos, built (with Julius Futterman's assistance) by Lucius Morris. I wish I still had them. BTW, anyone know whatever happened to Lucius? I have been trying to reconnect with him to no avail.
Back in the early 70s, when I met our mutual friend TL, I owned a double pair of KLH9s, too. AND I owned Lucius' last pair of his home-made Futterman monoblocks, with eight 6LF6s per side. AND I lived in Reston for one of those years and also experienced soggy diaphragms on the odd occasion. I kept up with Lucius for quite a while, but I have not seen or heard from him for at least the last 10 years, probably more. He never gave up on ESLs; he was a major US dealer for Audiostatic, and I once went to his home to listen to their all-out system. But Lucius did give up on tubes and OTLs; he was running the Audiostatics with huge and heavy NRG solid state amps, built in the midwest, now defunct. However, he used to admit to me privately that OTLs were still the ultimate way to go. I have been in and out of KLH9s several times over the 40 years since Reston.
I also had double KLH-9's, TWICE! From 66-70 and from 76-78.
Lucius used to work with Brian Cheney of VMPS, but Brian hasn't heard from him in a long time either. Too bad. A really good guy.
What going on with the SoundLabs ?.....How do sound with the Mod?...have you got the M1 going.?...Love these acoustat 6s...Thanks for your time
Chuck (Throwback) lives in or near Colorado Springs. He used to live in my area. Anyway, he told me privately that his house was in the path of the fire. He and his wife were evacuated, and as of two days ago he did not know whether his house had survived the fire. I would guess that he will know by this weekend. Hold the good thought for Chuck.
He had just been allowed back to visit his house. It was completely intact! A lot of the houses on his block had been burned to the ground....
I hope that his SL speakers suffered no smoke damage. Chuck was fearful that even if his house was intact there would be extensive smoke damage inside. Interestingly, Chuck's daughter had determined via an aerial or satellite photo that the house survived, even before it was confirmed by direct methods. This was last week.
I myself just got power back to my house after 6 days, in near-100 degree or actual 100-degree temperatures. The lack of power was really getting to me. It took about 12 hours for our top floor to become habitable after turning on the AC. Like Tyu said, I wonder what it will take for the naysayers to concede that there is climate change going on. Here we are looking at 3 more days of circa 100-degree high temps. (Truthfully, I am a bit reluctant to run the OTLs against the temperature gradient that my AC has to maintain. However, they are notably cooler with four 7241s per chassis vs six 6C33Cs.)
Wow....that sucks...it always HOT here...but 100-drz to hot for my OTLs...But it Not Fire!....glad to hear you an yours are ok....dont worry to much about the earth it well be here ...as you know way after were gone....if i get 25-30more years... we all...not just them.. well have got the ball good an hot...So be happy....goodluck
Here in balmy Bethesda, MD, supposedly not Calcutta.
Well he is a OTL/soundLab owner....this has to pull some wate with the Fire gods.....good for him...but what well the next fire breing...gOOD LUCK TO ALL in Colorado....
Thanks Ralph
Thanks Lew....
Goodluck to all of us....it just Colorado today.....
Hell of a perice to pay to live in the west....I think i just go drive around in my car....for no good resion...just kill more OZone ..We all NO that were not makeing it hoter...right...looks like about the time i leve this earth we be have ran it in the ditch....
What we rely need is another War!...Men love,s War...Got too right... his.story..
next to the spare tire, just because i like the color :)
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Lew theorized that humidity might make a difference ...As on most thing Lew is right!
Were at about 80% humidity here in fl...i run the Air..but i open the window to get fresh air...my panels LOST 5-6Db in a min...had to push the bias up to get them back to playing....So you are at the top of ESL spl output..good job...cant wate to here about your sound with your MA1...burn in the 6AS7..you get long life..sounds nuts but it a mustThese 48"X9" panels are so eze to work with... all the Acoustat are the next step of the JanZen...KLH...panel type
Look if i am geting the best topend i have ever got out of any esl ...your on top with the some of the BIGest ESL panels ever...you would think all the base output you get with the soundLabs...the high would be rolled down........the highs on the Acoustat stay the same as with one panel...i just add more panels to get more baseoutput...goodluck
Edits: 06/27/12
In a word, yes. The fewer the output tube sections the higher will be your output Z and the worse will be the ability to drive low impedances.
It is not surprising that the impedance of your speakers, and possibly the SPLs you can measure, fall at high frequency. The speaker is a giant capacitor, so impedance is inversely proportional to frequency. I think it is a mistake to make a big deal out of the numbers you are getting. Each pair of our speakers was built at a different time by the factory. SL is known to be constantly experimenting with types of mylar, the frame, the electrodes, the resistive coating on the mylar, etc, etc. Thus each individual pair of speakers may be different from any other, but in small increments. Also, I believe the bias voltage will affect impedance. Further, using your Rat Shack SP meter to evaluate an ESL is fraught with sources of error, due to the directionality of the RS meter vs the relative lack of directionality of the panels and the sheer size of the radiating area. My advice: replace the bad tubes, enjoy the sound (which you told me you were indeed doing), and forgeddaboudit.
Lew,
Coupla things. I measured the frequency response not only with a Radio Shack meter, but with an HP audio analyzer with averaged readings. Approximately the same result.
At the same location, simply replacing the Atma's with an Edge ss amp made a very big difference. Now the response was normal.
That you are driving the SL's with measured impedance less than 2 Ohms at high frequencies gives me hope that my tubes are at fault. I should find that out sometime tomorrow.
Looks like I was facing a couple of problems--bad initial hookup, bad tubes--which have kept throwing me off. Two problems together are more than twice as hard to solve as one problem.
I'm hoping that replacement tubes will signal the end of my difficulties and that I can indeed enjoy my system again.
I sent you an email. If you don't get it, check your SPAM file.
Regards,
Chuck
Altho I do own a Rat Shack meter, I find it worthless for measuring in-room hf response sitting 10-12 feet from the speakers. If you aim the meter as much as an inch one way or the other, the reading is quite different. Therefore, I would be at a loss to tell you that my in-room FR is not rolling off at 5kHz or 10kHz, also because my hearing begins to suck at 10kHz, but I can tell you subjectively that, if anything, the sound is a little brighter vs with the SL toroid. Dr. West might say that this is due to resonance created by the inductance of the AU90 transformer. Perhaps he has a point, but the sound has all the good qualities I could hope for.
Output Tubes 6AS7....
I have had the M60s for years...an i have a pr of Diy,ed MA1...these amps well run fine on the m60 4 tubes pr amp..the MA1 well run with 4 tubes pr amp!....the funny thing is the amps are the most stabel amps i have ever owened....The Sovtek 6as7...are great.. An all the 6as7s you get new MUST BE RAN ON THE HEATERS ONLY FOR i do 48 hrs...24hr well do.....An then thay well last for ever less there over bias.... but i have never lost but two tube in 8years an thay were the only match,et 6AS7 i ever got ....so i just dont get how you can lose tubes....well thay must be over bias,et...
Now as for this ESL mod ...i only have Acoustats but the interfaces are set up like the soundLabes some what ...i have had Acoustats from the 80s an by doing this mod i am geting the best highs i have ever got out of any ESL...even better than the Tube amps Made to drive the Acoustats.....Be for the removel of the res an caps in the primary of the high frc tranfourmers the MA1 coud not give good sound with the Acoustats... now the M60 give all the output i need...go figg..Thanks for your time an post on all the thing you done to you SLM1s...goodluck
Thanks, TYU. I thought the bad tubes might have been the answer, but if you were able to run the speakers with only 4 tubes, well, I dunno. I am still puzzled by the fact that I seem to be getting lower inpedance readings than everyone else.
It doesn't tell much to say that you are getting "lower readings than anyone else", since I am the only one I know who has actually posted data on line. (I believe you posted only SP levels vs frequency on SLOG.) If your readings are lower than mine, it is quite possibly due to the fact that Dr. West was lately experimenting with a new highly resistive coating on the membrane. My speakers were built probably last summer. But anyway, I don't know what readings you are actually getting, so I cannot judge. If you take a look at my data you will see that above 2kHz, even my speakers are 4 ohms and below. One thing that might help, if needed at all, is to reduce the bias voltage below the threshold level recommended by SL. I believe that Z will be to a degree inversely proportional to bias voltage. (I don't actually know this, but it stands to reason, since with no bias V the impedance would probably be infinite.) Anyway, of course first you need to replace those bad tubes, and like Tyu says, run the filaments for several days before applying B+.
Lew,
I sent you a message with these readings and my whole Odyssey to date, but apparently you never received it. I'll try again.
Yesterday, I had a metrologist friend over to make impedance measurements. Configuration of back-plate: no resistors, no capacitor, no inductor, no brilliance control, midrange control +3. The results are below:
Impedance in Ohms
Freq (Hz) AU Black/Pos spkr term AU Black/Neg spkr term
(per instructions)
40 4 9.8
50 5 12
80 8.8 5.9
100 12 4.3
200 23 2.5
400 24 2.2
500 24 2.3
800 20 2.4
1,000 17 2.6
2,000 7.4 4.5
4,000 3.4 4.8
5,000 2.7 3.5
8,000 1.9 1.6
10,000 1.6 1.2
16,000 1.3 .58
20,000 1.3 .46
In-phase hookup shows a more benign load (higher impedance) for the amplifier; but even then, the impedance at the higher frequencies is awfully low for any amp, but especially an OTL.
I found out about the tube problem after I did these measurements.
Regards,
Chuck
I cannot make out what you actually got with what hook-up at 40 and 50Hz, and at 100Hz I got a much higher number, assuming you saw 8.8 ohms (see SLOG), but above 100Hz, your readings with the "AU black pos terminal", meaning I hope that the doublet of screw terminals on one side of the AU primary were connected to plus, are very much consonant with mine as posted on SLOG. (I only took readings at 20, 50, 100, 200, 300, 400, 500, 1000, 2000, 5000, 10K.)
The right-most row of readings are no doubt the result of wiring the treble transformer 180 degrees out of phase with respect to the bass transformer. Mine were very similar; don't use that hook-up.
Right on all counts. I'm sure now that I have it hooked up correctly.
This is the point where I am wondering if the Bass transformer is rolled off by a choke. The readings look very much like the bass transformer is active above the crossover frequency.
Ralph, I believe the bass transformer has enough self-inductance to take itself out of the circuit pretty quickly above 2kHz. It cannot have much effect at all at 5kHz and above. My data suggest this, if I compare the AU90 transformer alone to the [bass + AU90] impedance readings at above 2kHz. With a 1.5mH inductor in front of it, the bass transformer alone gives 60 ohms impedance at 2kHz. Anyway, I am pretty sure Chuck (Throwback) is using an inductor, which is at least 1.5mH in value or higher.
Actually, no: no inductor. It came out clean when I removed the rest of the stuff--resistors, Brilliance Control, capacitors.
But I have to assume that it still represents a load at 20KHz. Have you done any measurements of just the bass transformer at that frequency?
The reason I ask is if there is self inductance, then its impedance should be going sky high if its not influencing the impedance at 20KHz. But all I have ever seen of ESLs is that impedance goes down as frequency increases. That really suggests to me that while the transformer may not be making any output, its still loading the amp and for no good purpose unless you like heat. Am I way off the mark??
You wrote, "The reason I ask is if there is self inductance, then its impedance should be going sky high if its not influencing the impedance at 20KHz. But all I have ever seen of ESLs is that impedance goes down as frequency increases. That really suggests to me that while the transformer may not be making any output, its still loading the amp and for no good purpose unless you like heat. Am I way off the mark??"
Here's the way I think of it, right or wrong: (1) Yes, I think the impedance of the speaker as seen via the bass transformer alone would by "sky high" at 20kHz, but no, I did not measure the bass tranformer alone (with no treble transformer in parallel) above 2kHz, because it was going straight up to the sky already at that frequency. I did it only from 20Hz to 2kHz in log intervals. Did someone else put out some data to the contrary? (2) I think the reason the speaker has a low impedance at very high frequencies is by far mostly to do with the speaker itself and its capacitative nature. So, when the speaker is seen by the amplifier, almost entirely reflected via the treble transformer at high frequencies, the impedance will be very low. The effect of the transformer should be a constant, related to the turns ratio, at all audio frequencies. I think R West himself recently wrote that the speaker is ~1600pF capacitor. (Can't remember, was some number between 1600 and 1900. These capacitances seem too low to me; I thought K Covi calculated the M1 as a 2uF capacitor.) Figure the impedance of a 1600pF capacitor at 20kHz and then divide that by the square of the turns ratio of either the SL toroid (75:1) or the AU90 (90:1). Gosh, I think the result would not correspond to reality, too high Z.
I would not assume that the amp is the primary cause of the roll off. Did you try the speaker with another amp?
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
Yes. Worked fine. In fact, the highs were too much with an SS amp.
It does not surprise me at all that with several dead output tube sections your hf response would suffer, but it is unclear to me whether you are upset about impedance readings or SPL readings. Like I said elsewhere, high frequency SPL readings off a large planar speaker are bad data.
Lew
I started measuring stuff only after my friend complained that my system "had no highs." Measurements confirmed this--measurements that with a different amp revealed a quite linear response. In trying to explain the difference, I ran the impedance curve.
The impedance curve was typical of an ESL. So, if the impedance curve was not wildly off and other OTL's seemed to be able to handle the load, I had to look at my particular amplifier's ability to handle the load.
It was then I discovered that some of the tubes were bad. As you have confirmed, bad tubes in an OTL circuit can really hurt the ability of the OTL to deal with low impedances.
I'll know more after I put in some good tubes.
Cheers,
Chuck
And see if that channel is OK? At least you would know the whole thing works. MAke sure the one complete amp works with both speakers. Then take the full complement of tubes and transfer it into the other amp and make sure it works. Once done you will know a few things :)
dee
;-D
True terror is to wake up one morning and discover that your high school class is running the country.
quote by Kurt Vonnegut
I actually found (just) enough tubes to outfit both amps. I thought I was in fat city because the guy who sold them to me included a number of extra tubes, each lovingly wrapped in bubble plastic. Turns out, most of those extra tubes were defective.
I am going to proceed roughly the way you outlined. I am just curious how the OTL works. What If I had only two tubes. Would the output impedance be outta sight?
For a circlotron output stage, output impedance, Zo = Rp/(2+mu), where Rp is the parallel sum of the plate resistances of the tubes on one phase of the output stage. So you can see that the more tubes in parallel, the lower will be Rp and the lower will be Z.
Lew
I didn't know the formula, but I remembered the principle.
Thanks,
Chuck
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