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SoundLab tranfourmer MOD

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Posted on April 17, 2012 at 15:32:09
tyu
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Posts: 963
Joined: April 19, 2011



Lew
Can you post your great Mod that you have put in your SoundLabs..An give your input on the sound...
I Did this Mod some years back with the Acoustat 121 stepup transfourmer setup.. Dr West...put the crossover in front of the low fre transfourer...An just left the caps in his MIXer....The New Fullrang Tranfourm on the SL topend... look like better sound...
This place is Dead but.... the info well be good for all OTL tube amps owners....
thanks







 

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RE: SoundLab transformer MOD, posted on April 18, 2012 at 09:52:07
Ralph
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Location: Minnesota
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The 1st drawing is the Acoustat. The 2nd is for Sound Lab.

The mods seem to follow two pathways. One is to remove the resistor as seen in the second drawing, along with the inductor, and change the cap value to 15-22uf. A lot of people remove the Brilliance control entirely.

The second path is to replace the HF toroid entirely with a new one that comes from Australia. So far from what I have heard with this mod there is no crossover at all for the HF toroid, but I suspect a cap of the right value in series with it will help out.

Either way the speaker is a lot easier to drive! Not only for OTLs, but people with transistor amps have reported the same thing, and in all cases it sounds better. Its not hard to see why- that resistor as shown in this example is a 40-watt device (some versions have 80-watt power ratings). It has to have that kind of power handling to survive- and the power to heat it comes from the amp. Take it out and the amp does not have to work as hard; sound quality is improved at all frequencies as a result.

The only issue with the 1st pathway is that the HF toroid should not have low frequencies applied to it else it could distort due to saturation. That is easily solved by simply decreasing the cap value, which has the added benefit of greater transparency. In some cases the cap is easily decreased as there are several in parallel and one can be simply cut out, in other cases the cap has to be replaced outright.

 

RE: SoundLab transformer MOD, posted on April 18, 2012 at 10:59:31
tyu
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Posts: 963
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Thanks for your input on the Sound of this type of setup Ralph....
I posted diff ESL tranfourmers setups years back as i had a pr of SoundLabes A1s..
After owening Acoustats for years an then going to the A1s it was a Dead short...for most of all the tubeamps an even the Krell KSA 250 i have...It never sound like a otl but the A1s were old ...An sounder funky
Anywho...I pull all the crossover out... An pull the center tap off the earth an the bias 0 of the high an low tranfourmers .... An grounded one end of the tranfourmers secdary winding to only the bias 0 ...Same end on bouth high an low Tranfourmers....So this mint the back stater was at the bias 0 only no earth just the bias 0....An then driveing the full winding on just the front stater...You no were the coating an bias are.....Less phase-shift...an got the best sound ever an was lot ezer to drive...lot of fun....But some one had too much money ...so i let him have the A1s for some of it ...There Still a lot of work to be done with ESLs
An OTLs....goodluck

 

RE: SoundLab tranfourmer MOD, posted on April 18, 2012 at 12:29:56
Lew
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Location: Bethesda, Maryland
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I cannot take the credit for this mod, although I was yearning for some way to get where I am now prior to learning about it. I was contacted by a guy named Will, whose posts on this subject can also be seen now on SLOG. Will and I used to contribute on the old SLOG site, but I had not been there for years, nor had I been in touch with Will. Anyway, Will announced to me that he had discovered a full-range ESL step-up transformer made in Australia (Will is Australian)that he was using to substitute for the Sound Lab toroidal treble transformer. The beauty of it is that because this is designed to be a full-range step-up (with a 90:1 turns ratio), it can be used in parallel with the SL bass transformer in the total absence of any actual crossover parts. (Before you ask, let me say that Will tried using the AU transformer alone to drive the SL panels; the bass was grossly deficient that way; you need the two transformers.) I did not believe the parallel set-up would work so well at first, because I guessed (wrongly) that operating the two audio transformers in parallel would result in a low input impedance that would be less than ideal for OTL amplifiers. But, as the story is told now on SLOG, I made some impedance vs frequency measurements using either the SL toroid or the AU full-range EI type step-up, and I proved to myself that there is no actual problem; the impedance is quite favorable for an OTL amplifier. At this point, it is as simple as (1)buy that step-up from Australia, (2) remove the SL toroid, the capacitors in series with it and the resistors in parallel with it, and (3) install the AU transformer directly hooked up to the pos input of the speaker, in parallel with the OEM SL bass transformer. You must take care that the AU transformer and the SL bass transformer are in phase; the leads are color-coded to help you figure that out. And you are good to go.

As Will is fond of reminding me, I still have the 1.5mH inductor from my old crossover, in series with the bass transformer. Based on his and one other person's results, that probably is not needed.

There is one more tweak that has not been mentioned. As you know, the mixer box places small value capacitors in series with each arm of the secondary of the treble transformer. It took a lot of work, but I have upgraded the quality of those capacitors; I found 8kV .01uF Russian milspec teflon film caps for sale on eBay. They are huge and require a lot of insulation, but they sound a whole lot better than whatever SL used in the mixer box, the "pie'ce de la resistance".

 

RE: SoundLab transformer MOD, posted on April 18, 2012 at 12:33:22
Lew
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Hi Ralph,
I hear that the Sound Lab display with speakers driven by MA1 amplifiers won some sort of award at CES. Did you "tweak" the backplates on those speakers (by altering the crossover in ways you discuss here)? Inquiring minds want to know. I am guessing you did.

 

Addendum, posted on April 18, 2012 at 12:42:41
Lew
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The 90:1 step-up transformers are made by Rob MacKinlay in Perth, AU. You can find directions to his website over on SLOG. Ironically, he had dropped these transformers from production in favor of using a pair of transformers dedicated for bass and treble, respectively. I bought his last pair, and they were used. As a result of the new interest, he geared up to make six more pairs. These are now already spoken for before they are even built. If enough more SL/OTL owners are interested, I am certain he will make more of them. Cost about $600/pair.

I messed around with Rob's new treble transformers as well. They have a 100:1 step-up ratio and can go about an octave lower than the SL toroid (to about 300Hz). This is a useful improvement, since it takes the crossover out of the most critical midrange. These EI types also do not need that power-sucking resistor in parallel with the primaries as does the SL toroid, a huge advantage over the toroid. I installed them in my friends pair of U2PXs with a low value capacitor in series to effect a 300Hz hi-pass filter (based on my Z vs f measurements, he only needed 8uF). He is quite happy with that. If cost is an object, Rob's treble transformers are less expensive than the full-range ones, and there would be no wait to get a pair.

 

RE: SoundLab transformer MOD, posted on April 19, 2012 at 09:45:14
Ralph
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That was 2011, 'Best Sound at Show', using MA-1s and stock SL.

I tried to get the mod installed for 2012 but no dice to my knowledge. This year there were problems with a music server in the room as well.

 

RE: Addendum, posted on April 19, 2012 at 10:02:21
Ralph
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So- in a nutshell- Rob's new transformer is simply a better sounding transformer?

 

I would put it this way..., posted on April 19, 2012 at 19:39:56
Lew
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in addition to the huge improvement in the impedance curve and the major increase in efficiency, it also sounds better. But the reason it sounds so much better certainly has something to do with the huge improvement in ..... etc.

Actually, at frequencies well above what formerly was the crossover point (ca 550Hz), the treble does also sound better (more extended, more coherent, more inner detail), so it may well be that I am liking the AU transformer per se better than the SL toroid.

 

Ok since it comes up here and there :), posted on April 22, 2012 at 18:27:55
Penguin
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I talked to a few people, exchanged emails with Rob, and he needs a minimum of four pairs to make another build. I am interested in finding people who want to try it. I also talked to Brian Walsh, and he said he knows one more nutcase who is interested in trying the transformers. I asked him if he would act as a central receiving and shipping point, so people would not feel strange about laying out the moneys for shipping and the goods. Brian is an established entity and his trustworthiness is beyond any questions. So with all of that mumbo jumbo, here is the deal: The trannies are now 377 $AU apiece...you know, interest and material cost increases, and other factors drive the prices. Rob wants a 20% deposit to start the production run. He takes credit cards. He could bulk ship them to Brian who could forward them to the lunatics who want to mod their speakers. Brian also expressed his concerns, since he is an SL dealer, that this mod is by no means condoned, or covered by SL, so if you burn down your speakers, or backplates it is entirely your liability, and nothing is covered by SL. if repairs have to be made to one of these speakers it is not clear, that SL can or is willing to make any repairs to any of the modified parts.

Now beyond all the scare and warning, i have modified my backplates extensively and working on them is not a very complex thing, so i am confident that most lunatics who are willing to take out portions of the backplate, replace transformers, etc. are comfortable doing so.


So let me know if there are any takes, send me email through the asylum mail :)


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

 

RE: Ok since it comes up here and there :), posted on April 25, 2012 at 08:19:50
Ralph
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I thought the term was 'inmates'? :)

 

RE: SoundLab transformer MOD, posted on April 25, 2012 at 13:24:17
tyu
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Well i have move the Soundlab an the Acoustats Transfourmers around...So i dont think this ONe tranfounmer is the ONLY one to work in this Mod?
There a lot of good Toroideld fullrang stepup out there....at the same $$ or less...theres better topend with toroids....MratinLogen moved on to them....thay do sound better!
I like any mod that gets better sound out of ELSs an Makes OTL work better on them....so why not go althe way...a pr of Eslsell for over $10k
OTL to drive them is over $10K...$1k worth of tranfourmers if this works the way some say....What the fear...thay well work in any other ESL for ever...What am i mising here..goodluck an thanks for all info



 

RE: Addendum, posted on April 26, 2012 at 09:18:34
KIS
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Lew

I have tried Rob's 1:100 transformer the way I now hook up the 1:90 transformer.

There is no need to use any cap even with the 1:100 transformer.

I prefer the sound of the 1:90 transformer.

Also tried out of phase and in phase on the 1:90 transformer. The difference in sound is subtle, despite your measurement saying otherwise. It will work, but in-phase is what I have them at now. No problem in letting the masses try in and out of phase connection of the Au transformer.

Will

 

RE: Addendum, posted on April 26, 2012 at 12:16:04
Lew
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The "masses" can do whatever they want. All I can say is that the impedance goes way low when the two transformers are 180 degrees out of phase, which is not so favorable any more for our OTL amplifiers. I don't have my data in front of me, but as I recall the impedance was 4 ohms-ish and lower across the bandwidth. Also, Ralph had the idea that there would be some unwanted heating of one or both transformers. Apart from that, the out of phase hook-up might actually be favorable for the usual SS amplifier.

Only other thing: I am pretty sure that Rob himself told me the 100:1 treble transformer would not be comfortable unless rolled off on the low end at about 300Hz. Whether he meant categorically to say that it is necessary, I do not know. Anyway, I too prefer the 90:1 full-range transformers.

 

RE: Addendum, posted on April 26, 2012 at 12:39:12
KIS
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"Also, Ralph had the idea that there would be some unwanted heating of one or both transformers."

No heat experienced. I was monitoring that.

"Only other thing: I am pretty sure that Rob himself told me the 100:1 treble transformer would not be comfortable unless rolled off on the low end at about 300Hz."

Tried it without the cap, did not experience saturation, so why put it there? Borrowing a line from you: "the cap can not ADD to the transparency, can it?"

Theorised as much we want, but the prove is in the carrying out of the experiment in real time.

 

RE: Addendum, posted on April 26, 2012 at 13:42:00
Ralph
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The cap *would* add to transparency *if* it helps the new transformer in some way to not have the lows moving through it. It might also help as it might help the overall impedance to be higher, which would result in less distortion from any amplifier. That would translate to smoother/more detailed.

 

RE: Addendum, posted on April 26, 2012 at 16:44:07
KIS
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Ralph

With all due respect, I heard it and you did not, therefore the comment.

But I see your theoretical point of view.

Will

 

RE: Addendum, posted on April 27, 2012 at 09:12:28
Ralph
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I agree you heard what you heard- no argument there.

What I am saying is that the road may not have ended there- if the impedance can be further raised at high frequencies the door would be open to lower powered amps and lower distortion out of higher powered amps.

In the old days (pre-toroid), you could drive a set of A-1s with 60 watts with no worries. I am wondering if all this work could make that happen again.

 

RE: Addendum, posted on April 27, 2012 at 10:16:23
KIS
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Your mention of having a cap in the signal is a two edge sword. Very similar to my experience below:

Years ago, I went down the part of cutting off bass below 100 Hz on my Quads ELS and adding a Sub-woofer for everything below 100Hz. Yes, the system sounded better with bass on a macro level, but suffered in the micro level - meaning that the beauty of the Quad midrange is loss by adding a cap in the signal path.

I tried all types of caps, but none made my Quad ELS sound anywhere close to how it can sound without a cap.

I preferred playing my Quad ELS full range (despite amplification and SPL down sides) and matching my subs to the natural roll-off of my ELS. I have since moved on, as it has its compromises.

Very similar argument to what you had proposed. There are upsides and well as down sides of using capacitors. For me, capacitor sounds too obtrusive and should be avoided where ever possible.

Anyone who persist with ELS (and its many shortcomings) are in it for low level detail and its magical midrange, so I doubt your suggestion of a cap is a long term answer for this group of people.




 

RE: Addendum, posted on April 27, 2012 at 10:36:16
Ralph
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Yes, I have had the experience with the Quad as well.

My point though is that you are also involving the amplifier, and all amps make distortion. Due to the ear's masking principle, the presence of distortion can mask low level detail- detail that can indeed be transmitted by a cap if executed properly.

So- the idea here is to see if the impedance can be raised (thus reducing amplifier distortion) by examining the way the bass transformer and the new transformer interact at frequencies above the 'cutoff' of the LF transformer. Maybe its not a concern, but it may well prove worth looking into.

 

RE: Addendum, posted on April 27, 2012 at 12:03:35
Lew
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Don't know about the Quad 57s, but the 63s have a wretched 220uF bipolar electrolytic in series with the input. All those lovely sounds are going through that horrid capacitor, which is in parallel with an equally lo-fi sand cast resistor, to form a filter which I gather protects the speaker from low bass transients OR is needed to equalize the frequency response. Ironic.

 

RE: Addendum, posted on April 27, 2012 at 12:14:02
Lew
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When I installed the 100:1 treble transformers in my friend's U2PXs (formerly my own U2s), I inserted an 8uF film and foil polystyrene capacitor in series with it, which in conjunction with the 70-ohm impedance I measured at 300Hz (across the 100:1 transformer in isolation from the bass transformer) was intended to create a hi-pass filter at that frequency. Based on what you say, I will de-install it next time I get a chance. I was only following recommendations from Rob.

 

RE: Addendum, posted on April 27, 2012 at 12:22:51
tyu
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KIS..You have it right...Thanks for your input... Less is more with ESl an OLts...well any tube setup...But your are left with the socalled...MIXer...That eats power an dropes SPL buy a good 3-4db...MartinLogan setup... That i have moved onto....from Acoustats An soundLabes May in the end be on the right track...with this type setup...For fullrang...an in the clx thay ran two way...one panel for highs an a flat one for mid-base...sounds better too me...Than any other.... an i can get great SPL out of 60 tube watts.....goodluck

 

RE: Addendum, posted on April 27, 2012 at 18:35:50
KIS
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With the 57s, they have a 1100pF to roll of the bass.

Remove this cap, and depend on the natural roll off. They sound better this way, but less SPL obviously.

Alternatively, use an air capacitor here. It is as good as having no cap IMO. You can not do this with the 63 and that is one of the reason why many still prefer the 57s. The original 1100pF cap in the 57, is not as bad as the 220uF cap found in the 63.

 

RE: Addendum, posted on April 27, 2012 at 19:10:40
KIS
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Tyu

I need to get use to your writing style, but you are worth deciphering. Most time I am only guessing at what you are trying to say.

With the implementation of the Au transformer, we can do away with the Soundlab cross-over entirely. This makes the current PX model probably more efficient than your beloved CLX.

As for the mixer cap eating away efficiency, I am not sure how the 0.015uF cap in series with the secondary high frequency transformer can eat away 3-4dB in your thinking. I doubt this, but I am not a trained electrical or electronic expert, so I will listen to your explanation.

Seeing that you have a vast knowledge on ELS and electronics, what are the consequences in removing the mixer altogether? What if I just hook up the two transformers together in parallel to drive one full range panel. What are we up against? Can we design transformers that can handle this?

I know there would be a lot of cross talk, but at lowish volume, it must sound quite exquisite. What sort of damage am I risking?

 

RE: Addendum, posted on April 27, 2012 at 20:38:23
Ralph
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There's gotta be some point where if the two transformers have different ratios, they will load each other and both would get warm if they are tied to the same load. Right now that's not a problem.

I've had the idea of a single transformer that does the whole thing for a while but never did anything about it. You wonder how far you can push this stuff. I think it would be neat if a speaker like the A-1 could be driven with lower-powered amps. That is likely going to mean that the impedance get no lower than 4 ohms at 20KHz.

 

RE: Addendum, posted on April 27, 2012 at 21:13:55
KIS
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Ralph

I am not a keen small amp believer went it comes to ELS speakers.

As you may well know, more tubes in parallel means lower impedance (if all things remains the same). Even with transformer coupled ones, it makes winding the OPT an easier task.

20kHz is not near high enough. To get really airy highs, a minimum target is 25kHz.

I do not know of any ELS that does not drop its impedance to 1 to 2 Ohms at 20kHz.

Coupled with your (and my) love for zero feedback, small tube amps is but a dream IMO.

Can 1500pF be wound into the secondary of the high frequency transformer? I believe that even 500pF is enough.

Lew, did you measure the Au Transformer secondary winding capacitance?

 

RE: Addendum, posted on April 28, 2012 at 05:51:54
tyu
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Here it is Ralph has hit it....

There's gotta be some point where if the two transformers have different ratios, they will load each other and both would get warm if they are tied to the same load. Right now that's not a problem.

It When you tie the tranfourmers togather...this is a Problem.. the caps can be what ever....... you lose output in the paraleling of the secdary of the tranfourmers... that cant be over came!....jUST One tranfourmer ..If it was as big as the A1s...maybe?
KIs

What if I just hook up the two transformers together in parallel to drive one full range panel.

No....You need two tranfourmers that are the same..then run them like the ML CSLs setup...Look you may only get the speakers to go down too. 40-50hz...but the gains are well worth it...well to me anyway...

An for what i know about ESL... it just hands on...if i have not done it.. an heard it ...I wont post about what i think.



..The ML setup is the only way to over come this that i see....look i have Acoustat an about 5 pr of ML here an i have redone all the panels it a must....ML makes Big money of saleing panels...thay are set up to fail....thay feed the bias only on one side..i run new bias feeds an the panels come alive... I got out of the SL A1...I new i would spend big money if i keep them.
But i am not in to anyone ESL...thay all work the same...one thing i do Know there a lot of room to get better sound out of the SL an other ESLs the bias is one place i would start with the sound lab.. a better bias tranfourmer would go a long way at geting better sound ...
goodluck..An thanks for any input on geting better sound

 

Very interesting ideas, posted on April 28, 2012 at 08:40:24
Lew
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Tyu, I like your idea of paralleling identical transformers, e.g., two of Rob's 90:1. As you suggest, however, the extreme low bass might suffer. One can only find out by trying. Will has the cojones and the wherewithal to do it.

You also mention a better bias supply. As Rob also manufactures and sells bias supplies for ESL, I wonder what you have in mind. What would define a "better" bias supply, compared to that which SL uses?

 

RE: Addendum, posted on April 28, 2012 at 18:32:51
KIS
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Thanks for your great insights Tyu.

Like you, I do not speak about things that I have not heard or tried. Theories often can get unstuck when it comes to reality.

ML set-up:

Having two transformers that are the same would require filters (resistor, cap or inductors) in the signal path to get the frequency response right. More filters less sound.

SL set-up:

Now we have come up with a solution that can do away with all the filters on the primary side of the transformer - which is a big plus. The only filter now is in the form of a small value cap (0.015pF) in series with the two legs of the high frequency transformer.

Lew has already used a 0.01uF teflon cap here instead of a 0.015uF cap without any problems. I will be using 0.0075uF teflon.

Comparing the above two filtering set-up, isn't the SL one less obtrusive now?

Big value cap and resistor is more damaging than small value cap and resistor - all things being equal.

Also I suspect that at 8kV the cap on the secondary is also going to be less obtrusive.

Like you already said, the ML set-up have to give away the low bass which the SL can do easily with its multi-tap monstrous bass transformer.

Will

 

Stand corrected, posted on May 4, 2012 at 13:04:44
Penguin
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Inmates....


But Ralph, have you thought of designing a tube amp that could drive the panel directly? Say 100+ watts no transformer, and enough voltage swing?


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..., posted on May 4, 2012 at 13:43:22
Ralph
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The voltages involved gives one pause. That's why you only see such amplifiers integrated into the speaker itself (where no-one can touch it), like the old Acoustat.

 

Lots of room , posted on May 4, 2012 at 13:56:59
Penguin
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Where the backplate goes :)

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

 

Now THAT... , posted on May 4, 2012 at 15:16:20
Lew
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would be fantastic, Ralph. Hint, hint.

 

Has anybody tried these?, posted on May 4, 2012 at 15:39:53
Penguin
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Site claims it works with soundlabs.... although the swing is only 3000 volts and the bias is adjustable to 5000 volts. I think the soundlabs use higher bias voltage...
True terror is to wake up one morning and discover that your high school class is running the country.

quote by Kurt Vonnegut

 

Soundlab is harder, posted on May 4, 2012 at 21:13:29
KIS
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Firstly the voltage is the highest of the lot.

Secondly, it is a one panel ELS.

Please remember why we have so much bass when the others struggle. The bass transformer has more turns than the High Frequency transformer. So the two transformers actually acts sort of like a RIAA section.

One transformer, one panel when driven only have highs and no bass.

If we go direct drive, we need some form of mixer, or crossover network.

The biggest problem is that a direct drive amp is almost illegal to sell. The only way to do it is a DIY Kit with very limited liability - maybe.

Unlike ordinary amps, we can touch the speaker cables and not get electrocuted. With direct drive, touching the speaker wires will kill.

 

RE: Soundlab is harder, posted on May 4, 2012 at 22:31:32
Lew
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Ralph has given a lot of thought to this problem, and I have not. So I leave it to Ralph to comment definitively, but the SL panel is no different from any other full range ESL in that it behaves like a giant capacitor. Thus the impedance is very high at low frequencies. Parameters like mylar to stator distance, bias voltage, size of the panel, etc, all affect the "size" of the capacitative load, but this is why we need the two transformers in parallel or the SL bass transformer alone to get adequate bass response from an A1PX or the like. Direct-drive amplifiers can be designed so as to produce more "drive" or power into bass frequencies and to gradually reduce the drive as frequency increases, so as to deliver power as an inverse complement of the load presented by the speaker. I am sure this is what Acoustat did back in the day; I KNOW that is how the Beveridge dd amplifiers work. So a "crossover network" as we know it should not be necessary. However probably there is some sort of filter that must be built into the input stage. Not as damaging as a conventional speaker crossover, because very low values of capacitance could be used, therefore of very high quality. Ralph?

 

If Ralph Builds One, I am on the queue nt, posted on May 4, 2012 at 23:36:55
KIS
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nt

 

RE: Soundlab is harder, posted on May 7, 2012 at 12:20:51
Ralph
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Sheesh. You could do a filter, or do something in a feedback loop, although I imagine that latter would be eschewed by a number of the crowd here :)

 

Dear Ralph,..., posted on May 7, 2012 at 15:32:39
Lew
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Was my thesis above basically correct?
If so, I guess it is a trade-off between small value caps in the signal path (and the dangers of very high voltages) vs transformers in the signal path. This is a familiar dilemma, encountered at many junctions in the audio chain.

 

more or less, posted on May 8, 2012 at 10:27:02
Ralph
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You don't need coupling caps if you are doing a direct drive amp- you can obtain the bias from the amp itself. But- what a scary thing to ever have to go near!

 

Used to work with old TVs back in the early eighties..., posted on May 8, 2012 at 17:20:27
Penguin
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There were some scary voltages in there :) Made you numb for an hour or two...


dee
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True terror is to wake up one morning and discover that your high school class is running the country.

quote by Kurt Vonnegut

 

RE: more or less, posted on May 8, 2012 at 20:24:17
Lew
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Perhaps I did not make myself clear; I was speculating that one might use some sort of RC network at the input, to contour the response curve of the direct-drive amp so that it would complement the response curve of the ESL. I was not thinking about coupling caps in the conventional sense of the word.

 

You were plenty clear enough, posted on May 9, 2012 at 09:34:55
Ralph
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The question is really twofold- do you *really* need to equalize, and if so, what's the best way?

But before that you have to sort out how to do the amp in the first place and not get killed. IMO that's a lot more important :)

 

This is hypothetical...,, posted on May 9, 2012 at 11:07:51
Lew
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so lets assume that the amplifier is safe, and we will not get killed. It has been done; I am unaware that any end-user of Beveridge or Acoustat speakers died during a listening session, at least not by electrocution (perhaps someone died in one form or another of ecstasy while listening to one of those speakers, which is not a bad way to go). I am also aware that we now have a surfeit of lawyers in the world, whioh accounts for the dearth of direct-drive ESLs, moreso than other factors.

 

RE: This is hypothetical...,, posted on May 9, 2012 at 12:19:57
Ralph
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Those amps were built into the speaker and caged to prevent shock. I imagine that stuff was a nightmare to ship...

Then the issue is, do you need EQ, and if so, passive or active? Active implies feedback; and I'm thinking that you might be able to tailor the amplifier to have a response that complements the actual curve of the speaker.

 

RE: This is hypothetical...,, posted on May 9, 2012 at 18:39:54
Lew
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I guess you have not been reading my last few posts; that is precisely what I was asking, whether one would need to equalize the response curve of the direct-drive OTL to complement the response curve of the speaker. From the little bit of reading I have done, that would seem to be needed, but I assume it could be done passively. I think there is such a circuit in my Beveridge amplifiers. Well, it doesn't matter much one way or the other; it was just something to talk about.

 

RE: This is hypothetical...,, posted on May 10, 2012 at 09:17:22
Ralph
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I was certainly reading them! The thing that really has had my attention since I first considered something like this is the high voltage, and how that relates to different speakers. Seems to me the SL needs more than the Beveridge, and its different enough that I am not convinced that EQ is actually needed either. I don't see it anyway in the SL as it is now, and direct-drive or not it would be a constant.

Its true that the SL uses 2 transformers of different ratios but I don't have enough data to be able to say that that is actually EQ. If so, it would be rather unpredictable as a lot would depend on the source impedance (the amplifier) and we already know that Dr. West does most of his work with a transistor amplifier. And it is true that the SL does act differently with an amp of higher output impedance (better, IMO) so it does not seem as if EQ is what the different ratio thing is about. But in lieu of another explanation, EQ is a good place-keeper for now.

I was also looking at schematics of the old Beveridge amp. I remember doing some mods on one of those years ago. I never did like how that op-amp thing is set up.

 

RE: This is hypothetical...,, posted on May 10, 2012 at 15:04:55
Lew
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The Bev is different also from any other present day ESL in the way it uses charge; there is no need for a separate bias supply. The diaphragm is low resistance type. Looking at the amplifier schematic (which I do have), I do agree it looks weird and do wish I could get someone to look at it who could update the circuit and possibly convert it to a balanced input. The equalization on the Bevs was needed to compensate for that acoustic lens through which the output of the speaker has to pass.

 

RE: This is hypothetical...,, posted on May 10, 2012 at 15:07:20
KIS
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The two transformers are definitely some form of EQ.

The bass transformer is wound with very thick wires and when they are played full range to drive the whole Soundlab panel, the natural roll of is around the 500 Hz (my ears tell me). There is no highs what so ever.

The mixer does the rest of the EQ work by bring in another transformer to perform the high frequency work.

The above is quite smartly done by obviously varying the turn ratio to give a balance sound.

Without EQ, direct drive amps straight onto the panels would only yield sound without much bass. Similar to vinyl without RIAA.

 

RE: This is hypothetical...,, posted on May 10, 2012 at 15:46:56
KIS
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The lens on the Bev is also an EQ feature to boost the bass I believe.

The Bev is like a horn loaded ELS.

 

balanced input on that would be easy. nt, posted on May 10, 2012 at 20:03:24
Ralph
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-

 

RE: This is hypothetical...,, posted on May 11, 2012 at 06:11:13
tyu
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Well i have had the Acoustat ESL direct-drive OTL amps ....an sold them..for the tranfourmer type setup....now you all are just talking as if this well be the best thing for your soundLabs....this is where i get off...
You still have a lot of work YOu can do... too get the better sound out of your ESLs....but i gess it ezer to look away from the work to....well dreams
It just one thing to the next with most..It just like doing all the MoDs to a OTL.. till it sofar away from where it was in the stock setup no one knows where you are...or what you have.. not even you ....but it GOT to be better...i have done this also but i STOPet....it means nothing...Well it means you always Lost...not for me..goodluck

 

RE: This is hypothetical...,, posted on May 11, 2012 at 10:57:46
Ralph
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Direct-drive amplifiers have never been my cup of tea either! Making the kind of power you need for something like a Sound Lab sounds really scary...

 

RE: This is hypothetical...,, posted on May 11, 2012 at 13:40:10
tyu
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OTLs....ESLs....on paper..look just right..in real life not so much...Amp get Hot as Hell an EAT AC power..ESLs can be Big...there not for eveyone....love to see a 6SN7 criltron preamp setup i could DIy would look like on paper....hint,hint...look it your work so...

ESL are all about there bias...bias bias bias, the way this is setup has a big afect on the sound..One thing i have said over an over is Dr West lets you set you own bias an this is a goodthing... but what dose he have in the speakers.. high V..or Low V tranfourmer ...like 1000v on the secdary side... thin the diodes.. or 300v an how about the Amps of the tranfourmes... i have seen ESL bias Xfourmers that were 1VA....a better one like 1000-1500..Then the doides.. 5-7VA xfourmer sounds way better...An better caps in the bias setup...but most just think well it just bias...better bias can give more output.. an way better base...An sweeter highs i have found...An it a eze fix...goodluck

 

RE: balanced input on that would be easy. nt, posted on May 11, 2012 at 16:28:10
Lew
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The input stage is very complex, to my eyes. But I am not comfortable with SS schematics. I have attached a copy. I have a better one here but it is not digitized. For sure I see there a complex equalizer network.

 

RE: balanced input on that would be easy. nt, posted on May 12, 2012 at 07:58:37
tyu
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Lew i think your looking at about 10kv...to get a Amp for the soundLabes.
It not going to happen...Balanced of not...goodluck

 

RE: balanced input on that would be easy. nt, posted on May 12, 2012 at 10:26:41
Lew
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Tyu, I don't want a direct-drive amp for my Sound Lab. I am happy with what I've got. I've tried to make that clear a few times.

I posted the schematic for the Beveridge amplifier (+/-3200V) for Ralph's benefit. And yours if you are intellectually curious to look at it. The Beveridge amplifier topology is not at all applicable to driving any other commercially available ESL, because they put signal voltage on the diaphragm, not the stators (or maybe both). The Bev speakers have no separate bias supply per se.

 

RE: balanced input on that would be easy. nt, posted on May 12, 2012 at 11:58:08
tyu
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An i thank you for your post an pic....post any thing you have too do with ESLs or OTLs...vary cool

 

I guess there is no interest..., posted on May 13, 2012 at 17:27:15
Penguin
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How do I get four sets together?


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

 

can we get just a tad more to the left in that photo? nt, posted on May 15, 2012 at 12:14:30
Ralph
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-

 

Here you go..., posted on May 15, 2012 at 19:24:52
Lew
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Hope this is better, so you can see the input, I presume. I have no idea why it comes out so small; the file should be identical to the other in all respects. Part of it includes, I think, a crossover and amplifier for the woofer, all of which I will throw away.

 

much better, posted on May 15, 2012 at 19:37:51
Lew
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see here

 

And more better, posted on May 15, 2012 at 19:38:52
Lew
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Here.

 

RE: And more better, posted on May 16, 2012 at 08:31:56
Ralph
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I think you could apply the inverted signal to the base of Q2 using a coupling cap and a series resistor of about 15K. Sure is a lot of EQ in this thing!

 

RE: And more better, posted on May 16, 2012 at 11:43:56
Lew
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Why, I wondered, do they use that series resistor? I had a hunch it is to create a hi-pass filter in combination with a parallel capacitance, but why choose such a hi-value R, when it might be more efficient to use a lo-value R and a correspondingly higher value of C? If you selected a 15K resistor, would you then also halve the value of the R in series with the input of the pos half of the drive signal? (It's 33K, I think. Did not consult the schematic.) Also, wouldn't you have to mess with the ground connections?

 

RE: And more better, posted on May 16, 2012 at 12:22:07
Ralph
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Yes, one of those things that the designer is not around to ask about. You shouldn't have to mess with grounding.

 

Designer = Roger Modjeski, posted on May 16, 2012 at 12:40:33
Lew
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Rumors of his death are exaggerated, to paraphrase Mark Twain.
However, I have heard that he is reluctant to comment on this schematic. He sells upgrades to these amplifiers, or so it is said. In an interview with respect to the history of Beveridge speakers and the writing of a Harold Beveridge bio, Mr. Modjeski was reported to say that this was one of his very first designs and that he and Beveridge parted company very soon thereafter.

Perhaps I can draw up what I think you mean, and you can comment.

 

RE: Designer = Roger Modjeski, posted on June 11, 2012 at 05:23:09
tyu
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Lew an others
Maybe we can move back here....for other so if thay run into the SL mod in tiime... thay can get some info.... or what ever ...
To Me it looks like Jim got it right with Acoustat "befor c mod" as for geting the best output out of the high frc. tranfourmers

But i gess Dr. west an jim were facet with people needing to driver these ESL at full output...so this led to the C mod an the setup on the soundLabs.... like thay gave up the best sound for the most sound output..

look can any one give just a drawing of the SL setup

Some of the best sound so far with the Acoustats.. with this setup..the M60s do sound good..
the 60years old pr of Dynaco MK3s...with the Stock 60years old tubes 6550 GEs...an a 6AN8...this is sweet as honey...an it well drive you out of the room...it louad...best highs i have ever got out of any ESL to date...

So were looking at 6 days i had this mod in an i still have to get up in the morning an see if the sound is still there...may be the output tranfourmer on the MK3 match the tranfourmers in the Acoustats interfaces but it work great...Thanks for any input on geting good sound out of OTLs an ESL....goodluck



 

RE: SoundLab transformer MOD, posted on June 18, 2012 at 09:16:29
tyu
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Well it been 10 good day with this type of Mod in on my Acoustats
so now like lew an some others i am looking at a cap on the input of the high frc tranfourmers primary ....so i put a big 40mf oil cap

This is how it looks on paper...Ralph has to say..

The only issue with the 1st pathway is that the HF toroid should not have low frequencies applied to it else it could distort due to saturation. That is easily solved by simply decreasing the cap value, which has the added benefit of greater transparency.
In some cases the cap is easily decreased as there are several in parallel and one can be simply cut out, in other cases the cap has to be replaced outright.


But then there this truth some of us beleave...
KIS
Tried it without the cap, did not experience saturation, so why put it there? Borrowing a line from you: "the cap can not ADD to the transparency, can it?"

An there more...
Ralph
What I am saying is that the road may not have ended there- if the impedance can be further raised at high frequencies the door would be open to lower powered amps and lower distortion out of higher powered amps.

KIS
Very similar argument to what you had proposed. There are upsides and well as down sides of using capacitors. For me, capacitor sounds too obtrusive and should be avoided where ever possible.

Anyone who persist with ELS (and its many shortcomings) are in it for low level detail and its magical midrange, so I doubt your suggestion of a cap is a long term answer for this group of people.

More yet from Ralph

So- the idea here is to see if the impedance can be raised (thus reducing amplifier distortion) by examining the way the bass transformer and the new transformer interact at frequencies above the 'cutoff' of the LF transformer. Maybe its not a concern, but it may well prove worth looking into

Then Lew
All those lovely sounds are going through that horrid capacitor, which is in parallel with an equally lo-fi sand cast resistor, to form a filter which I gather protects the speaker from low bass transients OR is needed to equalize the frequency response. Ironic.

To me this gets funny that Dr.west would ever do the same thing
Dr.West uses lo-fi sand cast resistor in any ESL....this is moronic
But we all no this....back to My 40mf cap...
well here what it sounds like to me... if you have ever used a good pasive preamp...with no gain... that what i here with nothig in front of the high frc tranfourmer....if the input is at it best you get the best output out of the ESL...so with the cap in...the topend get rolled down.. like 1/2 db...an the cap can sound a little less detail and its magical midrange....
So then i get to looking at all the RF..an other hash that coming in to the ESL...like AM..FM..TV...an others

So i get some help from My old MartinLogans...Thay drop a Zobel in on there High frc tranfourmers all the time.....So i ran a 8ohm 200 watt from just in front of the 40mf cap down though a 20mf polstrine to the Neg input of the tranfourmers...

My ESL have been set up this way for 3 days .....an it sounds like i now have a Vary good preamp in ...an it the best yet...We got get the noise OUT....this is one way of doing it..an it sounds sweet....So if you do use a cap.. this works....NOw i am useing the same 50watt tube amp to drive this.... so it is not eating power with the Cap an Zobel in...With the cap an Zobel in i may be geting a littel more output....If it was less output... it would be the deal braker.....Goodluck

 

RE: SoundLab transformer MOD, posted on June 3, 2020 at 12:53:30






Hello,

I recently purchased a very unique pair of Soundlab speakers that are of a hybrid design, and I believe the only pair made. They consist of a panel for the highs and the mids, and a separate section with a conventional woofer for the lows. The pair are similar to the old dynasty series, but with bigger panels, and a 12 inch woofer for better performance. According to the factory, they were built sometime around 2000-2005, and were custom made for the original owner.

After several hours of listening, I am quite taken with the level of transparency these speakers have and life like scale they present to the listener. The highs are incredibly smooth, and bass response goes quite low. However, there is one major flaw to the sound that I hope can be alleviated. There seems to be a upper midrange suckout, or lack of detail in the upper bass. This is a problem for me because in my view the bass is the very foundation of the music and if lacking in any way, makes the music fatiguing to listen to.

I'm resurrecting this thread in hopes that some of the mods mentioned here might help, and perhaps make the speakers an easier load for my Ma-1's.
Also, I must mention I have a whole lot to learn about what's going on in this speaker, and electronics in general, and hope for some guidance with this project. Attached is a diagram that I made, using a older version I found online, but modified to show how these hybrids are setup.

 

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