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CharlieM 4th June 2008 09:34 AM

Carver TFM amps for ESL's ??
Hi All,

Is anyone here using a Carver TFM series amp to drive their ESL's?

I'm almost finished my hybrid ESL project (will post pics soon) and I have a pair of Carver TFM25's for bi-amping with active X-overs. The esl trannys are 100:1 turns ratio. I've read that ESL's are a nasty load and I'm terrified they might smoke my beloved Carvers.

Anyone out there please share your expreriences here...


WithTarragon 4th June 2008 02:01 PM

It's a good question.
I used Carver TFM 15 (100 watt version) on the Magnepan SMGa (magneplanar & not a true ESL). They worked fine. Although when played loud they had some difficulty (they worked better with an Adcom GFA555 at higher levels). Bass was still shy however.

I used the same TFM on my Martin Logan Aerius (hybrid ESL: a closed box woofer with a ESL crossed at 500Hz). The TFM was fine at low levels, but the sound was not great at high levels (ultimately, I preferred my Adcom GFA 555). The issue about the dependence on level, is not entirely the fault of the amp, the martin logan aerius itself my have problems at high levels (loss of an "effortless and dynamic sound").

I think part of the problem folks have is that there is never enough bass (unless the panels are huge) and there are also serious headaches trying to get these properly positioned in the room. Consequently, some try to fix the problem by swapping amps.

I would not worry about harming the amp, the power supply & output devices are probably up to the task, unless the impedance really drops or is played really loud. I think the sound would distort sufficiently to give you ample warning.

moray james 5th June 2008 08:06 PM

The more the better...
Charles give the Carver a try and see that's all you can do. With ESL's the general rule of thumb is the more ouput deviced and power supply you have the better. That said there are always exceptions to the rule (kind of) and different people have different expectations. I once ran a set of Eros panels in a hybrid set up with a pair of Antique Sound Labs Wave 8 mono blocks on the panels and they sounded very good and played a lot louder thann you would guess. So give the Carvers a try. When is ETA for lift off?

CharlieM 6th June 2008 02:45 AM

ETA for liftoff?
ETA for liftoff is not real clear right now. The kids are coming to spend their summer vacation with me so I expect the project will likely be delayed some more. The good news is that (except for some EQ components) I have everything needed to finish the project. One of the boxes is completed and the other one is almost done.

I haven't started on the esl panels yet but I have all the components. I still have to build a shelving EQ to compensate the dipole rolloff but that can be done after blast off. The perf metal I got from Russ looks to be about 50% or so open area with small enough holes that I should get max efficiency with 1/16 foam tape spacing. Still, I wish now I had designed for larger than 12x48 stators (effective driving area will be even less) Sanders' book recommends .070 minimum stator/diaphragm spacing so I also ordered some .013 double-sided tape which can be added to bring the spacing to .075" -- I still have to decide on .062 or .075 spacing. I won't be crossing over real low so I shouldn't need a lot of spacing but there will be those 10" woofers thumping in close proximity, which may tend to drive the diaphragms into the stators. Also, I need to figure out whether to tension the 6- micron diaphragms mechanically (somehow) or by heat-shrink or some combination thereof.

I'm really flying blind on this project because I've only ever heard an esl play once for a few minutes at low volume level and I don't have a feel for how much SPL can be produced by a given surface area. I've never been satisfied with the bass from any speaker I've ever owned (volume was ok but they've all sounded either boomy or somehow colored). I've never heard a TL speaker before but I'm expecting some very clean uncolored bass from this one-- my only concern is how well it blends and whether or not the esl panels are large enough to produce a decent SPL. I listen to traditional jazz, not rock, but I do like to crank it up on ocassion. If the panels are adequate, power should be adequate too: woofers and esl's will be driven separately by a pair of Carver high-current amps (225W/ch into 8 ohms or 450W/ch into 4 ohms). No matter what they sound like, I don't think I could muster the time and energy to do it over again.

by the way, it's good to hear all of you here!


moray james 6th June 2008 03:49 AM

not to worry...
Charles just so you know the active driven area on an Acoustat panel is 6.75 x 43 inches so that's 290.25 sq inches. your panel is 12 x 48 inches so that is 576 sq inches. So your single panel is almost the area of two acoustat panels which make up a set of 0ne plus 0nes. The 0ne plus 0ne playing full range can play loud by most peoples standards and since you are running limited bandwidth you are laughing. The Acoustat's have a stator spacer of about 1/16 inch so you dont need more than that and could do fine with less. Slow and steady will win the race. Do a good job on the panels that is important.
Had I known before that you were planning to coat your own I would have strongly advised against that as an option. Not to say that you cannot make a safe working set but they will not be as uniform nor as well insulated nor will they look as good as if you had had Russ do the coating for you. Further Russ's panels would come with a warranty and yours now do not.
I am not trying to pick on you I just want to take this opportunity to remind others that coating your own perf metal stators is not as simple as it seems and most powder coaters will not do a much better job (aside from cosmetics) than the average DIYer will. You only get one chance to powder coat and if you mess it up you throw the panel away and start again. Spray cans rollers and brushes are a pita. Some folks have had success with a base coat of latex then a bunch of urathane top coats. Wagner may have suggestions in his book. Perhaps others here can comment on what worked. Even if they work don't go showing folks how safe they are by putting one hand on the back stator and one on the front while playing loud music. That's why I recommend a recognized pro coater do the job or simply use insulated wire stators. These things can kill.

CharlieM 6th June 2008 09:32 AM

Coating the stators
Thanks for the info on the Acoustats - - that's a relief.
About coating the stators, I'm pondering the following options:

Option 1:
Roll on multiple coats of latex house primer, then spray overcoat with a semi-gloss black Krilon or equivalent. Can possibly spray apply the latex primer if it has a sprayable viscosity.

Option 2:
Spray apply multiple coats of an automotive 2-part polyurethane primer and/or clearcoat, then overcoat with semi-gloss black Krilon.

Option 3:
Find a powder coater to double-coat the stators.

In any case, I will place the smooth side of the perf's toward the diaphragm and I won't use any coatings containing metallic oxide fillersm which might be conductive. Practically all black paints are colored with carbon-black, which is probably conductive, so I would only use black paint for the final topcoat. I do have an air compressor and spray guns if I opt for an automotive polyurethane. Too bad that paint manufacturer's don't show dielectric properties on the container labels-- I will research that to the extent that I can.

Any further advise is appreciated!

Calvin 6th June 2008 11:06 AM


I would recommend not to use Krylon in black since Carbon black is one of the ingredients. So the stuff is conductive and you won´t want to have a conductive surface on your stator. Slightly dissipative ok, but not conductive! Very probabely the resistance against track buildup will be low too.
Apart from safety aspects such a conductive layer as top coat tends to ´explode away´ when a flashover occurs. Looks funny hen you have a basecoat of different color ;-)
If you want to use it though you have to encapsulte the ´conductive´ layer with a thick layer of eg. clear PU.

For Diy I´d recommend a modification of option 3.
Find a coater that powdercoats the sheets as thick and even as he can (100µm will be alot here already). A good powder is Rilsan and alikes.
A double coat with the first layer preferabely in white (or pure) and the second layer in the color of your choice -even black, but check the datasheets of the powder suppliers first!
Add to this a a rather thick clear wet coat of common PU laquer (used for staircases or naval applications) with at least 4 layers on each side (turning the panel 90° with each new layer, holding the spray nozzle ~45° tilted toward the surface to really get a thick coat over the edges of the sheet´s holes). It takes a lot of time and you waste much of the laquer (5-10L), but the result is a nice even thick and (!)safe(!) coating even if the sheets have not been sanded before.
This way the surface of the coating becomes the nicely rounded soft look one knows from ML panels and the panel is safe to touch (when all steps are really carefully and properly executed!)

Such a 2-material compound coating is probabely the best one can have for metal sheet stators.


CharlieM 6th June 2008 01:14 PM

I read somewhere that you would have to touch both stators at the same time to be in danger of electrocution. Is that true?

If that's the case, my beam-splitter cabinet design would allow completely isolating the rear stator with barrier screens attached to the side openings behind (and on each side of) the esl panel-- you'd have to see the design to follow me on this but I can make the rear stator inaccessible to touch with no problem.

Would isolating the rear stator eliminate the hazard?

moray james 6th June 2008 07:48 PM

What matters is where ig goes...
you can get a shock from either stator if the dielectric fails and you touch it there. If you have one hand on either stator and the insulation is too weak then you will receive full potential straight across your heart. That's tha part that you want to avoid.
If your insulation job is a good one then there will be no shock hazard at all the key word here is "if".
So perhaps you are starting to get some appreciation for the quirks of insulating perf metal. Mil spec insulated wire is tested and almost perfect (nothing is perfect). But you are where you are and I don't suppose that you have extra panel to experiment with? I would have Russ get his coater to do the job for you but that would be my choice. And people tell me that making wire stators is a pain. Well I guess it all depends upon your point of view. Calvin has current hands on with the newest dielectrics so his advice would be good.

CharlieM 6th June 2008 11:40 PM

revised coating options
Moray, Calvin... you guys are a great asset!

I live alone (no kids in the house) and I will be using grills on the speakers so the shock hazard is minimized.

Russ would have sold me ready made panels cheaper and no doubt better than I can make them myself but part of the DIY attraction is the learning and the doing-- otherwise we'd all be opting for Martin Logans, right?

Calvin-- thanks for the tips, especially the non-conducting topcoat. I do have some spray painting experience so I may go that route after weighing cost and hassle of powder coating. I've now revised my options as follows:

Option 1 (can't do at home):
white powder coat + black powder coat + polyurethane clearcoats

Option 2 (can do at home):
black basecoat + 10-20 mils 2-part automotive polyurethane clearcoat (using a fast catalyst, all coats dry-sprayed and allowing gel-time between coats-- all to facilitate buildup on sharp edges)

Feel free to critique !!

Calvin-- can email pics of the one cabinet that's finished if you like-- cant figure out how to post them here.


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