Poll

Direct Drive ESL Amplifiers for all

I have ESLs and I would like to explore direct drive
10 (16.9%)
I can do basic re-wiring myself
11 (18.6%)
I need a technician to adapt my speakers
2 (3.4%)
I want to send my speakers for Roger to do it
1 (1.7%)
I want to make my own ESLs
6 (10.2%)
I have made ESLs and need a good way to drive them
1 (1.7%)
I find ESLs fascinating and want to know more about them
15 (25.4%)
I have read DIY articles and toyed with the idea of making some
6 (10.2%)
I think a DIY ESL can achieve excellent sound and is a rewarding project
6 (10.2%)
I have read DIY articles and find them confusing or unclear as to what to do
1 (1.7%)
The drive systems seem poorly conceived in the DYI articles
0 (0%)

Total Members Voted: 26

ESL Independence Day

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Baranyi

Re: ESL Independence Day
« Reply #60 on: 7 Sep 2012, 01:47 am »
Yes with Servo amps.

Roger A. Modjeski

Re: ESL Independence Day
« Reply #61 on: 9 Sep 2012, 06:42 pm »
What we need is a kit to accompany the new amp. Building ESL panels can be relatively easy. Sourcing parts definitely isn't. Instead of buying used antique Accoustat panels, with their rather thick and heavy panels & membranes, a simple panel can be designed with precut insulated perf-metal sheets, some copper foil, a suitable Mylar (the tricky part) diaphragm, and quality double stick tape. With the right supplies this should be a one day project. Especially if flat panels are desired. Roger's, amp would make all of the related transformers and bias supply, and their related headaches, unnecessary. If you desire lots of volume, a woofer and crossover would be required. Done right, it could be easier than assembling a backyard swing set.

steve

I could make such a kit available. I do have heat shrink mylar available now for those who want that. Currently I am still a fan of the Acoustat method of using the plastic light grill as a stator with wires attached. However this is a bit difficult for the hobbyist as there is significant tooling and jigs required to stretch and glue the wires. I  have a 30% less deep light grid and a very good tubular aluminum frame to go around my panel and stiffen the grid at 1 foot intervals.

Perf metal sheets are popular though they need to be put in a rigid frame and perf metal is actually rather expensive. (perhaps someone knows a source better than Harrington and King). Then there is the coating which has to be done and tested for possible arcing spots which have to be touched up.

All things considered, I still recommend the Acoustat panel for its low cost and availability.

Roger A. Modjeski

Re: ESL Independence Day
« Reply #62 on: 20 Sep 2012, 11:49 pm »
Now taking orders for the stereo direct drive amps for Acoustat to be delivered early 2013 or sooner. In a black metal chassis the price is $4,000. I will also make available a unit in the RM-200 style with wood base at $4,800.  A $1,000 deposit will secure your order. Please write ramtubes@gmail.com if you are interested.

The amps will drive up to 4 panels per side and supply 5 KV polarizing. You can then sell the transformers as you no longer need them. Connection is via three banana jacks directly to the 3 wire panels. Chassis are plain black aluminum, balanced XLR or RCA input. EQ must be provided by the user and I suggest a 30 band analog EQ from Yamaha Q2031B or DBX 1231 as it will do a better job than the EQ that is in the transformer box and allow you to correct for room and personal taste. We have listened to these units and found them to be quite neutral.

The mono amps will drive up to 8 panels per side and sell for $8,000 per pair.

« Last Edit: 22 Sep 2012, 03:29 pm by Roger A. Modjeski »

Jazzman53

Re: ESL Independence Day
« Reply #63 on: 21 Sep 2012, 12:58 am »
Perf metal sheets are popular though they need to be put in a rigid frame and perf metal is actually rather expensive. (perhaps someone knows a source better than Harrington and King). Then there is the coating which has to be done and tested for possible arcing spots which have to be touched up.

All things considered, I still recommend the Acoustat panel for its low cost and availability.

OnlineMetals.com sells precut steel perf pretty cheap:  .036 x 12 x 48 / 40% open / .125 holes @ $20 each, and you can order custom sizes.
I would love to try my hand at building the insulated wire / light diffuser stators you described, and if you have any build photos, I would love to see them.

« Last Edit: 22 Sep 2012, 03:50 pm by Roger A. Modjeski »

gnnett

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Re: ESL Independence Day
« Reply #64 on: 22 Sep 2012, 04:11 am »
Hi Roger

Is the EQ required to generally counter a rising response with frequency and therefore could this be achieved by progressive reduction of panel area driven with increasing frequency ala spectra versions of acoustats? Understand that this would not be easy to achieve and that the equalisers you describe would both simplify the iterative process and provide greater flexibility to address the other issues you describe.
Regards

Grantn

Roger A. Modjeski

Re: ESL Independence Day
« Reply #65 on: 22 Sep 2012, 03:13 pm »
OnlineMetals.com sells precut steel perf pretty cheap:  .036 x 12 x 48 / 40% open / .125 holes @ $20 each, and you can order custom sizes.
I would love to try my hand at building the insulated wire / light diffuser stators you described, and if you have any build photos, I would love to see them.

Thanks for the suggestion. I encourage those interested in making their own panels to visit Jazzman's site. I have found his methods to be very practical and thoroughly explained.  http://jazzman-esl-page.blogspot.com/2010/01/building-stat-panels.html

I would also suggest this one http://www.onlinemetals.com/merchant.cfm?pid=13500&step=4&id=1003&top_cat=0. It is 1/8 " thick. One might go to the 1/4 inch hole size.  If you use the steel that's only .036 that is pretty thin and would need some bracing internal and external to maintain a constant gap.


Roger A. Modjeski

Re: ESL Independence Day
« Reply #66 on: 22 Oct 2013, 09:24 pm »
We have now delivered five direct drive amplifiers to Acoustat users. We also sold one user 8 panels to build his own speakers. We are accepting orders for the stereo unit at $4500 and the mono pair for $8000.

Jazzman53

Re: ESL Independence Day
« Reply #67 on: 22 Oct 2013, 11:59 pm »
Thanks for the suggestion. I encourage those interested in making their own panels to visit Jazzman's site. I have found his methods to be very practical and thoroughly explained.  http://jazzman-esl-page.blogspot.com/2010/01/building-stat-panels.html

I would also suggest this one http://www.onlinemetals.com/merchant.cfm?pid=13500&step=4&id=1003&top_cat=0. It is 1/8 " thick. One might go to the 1/4 inch hole size.  If you use the steel that's only .036 that is pretty thin and would need some bracing internal and external to maintain a constant gap.

Good point.  My preference for perf metal stators is 18-gauge (.048") with 1/8" max hole size, which gives very good efficiency.  Online Metals does not offer a suitable perf in that thickness, but I've found that their 20-gauge (.036") perf works just fine for 12" wide panels with 2 center-support spacers; especially if you bond on a couple of steel bars for mass and support as shown in the photos below.   The photos actually show a panel made with even thinner .030" steel perf, 51% open with .117 diameter holes (very efficient!)--- with a couple of 1/2" square iron bars bonded to the rear stator for strength and dampening.  The square bar stock is precut 1/2" x 48" purchased from Home Depot ($6 each).  The added steel bars work very well for damping vibrations.

Curved panels can use thinner perf but the .036" perf from Online Metals works OK for 12" wide flat panels.  I would not go thinner than .036 for flat panels.  As is always the case with metal perf stators, flatness is an issue and you can't count on any perf being perfectly flat... so I also advise using short spans between the center support spacers to accommodate stators that aren't perfectly flat.  Sanders' Cookbook recommends setting the span between support spacers at 70-100 x d/s (diaphragm/stator spacing) but I recommend closer to 70 than 100 for the reasons just stated.   :thumb:





 
 

     

Roger A. Modjeski

Re: ESL Independence Day
« Reply #68 on: 23 Oct 2013, 02:33 am »
Good point.  My preference for perf metal stators is 18-gauge (.048") with 1/8" max hole size, which gives very good efficiency.  Online Metals does not offer a suitable perf in that thickness, but I've found that their 20-gauge (.036") perf works just fine for 12" wide panels with 2 center-support spacers; especially if you bond on a couple of steel bars for mass and support as shown in the photos below.   The photos actually show a panel made with even thinner .030" steel perf, 51% open with .117 diameter holes (very efficient!)--- with a couple of 1/2" square iron bars bonded to the rear stator for strength and dampening.  The square bar stock is precut 1/2" x 48" purchased from Home Depot ($6 each).  The added steel bars work very well for damping vibrations.

Curved panels can use thinner perf but the .036" perf from Online Metals works OK for 12" wide flat panels.  I would not go thinner than .036 for flat panels.  As is always the case with metal perf stators, flatness is an issue and you can't count on any perf being perfectly flat... so I also advise using short spans between the center support spacers to accommodate stators that aren't perfectly flat.  Sanders' Cookbook recommends setting the span between support spacers at 70-100 x d/s (diaphragm/stator spacing) but I recommend closer to 70 than 100 for the reasons just stated.   :thumb:





 
 

   

nice panels Jazzman. Do you have some capacitance measurements? What is your typical diaphragm to stator spacing and polarizing voltage?  I have found that lower distortion at high levels is obtained when the polarizing voltage is half the voltage that produces noise in the panel. Although some say to put the polarizing right below the noise value but then the noise is occurring on peak signal though it is covered up by the music. Reducing the polarizing really cleans things up at high levels.

Hank

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Re: ESL Independence Day
« Reply #69 on: 12 Mar 2014, 05:29 pm »
I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces.  This direct drive topic is interesting, BUT I can't afford this $4500 amp.  Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market? 

Roger A. Modjeski

Re: ESL Independence Day
« Reply #70 on: 8 May 2014, 07:17 am »
I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces.  This direct drive topic is interesting, BUT I can't afford this $4500 amp.  Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market?

DD amps are rare, only Beveridge and Acoustat made them.  You can buy a pair of used Acoustat amps for around $2000. If you have trouble with them I can fix them. The Beveridge is only suited to his speaker.

Don't bother upgrading the parts in the interfaces, it won't make much difference. The problems are in the concept not the parts.

OzarkTom

Re: ESL Independence Day
« Reply #71 on: 8 May 2014, 10:41 am »
I bought a pair of Model 3 Acoustats a few months ago and now have the parts to upgrade the caps and resistors to upgrade the interfaces.  This direct drive topic is interesting, BUT I can't afford this $4500 amp.  Is there a make and model DD amp that is affordable and will do the job that I could look for on the used market?

I have seen some Acoustat DD amps sell on Craigslist for as low as $500 for the pair. It is a night and day difference between the DD amps and the interfaces. 100K amps cannot make the interfaces sound near as good.