Custom ESL using quest panels

MartinLogan Audio Owners Forum

Help Support MartinLogan Audio Owners Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
@Leporello I just went with these transformers because they seemed like the best shot I had with the information I had to work with.

I'm not entirely sure of what I'm doing here, but it seems to be working.
The problem I see with using a power transformer as an audio transformer is the non-flat frequency response. Secondly the proper core material in an audio transformer is M6 steel which contains some silicon to increase permeability. In addition nickel is added to increase the permeability further and reduce the hysteresis. higher permeability means less windings required for coupling. Less windings means lower resistance and lower power loss, Bad hysteresis creates distortion. A typical audio transformer for a tube amp will have distortion below .1%. I have never measured a power transformer at high frequencies. But if harmonic distortion is bad so will be the inter-modulation distortion and the sound will be harsh. Maybe the core material in toroidal transformer is more ideal, I have no experience with that. But I do know that toroidal cores saturate more easily, so if there is any offset on the output of the power amp, and also because of the lower winding resistance, as fairly large current could flow decreasing the ability for high output. I am assuming with big panels you want pretty big output?
I would really be interested if someone had run some distortion numbers using a power transformer as a step-up. If transformers were so easy, then people would not spend a fortune on moving coil step-up transformers. I know its low signal level and needs tons of shielding, but low distortion is a primary driver there.
Of course for the adventurous, you buy an EI core and wind your own. The secondary can be very thin wire, since the electrostatic panels don't load the transformer much and impedance is very high.
I had a set of Accustats at one time. They used a transformer with a higher ratio to get the bass boost and crossed it over in the bass region. Worked very well.
Hearing is believing.

I wouldn't recommend my cheap toroid setup for driving full range ESLs, but I can attest from experience that a tandem pair of single-primary 50VA 230V/6V toroidal power transformers (75:1) works quite well driving hybrid ESLs operating above 200Hz, and the sound quality is excellent.

Around 2009, I was inspired by a much-respected ESL builder on the DIY Audio Forum to tryout the tandem single-primary toroidal power transformer setup. I liked them so much that I started using them in all of my ESL builds.

I originally used the tandem toroids to drive 4ft2 perf-metal panels, and later (2015) to drive my newer segmented wire-stator panels.

For years I've fed these cheap power toroids with ridiculous power from multi-hundred watt RMS amps, and I've never smoked one. Their cost vs performance is just icing on the cake and makes building ESLs accessible for more people.

Linked below are a couple of posts from "Calvin" on the DIY Audio Forum. The second post includes response plots comparing the inexpensive power toroids to the excellent ESL-specific Aplimo transformers.


Power toroids for ESLs

Comparison to Aplimo ESL Transformer
Last edited:
Very interesting link. I did come to the same conclusions that an ESL transformer is different from a tube output transformer. It could be true that the frequency response is quite close between the two. So far I have not seen any distortion figures for each one. Dayton Write claims 0.1% distortion for their speakers and he claims it is all caused by the transformer. I had a read of your webpage, quite impressive. I like the idea of a segmented panel. After all these years, I never build one, though I also read the Sanders book. Here is a plot of the Dayton Wright speaker with transformer. No fancy computer plot here. This was done in 1977, so yes I have been at it for many decades. The two plots represent a 100:1 and a 50:1 turns ratio. The reason why the plot does not drop below 3 ohms is because there is a series 3 Ohm resistor to prevent a high frequency short.
I should measure the distortion of the dedicated transformer and the transformer from triad loaded with a dummy capacitance. Also this transformer is used for bass, so the core has to be big so it won't saturate and modulate the high frequencies. I think a good test would be to do the IHF IM, using 60Hz and 1KHz tones and look at the intermodulation products. This may not apply for electrostatics that do not produce any bass. I am a guy that measures first and then listens.


  • DaytonWrightImpedance.jpg
    2.1 MB · Views: 0
Sorry this post does not really help with your project. I don't know where MartinLogan sources their transformers. Since production is in Ontario, Canada, a good bet is that they are working with Hammond because they have the experience making ESL transformers since the 1970s, in addition to making tube output transformers. If you are looking to get an oem transformer for those panels you are putting so much effort into them, give them a call to see what they come up with.