Series-Connected Single-Ended Output Transformers in ESL

SlunkBoy

Member
2007-01-08 8:39 pm
Are there any drawbacks to substituting two single-ended output transformers (as pictured) for the typical push-pull arrangement in an ESL? I would avoid this sort of thing in a tube amplifier because the bias current would still cause the cores to saturate, but since there is no current flow in an idling ESL, I can't see an issue. Am I missing anything?



Thanks,
Nick
 

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Am I missing anything?

Nope, nothing wrong with your idea.
Quad, Audiostatic, and a few other manufacturers use this technique as do many DIYers.
Usually the primaries are put in parallel rather than series to get higher step-up ratio if primary turns and core area are adequate for operation without core staturation to the LF bandwidth desired.
Quad ESL-63 circuit attached below.

Another alternative for single-ended transformer use is a virtual center tap:
http://www.diyaudio.com/forums/plan...up-measurements-part-1-2-a-5.html#post3323312

If leakage inductance is low enough you can even use 4 transformers in series-parallel combination:
DIY-
http://www.diyaudio.com/forums/plan...up-measurements-part-1-2-a-3.html#post2861741
Jazzman's DIY Electrostatic Loudspeaker Page: The Electronics Package

Audiostatic-
http://www.diyaudio.com/forums/planars-exotics/163766-long-throw-esl.html#post2130964
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I agree this should work okay, assuming suitable transformers. It also has the added advantage that each transformer is subjected to only half the voltage that would be seen by a push-pull transformer.

This very technique was used in Acoustat's full-range Spectra series. Two identical transformers have their primaries connected in parallel (but out-of-phase), with each secondary driving one stator. This resulted in a much more reliable transformer, and I am not aware of any Spectra transformers having a high-voltage failure. The same could not be said of Acoustat's earlier MK-121 series speakers, where the push-pull transformers are subjected to the full peak-to-peak voltage. Those transformers can arc-over if overdriven, despite improvements over the years (i.e. the Medallion transformers had better arc-over protection than the original design).
 
Sure there are drawbacks: the impedance will be lower.
Till so far any Antek or other "simple" toroidal transformer is not capable for the low frequency range. Many other esl transformer too and most have impedance problems if used full range.

Are there any drawbacks to substituting two single-ended output transformers (as pictured) for the typical push-pull arrangement in an ESL? I would avoid this sort of thing in a tube amplifier because the bias current would still cause the cores to saturate, but since there is no current flow in an idling ESL, I can't see an issue. Am I missing anything?



Thanks,
Nick
 

Tinners1983

Member
2013-11-04 10:27 pm
Sorry to drag this up, may I ask what is probably a really, really dopey question. Is it possible to connect the secondaries of two output transformers together, if one is single ended, and one push pull?

I'm hoping that the issues with the air gap etc are all confined to the primary. I'm trying to drive the same speaker(s) from an amp with two power amps.
 
Sorry to drag this up, may I ask what is probably a really, really dopey question. Is it possible to connect the secondaries of two output transformers together, if one is single ended, and one push pull?

I'm hoping that the issues with the air gap etc are all confined to the primary. I'm trying to drive the same speaker(s) from an amp with two power amps.

Sure it is possible but at a cost: more difficult to drive because impedance will be low. And because of that, frequency response is less good, distortion higher. And last but not least: efficiency is lower.

A real good esl transformer has less problems overall but also at a price: its more difficult to to make so it cost more money.