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Old 21st April 2005, 08:42 AM   #1
Nuuk is offline Nuuk  United Kingdom
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Default GCs and ESL

Electro Static Loudspeakers are notoriously difficult loads for an amplifier so I wondered if there is a GC configuration that would drive an ESL properly, and if so what would be the specification?
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Old 21st April 2005, 12:51 PM   #2
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The problem with some ESLs is that they have very low impedance at high frequencies, and that can cause some solid-state amps to trigger the protection circuits.
Maby a 3//LM3886, with 0,47R in series with each output would work fine.
And a PSU voltage at around +/-24V, no more than that.
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Old 21st April 2005, 12:58 PM   #3
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Quote:
Maby a 3//LM3886, with 0,47R in series with each output would work fine.
What's a 3//LM3886 Uncle Carlos?

And I guess an inductor on the output wouldn't hurt!
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Old 21st April 2005, 03:22 PM   #4
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Originally posted by Nuuk
What's a 3//LM3886 Uncle Carlos?
It's 3 paralleled LM3886 chips.
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Old 21st April 2005, 04:54 PM   #5
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Quote:
It's 3 paralleled LM3886 chips.
Do you really think that it would take that much? I have heard of an LM3386 with just 1000 uF caps running Martin Logans without problem.
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Old 21st April 2005, 06:16 PM   #6
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Originally posted by Nuuk
Do you really think that it would take that much? I have heard of an LM3386 with just 1000 uF caps running Martin Logans without problem.
Yes, it depends on the speaker.
Some ESLs have less than 1 ohm impedance near 20Khz.
For some amps this is a short.

Try it first with a single chip, and a big heatsink.
If it gets very hot and kicks in the over-tempreature protection, you know you have to do something.
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Old 21st April 2005, 08:38 PM   #7
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I have never tried ESL's but I think they need an amplifier capable of delivering a lot of current, transformer with 500VA and nice caps, for example.
But this also depends on the sensitivity of the speaker.
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Old 21st April 2005, 09:47 PM   #8
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I drive a pair of Quad ESLs with my LM3886 amp daily. I put the standard parallel LR in series on the amp output and have never had the amp complain about the speakers at all. It sounds great, except that the 30W or so I am getting from the amp per channel is a little low for those speakers, limiting the distortion-free playback volume to something a little below bleeding ear drums level.

My amp is in an aluminum box with 1/4" thick sides and a cover that is all 10" x 13" heatsink with numerous fins. The amp chips are bolted to the cover of the box. I have never been able to detect more than 1 or 2 degree rise on the amp's cover, no matter how loudly or how long I play the amp. If I recall correctly, the transformer is a 320 VA and supplies both channels. I have about 112,000 uF in the power supply.

It is not necessarily true to say that ESLs are low Z at high frequencies. It is true that capacitors are low Z at high frequencies, but ESLs are much more complicated than a simple capacitor. If you test the impedance of an ESL with its transformer(s) you'll find that the impedance varies all over the place, inductive at some frequencies and capacitive at others. Typically it dips pretty low at some frequencies, and tends to go quite high at low frequencies. The impedance of the speaker also varies somewhat with the amplitude. None of that should make much difference if the amp has a low output impedance.

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Old 21st April 2005, 10:22 PM   #9
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Quote:
Originally posted by carlosfm


It's 3 paralleled LM3886 chips.
Will 4 x LM3875 work (at +/- 24Vdc for 25W) ?

Will 8 x LM3875 work (at +/- 35 Vdc for 56W) ?



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Old 21st April 2005, 11:44 PM   #10
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Quote:
Originally posted by nina

Will 4 x LM3875 work (at +/- 24Vdc for 25W) ?
Will 8 x LM3875 work (at +/- 35 Vdc for 56W) ?
Sure it will, but why use multiple chips in parallel when you can make a much simpler circuit with one or two chips that provides the same output power? You can get 120W out of a single LM4780.

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