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Power handling capability of original Quad esl 57s

After many years of hearing about how wonderful the original Quad esl 57s are, I finally found a near mint late serial number pair. I'm in audio heaven! I used to own the 63s and the 989s, and these are much better ( in the sweet spot).

Now my question: what is the power handling capability of the 57s? There seems to be some confusion here. According to the original manual, it is safe to use any amplifier as long as it does not produce more than 33 volts at any impedance. This is an interesting specification because it does not differ from the 63s.

Ok, let's do some math. At 8 ohms, 33 volts into 8 ohms gives us
33^2/8 = 136 watts! At higher imoedances, power must drop, so at 30 ohms, the speaker can only take up to 30 watts.
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ct0517's avatar
ct0517
2,041 posts
 
Tuttles

I share your enthusiasm for these speakers.

I have tried different SS / Tube amps with mine.

The original 303 amps they came with were good for 28 wpc at 16 ohms and 45 at 8 ohms.

I have a 405 amp.
Quad recommends resistors be put in the 405 100 wpc amp to limit its output with them.

Does anyone know what power this limits the 405 amp to - I am assuming about 50% ? This would answer the question as well.

I agree with Stanwal that they need very little power to sound "full".

And I am surprised at how good they sound with the 33 pre and 405 amp. These vintage Quad gear are readily available.
rrog
1,958 posts
 
I believe it is 25 watts, but the original Quad II amplifier is only 15 watts.
dracule1
1,085 posts
 
The original 57 was designed to be used with 15 to 20 watt amp, because the early production did not have protection circuitry and people fried the speakers. Later versions, came with protection circuitry. There are new protection boards you can buy. With them installed, I've heard people using 150 to 200 watt amps without frying them, but I guess they are careful not to play cannon shots through the 57s.
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tuttles OP
1 posts
 
Thanks for all the input, folks! I do have a pair of 405-2s, with the voltage limiter installed. This reduces the output of the 405-2 to 50 watts into 8 ohms (20 volts maximum). For the price of a used 405-2 (around $250), the sound is amazingly good.

But, the 405-2s don't reveal the full glory of the Quad's legendary midrange. The best amp I've tried so far is the Macintosh MC275. A truly spectacular marriage of two audio legends. The Quad II is widely recommended, but it has such high distortion at even moderate volumes, I can't seriously consider using it.

I'm seriously considering installing the protection circuitry, but I'm worried about their audible effect on the sound.
ct0517's avatar
ct0517
2,041 posts
 
The 405 works well. The sound I heard taking it easy with a Music Reference RM9 was amazing. One knowledgeable member has commented on the protection circuit in my review of them.
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