Amp impedance setting to drive ESL57s

[Richard (Wales)]

Hi

I am about to connect a valve amp to my ESL57s, and need to know what impedance I should set the amp to?

I know the ESL57s don't follow the rules, so which is the best option, 4, 8, 16R ?

With thanks

Richard.

[analog_sa]

Why don't you just try and see which tap sounds best?

[Nigel Goodwin]

Originally posted by Richard (Wales)
Hi

I am about to connect a valve amp to my ESL57s, and need to know what impedance I should set the amp to?

I know the ESL57s don't follow the rules, so which is the best option, 4, 8, 16R ?

With thanks

Richard.

What do the specs say on the ESL57's? - are they totally capacitive?, or do they have an impedance rating as well?.

I've just tried a quick google, have a look
here.

ESL57's were always notorious for being difficult to drive, and I would think the matched impedance requirement of a valve amp would make it even more so?.

Historically though, back in their time, speakers were generally 16 ohm, it wasn't until much later that 8 ohm became the norm.

[Bazukaz]

Lower impedance amplifier is better , because it can deliver higher currents.

[Nigel Goodwin]

Originally posted by Bazukaz
Lower impedance amplifier is better , because it can deliver higher currents.

Not for a valve amplifier, they use impedance matching, maximum power is developed into the correct impedance!. Using the wrong impedance speakers can damage the amplifier!.

[AndrewT]

Hi,
els57 was designed when valve (tube) amps ruled the world.
that's where 57 of 1957 comes from.
The result is that valve amps can drive the els57s very well when set to the correct impedance. Don't listen to these youngsters.

I just looked up the QUAD site but their history does not mention the speaker.

There are lots of links in google and at least some of them must give guidance on impedance setting.

BTW running your valve amps with open circuit (no load) will damage them but wrong impedance setting is much less likely to do any harm. Your could insert a line resistor and set to 8ohm and try measuring current and voltage when on either and/or both of pink noise/white noise to get an average speaker impedance.

Good luck/searching

[moray james]

Listening to each setting and see what sounds best is a safe bet. It has been my experience that most output transformers tend to sound best when the entire secondary has a load on it. When you use a lower impedance tap you are left with the rest of the winding unloaded and flapping in the breeze. Yes you will transfer less current using the highest impedance tap but you get the benefit of a full secondary winding load. Only one way to find out though. Impedance matching auto transformers can also help matters a lot but they are not cheap. Good luck have fun regards moray James.

[Fanuc]

Hi,

A unusual aspect of the original Quad ESL57 is that the load impedance falls to 2 ohms at above 10-15 khz. This is the opposite of floorstanding speakers with decent bass which tend to dip down to 2 or 3 ohms at sub 100 Hz.

I don't think a single ended triode amp is the way to go though, as single-ended (Ip = Iq) designs even on a 4 ohm tap, so the maximum output current is fixed at a particular value depending on the quiescent current.

[Richard (Wales)]

Hi

Thanks to everyone for the replies.

Before posting I hunted through endless sites looking for the answer to this seemingly simple question, including one site with the full original instructions for these speakers, and found nothing.

This site has
http://www.quadesl.com/quad_main.shtml
a graph of the impedance of the speakers, which as you can see varies from about 32R at low frequency to about 3R at high frequency.

Anyway, as suggested I have tried all 3 options and settled for the 8R.

The amp is a Radford STA15 Mk III, which are supposed to be pretty bulletproof.

I will try with a pair of Leak TL50+s next, when my passive preamp arrives.

With thanks

Richard.

[moray james]

I used to own an St 15. A buddy of mine who is running Acoustat 0ne plus 0nes ( a worse load than the Quads) has just switched over from a 200 watt per channel Audio Research amp to a set of NuForce Ref 9.02's. He just got a set of auto transformers and was shocked at the difference in performance of his 65 lb ARC when running the autoformers. In the end he opted for the NuForce amps along with the autoformers. The Nuforce have a 300 watt SMPS per mono block and as I said the ARC is a beast. So I think that your Radford would probably appreciate the improved load offered by the autoformer. I think that you can buy a set on approval and only be on the hook for the return shipping if you don't like what you hear. Regards Moray James.