Quad service

You might want to check what the “protection board” is.

In the past Quad could fit an “electronic clamp”, which shut off the loudspeakers to protect damage to the transparent membrane which produces the sound. You just need to ensure that this won’t damage the Naim amps.

Jim - IIRC Quad service when I had a FM4 serviced earlier this year, the service centre is up the road in Huntingdon. I don’t think it is the same address as historically, but still in Huntingdon.

Of the 7 sold prices for ESL 57s on Fleabay, the highest any pair has made recently is £300 for a pair.

A speculation - using Quad to service ESL 57s might still make sense if one believes that a freshly Quad-serviced pair will sound much better than a pair bought from eBay.

It does seem likely to me that a freshly Quad-serviced pair will sound much better than a pair bought from eBay - but whether it makes sense depends on one’s system, budget, taste, etc.

It’s still not expensive for effectively brand new speakers of such a classic design.

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How would I check that?

@NeilS Hi Neil - sorry to bother you, but do you think my 135s would be safe to drive a pair of vintage ESLs if the speakers have been serviced by Quad and a protection board fitted into them?

Does the board protect the speakers from the amps or the amps from the speakers, or vice versa?

The clamp turns off the ESLs, so in theory the amp could be affected.

I have never experienced this, but I have three pairs of ESLs in the system, so I suppose that they can soak up more power input.

We usually reduce the voltage rails for customers using ESLs, but I’ve not heard of this protection board before.
The standard voltage rails for 135s are +40V & -40.6V, so worth checking with a tech at Quad to check if that will be okay.



IIRC this was termed “crowbar” protection, which would essentially present the amps with a short circuit. In theory they should immediately shutdown, but perhaps @NeilS has some service experience with amps that have encountered this protection from Quads. I do recall Sheila advising me to tell customers to avoid any Quads that had this crowbar protection (IIRC mostly just early ESL63s) onboard as amp damage was a possibility.


I do recall a 180 sent in for repeat repairs (three times) with one channel completely destroyed each time. I didn’t get any feedback regarding the reason why, but it was definitely being used with ESLs.



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