Quad ESL-57 Service manual

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Hand-Builders of Fine Music-Reproduction Equipment

❦

Precision Electro-Acoustic Research Laboratory.

No. 200, 2137 33 Ave. SW; Calgary, AB; T2T 4X3

Ph: +.1.403.244.4434 Fx: +.1.403.244.9026

Web:

http://www.pearl-hifi.com

E-mail:

[e-mail]

This document has been prepared as a public service and

is intended for unrestricted distrubution.

Any and all trademarks and logotypes used herein are

the property of their owners.

Please note that the links in the PEARL logotype above are “live”

and can be used to direct your web browser to our site or to

open an e-mail message window addressed to ourselves.

General

The notes in this section are for the guidance of the engineer who has so me experience of ca rrying out repairs to

these speakers together with the necessary proper materials for the repair.

The QUAD electrostatic speaker consists of five components: two bass units, one treble unit, an audio transfo rmer
uni t a nd an EHT supp l y unit. I f a ny repa i r s a re necessa ry, it should be ascerta ined whi ch o f t h e five compone n t s i s t h e
cause and that component should be either replaced complete or repaired as appropriate.

Fault Diagnosis

Loss of Sensitivity

Check the EHT voltage, which should be: Bass 6Kv + 7%; Treble 1.5Kv + 7%.

If low, check, by disconnecting, whether due to leakage in speaker unit or fault within EHT unit. Voltages must be
checked only with electrostatic meters, as the current drawn by other types may itself damage the rectifiers.

Distortion

1. Make sure that the speaker is really at fault by comparison with a second electrostatic speaker, using a QUAD

amplifier.

2. Check EHT voltage.

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Quad Electrostatic Loudspeaker

Service Data–Model ESL 57

3. Suspect intermittent breakdown in speaker units.

4. Suspect intermittent breakdown in audio transformer unit. (Note: a fault in this unit is very unlikely).

No Output at All

Suspec t EHT unit or audio transformer unit af ter checking more ob vious things like external connections, not for-

getting the leads under the transformer unit connecting the input sockets.

Background Noise

One cause of background noise in the electrostatic loudspeaker is internal discharge of the EHT supply at times
of high humidity, or high voltage, or both. This may be reduced by lowering the EHT voltage and a tap is p rovide d on
the EHT mains transformer for this purpose.

Befo r e t he EH T u n it i s to uch ed th e m ai ns s ho u ld be co mpl et e l y dis con n ected a nd t he l ou dspe ak er l e ft to st a nd f o r
two hours to ensure it is completely discharged.

The connectio n s to the EHT rectifier block are normally take n from tags mark ed C ommon and 61 0V. The l a tt er is
the righthand end tag and next to it is a blank tag marked 590V to which should be transferred the lead normally con­nected to the 61 0V tag. Background noise may also be caused by discharge of the EHT from points external to the
loudspeaker units, at the tags on the rectifier block for example, if a hair of felt or piece of fluff comes in reasonably
close proximity to that point, or if a spike of solder or sharp point of wire permits corona discharge.

Where EHT leakage occurs via a bass unit, this is sometimes found to be discharging from one of the eyelets
around the periphery of the bass unit plates, probably to one of the aluminium brackets. In such cases a satisfactory
repair can b e effec ted by slitting the polythene tape round the ed ges of the unit, opening the dustc over frames and
insulating the leak by applying a single layer of similar polythene tape all round the periphery of the internal plates, on
top of the existing sealing tape, and reassembling the dustcovers, again with polythene tape.

Other internal failures of insulation will probably necessitate replacing the loudspeaker unit affected.

Mechanical

If the dust seal covers should be torn, it may be necessary to replace the complete unit as there will have been
ingress of dust, which causes loss of sensitivity of the unit concerned.

Dismantling the Speaker

The loudspeaker should be switched off for about two hours before the grilles are removed, so as to ensure the
EHT unit has completely discharged.

The component loudspeaker units of the QUAD electrostatic loudspeaker must be handled with the utmost care,
partly because when not supported by the rigid frame of the cabinet they are more liable to physical distortion which
wou l d reduce th e small intern al clearances, and pa rtly becau se the dus t covers are necessarily made of v ery thin and
therefore fragile plastic film.

At the rear of the tre ble unit are four pins lo c ate d in the woo den str uts of the c abinet, and as these rep resent an
additional hazard to the dust covers of the treble unit, the positioning of this unit requires particular care.

Soldered joints should be smoothed and rounded and all spikes of solder, wisps of wire, etc., removed as these
would tend to cause arcing at the high internal voltages used.

Removing Front and Rear Expanded Metal Grilles

The rear grille is held only by the screws around its periphery. For the front grille it is necessary first to remove the
side mouldings, the staples through the metal beneath them, and the screws under the baseboard.Then the bottom
edge of the grille is lifted gently outwards and upwards until the top rear edge may be slipped out of its groove in the
cabinet, when the whole grille will be free. Care must be taken not to strain the top curved section during removal or
the metal may split.

Replacing the Front Grille

Replacement grilles are normally supplied cut and partly preformed so the procedure is as for refitting an existing
grille . I t m ay be fou n d h e lpf ul when w o rking sing l e h a n ded, having ins ert ed t h e t o p ba ck edg e o f t h e s h ee t i n t o t h e s lo t
in the cabinet, to hold the bottom edge of the grille under slight tension to the bottom of the wooden frame by means
of elastic ban ds and simp le hooks of w ire, such as an o pened paper clip, a n d then to use a bar of wo od slightly lon ger
than the width of the sheet, and with a good flat face, to bed the grille to the frame by moving the bar progressively
down t he face of t h e g ri l l e, tacki n g th e s ide s a s y o u go, final ly securi n g t he bo tto m edg e wi t h t h e scr e ws r e m o v ed f r o m
the old grille. Do not forget to fasten the earthing lead to the grille.

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