German
version
French
version (expected soon)
One Thing Audio
Quad
Instructions, ESL 57, Refurbishing
Warning
ELECTROSTATIC LOUDSPEAKERS CAN REMAIN CHARGED UP FOR ANYTHING UP TO TWO HOURS AFTER BEING UNPLUGGED FROM THE MAINS. If possible, unplug them from the mains and leave them overnight to discharge. If you cannot wait this long, with a probe or something similar, short out the HT to chasis or "ground" - the HT being the "T" (treble contact) on the HT board, or the "B" (bass contact) on the HT board."Chasis" or "ground" meaning the metal frame of the mains transformer - any metal part of this frame representing HT - , "0" volt or chasis ground. Warning: short out BOTH terminals (TREBLE AND BASS) AS THERE ARE TWO INDEPENDENT HT SECTIONS ON THIS BOARD, so they must be discharged separately.
Checking the audio transformer 
To check whether the ESL 57 audio transformer is working correctly measure with a multimeter:
- between pin no 7 and ground the reading must be between 1.7K and 2K
- between pin no 9 and ground the reading must be between 1.7K and 2K
- between pin no 1 and ground the reading must be around 185K
- between pin no 5 and ground the reading must be around 185K
Resistor/capacitor identification
Below are the positions and identification of components on the underside of the ESL 57 Audio transformer. Whereas the "wattage" ratings of resistors are not critical, it should be remembered that each resistor should be capable of handling instantaneous peak voltages of at least 3kV.
Colour code of resistors
180K (brown, grey, yellow)
150K (brown, green, yellow)
270K (red, violet, yellow)Capacitors
2 x 560 pf (in parallel)
1 x 560 pf
Fitting a replacement bass panel
Remove front grille. This is held on by staples down either edge (prime up and pull out with pliers) and remove the line of small countersunk wood screws along the bottom of the grille, including the earth strap, Double check that all staples and screws have been removed, and pull the grille gently forward from the bottom edge, at the same time pushing the top curved section backwards to release the grille from its 'slot'. Do not force it if it is reluctant to 'pop' out of the slot, but continue gently raising and lowering the grille whilst pushing backwards on the top curved section. It will eventually release itself.
Remove the aluminum clamps at the top and bottom of the center treble panel, each of which is held in place by 2 wood screws Note: again, even with the screws removed, these clamps may not easily pull out. Ease out gently with the sharp edge of a chisel trying not to do too much damage to the wooden 'lip' which holds the clamp in place.
The defective base panel must now be 'slid' towards the center (obscuring the treble panel). This is best achieved by using a flat implement (a wide decorator's scraper is ideal) Inserting it between the inside edge of the 'speaker frame and bass panel, and gently easing the latter away from the frame. The panel need move inwards only far enough to clear the two metal clamps (top and bottom) which support the bass panels at their outer
edges. Once the panel has moved beyond this point it will be freed from the frame. Lower the panel forward from the top and allow the panel to rest on a soft surface (carpet, whatever).Before attempting to unsolder the 3 wires from the connection block, make a note of the order and position of the 3 colored wires (usually black, red and white). The panel will not work if any of these wires are transposed upon reconnection. Next, make up a protective panel (cardboard, hardboard etc.) which will allow the 3 connection posts to be exposed whilst covering at least the bottom area of the rear dust cover as solder splashing onto the dust cover will penetrate it and could damage the bass panel (cover the entire area of the dust cover if this feels safer). Re-solder the 3 wires onto the new panel making sure the solder runs freely over the tip of the connection posts
REASSEMBLE IN THE REVERSE ORDER OF THE ABOVE
Fitting a replacement treble panel
Please observe that treble panels have 2 sets of wires. These are: BROWN and BLUE to front of panel. BROWN, BLUE and RED to rear of panel. Although front and rear share the same colors (brown and blue) they are NOT interchangeable. Transposing any of these wires will cause the panel to malfunction. The connections are designated thus: FRONT BROWN, FRONT BLUE. REAR BROWN, REAR BLUE. The RED wire connects to the 1.5Kv terminal on the EHT board (or block). In some cases, it may be found necessary to extend this wire to make it reach. Use a smooth soldered joint and insulate well with PVC tape, finishing off, if possible, with a short length of heat-shrink tubing over the PVC tape. Before soldering, always place a protective 'panel' (hardboard, cardboard etc.) behind the bass panel to prevent solder splashing onto the dustcover.
Unscrew the four bolts securing the audio transformer, and carefully turn the audio transformer upside down, avoiding putting undue pressure on the leads feeding through the grommet.
7 = Treble (rear, brown)
8 = Treble (front, brown)
11 = Bass (rear, usually white)
12 = Treble (rear blue)
14 = Treble (front blue)
15 = Bass (front, usually black)* This board limits bass to the treble panel and should be incorporated in all ESL 57's prior to serial no. 16800 (One Thing Part No. TMB1)
Avoid damaging the new dustcovers by 'snagging' them on the sharp spikes protruding from the front of the two panel bracing supports (center of speaker). These 'spikes' are best removed unless the loudspeaker is to be bumpily transported. If the unthinkable should happen, it is permissible to repair small tears with sellotape.
Felting on rear of treble panel
Try to remove this with the two wood 'spacers' intact (in other words, separate the felting from the treble panel's frame by gently prising the spacer away from the panel - leaving the felting attached to the spacer). If the assembly falls apart, get rid of all the staples and glue together with small 'daubs' of contact adhesive. Again, use contact adhesive (sparingly) to reattach the felting to the treble panel, allowing the two surfaces to go 'tacky' before pressing them together.
Tensioning the dust covers
The dust covers on bass & treble panels have been pre-tensioned in our workshop, and in most cases no further tensioning will be necessary. However, when fitting to a '57 frame it is necessary to put a slight curvature in the unit: this will apply greater tension to the front dust cover but somewhat reduce the tension to the rear cover. It is possible to take up the slack by applying gentle heat to the cover from a conventional hair dryer. In most cases, the 'hottest' setting will be necessary to shrink the cover, but DO NOT dwell in one spot: keep the hair dryer moving and withdraw as soon as the material shrinks. Only a certain tension can be achieved, and this is quite adequate; further dwelling on already tensioned covers could produce a burn hole !
Original Solid Resin Block
Quad's original solid resin block. Note mains input connections are transposed compared to later boards. Few of these blocks around these days.
Wax filled block
Wax filled block, the type most commonly found in ESL 57 loudspeakers. This type of block can be rebuilt at a small saving over the new board (below). Performance is identical.
Note: In the mid-eighties this version was replaced by a wax-dipped board without tray, but connections remain the same.
One Thing Replacement Board (no longer available)
Fit with track side of board to REAR of speaker (component side facing bass panel). It will be found easier to solder all wires onto the solder pins BEFORE mounting the board onto the transformer frame. If wires are too short, extend with similar wire, soldering the joints and well insulating. Ideally, finish off with heat-shrink tubing. Solder sparingly onto pins, ensuring that solder 'slithers' don't drip onto the board.
First, connect the wires from the mains transformer, ensuring that the grounded wire (connected to the frame of the transformer via a solder tag) goes to GND (point B) on board. Use this same pin or, if more convenient, the GND pin at top of board, to connect the ground (black) wire which feeds through the frame of the loudspeaker from the audio transformer.
Solder bass (fat red wire) and treble (thin red wire) onto pins as indicated. Screw the standoff posts onto the board, and the assembly onto the transformer frame, using the drilled holes which give the lowest mounting position.
One Thing ESL 'Super' Board
For clarity, the latest board is shown in its 'mirror-image' - in other words, looking at the component side of the board. As with the earlier board, this latest version is mounted on Quad's transformer frame with the 'track' side of the board to the rear of the speaker, component side facing the bass panel. 3 sets of holes are provided, and again the set of holes should be chosen to give the LOWEST mounting position relative to the top of the mains transformer.
Important Note: Some ESL 57's (serial No. higher than 50.000 - but many more will have been 'updated' with newer power supplies) will need two mounting holes drilling higher up the frame to allow the bottom of the EHT board to clear the top of the mains transformer (ensure that the board sits 2/3 mm above the level of the mains transformer)
ALWAYS USE THE INSULATED SPACERS AND SCREWS PROVIDED
ESL 57 replacement treble panels are guaranteed against manufacturing failure for one year from the date of purchase, but this excludes damage caused by misuse or overdrive. In this respect it is strongly recommended that a protection board (OT CLP4 ) be fitted which helps to protect the treble unit should excessive drive be applied in error. The protection board WILL NOT affect the sound when the speaker is being driven at normal listening levels. The CLP4 protection (or 'clamp' board) is supplied with clear, step-by-step fitting instructions. Get it clamped! - Irrespective of amplifier power, this is a vital requirement for any electrostatic loudspeaker, and is currently used in all commercially available designs (including Quads prestigious 988 & 989).
The
CLP4 Clamp Board is designed to significantly reduce the likelihood of damage to the Quad ESL 57 loudspeaker when used with higher power amplifiers. It will NOT permit the loudspeaker to be driven at higher levels, but will limit or 'clamp' input voltages exceeding 33 volt peak music power, the level beyond which damage could occur to the treble panel. ESL loudspeakers may be driven at 'realistic' levels providing the sound remains clean and undistorted. If distortion appears, reduce the volume until the sound is clean. This must always be the 'gauge' for the proper and sensible operation of an electrostatic loudspeaker. An ESL 57, properly working, and with the CLPl installed, will produce some of the best sound in the world from a loudspeaker: it is about QUALITY, not SPL (Sound Pressure Level).
Fault conditions: A fault condition can cause loss of efficiency in an electrostatic loudspeaker, which in turn demands higher amplifier drive conditions which may damage the loudspeaker. The risk of damage will be reduced by the action of the CLP4 Clamp Board but the onset of distortion will occur earlier. If this appears to be the case, it may be necessary to get the 'speakers serviced.
Other possible causes of distortion: contrary to popular belief, ESL 57s do not respond well to low powered amplifiers. This is because electrostatic loudspeakers are, in general, relatively low in efficiency and low-powered amplifiers rapidly run into clipping conditions when 'realistic' sound levels are required. Electrostatic panels perform best when under the 'iron grip' of a good amplifier with low distortion, and good control is seldom synonymous with low power.
Fitting the CLP4 Clamp Board
First, make up a protective 'plate' or panel (hardboard or the like) to place against the rear of the bass panel (this will protect the bass panel in the event of the drill bit 'snatching'). The Clamp Board fits (track side towards dust cover) to the INSIDE surface of the left-hand corner brace, viewing the 'speaker from the rear (see illustration). First, using the Clamp Board as a template, drill two 'pilot' holes through the brace, then enlarge the two holes with a 5mm bit. Thread the cable-tie through the holes in the corner brace and Clamp Board, securing the latter firmly to the inside surface of the brace. Cut off excess cable-tie. Note: the cable-tie locks permanently, and can only be released by cutting with side-cutters or similar.
Unscrew the four bolts securing the audio transformer, and carefully turn the audio transformer upside down, avoiding putting undue pressure on the leads feeding through the grommet.
later type after S/NO 16800
7 = Treble (rear, brown)
8 = Treble (front, brown)
11 = Bass (rear, usually white)
12 = Treble (rear blue)
14 = Treble (front blue)
15 = Bass (front, usually black)Thread the two leads from the Clamp Board and solder to posts 7 & 9 on the later transformer or those marked X on the earlier transfer polarity is not important.
earlier type before S/NO 16800
* This board limits bass to the treble panel and should be incorporated in all ESL 57's prior to serial no. 16800 (One Thing Part No. TMB1)
Refit the audio transformer.
When refitting the audio transformer, check that none of the numerous wires passing through the transformer's rubber grommet are trapped under the encasement of the audio transformer. Do not 'plonk' the transformer down in situ, but rather slide it in from the rear of the frame, pressing down gently, and encouraging each wire to 'loop' upwards and lie gently against the bass panel's rear dust cover.
Take your time. Be logical and methodical. A good electrostatic speaker can entrance you for 25 years: a bad electrostatic 'speaker will exasperate you in 25 minutes!
If you are happy with your work, provide an audio signal and connect the speaker to the mains supply. IF FOR ANY REASON you need to re-check anything, do PLEASE remember to disconnect the speaker from the amplifier and AC mains, after which discharge the HT in the manner described in paragraph 1 headed 'WARNING'.
