SDS Audio Labs - Quad Electrostatic Loudspeaker FAQ

Original Quad Electrostatic Speakers

I just got a set of quads and I want to try them, what should I do?

All true electrostatic loudspeakers must be powered up which is typically done by plugging them into the wall. The original Quad ESL's are no different. They use a round Bulgin plug (or an IEC connector on the very latest ones) to plug the speaker into the wall. They also have a voltage selector on the power supply to allow a single supply design to be used world-wide. The speaker can take a while to charge up. The diaphragm coating used on the original Quads has not held up very well over time, and what used to take a few minutes to charge up, can now take a day or more depending on the age and condition of the panels. The speaker will not play or play very quietly until it is charged up. resist the urge to turn up the volume to compensate! The treble panel can be damaged by overdriving, and it's the audio signal that does the damage. A Quad ESL is about as sensitive as a normal cone and dome speaker, so do not turn up the volume beyond the normal range used for a more conventional speaker. You won't do any damage playing the speaker before or as it's charging, but care should be taken to not turn up the volume excessively to compensate for the lack of output from an uncharged speaker.

I've left the speakers charging for days, and they still are quiet, or one of them is quieter than the other

The Quad ESL's are quite old, and the diodes in the power supplies were made during the early days of semiconductors. As such, the diodes in the rectifier portion of the power supplies of the Quad ESL's often go bad over time. This results in a low output in the power supply that charges the speaker panels, and thus low output from the speakers. This is the most likely cause of a set of speakers having an output imbalance. This imbalance will result in a speaker that still sounds "correct" tonally, but the output is low across the entire sound spectrum. The solution to this problem is to rebuild the rectifier portion of the power supplies.

My speakers work fine, but the lights on the power supplies are not lit

The lamps are purely ornamental, and do not change the function of the power supply when they burn out. They are Neon bulbs and will burn out over time. I replace the neon bulbs in the holders with a small circuit board containing LEDs that will last for many many years.

My speakers have no treble, like someone put a sleeping bag over the speakers

This is a classic symptom of a blown treble panel. The reduction of treble and upper midrange, can vary with the degree of damage to the treble panel. Make sure the speaker has charged for a day or so to eliminate the possibility of slow charging. If the speaker is over-driven the treble panel will arc and fail if there is no treble protection circuit installed in the speaker.

My speaker seems to be lean in the bass and when I put my ear up to the front grille, one of my bass panels (on the left or right sides) seems to have little or no output

The diaphragms can split in a bass panel, but that isn't very common. What is more common is the diaphragm coating evaporating over time, and the diaphragm will not fully charge up.

My quad ESL is making thumping or hissing noises when powered up, but no music is playing (or the amplifier isn't even powered up)

This is most likely dirt stuck inside one of the panels (most likely a bass panel). This is often caused, after a bass panel dust cover has split and is allowing dirt to be pulled into the bass panel. This can often be repaired by letting the bass panel discharge (over a day or so) and then vacuum out the panel through the front and back stator, then reinstalling a new set of dust covers.

What's with the burlap and horsehair pads haphazardly tarred in place on the back of these speakers?

Those are there to dampen the rear wave coming out of the back of the speaker and also to reduce the "Q" of the bass panel resonant peak. Some folks think they sound better without them. I always welcome people to experiment with removing them (just leaving the back off the speakers is the easiest way to test it out), but keep them around in case you change your mind or sell the speakers.

Do you have this spare part that I need for my Quad ESL?

I have a limited selection of spares, and they are parts that have come out of other Quad ESLs. It can't hurt to email me, but there's a good chance that I don't have what you need.

There are several people rebuilding Quad ESL's. Why should I choose you?

I suggest you look around and make up your mind based on previous work, customer satisfaction, and comfort level with each vendor. I have been rebuilding the original ESL's for over 20 years, and publish my techniques and methods.

How long does it take to rebuild my Quad ESLs?

It varies, I do Quad repairs as a hobby and sideline business. I typically take 2-4 weeks for a rebuild, but I also often have a backlog. I sometimes travel for work, and in the summer and winter I spend a lot of time outdoors enjoying New England, so the turn-around time can vary. Please e-mail me and I'll estimate the time to completion and get you in the queue.

I'm pretty handy, can I rebuild these speakers myself?

Yes you can, there is nothing magical about fixing these speakers. It is fairly involved, and expect to spend many hours on it. It takes me around 40 hours to rebuild a pair and I'm no stranger to the process. The easiest way to rebuild these speaker yourself is to get a kit from ER Audio. They sell a kit specifically for the original Quad ESL

Quad ESL-63, 988, 2805, and 2812 Electrostatic Speakers

My speakers are making a thumping or a sizzling noise with the speaker powered up but the amplifier off or not playing music.

The vast majority of quad panels are assembled with a thermoset glue that degrades over time and gets brittle. There appears to be many potential causes of this degradation, including ozone from the charged panels themselves. The result is that the perforated stator elements break free from the nylon support structure and are pulled into the diaphragms. Shown below are two videos that demonstrate the issue.

Thumping Quad Panel

Bad Stator Glue

Do the electronics need to be rebuilt?

The Quad electronics are surprisingly reliable. In a rebuild, I replace the electrolytic capacitors, and the input connectors if desired.

Is there any difference in the internals of the various versions of the new Quads (63, 988, 989, 2805, 2905)?

The earliest Quad ESL-63's had panels that are different than all the newer speakers. The panels of the majority of the 63's, 988's, 2805s are identical in construction and performance. The electronics has slightly changed over the life of the 63's. Anything newer than the 63's have electronics that is functionally the same.

I'm pretty handy, can I rebuild these speakers myself?

ER Audio Rebuild Kit

Misc Questions

Which Quads do you prefer?

That's a hard question. In a small room, the original ESL's are really in their element. They have a midrange transparency that is jaw dropping on the right equipment and recordings. But the original ESL's don't have the bass extension and control of the newer Quads. They do not have the dispersion and treble refinement of the newer Quads. In a larger room, the newer Quads really come into their own. I own both, but find myself listening to a pair of 63's most of the time. The newer quads are easier to find, and are more likely to be in operable condition.

What amps, cables, cords, etc should I use with my Quads?

I'm a fan of tube amps, so I would use that on any of the Quads of any vintage. but that's my personal mania. For the original ESL's, about 15 watts is all the power you need (more will break the speakers). I'm also a fan of Canare interconnect and speaker cables. Good performance and reasonable cost. The quads will not benefit from expensive power cords.