Quad 988 mod review

I just had the Quad 988's modded by Kent McCollum of Electrostatic Solutions. He swapped out the factory input electrolytic cap for North Creek Zen film caps and Sonicap bypass caps. Along with a few other things.

I had mentioned to him before the upgrades, I felt like the mids were lacking. Especially noticeable when listening to female vocalists when singing with a band. The instruments would drown out her voice (an exaggeration of course), like her mic was turned way down.

Now. The female vocalist has been brought forward on the stage and is part of the band rather behind. Major improvement and very noticeable. Her voice is natural now, in balance and tone.

Overall, instruments are more focused and clearer. I can hear more of the overtones from acoustic strings. Very natural -- closet to the real thing I have heard from my system.

Highs are very articulate now also. Cymbals are crisper and really ring naturally.

Horns are incredibly focused and accurate. Its amazing the depth of the overtones heard from brass and woodwinds.

Its like I'm listening to a whole new system -- I'm really stunned at how major the improvements are
What was the cost of the upgrade? Thanks.
Sorry for the super-late response, I have not checked this thread in a long time. Below is a "cut-n-paste" of Kent McCollum's classified he is running now-a-days. His charge is $995.00

"Electrostatic Solutions announces our Reference Update for the Quad ESL988 electrostatic speaker. We consider the ESL988 a standard setting speaker in its stock configuration, but with careful updating of the speaker overall performance can be greatly enhanced. Our update addresses the major problem areas of the speaker as delivered in stock form: heavy grille cloth, low quality passive audio components, wire, speaker connectors and poor internal wire routing.

Our 988 Reference Update consists of the following:

- The stock R/C Network is replaced with quality film capacitors and a Mills MRA-12 resistor. In stock form the R/C Network consists of a 220uF electrolytic capacitor and sand-cast resistor. The R/C Network is wired in series with the audio input and is the first thing the audio signal sees inside the speaker. Electrolytic capacitors are not know for good audio signal performance but were chosen for this application based on size and cost considerations. As you can see from the pics the film type capacitor is physically huge and certainly vastly more expensive than electrolytic type capacitors.
- Film capacitors are North Creek Music Zen/Crescendo types. A new board is installed next to the delay line assembly on stock mounting points.
- The stock motherboard is modified replacing the input load resistors and coupling capacitor. SoniCap Gen I and Mills MRA-12 resistors are installed on the modified board.
- FS2 polyswitch is eliminated from the signal path. FS2 is implemented as a safety feature and is intended to prevent any damage to the input components due to small power amplifier clipping. This safety feature was added late to the production run of the original ESL63 and was carried over in the 98 series design. Basically you have an MOV type device wired in series with the audio signal. A much better solution is to use an appropriate size amplifier, in the 50-100watt range and this will eliminate any power amplifier clipping issues. Additionally, once the speaker is updated, power handling ability of all audio signal components is increased by a factor of 4.
- All stock audio signal wire is replaced with audio grade wire, 14AWG high-purity copper, Teflon insulation.
- Input audio signal wire is re-routed in the plinth. In stock form the input signal wire routes on top of the AC connector!
- New audiophile grade 5-way binding posts are installed.
- The EHT power supply circuit is revised. In an attempt to improve speaker sensitivity Quad raised the polarizing voltage on the 98 series. This voltage increase raises sensitivity by a mere 1dB but can greatly reduce electrostatic element life. We believe this is a bad trade-off in performance versus service life and reduce the polarizing voltage to the original Quad ESL63 standard. This modification, in addition to turning the speakers off when not in use, will dramatically increase element service life. The slight loss of sensitivity is meaningless in any real sense and user feedback reports that speaker sensitivity is actually increased!
- New acoustically transparent grille clothe. We believe the best performance is achieved with no grille cloth, but an improved grille cloth will be fitted if desired.
- Complete speaker performance test and update documentation. This includes circuit diagrams showing all component value types and locations, circuit revisions and pictures of the speaker before and after the update.
- Return freight in North America.

We have spent nearly 3 years developing our Reference Update evaluating the results in a wide variety of systems. Updates do not in any way damage or permanently alter the speaker. All updates are completely reversible if desired. Customer feedback for both our ESL988 and ESL63 Reference Update has been overwhelmingly enthusiastic.

What can you expect from the updated 988?

- DETAIL: Speaker resolution is increased providing more detail and musical texture. This does not come by a mere change in tonal balance. Overall speaker tonal balance and presentation remain unchanged. There is simply more ‘there’.
- SOUNDSTAGE: Soundstage size and definition are increased. Ambient cues are enhanced and the slight recessed quality of the midrange, especially on female vocals, is eliminated.
- DYNAMICS: The dynamics of the speaker are constrained by the poor passive components. They are far from stable and change greatly over time, especially the R/C Network electrolytic capacitor. Removing this bottleneck enhances the speaker’s macro and micro dynamic capabilities.

Electrostatic Solutions offers a 30-day money back guarantee of satisfaction and a 3-year service warranty on all our products and services. Turn-around time for our Reference Update is 10 days after receipt of your speakers.

Electrostatic Solutions offers sales, service, updates and parts for classic electrostatic speakers. Please drop us an email if you have any questions or call 913-208-7657."

--cut-n-paste from Kent McCollum of Electrostatic Solutions classified add on Audiogon.

Link to more info; http://www.estatsolution.com/
I did a similar upgrade myself to repair my 989s whch have become very senstive to treble transients (it shuts down)
I ended up having to replace the evil bendix lytic with film caps, bypassing the FS2, upgrading the input R to Mills 12W 1.5 Ohm, the transformer resistors with Caddock,
and most importantly the small 1.5uF cap between the 4 resistors with a film cap.
I have had no luck with cap bypassing so far.
bypassing one cap with a different brand always gets me phase problems (moving violins and vocals shifting forwards and backwards.
This mod is essential to do these quads justice.