Using tube amp with electrostatic speakers.

Thanks for the info Lewm!

Andy

To summarize what Lewm said above (that he and Will have tried in their speakers) :
1. You can remove the brilliance control (or short the terminals) which is in series with the Toroid transformer (I removed the brilliance control and put in discrete resistors but will remove it entirely per Lewm's recommendation).
2. You can increase the shunt resistor value (mine had 10 ohms 4 - 2.5 ohm resistors in series) to lower the frequency of the pole (with the 36uf capacitor) from 440hz to a lower value.
3. Dr. West said it would not be an issue to increase the value from 10 to about 12-14 ohms with the toroid ll (I'm sure this is very conservative) to move the frequency pole lower.  Lewm suggested 20 ohms.  From my recollection, the concern that Dr. West had about increasing the shunt resistance was saturating the toroid transformer.  The toroid ll transformer offered by Soundlab is much larger than the toroid l.  I believe Dr. West said that it can handle an increased resistance without saturating.
4. You can use a better quality shunt resistor and it may add some minor benefits.

Regards,
Gary

Gary, That's a pretty accurate summary.  The notion to remove or bypass the brilliance control is actually older than the ideas to modify the backplate that came from Will and me.  

I remain puzzled that Sound Lab would upgrade to a larger toroid with presumably a better low frequency response and then continue to use the same values of R and C, thereby maintaining the same old crossover point (at round 440Hz for the values 10 ohms and 36uF).  But I don't actually recall what values SL used as OEM standard with the "old" original toroid, so it could be that the old values were actually something less than 10 ohms with something less than 36uF capacitance, which together or separately would give a higher crossover point.  Therefore, the values of 10 and 36 are "new" to Sound Lab.  As I now recall, the old values might have been 6-8 ohms (depending upon year of manufacture) and maybe 32 to 34uF.

Lewm,

For some reason, I did not ask the question of what resistor value is currently being used in the updated back plates with the Toroid ll when I discussed my upgrade.  Dr. West did confirm what you disclosed that the Toroid ll will not saturate as early as the Toroid l so you can increase the resistor value (I just don't know what they are using now, maybe someone else will chime in).

I have always wondered what the hot rod upgrade is for the Soundlab backplate.  Do you know what this upgrade is?

Atma-sphere - I agree that I am limited in power that can be delivered in the bass region of the speaker due to the high impedance of the speaker and the voltage that can be delivered.  Dr. West told me that the wattage claims for Soundlab speakers were to give people an idea of what kind of amplifier to buy (but he really mean't the wattage to infer what the power supply rails would be to adequately provide bass).

Regards,
Gary

I always loved the large Sound Labs speakers so when they announced their new 545 series I thought great! Got them in and after trying them with several different amps over 30 days (including my Atmasphere Novacrons) they just didn't have the magic that the larger Sound Labs  panels had. And yes I tried them with Zero Autoformers still without much success. To bad because they were made beautifully, got them in Birdseye maple. 

(Dealer disclaimer)