Posted by Lew on October 29, 2002 at 13:49:35:
In Reply to: Back Plate Tweaks posted by Matt Rogers on October 29, 2002 at 08:09:32:
What is the benefit of going toroid? Dunno. Have not heard an SL spkr that did NOT have the toroidal trannies in recent years, but most folks say you get better highs and midrange. (Surprise!)
What values of R and uF should I be trying? Sounds like you are in the correct ballpark. The factory circuit for the conventional treble transformer and/or load-insensitive amplifiers (if there is such a thing) is 48uF/6ohms. For spkrs with the toroid and/or load-sensitive amps, the recommendation is 24uF/12ohms/15mH (inductor). Yes, Sound Labs will sell you the parts in kit form. Some folks, like Kevin Covi and Roy, who have A3s with toroidal transformers, are experimenting with a 24uF/10ohm network, but they have made further modifications to the backplate that also help the impedance characteristic. (See archives.)
I have read in this site that some x-overs have 12R and 24uF including 15mH pararelled to the resistors. Others have 48uf and 10R. Should I be toying with some inductance here? (See above)
The Kevin Covi tweak (elsewhere on this site) on his A3 does not sound right to me. How does he get away with the overlap of frequencies (6dB slope) if he had the two x-over points meeting at 350Hz? I don't quite understand the question. AFAIK, Kevin uses a 1 mH inductor in series on the bass transformer and a 24uF/10ohm network on the treble transformer. (See also above.)
12R made the sound of my Pristines really aggressive, is there some tweak that I could apply here? If you already have installed a 12R/24uF network, then try adding the 15mH inductor in parallel with the resistors, as per the factory recommendation. But I don't know if you need this with the standard treble transformer. Better yet, upgrade to the toroidal transformers AND then add the inductor.
How do I listen for transformer saturation? (I supppose it will sound pretty lousy at frequency extremes, but otherwise I can only think of funny answers to this question.)
Has the bass trans been changed over the years of production? Are all models using the same trans? Dunno.
How does Roger West sets the x-over points? Carefully.
Will Roger West send out toroids and parts for upgrades? Yes.