Posted by Lew on April 21, 2004 at 08:13:44:
In Reply to: Re: M series tone controls posted by avsgroupie on April 20, 2004 at 22:03:29:
Answering your questions by number:
1. Good question. I think it's a series potentiometer; I cannot find the schematic on my
computer at the moment. If you are sophisticated enough to ask this question, then the wiring
will be obvious to you when you look at the backplate circuit.
2. So far as I know, the answer is "yes, the mid control only chooses among the several choices
of inductance". BTW, others who have taken measurements have told me that the +3db setting,
which removes all inductance preceding the bass transformer, is to be avoided (if you are using
an impedance-sensitive amplifier) due to the low midrange impedance that results.
3. Probably but not dramatically. The impedance will be determined largely by the natural
character of an ESL to behave like a capacitor and have a very high impedance at low frequencies.
Perhaps Roy or Kevin Covi can comment on these questions and especially your question on
phase effects. (I don't think the bass control would have much effect on phase, and the mid- and
hi-pass filters are first-order Butterworth types, which is reasonably benign wrt phase, unless
one has incorporated the factory recommended "high impedance" modification, which involves
the addition of an inductor in parallel with the input to the treble transformer, thereby changing
the character of the hi-pass filter to one with a 12db/octave slope. The latter set-up perhaps
could have an unfavorable effect on phase response.