Moog Filter!

[Sean Costello]

Tony Allgood wrote:
> 
> Rene >This also explains why the self oscillation stops below some
> frequency.
> 
> This is so true, but it doesn't explain why the new MiniMoog made in
> Wales oscillates across the spectrum. The manufacturers say this is a
> bonus feature, ie. better than the original. 

The new Wales Minimoog probably uses a different coupling scheme. Most Moog
filters (such as the Prodigy, Rogue, and Tom G.'s scheme) have a different
coupling scheme for the differential output amplifier, that produces a more
constant Q throughout the audio range. However, I would not call having constant
Q in the Minimoog filter a "bonus." As far as I understand things, the drop-off
in Q in the bass register of the Minimoog filter contributes to the great bass
sound of that synth. The same characteristic can be found in the TB-303 filter.

As far as constant Q in a Moog filter, I would think that this would only be
important when the filter is being used as an additional oscillator (such as in
the Multimoog, where it is used as an FM source). For this to really be useful,
the filter must be temperature compensated. The Micromoog/Multimoog had a nice
way of doing this, where the filter expo convertor was on the same heated 3046
chip as the expo convertor for the modulating oscillator. 

Sean Costello