[sdiy] Moog ladder filter transistor pairs matched or not..??

[Michael E Caloroso]

You won't be able to match the resonance without simple calibration.

I own an early RA Moog Minimoog with all five transistor pairs matched
in the filter.  I have played two other RA Moog Minimoogs earlier than
mine and the resonance quality of the filter of both were very close
to mine.

When I play later minimoogs with only the top and bottom transistor
pairs matched, the resonance quality is different from mine and they
were all different from one another.

The big reason is the unmatched emitter resistance slope between the
unmatched pairs, thus the poles of the 6dB/oct RC product of those
pairs will not be in the same position between filters (read: the
resonance changes).  The only calibration that will fix this is one
that varies with cutoff current and feedback (resonance) signal in the
ladder and that is far more trouble than it is worth.

MC

On 2/24/14, Mattias Rickardsson <mr at analogue.org> wrote:
> ...the resonance will not match between voices *without proper calibration*
> ,
>
> or
>
> ...the resonance will not *even with calibration be able to* match between
> voices?
>
> /mr
>  Den 23 feb 2014 20:56 skrev "Michael E Caloroso"
> <mec.forumreader at gmail.com
>>:
>
>> If you're only using it in a monophonic system, you can get away with
>> the top and bottom matched pairs.
>>
>> The minute you use it in a polyphonic system, you need all 5 pairs
>> matched or the resonance will not match between voices.
>>
>> MC
>>
>> On 2/18/14, Gordon JC Pearce <gordonjcp at gjcp.net> wrote:
>> > On Tue, Feb 18, 2014 at 09:12:22AM -0500, Jean-Pierre Desrochers wrote:
>> >> You are probably right Tom,
>> >> I remember now reading something like what you just stated..
>> >> In fact what I need to know for my future projects
>> >> is what are the 'picky' transistors that absolutely need matching..
>> >> in that design. I don't care spending some time
>> >> on my tranny matching rig to make sure the VCF
>> >> works as it's supposed to.
>> >>
>> >> JP
>> >
>> > Having tried matching diodes and transistors, I have come to the
>> conclusion
>> > that - particularly with cheap Chinese parts bought for pennies per
>> hundred
>> > - any random two you pull out of the bag will be Pretty Damn Close.
>> >
>> > --
>> > Gordonjcp MM0YEQ
>> >
>> > _______________________________________________
>> > Synth-diy mailing list
>> > Synth-diy at dropmix.xs4all.nl
>> > http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>> >
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>