MOTM

I have updated the bracket page of my website to include a photo that shows
all 4 sizes of the brackets.
http://www.wiseguysynth.com/larry/bracket.htm

Tomorrow I will be packaging many of your Stooge panel and other stuff
orders.  I plan to upset several people in line behind me at the post office
on Monday and Tuesday.  :)

Thanks to everyone that ordered stuff from Dave and I in 2001.  I really
appreciate everyone's understanding when delivery was not quite as quick as
we had hoped.

Special thanks to Paul for his willingness to farm out some of the metal
work (and huge profits <snicker>) to Stooge contractors.  And, of course,
thanks to Paul for MOTM.  Otherwise, we might be stuck with only Synth.com.
:)

I plan to resume work on the Joystick interface soon.  But, not before
EVERYTHING that is ordered has been shipped.

Beta testing of the breath control modification for the MOTM-850 is
complete.  Thanks Dave Trenkel.  It seems to work fine with the BC-1, 2, and
3.  However, the range seems to vary slightly for the different models. So,
one resistor may be different depending on which BC model you have.  Of
course, you can use a trimmer instead.  I will add a modification page for
the 850 to my website sometime in the next couple of weeks with schematics,
photos, and more.

Best to all,
Larry Hendry
www.wiseguysynth.com

Has anybody bothered to tweak their 410 so that the filter 
frequencies are all the same when the FREQ pots are all set to the 
same value?

I've noticed that if I pump a 1000 Hz sine wave into my 410s and then 
adjust the FREQ knobs so that each filter output is at its loudest, 
the FREQ knob settings vary between 3.0 and 5.0. That's quite a range 
and makes it rather difficult to correlate a FREQ knob setting to a 
Hz value when trying to dial up formants for speech synthesis.

Since the filter resistors are inside the Vactrol they can't be 
changed. Changing C6-C8 is unlikely a solution since caps are not 
available in a wide variety of values with 1% tolerances. It looks 
like the best solution is to tweak the Vactrol LED current through 
R54, R57, R60.

I was wondering if anybody has already done this on their 410, or has 
another solution. Or am I just being a nutcase?

At 8:50 PM -0700 12/16/01, Scott Juskiw wrote:
>
>Has anybody bothered to tweak their 410 so that the filter
>frequencies are all the same when the FREQ pots are all set to the
>same value?
>
>I've noticed that if I pump a 1000 Hz sine wave into my 410s and then
>adjust the FREQ knobs so that each filter output is at its loudest,
>the FREQ knob settings vary between 3.0 and 5.0. That's quite a range
>and makes it rather difficult to correlate a FREQ knob setting to a
>Hz value when trying to dial up formants for speech synthesis.
>
>Since the filter resistors are inside the Vactrol they can't be
>changed. Changing C6-C8 is unlikely a solution since caps are not
>available in a wide variety of values with 1% tolerances. It looks
>like the best solution is to tweak the Vactrol LED current through
>R54, R57, R60.
>
>I was wondering if anybody has already done this on their 410, or has
>another solution. Or am I just being a nutcase?

Possibly, yes, to all three questions :)

I could see why they wouldn't be the same.  The Spectrol 149 pots have a
10% tolerance.  You also have a number of resistors, a cap, two
transistors, and a vactrol, for each filter.  None of which are matched nor
precision parts.  I'm no EE, but I've also read that vactrols aren't
perfectly linear.  So even if you tweaked the resistor values to get the
knob settings to be the same for one set of settings, it might not be
temperature stable or matched up for some other setting.

Rather than monkeying around with a mess of 1% resistors and possibly not
getting anywhere, maybe you could simply adjust the position of the knob in
relation to the pot's shaft.  That would be a much less invasive procedure.