MOTM

John Speth wrote:
>
> I'd like to share a couple of MOTM modifications that I found 
> useful.  Both are simple and useful.
> 
> M120: Socket U3 (74HC08 quad AND) and experiment with using a 74HC86
> (quad XOR) instead.  The two devices are pin compatible.  Just make
> sure you use a 74HC86.  I used a 74HCT86 from Radio Shack and it
> worked fine.  The reason for the change was that I was sometimes
> bothered by the fact that, for low frequency signals on one of the
> inputs, the counter would sometimes (1 in 16 chances) come to rest
> at all 0s and, therefore, completely silence the output.  Using
> an XOR assures this can't happen.  The sound is definitely not as
> complex as with using AND gates but it does have a different
> character.

I tried the 74HC86, and it worked fine, but I personally prefer
the 74HC08 most of the time.  Putting a good double-wiper socket
in is a good move as it gives you the option of trying out the
other chip any time.  Perhaps a daughter-board could be plugged in
here to allow more complicated logic operations.  (I'll comment
more if I get something going.)

> M800: Solder a wire from the collector of Q1 to the unused pin
> of the trigger jack.  I tack soldered a wire from R1 on the
> component side to J2 and tie-wrapped it down.  This allows the
> EG to function as a complete ADSR with only a gate signal and no
> trigger.  It will function as shipped when a trigger plug is
> inserted.  I'm surprised this wasn't designed in.  I wonder if
> it might be better to use a series resistor of about 5K in
> this wire to protect against transients when inserting and
> removing a trigger plug.

Thanks for the insight.  I was thinking of wiring up a simple
discriminator circuit with a diode, a cap, and maybe a resistor
to act as a gate-to-trigger extractor, and putting that on the
switch of the trigger input jack.  If this resistor / wire
jumper gets Paul's blessing, I'll do it tonight!

> Does anybody else have any useful mods?

Ring modulator - change the "unbalance" resistor R15 from 100K
to 220K or even 300K.  I prefer 220K.

Sample And Hold - Clip diode D4 out to make the internal clock
more "square", this makes tracking sound right.  To get an idea
of how this alteration would sound, plug a square-wave LFO in as
the external clock and listen to the tracking mode.  Of course,
you might like the semi-tracking sound provided by the internal
clock better ...

Regards,
 
Roy Tate
roytate@...
http://www.ionet.net/~roytate