MOTM

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.

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.

Does anybody else have any useful mods?

John Speth
Object Engineering, Inc
mailto:johns@...

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