ASM-1 Tips

Christopher_List at Sonymusic.Com Christopher_List at Sonymusic.Com
Thu Jan 9 17:53:36 CET 1997





The following tips will be included in an info packet that I'm sending out
with the faceplates, but I figured I'd send it to the list for anxious
builders and for those who are gettiong faceplates....

I finally completely finished my first ASM-1 last night and tuned the VCOs
and everything. These VCOs are fantastic - seems like they have better
range and tracking than my tri-square VCOs. They also seem to synch a
little bit when really close together, which, as far as I'm concerned, is a
feature. That's because I love PWMing (or FMing) VCO #2 from VCO #1 and
tuning them to perfect 5ths or a fifth and an octave. What a GREAT sound -
buzzy and mean - run it through the filter with an 80/20 mix of LP/HP and a
lot of Q - yum yum! Then you take VCO#2 and run it BACK to the synch in on
VCO#1, and then you... and then..... and you can even..... :)

- Enjoy!

- Chris


VCO

1.   I prefer a 3M rather than a 1.5M resistor on the fine tune. This way
the full range of the fine tune knob is exactly one octave...
2.   I realized only after making the faceplate that I usually run both
VCOs off of the same CV input and that it would be nice (and save a patch)
to have an extra CV input that connects (via 100K resistors) to the CV
summing nodes of BOTH VCOs. I put this extra jack on an unmarked section of
the panel right next to the glide output, since I often connect the glide
to the VCOs.
3.   Another way to save on patch inputs that are often used the same way
is to make the Sync input on VCO #2 a SPST switch rather than a jack.
Hardwire to the switch input to the output of VCO #1.
4.   The Initial PW is a pot that is connected to + and - V. Note that with
this set up, and a 100K input resistor, the PW will hit 0% and 100% VERY
quickly - I'd suggest replacing the 100K resistor for this PW input to 300K
or 330K.


VCF

1.   An "inverting scale" CV input can be created by connecting the jack to
   the WIPER of the pot, then connecting the + side of the pot to the 47K +
   input resistor, and the - side to the 47K - input resistor. Note that
   this is an exponential input - not linear. Also note that with 47K
   resistors, if you turn it all the way to the + side you will actually be
   amplifying your input voltage - a +5v input will wind up acting like a
   +7.5v input. If you want it to act like +5v, you should use 61K
   resistors in place of 47K. I like my depth pot to be more sensitive, so
   I use prefer 56K or 62K resistors. With a 100K pot, and matching
   resistors of value R, the amplification level when the pot is turned all
   the way up will be (100K/R - (100K/100K+R)) turning the pot all the way
   down results in a negative amplification of the same amount and
   centering the pot results in a 0 input voltage.

2.   The cross fader output between high pass and low pass is made as
   follows;
·    Connect the low pass output from the PCB to one side of the pot and
     the highpass output from the PCB to the other side of the pot.
·    There are three TL082 opamps in the VCF, call the middle one on the
PCB "Joe".
·    Remove the three 100K resistor to the right of Joe.
·    Remove the 33K resistor to the left of Joe
·    Connect a jumper wire between pins 6 and 7 on Joe
     (those are the two middle pins on the right side) using the holes
     that were supposed to be used by 2 of the 3 100K resistors.
·    Run a wire from the wiper of the HP/LP pot x-fade pot to the lower
     of the two holes that were supposed to be used by the 33K resistor
     (this is the hole closest to Joe).
·    Connect the bandpass and notch outputs from the PCB to a faceplate
     mounted SPDT switch - the notch output is your HP/LP x-faded output.
·    Connect the middle of the switch to the output jack on the faceplate.


ADSR

1.   You can add an LED to the ADSR gate input so that you can see when the
gate is active. Simply connect a 910 ohm resistor to the top pin of the
.001uF cap in the ADSR circuit, connect an LED between this resistor and
ground. The flat edge on the side of the LED is the ground side.
2.   Maybe I did something wrong, but my ADSR had troubles when driven from
a bi-polar input signal (like the output of the LFO). I thought the LM358
woun't have a problem with this and would automatically clip the negative
input signal - but maybe not. To correct this, I simply soldered a diode
between the gate input jack and the wire to the PCB (stripe on the diode
goes on the PCB side).

VCA

The initial level pot is connected to ground and +V. The wiper acts as a CV
input. I used a 300K input resistor and not 100K or 220K. That way you have
Vout = Vin when the pot is turned all the way up.







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