I built two CGS VCOs this year, and purchased kits with the special
parts for the ASM-1 VCO here.
http://www.elby-designs.com/shopping/enter.html
The `special components’ kit for the ASM-2 contains the following
harder-to-get components:-
1. 2 off MAT-02
2. 3 off J108 transistors
3. 2 off 1K, 3500ppm TEMPCO plus 2 off 62R 50ppm (giving a 3300ppm result)
4. 3 off LM329-6V9
This kit is sold for $65.00. I bought two of a different kit that
contained 1 LM394, 1 J108, and 1 TEMPCO resistor set, for about $50. You
could ask about this or just take the 2 LM329 even though you don't need
them.
If you use this 1K 3500ppm TEMPCO resistor, you will NOT want to add the
62 ohm resistor in series. I found that with a 56K 1% resistor, as in
Ken's schematic, and the 100K 1% resistor in series with the SPAN
trimmer, it was not possible to tune to 1V/octave (span trimmer all the
way down to zero was not enough). I had to remove the 62R resistor,
which was a pain to install in the first place - it required cutting a
trace. The 62R is supposed to change the tempco to 3300ppm, but I
haven't noticed a problem. Temperature stability isn't that big of a
concern for me.
I built the VCO circuit a little differently, changing the design a bit.
I left it very minimal, omitting the CV1 and CV2 Serge-like FM inputs,
adding a fine tune panel pot, and using a 1.5M instead of 150K to set
the initial linear current for a lower initial frequency - this is
described in the ASM-1 VCO literature. I used an LT1013 for IC1. The
only outputs are a DC-coupled saw and square wave. I have both of these
going +/-5V. The square wave comparator runs off the DC coupled saw, so
it has no low frequency limit. My objective was to get a pair of stable
VCOs with exponential and linear FM, sync, and PWM. (Email me if you
would like the schematic.) I did not include the waveshapers mostly
because of panel space, but also because I have a lot of wave shaping
capability in my synth (two Blacet Miniwaves, a CGS Wave Multiplier,
MOTM-510 Wave Warper, MOTM-120 Suboctave, etc). It would be fun to play
with those waveshapers! But it didn't fit into my "master plan" for the
synth. The CGS VCOs stand proudly next to a pair of MOTM-310s and I use
them interchangeably. The MOTM-310 may be more stable, but I haven't
noticed. CGS rocks!
One last point of comparison with the MOTM-310: I had hoped to get off
cheap, but with the Schaeffer panel, three $7 pots, $25 special parts, a
Stooge bracket, some RN55E resistors, etc, the costs added up to the
$150 ballpark for one CGS VCO. You can get a MOTM-310 kit for only $209.
It is a great VCO, but it doesn't have linear FM or sync. I am glad I
have both the MOTM and the CGS VCOs. The other two in my rig are MOTM-300s.
-Richard Brewster
Jay wrote:
parts for the ASM-1 VCO here.
http://www.elby-designs.com/shopping/enter.html
The `special components’ kit for the ASM-2 contains the following
harder-to-get components:-
1. 2 off MAT-02
2. 3 off J108 transistors
3. 2 off 1K, 3500ppm TEMPCO plus 2 off 62R 50ppm (giving a 3300ppm result)
4. 3 off LM329-6V9
This kit is sold for $65.00. I bought two of a different kit that
contained 1 LM394, 1 J108, and 1 TEMPCO resistor set, for about $50. You
could ask about this or just take the 2 LM329 even though you don't need
them.
If you use this 1K 3500ppm TEMPCO resistor, you will NOT want to add the
62 ohm resistor in series. I found that with a 56K 1% resistor, as in
Ken's schematic, and the 100K 1% resistor in series with the SPAN
trimmer, it was not possible to tune to 1V/octave (span trimmer all the
way down to zero was not enough). I had to remove the 62R resistor,
which was a pain to install in the first place - it required cutting a
trace. The 62R is supposed to change the tempco to 3300ppm, but I
haven't noticed a problem. Temperature stability isn't that big of a
concern for me.
I built the VCO circuit a little differently, changing the design a bit.
I left it very minimal, omitting the CV1 and CV2 Serge-like FM inputs,
adding a fine tune panel pot, and using a 1.5M instead of 150K to set
the initial linear current for a lower initial frequency - this is
described in the ASM-1 VCO literature. I used an LT1013 for IC1. The
only outputs are a DC-coupled saw and square wave. I have both of these
going +/-5V. The square wave comparator runs off the DC coupled saw, so
it has no low frequency limit. My objective was to get a pair of stable
VCOs with exponential and linear FM, sync, and PWM. (Email me if you
would like the schematic.) I did not include the waveshapers mostly
because of panel space, but also because I have a lot of wave shaping
capability in my synth (two Blacet Miniwaves, a CGS Wave Multiplier,
MOTM-510 Wave Warper, MOTM-120 Suboctave, etc). It would be fun to play
with those waveshapers! But it didn't fit into my "master plan" for the
synth. The CGS VCOs stand proudly next to a pair of MOTM-310s and I use
them interchangeably. The MOTM-310 may be more stable, but I haven't
noticed. CGS rocks!
One last point of comparison with the MOTM-310: I had hoped to get off
cheap, but with the Schaeffer panel, three $7 pots, $25 special parts, a
Stooge bracket, some RN55E resistors, etc, the costs added up to the
$150 ballpark for one CGS VCO. You can get a MOTM-310 kit for only $209.
It is a great VCO, but it doesn't have linear FM or sync. I am glad I
have both the MOTM and the CGS VCOs. The other two in my rig are MOTM-300s.
-Richard Brewster
Jay wrote:
>on 10/12/04 9:12 PM, bbluthang at jumpswine@... wrote:
>
>
>
>>the first one has a LM394.
>>the 2nd got a 2SC1583 (the shop selling 394's went belly-up, 1583's
>>are starting to dry up too)
>>it works fine, but i'd like to find some more LM394 or MAT-02 for the
>>next two.
>>The tempcos were tiny little things, size of 1/8W resistors, got them
>>from a friend.
>>
>>
>
>So, anyone got a reliable source for any of the above transistor pairs?
>
>
>
>