ASM-1

[Magnus Danielson]

>>>>> "KL" == Kevin Lightner <majmoog at synthfool.com> writes:

Hi Synthfool!

 KL> I've just finished assembly on my first ASM-1. (Sorry it took so long to
 KL> do, Gene!)

 KL> First off, I'm very happy to say that it all worked upon it's first power
 KL> up!  Yeahhh!:)

Congrats! But this also shows just how easy it is if you pay some
attention to details...

 KL> However, if some of you already experienced ASM-1 folks don't mind , I have
 KL> a few questions to ask.... :)

Sure.

 KL> First a descriptive-
 KL> My ASM-1 uses 2N3904s (instead of the MAT02) and KRL 1.87K 3% tempcos
 KL> (similar to Arp).
 KL> The pairs and tempco are bonded to each other for each VCO.
 KL> The FETS are 2N4391's.

Sounds reasnoble.

 KL> I didn't have any 30pf caps for the VCF or 18pf caps for the VCO's.
 KL> Instead, I used 33pf caps for both.

Well, if you change the integrator capacitor will your rest-frequency
change. According to an old analysis I did will the rest frequency
(unmodulated frequency) be:

	       3
	f  = -----
	 0   C * R

where

f0 = rest frequency in Hertz
C  = integrator capacitor capacitance
R  = value on the collector resistor of Q1 up to +Vcc

So for C=22nF and R=150k (like in my schematics) you get f0 = 909.1 Hz
which is close to A5 (880 Hz).

If you used C=33nF and R=150k you would get 606.1 Hz. Detune to happy
tweaking range.

The cursuit isn't cut-troat tricky on that capacitor, it happily
adjusts.

The 18 pF will change the reset time for the JFET, if made too large
this will effect the frequency-linarity of the core (which IS
operating in full linarity). 33 pF should be pretty safe, you have
moved the VCO down anyways...

Go measure the lower and upper frequency you can modulate it to, it
would be interesting to see where it lands. Also the rest frequency
would be nice (0 mV at pin 1 on U1-A).

 KL> It's about 80% 1% metal film resistors (the vco summers and other criticals
 KL> are 1%), but the rest are 5% carbon film.

I used 1% except where I couln't get anything else... then I was
forced to fall back to 2% (big tears...).

 KL> Standard sockets (not machined) were used. (Generally, I use machined but
 KL> this is a LOT of IC's :)

What? Did you put the ICs in sockets????

I soldered mine on directly and haven't had the need to replace a
single one... sockets just creates more errors in the long run.

 KL> Board is wholly defluxed (and gorgeous!)

Yeah, I know the feeling!

 KL> My current draw is 103ma (+15volts) and 118ma (-15volts).
 KL> (Strange for me to see the negative rail drawing more than the positive.)

If you look at the schematics you will see that there is several
non-balanced use of power. Just one VCO has 3 direct uses and several
indirect (Op-amps work mostly in either of the two 15 V jumps and
others work fully balanced - the power attachment does have anything
to do with it, it is just how the source their output current).

Why did you measure the currents if you didn't suspect a difference?

 KL> Everything appears to work fine. Waveforms are of great shape, noise is
 KL> good, VCF works, etc.
 KL> The VCO's seem very stable too. :)

 KL> I haven't really hooked up pots and used or played the unit.
 KL>  I've just gone through each "module" functionally.

What keeps you from doing it? Go at it!

Cheers,
Magnus