[sdiy] sucess stories :)

[Magnus Danielson]

From: "Nils Pipenbrinck" <np at inverse-entertainment.de>
Subject: [sdiy] sucess stories :)
Date: Mon, 30 Jul 2001 00:25:32 +0200

> Hi folks,

Hi Nils,

Please allow me to toss in some comments...

> I spent the weekend building my asm-1 vco.. Of cause I didn't oscillated at
> first (but turned one of the opamps into a cloud of smoke). Anyways.. after
> reading the diy-list archive archive I found everything to fix it.

Ah, you got some fresh grey smoke in your lab...  ;)

> Just in case someone is going to build the asm-1 vco and is lurking on the
> list here are a couple of hints:
> 
> The LM311 voltage comparator has a pin called "ground". (that's pin 1). Even
> if it's called ground it should be connected to -15V to work properly. It's
> also a good idea to connect pin 5 and 6 (balance and strobe).

The VCO schematic has the flaw that I was too lazy to cook up a
propper symbol for the LM311. This causes some confusion unless you
have a sufficient hunch of electronics, the LM311 datasheet AND spend
some time pondering over the problem. Bug me like hell and I just
might fix it. The thing is that it is not just opening up the CAD
tool. I have to rehack some Postscript code as well as investigate a
property I have not tried out before in my postscripthacked schematics.

> The 18pF cap behind the LM311 is somewhat critical. I think it depends on
> the Fet used, but for me the fet didn't discharged the integrator-cap. I
> replaced the tiny 18pF with a 47pF. That fixed the problem.

Indeed. It forms a time-constant to ensure propper length of reset
time. If this time gets too low, it fails to empty the integrator-cap.

I haven't spent the quality time on that time constant issue, but this
is IMHO one of the single biggest troubles in getting the VCO started.

> Also, it's a rather good idea not to solder the expensive MAT-02 into the
> board when you test it. Next time I'll first use two 2N3904 and replace them
> when the vco is working. (I learned that the hard way).

What? Did you blow the MAT-02????

> Bye,
>     Nils
>     (now a proud owner of his first selfmade vco)

Good to hear Nils! Enjoy!

Cheers,
Magnus - one of those annoying ASM-1 guys