ASM-1 up and running

Bob Zimmer bzimmer at voicenet.com
Fri Oct 4 18:55:50 CEST 1996


At 08:14 AM 10/4/96 +0100, you wrote:
>>   Just thought I'd mention, I have my ASM-1 project up and running. I
built it
>> with the maximum amount of pots and jacks. Almost everything worked
Much text deleted!

>>    One thing that has me stumped is that the with really low frequencies
>> (like less than 1 hz), the output of the LFO seems to be asymetrical. On
>> the triangle wave, the rising part takes a lot longer than the falling
>> part. On the square wave, the voltage stays low for much longer than it
>> stays high. I believe I just used a ceramic dip capacitor, could this be
>> the problem ? Apparently it's discharging faster than it's charging at low
>> frequencies. Also, although my LFO goes well up into the audio range, it
>> stops oscillating when it gets below around .2 hz. Of course I'd like the
>> LFO to do really slow sweeps. As far as I know I put the proper components
>> in.
>>   Anyone have any suggestions ?
>
>Well, I try to avoid the ceramic cap's as much as possible... they leak 
>considerable more than certain other type's in the same range. When I go about
>building my ASM-1's I will use plastic caps (probaly polypropylen... they are
>quite cheap anyhow). There are polypropylen's available at 1uF (not as cheap,
>but you use up only one per ASM-1 board....). You can use polycarbonate or
>polystyrene as well... mylar (polyester) should also make an improvement...

I have finished my ASM-1 as well and am having different problems, but I
think that mine are pilot error! (;^)  I have a rack chassis on order and
temporarily have assembled the panel using holes in the top of an old shoe
box just to hold the parts in place to try things out!  I'll put a picture
(for laughs only please!) on my home page in the near future!

I noticed the same low end limitation in the LFO.  I did use polypropylene
caps, first quality ICs and 1% metal film resistors throughout the ASM-1.  I
felt the slightly higher cost was worth it to make the unit as good as
possible.  All first quality IC's added about $6.00 over the cost of
surplus, and I got the metal films for $.09 each with the ones (such as 1K
and 100K) bought in quantity being under $.04 each.

I think that the waveform problems are inherent in the very simple circuit
design.  In testing the LFO in actual CV use, I found that it is really
difficult to 'hear' the 'imperfect' waveforms.

The LFO range seems to be about .2Hz to 800Hz or so.  I'm planning to try
changing the timing cap and rate pot values along with a range switch to get
into lower frequencies.  If I get this working well, I'll post this and a
couple of other mods on the home page when they are done.

Bob

  >=== Bob Zimmer -- Philadelphia PA ===<
  >=== bzimmer at voicenet.com          ===<





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