my few ASM questions...

[John Speth]

Concerning the saw-tri convertor for the ASM1, I prototyped this circuit recently and I got disappointing results in 2 parts:

1. The flyback or vertical edge of the saw was too slow causing a little glitch at one of the peaks of the triangle.  I naturally dealt with this by using a single pole LP filter on the output op-amp by putting a cap across the feedback resistor.  I reduced it a little but I found I had to make a tradeoff between high frequency integrity (my max was 10KHz) and glitch reduction.  No satisfactory tradeoff was achieved.

2. Another problem was that I was able to correlate a problem with the saw-square op-amp circuit to a little ripple in the sawtooth ramp which also showed up in the triangle and, coupled with the problem from #1, it made a ratty triangle at high frequencies.  I noticed that the saw output amplifier has a slightly reduced gain while the square output amplifier is operating in the linear region.  The square output op-amp is configured as a very high gain amp that saturates rail-to-rail.  When the input signal just crosses 0V and the amp is not yet saturated, the sawtooth output amp shows a little flattened section of the sawtooth ramp and it's especially noticeable at higher frequencies.  I wonder if I might have a power supply problem.  Again, it's not as noticeable at lower frequencies but it's always there at any frequency.  Does anybody else see this in theirs?

I experimented with several saw-tri converters (LM3900, Electronotes HW recitifier, on/off switching transistor Steve mentioned).  Best results were attained using the Electronotes HW rectifier.

John Speth
Object Engineering, Inc.
johns at oei.com

-----Original Message-----
From:	Steven Maietta [SMTP:SMAIET01 at ucis.vill.edu]
Sent:	Friday, April 17, 1998 9:20 AM
To:	synth-diy at mailhost.bpa.nl
Subject:	my few ASM questions...

OK before I start soldering, a few easy questions...

1-In the info I got with the board, using the ASM with a keyboard was
brought up.  Something with input/output buffers ...I am not really sure..
Can anyone fill me in on any tips to make it run smoothly with my KBD/ JKJ
CV4 MIDI/cv steup?

2-Has anyone done the saw to triangle mod and if so, how did it go?

3-Lastly, does anyone have any of the proper Tempco resistors or MAT-02's
left from their experience?  Is the difference really that drastic?

Thanks for any info!!!  Got the SynthDIY ASM archives, recent posts, info
packet, c-list's faceplate, and the web-page.. I'm ready!!

~Steve