[sdiy] Ultrasonic VCO question for Ian Fritz (or whoever)

[Grant Richter]

You guys are talking about two completely different designs.

Ian is referring to his design for a triangle VCO, which uses Franco
compensation, being bipolar there is no amplitude shift with the
compensation.

Magnus is talking about Gene's modified Mikulic ramp oscillator as used in
the ASM-1.

Now be nice, or no one gets fruit cup.

> From: Magnus Danielson <cfmd at swipnet.se>
> Date: Mon, 28 Oct 2002 19:08:57 +0100 (CET)
> To: ijfritz at earthlink.net
> Cc: sbernardi at attbi.com, synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Ultrasonic VCO question for Ian Fritz (or whoever)
> 
> From: Ian Fritz <ijfritz at earthlink.net>
> Subject: Re: [sdiy] Ultrasonic VCO question for Ian Fritz (or whoever)
> Date: Mon, 28 Oct 2002 10:19:57 -0700
> 
>> Magnus --
> 
> Ian,
> 
>>> The compensation will distort the waveform for higher frequencies but trade
>>> from waveform accurateness (which is bad to start with due to the reset
>>> slope,
>>> I've seen it and it's not excessively nice) for better tracking abilities.
>>> What can be a problem is that the compensation leads to a slightly lower AC
>>> amplitude and raises the DC offset as the frequency raises and compensation
>>> starts to kick in.
>> 
>> 
>> How can you say you say you have "seen it"?  Have you built this circuit?
>> Where did you get the schematic if you don't have the EN issues?
> 
> If you would have bothered to read the ASM-1 webpage (the one which I happends
> to maintain), it says in clear-text (Gene's original text I might add) that
> the
> VCO is "substantially borrowed from Electronotes". I have build the ASM-1 and
> followed Genes schematics and description like many others. I've then tossed a
> sampling scope at it, which is not very strange either. I actually have stored
> away the sampling of the sawtooth at different frequencies.
> 
> I don't even know which of the Electronotes Gene is refering to. It is
> probably
> not the same, but the compensation form seems to be the same. I trigged on the
> description of it, not the specific EN in question.
> 
>> Why so you think the DC offset would change?  This is a tri oscillator, so
>> I see no reason for the pos and neg half cycles to be affected differently.
> 
> It is actually quite obvious. The compensation robs the lower end of the
> waveform by the resistor offset, but the waveform stops at 5 V regardless due
> to the comparator curcuit. This is clearly visible (on a scope) when driving
> the oscillator up to its far upper end.
> 
>>> IMHO, this is a fair trade anyway, since few depends on the
>>> accurate waveform and spectrum distribution about 50 kHz or so.
>> 
>> Plus that, the module only uses the square output (to drive a digital
>> waveshaper).
> 
> Well, I assume this is a result of it's use in your Electronote, but if you
> look at the same compensation scheme for direct use of the sawtooth, your in a
> different situation.
> 
> Cheers,
> Magnus
>