[sdiy] eml 101 VCO: continuously from tri to sqr to saw

[Scott Gravenhorst]

ganesha <goaqihai at yahoo.co.uk> wrote:
>Thanks, that's some really interesting information. If
>you get the chance to measure it that would be really
>interesting. I also didn't know that the 8va was the
>saw 1 octave up

I have a circuit I found - I have no idea where, it is a scan from some
article by H. Millian called "Melodic Sawtooth".  It uses both halves of
a 741, but I'll bet many other opamps will work as well.  It can produce
a saw wave of twice the frequency of the input to the circuit (also a saw).  

I don't seem to see any web articles where this is, but it's a pretty
simple circuit.  It creates it's own internal square wave at the same
frequency as the input saw, the square is then added to the original wave
and the output is a sawtooth of exactly twice the input freq, but 1/2 the
amplitude.

The circuit also has a PWM input that can modify the transit point of the
internal square wave and thus makes the output something that is not
sawtooth exactly.  When the PWM is adjusted correctly, the output is a
true saw at 2F.

Hopefully this helps somewhat.


>regards, kris
>--- ニコラス・ケント <ndkent at optonline.net>
>wrote:
>
>> 
>> On Apr 1, 2006, at 4:41 AM, ganesha wrote:
>> 
>> > Hi all,
>> >
>> > Probably a complete newbie question but I like the
>> way
>> > you can change the waveform continuously from tri
>> to
>> > square to saw on the eml 101 vco's. I would like
>> to
>> > use that on a vco module I'm building myself, but
>> I
>> > have a question about the schematic:
>> > http://www.krinkel.be/sdiy/eml101.jpg
>> >
>> > What kind of potmeter is used because it seems to
>> have
>> > a connection in the middle where you can connect
>> the
>> > square waveform?
>> >
>> > regards, Kris
>> >
>> 
>> That's what I've been asking about too the last
>> couple days. Those  
>> pots in general, not the circuit you are looking at
>> in specific.
>> 
>> As a whole the EML uses a bunch of those pots in the
>> synth. So  
>> perhaps if "FA" is a really odd (or not)  taper
>> maybe it was chosen  
>> because they had a supply of them and could cut down
>> on the number of  
>> different parts? Sooner or later I'll try to measure
>> one.
>> 
>> FWIW the "8va" in the schematic is actually a saw
>> one octave up.  The  
>> knob's legend draws the entire range of output as
>>   tri -> "sloped square" ->square -> saw -> doubled
>> saw
>> so it has at least one weird transition you've not
>> mentioned (the  
>> last 3 waves)
>> 
>> So that brings to mind that perhaps a same-octave
>> saw would do  
>> something less desirable??
>> 
>> If you are really keeping track OSC 1 doesn't have
>> any mixing scheme  
>> and Osc 4 has a simpler tri to square option.
>> 
>> Further weirdness comes with the wave choices on the
>> EML 100 (if  
>> anyone is keeping score)
>> cosine(?) -> square/cosine -> square
>>   tri -> square/tri (not the "sloped square") ->
>> square
>> 
>> Of course in your case what you get with simplicity
>> is to me is  
>> spoiled by not having CV control on any of this.
>> 
>> oh, and then the 100 (not the 101) gets their mixed
>> multimode filter  
>> output to go LP->BP->HP->BR->LP via a pot
>> But I don't have the schematics to the 100 filter,
>> and as usual no CV  
>> control of that.
>> The 101 does a simpler LP -> BP -> HP
>> 
>> P.S. you can get the entire 101 schematics off the
>> EML yahoo group.  
>> I've still not sourced a set of 100 schematics
>> though I have some  
>> pages marked "100 and early 101" apparently for
>> servicing  
>> transitional 101 units.
>> 
>> ndkent
>> 
>
>
>
>		
>___________________________________________________________ 
>To help you stay safe and secure online, we've developed the all 
>new Yahoo! Security Centre. http://uk.security.yahoo.com 
>

---------------------------------------------------------
- Where merit is not rewarded, excellence fades.
- Hydrogen is pointless without solar.
- What good are laws that only lawyers understand?
- The media's credibility should always be questioned.
- The only good terrorist is a dead terrorist.
- Governments do nothing well, save collect taxes.

-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
-- FatMan: home1.gte.net/res0658s/fatman/
-- NonFatMan: home1.gte.net/res0658s/electronics/
-- Autodidactic Master of Arcane and Hidden Knowledge.