_[sdiy]_ICL8038 worst ic off all time!

[Scott Gravenhorst]

=?iso-8859-1?q?Karl=20Dalen?= <karldalen at yahoo.se> wrote:
>Scott,f,jg...fio....,,n>>
>> >Hmm, i dont think the VCO sucks,as i remember, BJ showed once many
>> years
>> >ago that you could build a remakable advanced VCO out of a 4046 IC!
>> Well,
>> >at least a "very high frequency LFO" with sync and 4 quadrant
>> modulation
>> >on the square, if im not remebering completely wrong, thats not bad for
>> >such a cheap and simple IC. Or one could use the HC version and do a
>> >nice DC to 30Mhz function generator. I say forget about the 8038! 
>> 
>> Looking at the spec, a 4046 is rated at 1.3 MHz, the 74HC4046 version
>> runs
>> at max 17 MHz.  The VCO is fine, it's the current source that isn't very
>> good.  Check the TI docs, it has a whole section on the technicals of
>> the VCO.
>
>I have managed to squeese up a HC4046 to just abowe 30Mhz, 
>i sat down a evening a selected among some manufacturer lots,
>its a horrible design all in a closed ohven since i only use 
>it as a function generator! Most of the HC i tried out did 20-24Mhz.
> 
>> I built up that circuit by Bjorn Nilsson(?) and couldn't
>> get it to track a linear CV.
>
>As far as i can remeber the thing when it was discussed
>he did mentioning someting about the tracking and some 
>sugestions to solve that, i think he said something about
>it could be used up to a 1,5 2khz range with fairly good
>tracking, bass range i cloudly remember.
>
>Hmm, i recall that Grant Richter did use the saw
>tooth trick BJ mentioned in one of his modules?!
>Darn clever thing to pull out a sawtooth out
>of the 4046 anyway!! I think it was something about 
>dissconecting one end of the charge cap and connect
>that end to gnd or +5V!? 

It's a summer connected to both sides of the cap.  Each cap
lead is buffered with a TL074 opamp.  A third opamp performs
the summing operation.  The cap is inside of a CMOS transistor 
bridge which charges the cap in one direction, then reverses.  

My problem with it may have been trying to operate it at too
high a frequency or more correctly, too high of a charge 
current.  It may not have linearity problems with lower currents.  
If that's true, then using a smaller cap could allow higher 
frequencies.

>KD
>
>> >Speaking of function generators, you can use a PNP expo on the I set 
>> >pin on the MAX038 to convert it to a expensive VCO!
>> >
>> >KD
>> >
>> >
>> >Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på 
>> >adressen http://se.docs.yahoo.com/travel/index.html 
>> >
>> 
>> =========================================================  
>> - 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.
>>  
>
>Höstrusk och grå moln - köp en resa till solen på Yahoo! Resor på 
>adressen http://se.docs.yahoo.com/travel/index.html 
>

=========================================================  
- 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.