[sdiy] Buchla 258

[Grant Richter]

Ian Fritz had a nice design that uses an LM318 for the hysteretic  
comparator.
(Ultrasonic VCO in Electronotes)
It has advantages over the LM311 in the triangle core design.
The 311 is open collector which has unsymmetrical drive for plus and  
minus excursions.
The 318 has a bipolar output stage which has more symmetrical drive.
Don't load the 318 output. It throws off the symmetry off.

A nice symmetrical triangle wave is good for making a low THD sine  
wave output.

This brings up one of my pet peeves.

An oscillator produces a sine wave (from the Latin root, oscillare,  
swung).

If a VC? does not have a sine wave out, it is a function generator  
(VCFG), not an oscillator (VCO).
Total nit-picking, I admit.


On Feb 7, 2006, at 12:04 AM, mark verbos wrote:

> Aaron,
>
> be careful. In the modded verison on my site, I replaced the  
> discrete OTA with a 3080, Don didn't do that. The discrete  
> comparator allows him to derive a sawtooth in the waveshaper. There  
> is a discrete comparator circuit very much like this one in "The  
> Art Of ELectronics." He switched to 311's in his later oscillators.
>
> Mark
>
>
>
>
> Aaron Lanterman wrote:
>> As an addendum to my last e-mail asking for triangle VCOs - my  
>> comments about Buchla before (the discrete OTA) was in regards to  
>> a 259 I think (or maybe it was the Easel 208, I don't remember now).
>> Anyway, the 258 is different - looking at Mark Verbos' version, I  
>> see the 3080, and the LF356 forming the integrator - and then  
>> there's three transistors forming - what is that? I'm guessing  
>> it's some sort of discrete comparitor, but I'm not sure why Buchla  
>> would want to use that if he had 311s available...
>> I need up look up discrete BJT comparitors to figure out what's  
>> going on, I think...
>> - Aaron
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