[sdiy] 4069 VCO to get started? My answer

[Nicolai Czempin]

Scott Gravenhorst wrote:

>If "LS" is short for loud speaker, it "kills" the signal because it's
>resistance (or impedance) is very low and draws more current than your
>output circuit is capable of providing.  Your Oscope has an impedance
>(input impedance) of a million ohms as opposed to your LS which is
>probably 8 ohms.  A loudspeaker should be connected to a circuit like a
>VCO only through an appropriate amplifier.  You can build such an
>amplifier, it doesn't have to be commercial, but you do need an amplifier.
>  
>
Perhaps now you see why I'm starting with "crap". Because now I have 
first-hand experience about something drawing more current than I can 
provide. If I just get something that works, with all the caveats being 
taken care of, the learning effect isn't half as great for me.

>It also sounds like you need to take some time to do a bit of reading. 
>  
>

Trust me, I'm doing a *lot* of reading. Doesn't stop me from wiring up a 
few circuits in between the reading, though :-)
An EE colleague of mine said that the single transistor is esssentially 
the pre-amp already, but that I need a "proper amp" "after" it.
I have two kits from Conrad, one is for a Preamp, one for an "Endstufe" 
(not sure what the English word is for that). Will the preamp suffice 
for me to get a stable (in the sense that it doesn't suddenly stop as 
with the simple transistor) signal, or do I have to build both, or 
should I stay with the one transistor and connect that to the "Endstufe"?
These kinds of questions, really basic electronics, are what I'd like to 
keep off this list; which is why I was asking for other resources (a 
mailing list such as this one perhaps) more suited to such questions.
I'd like to reserve this group for the specific Synthesizer-related 
questions, to not use up so much "expert karma" :-)

>The 4069UB VCO already IS simple.  And it's about as simple as it gets,
>unless you really want something that is crap.  I can make an oscillator
>with 3 parts, but it won't be musically useful - so I don't bother.  
>
>The 4069UB VCO is composed of 3 basic circuits blocks that you should
>strive to understand, those are an integrator, a schmitt trigger and a
>current source.  There are many books, one being "The Art of Electronics"
>(which was probably already mentioned). 
>
Yes, it was mentioned by me that I'm reading it :-)

> Building things will give you
>only a certain level of understanding, but not full understanding.  If I
>were you, I would start reading about things like basic opamp principles,
>ohm's law, transistor basics, etc.  
>
I am. In fact, I won't shy away from reading 90 % of all the literature 
required of an MEE. All in my "copious spare time". I do want some 
connection to real life every now and again, however.

>Integrators are used in both VCOs and
>VCFs, also envelope generators and other things.  Schmitt triggers are
>also everywhere in analog music devices.  These things need to be
>understood as building blocks before you'll understand how a VCO or other
>module works.
>  
>
Well, for me the first building block is to understand how I can get 
anything to oscillate.
And the next step is to make it voltage-controlled.
Slowly but surely I am working my way towards something musically useful.
I won't PCB any of the "crap", I'll just wire them up on the breadboard, 
scratch my head why they don't work, "debug" a little and lo and behold, 
they work.

>And again, a 4069UB inverter gate IS AN ANALOG DEVICE.  ALL DIGITAL GATES
>ARE ANALOG DEVICES.  PERIOD.  They operate with high gain and are
>nonlinear, but they are still analog.  The 4069UB inverter is just an
>amplifier made of 2 transistors.  Don't think of this circuit as a
>bastardized approach to using "digital" parts, that won't help you.
>  
>
I got the point :-)

Wow, I'm really looking forward to building and fully understanding that 
4069 cicuit one day. That day may not be that far away :-)

What puzzled me was not the general idea of an integrator or 
Schmitt-Trigger. What did so was that the circuit showed the building 
blocks simply as digital inverters. And I was wondering how on earth an 
inverter can be one thing in one part of the circuit and another thing 
elsewhere.
So perhaps to make it clearer the symbol in the schematics could be 
changed to reflect the functional usage.