[sdiy] Okay, I give up :-)

[Nicolai Czempin]

Scott Gravenhorst wrote:

>Nicolai Czempin <nicolai.czempin at alcatel.de> wrote:
>  
>
>>Okay, I'll build the 4069 circuit. I cannot hold out any longer.
>>It has been mentioned that parts can be left out.
>>So, do I just leave out the whole "current sink" part and connect the CV 
>>directly?
>>    
>>
>
>No, this won't work.  The circuit wants a current sink to ground. 
>
Ah, but please don't anthropomize circuits. They hate it.
SCNR

> You
>cannot voltage control this circuit without either the 2 transistor (or
>other design) expo current sink in the original drawing or the linear
>current sink that I used in place of it.  They current sink type needs to
>match the CV type for the CV to make a sensible musical scale.
>  
>
I think I'll stick to the expo; as far as I understand with my tiny 
brain, this would mean that connecting the keyboard via the MIDI2CV 
would work as expected.
Out of curiosity, why are you going linear?

>>Can I leave out the "pulsewidth modulator" part if I'm happy with just 
>>the saw out for the moment?
>>    
>>
>Yes, and it can easily be added later. 
>
So, I basically just cut the 47k resistor (and the rest, of course) off 
"virtually"? Seems strange that it would make no change to the rest of 
the circuit. So far my (extremely limited) experience has been that if 
you change just one small bit in a circuit, everything else changes :-)

I did buy all the necessary components just in case (plus the only 3080 
they had in stock---don't know what I'll use it for, but I feel part of 
the 'in crowd' now ;-), enough to make two of them.

> PAY ATTENTION TO THE PINOUTS IN
>THE DRAWINGS.  If you deviate from that (as I did at first) you could have
>problems, especially in the PWM section, should you decide to add it.
>  
>
Yup, I did do my homework...

>Note that if you add the PWM, the circuit will have 2 outputs.  One is the
>saw out and is not affected by PWM, the other is the PWM output which is a
>pulse where the width is controlled by the PWM CV.
>
>  
>
>>Do I have to keep anything in particular in mind when cementing the 
>>transistors together?
>>    
>>
>
>Flat side to flat side.  Good thermal contact.
>  
>
I had gathered the flat side part by looking at the web page. And I 
guessed that perhaps I don't want to cover the babies with too much 
glue. What I was wondering was whether I need some special kind of glue 
or whatever.

>  
>
>>What do I do with the "pwm" connection? I'd guess some kind of voltage, 
>>but can I just ignore it initially?
>>    
>>
>
>If you build the PWM part, the input is a control voltage.  That voltage
>controls the pulse width of the PWM output and makes a nice voltage
>controllable timbre.  A cool sound when driven by a slow LFO, or you can
>plug an envelope generator into it or whatever you imagine, even an audio
>signal to get some weird sounds.
>
>  
>
Looking forward to having stuff to connect there.

BTW my 741 circuit did actually work with just the one transistor. At 
least there was no "sudden stop" of the sound the next day. I guess I'll 
have to learn to adapt to these kinds of things that work one day, then 
don't the next, or vice versa. You don't get that kind of effect in 
software (much)---except for the odd HeisenBug every now and again.