[sdiy] Okay, I give up :-)

[Scott Gravenhorst]

Nicolai Czempin <n.czempin at gmx.de> wrote:
>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?

Quite honestly, because I'm really not that interested in patching the pitch
CV path (go ahead, say that 5 times real fast).  The pitch modulation
requirements I have are rather simple and can be accomplished with my FatMan
VCOs' 555 pin 5 input.  The only exception to this is a tonal noise source
which I can do by building it as a separate 'voice'.  This eliminates the
usual temperature compensation required for expo VCOs and VCFs.  For me,
it's cheaper.  For what I use a synth for, I do not feel limited by 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 :-)

That depends on what you change.  Yes, your description is accurate and that
will work.

>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.

Someone else?  


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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
-- Linux Rex         | RedWebMail by RedStarWare
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