[sdiy] Gah, hilfe!

[Scott Gravenhorst]

My wild stabbing in the dark would have me try a standard linear voltage to
current converter a la the FatMan VCF (IC13:D and Q8 or Q9), essentially an
opamp set up as a summing amp, output of opamp feeds the base of the
transistor (PNP), emmiter goes to inverting input, current output is the
collector which goes directly to the 3080 Iabc input pin.  Input voltage is
fed through a resistor to the inverting input.  A zero input voltage then
allows a zero output current and as the input voltage rises, so does the
output current drawn from -V through the internals of the 3080, out the Iabc
pin, through the collector-emitter to the summing node virtual ground.  A
diode can be used to prevent reverse current into the base of the transistor.

=?iso-8859-1?Q?R=F6nnberg_Niklas?= <nikro at itn.liu.se> wrote:
>Thanks Scott for your fast reply! Well, I think you're right. 
>
>Any suggestion on how to either (A) convert the outgoing trigg from the
>uppermost TL074 opamp to current but retain the nice small pulse created by
>the 100nF capasitor or (B) how to change the whole circuit between the
>three diods and the CA3080 or (C) how to change the circuit and adding a
>potentiometer for adjusting the VCA decay time (never heard that from me
>before...)? 
>
>(I think I need to redraw the schematic and number each component...)
>
>Best regards
>
>/Niklas
>
>
>-----Original Message-----
>From:	Scott Gravenhorst [mailto:music.maker at gte.net]
>Sent:	Mon 6/7/2004 10:32 PM
>To:	synth-diy at dropmix.xs4all.nl
>Cc:	
>Subject:	Re: [sdiy] Gah, hilfe!
>I'm no expert here, and have no experience with the 3080...  But I think
>it's supposed to be current driven where the current Iabc actually runs
>from the Iabc input to -V.  Or at least that's the way an LM13700 works. 
>It doesn't look like you have a current source driving the 3080.  ??  Or
>perhaps I don't know a current source when I see one.
>
>=?iso-8859-1?Q?R=F6nnberg_Niklas?= <nikro at itn.liu.se> wrote:
>>Hi guys!
>>
>>I've been stumbling around trying to get a sort of snare like drum sound.
>>But I can't get it to work. The problem I'm currently trying to fix is to
>>get the simple VCA to open when the circuit is triggered. Well, soon I'm
>>going to throw it out the window hoping nobody is passing below...
>>
>>http://www.itn.liu.se/~nikro/diy/snaredrum.gif
>>
>>Please, help me!
>>
>>Best regards!
>>
>>/Niklas
>>
>
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>
>-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
>-- Linux Rex         | RedWebMail by RedStarWare
>-- FatMan: home1.gte.net/res0658s/FatMan/
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>-- Autodidactic Master of Arcane and Hidden Knowledge.
>
>
>
>

---------------------------------------------------------
- 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.