[sdiy] 5v ADV Bass / AD EG Question.

[Bill Berzinskas]

i think i get the jist of this..    just to clarify..

the ota will still be running on 0v and GND..   but where the inputs have a 
resistor going to ground, this is where i would hook up to virtual ground? 
and everything else would be the same?

----- Original Message ----- 
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, March 17, 2005 4:12 PM
Subject: Re: [sdiy] 5v ADV Bass / AD EG Question.


> Another way to achieve this is by using an opamp to create a virtual
> ground.  Essentially, this is an opamp, output connected to - input,
> + input gets a voltage from an equal resistor voltage divider from v+
> to PSU zero volts.  The output of the opamp will then be a virtual
> ground from which V+ looks like +2.5 volts and from which PSU zero
> volts looks like -2.5 volts.  Now you can treat the circuit as if you
> have a +/- 2.5 volt supply.  Inputs and outputs are referenced to the
> virtual ground, not PSU zero volts.  The opamp, as well as the OTA is
> powered from +5 volts and 0 volts.  This technique would work for low
> current applications.
>
> <jays at aracnet.com> wrote:
>>If it is between gnd and +5 then you will probably have to bias
>>the input to ~+2.5 volts. Basically V+/2. You'll have to be
>>careful since the 3080 has a fairly low input voltage for low
>>distortion so bias become critical.
>>
>>Also be careful. If the Iabc pin gets to much current it can fry
>>the CA3080. So at least in prototyping the circuit add a current
>>limiting resistor.
>>
>>Crude calculation:
>>V=IR, R = V/I, V=5, I=.001 (1ma), R=4.7K or 5.1K should work.
>>
>>Jay S.
>>
>>
>>
>>Bill Berzinskas <wberzinskas at nc.rr.com> wrote :
>>
>>> well.. i breadboarded this this morning..  and
>>> most everything seems to work..  except the vca..  any thing
>>> specific i need to do to get this 3080 vca working on 5v?
>>>
>>>
>>>
>>>   ----- Original Message ----- 
>>>   From:
>>>   Bill
>>>   Berzinskas
>>>   To: Jay Schwichtenberg ; synth-diy at dropmix.xs4all.nl
>>>
>>>   Sent: Thursday, March 17, 2005 11:16
>>>   AM
>>>   Subject: Re: [sdiy] 5v ADV Bass / AD EG
>>>   Question.
>>>
>>>   preciate that jay..   good
>>>   article..  it'll prob take me a bit to get through the math tho.. lol
>>>   ..  :-)    time to break out my math book from last
>>>   semester..
>>>
>>>
>>>     ----- Original Message ----- 
>>>     From:
>>>     Jay
>>>     Schwichtenberg
>>>     To: Bill Berzinskas ; synth-diy at dropmix.xs4all.nl
>>>
>>>     Sent: Thursday, March 17, 2005 11:10
>>>     AM
>>>     Subject: RE: [sdiy] 5v ADV Bass / AD EG
>>>     Question.
>>>
>>>     Bill,
>>>
>>>     2)
>>>
>>>     Another issue is that the attack, decay and release
>>>     pots on envelope generators are typically log pots, a non-linear 
>>> scale.
>>>     So if the digital pots you use are not log they may not give you the 
>>> timing
>>>     resolution that you are use to. One techinque to do that is buffer 
>>> the pot
>>>     and add a resistor. Picking the right resistor and placing it 
>>> between the
>>>     wiper and the other ends of the pot (assuming using pot as 
>>> attenuator
>>> between signal and gnd) can give you log or expo curves. Try
>>http://www.geofex.com/Article_Folders/potsecrets/potscret.htm for
>>that > info. >   > Good luck. > Jay S. > > -----Original
>>Message-----From: > owner-synth-diy at dropmix.xs4all.nl >
>>[mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Bill >
>>BerzinskasSent: Thursday, March 17, 2005 7:36 AMTo: >
>>synth-diy at dropmix.xs4all.nlSubject: [sdiy] 5v ADV Bass / AD EG >
>>Question. > Hello everybody..  just woke up to a > crazy
>>little burst of snow here in NC..  wierd..   > >
>>  > Anyhow..   As you probably know i'm > modding
>>the bejezzus out of my adv-bass..   In my quest to make
>>> it digitally controlled, i've hit a few snags..  so maybe
>>you can > help me out.. >   > 1) I am converting it to
>>digital > control..  mostly thru digital pots..
>>a few things with > DAC..  so.. for the digital pots, i have
>>to use 5v input, and rather > then use way more opamps then i
>>want to deal with, i would like to make it > operate on 5v
>>possibly with a bipolar or just 12v output stage if >
>>necessary..   So.. >   > I've done some crude
>>experiments with the > Trigger section just to see how it reacts
>>to switching from +/-12v to just > +5v..    I've
>>tried with tl082s..  and i just can't > get the trigger
>>ratio right.. and it always triggers.. so.. since i broke > down
>>and got a few lm324s, i tried those.. and it seems to be working
>>> correctly..   i then went on and built the impact
>>part using the > digital potentiometers..   all good so
>>far..   if i > just switch all my opamps in the design,
>>will it carry through the rest of > the circuit properly? >
>>  > 2)  I plan to use a digital > potentiometer to
>>control the decay time..   but the highest > value i
>>can come up with is 100k.. so i'm thinking i can change the >
>>capacitor and get about the same decay time?   any >
>>recommendations for a value? >   > thanks guys!  :-) >
>>--billie >
>>
>>
>
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