[sdiy] 5v ADV Bass / AD EG Question.
Scott Gravenhorst
music.maker at gte.net
Thu Mar 17 22:34:13 CET 2005
"Bill Berzinskas" <wberzinskas at nc.rr.com> wrote:
>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?
Yes, the OTA is powered by +5v and 0 volts. Biasing of the OTA is then
identical to any dual supply set up. This means that you need only the one
+V/2 reference. OTA circuits that I've seen all have a large resistor (like
100K) from signal input to OTA input, then there's a small resistor (like 1K)
from OTA input to virtual ground. This automatically biases the OTA input.
If one OTA input is unused, it should be sent to virtual ground through a
resistor of a size equal to the small resistor on the other input.
I forgot to mention that an LM324 should work for the opamp needed, spec says
PSU down to 3 volts.
>
>----- 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 >
>>>
>>>
>>
>> ---------------------------------------------------------
>> - 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.
>>
>>
>
>
---------------------------------------------------------
- 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.
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