[sdiy] 5v ADV Bass / AD EG Question.
Bill Berzinskas
wberzinskas at nc.rr.com
Thu Mar 17 23:59:57 CET 2005
just finished trying this.. any no go.. any suggestions?
i am getting 2.5v out from the opamp i added.. and i have both inputs
connected to this virtual gnd via 780 ohm resistors.. i am seeing a
change in pin5 when i send Envelope to it.. i've tried a few other chips..
still no go.. wheee
----- Original Message -----
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Thursday, March 17, 2005 4:34 PM
Subject: Re: [sdiy] 5v ADV Bass / AD EG Question.
> "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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