[sdiy] 5v ADV Bass / AD EG Question.
Scott Gravenhorst
music.maker at gte.net
Thu Mar 17 23:53:05 CET 2005
Also, for this to work, your signal inputs must be referenced to virtual
ground, not PSU zero volts.
music.maker at gte.net wrote:
>"Bill Berzinskas" <wberzinskas at nc.rr.com> wrote:
>>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
>
>The external input should also connect to at least one OTA input through some
>larger value resistor. Are you seeing 2.5 volts from 5v to virt.gnd and -2.5
>volts from 0v to virt.gnd?
>
>>
>>----- 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.
>>>
>>>
>>
>>
>
>---------------------------------------------------------
>- 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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