finally was : last time i promise was: [sdiy] 5v ADV Bass / AD EG Question.

[Bill Berzinskas]

finally got this working if anyone cares..  :-P
had to change alot..  mostly the bias input resistors,  and the resistors 
going from the VCO to the 3080..  also reworked the output stage..  got it 
going pretty good now..   big thanks to midwest-analog.com and m.bareille.. 
i actually realized that the DS7 VCO is the same vco core that i've been 
using for my modular..  wierd..  anyway, between the 2, and some tasty 
programming bits, me and my buddy steve (thanks for da help buddeee), gave 
birth to a digitally controlled analog kick drum.   It sounds really good 
overall..  the digital pots are a bit noisy, but acceptable for this 
application..   i think once we do a digi controlled MODULE, it will be alot 
better sounding with DACs..   anyway..   later.. thanks for the help 
everyone..

----- Original Message ----- 
From: "Scott Gravenhorst" <music.maker at gte.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Friday, March 18, 2005 9:36 AM
Subject: Re: last time i promise was: [sdiy] 5v ADV Bass / AD EG Question.


> In most cases (and I think this one qualifies), the virtual ground you 
> create
> is to be used wherever you have a ground symbol in the original schematic,
> assuming the original is a dual supply design.  All the virtual ground 
> circuit
> does is create a stiffened reference point halfway between the power 
> supply
> rails.  All audio signals should be referenced to virt. ground, both for
> output and input.  All internal grounds, such as grounding the + input of 
> an
> opamp are also virtual grounds.  The rails still go to the IC pins they 
> always
> did.  This will work because a dual supply schematic will differentiate
> between ground, V+ and V-.  Don't confuse V- (or in your case PSU zero 
> volts
> sometimes referred to as "ground" when operating as a true single supply) 
> with
> the virtual ground.  This is very important.  The only reason you need the
> virtual ground is because you don't have a dual supply.  The virtual 
> ground
> creates this as a reference to fool the circuit into operating off of a 
> single
> supply.  In reality, however, the presence of the virtual ground and it's
> proper application turns your single supply into a dual supply.
>
> "Bill Berzinskas" <wberzinskas at nc.rr.com> wrote:
>>now that i think of it..   i'm using the VCO from the lmX58 family.. which
>>uses a virtual ground as well. . would this have an effect on the VCA?
>>
>>----- Original Message ----- 
>>From: "Nils Pipenbrinck" <np at inverse-entertainment.de>
>>To: <WBerzinskas at nc.rr.com>; "Synth-DIY" <synth-diy at dropmix.xs4all.nl>
>>Sent: Friday, March 18, 2005 8:24 AM
>>Subject: Re: last time i promise was: [sdiy] 5v ADV Bass / AD EG Question.
>>
>>
>>> WBerzinskas at nc.rr.com wrote:
>>>
>>>>Hello Jay..  Thanks for the info... schematic -
>>>>http://midwest-analog.com/bass.html
>>>>
>>>>
>>> I just had a short view at the VCA, and spotted some things that look
>>> wrong:
>>>
>>> First off you reference the signal at the inputs to GND. Don't connect 
>>> the
>>> 680ohm resistors to ground but to the virtual ground instread (2.5V in
>>> your case.).
>>>
>>> Then you should adjust the voltage divider (100k / 680ohm into pin2). 
>>> The
>>> input of the 3080 OTA likes to see a signal difference of something
>>> between 75 and 150 mV at it's input terminals. (it's a matter of taste 
>>> how
>>> much distortion you want, the higher the input, the more distortion 
>>> you'll
>>> get). Also out of the blue, the impendance of the voltage divider looks
>>> higher than nessesary. I would choose a value of 22k for R21 and pick R1
>>> and R2 that you'll see a 100mV difference at the inputs.
>>>
>>> Last thing, and most probably the cause of all troubles: The output of 
>>> the
>>> OTA is a current output. You won't see a usable voltage at the output
>>> until the current can flow, and I'm not sure if the opamp at the output
>>> will do this job. You need a resistance between the output and the 
>>> virtual
>>> ground to turn the current into a voltage.
>>>
>>> Nils
>>>
>>>
>>>
>>>
>>
>>
>
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