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

[jays at aracnet.com]

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
>