[sdiy] super simple portamento / slide / glide / slew limiting circuit?

[Tom Wiltshire]

On 13 Jul 2011, at 17:30, Todd Sines wrote:
> 
> On Jul 13, 2011, at 12:28 PM, Scott Nordlund wrote:
> 
>> 
>>> Trying to mod my Roland CMU-810 synth expander module for portamento / slide / glide / slew limiting over the CV input.
>>> [and maybe audio in]
>>> 
>>> Anyone done this, or can suggest a proper portamento circuit that could be used to add to the input ..
>>> 
>>> The electro-music post suggests it'd be as simple as 3 components: a pot, a cap, and an op-amp... 
>>> http://electro-music.com/forum/post-149264.html
>> An RC circuit will give you an exponential portamento (constant time). It's possibly more of a "classic" sound, but it might be a little wonky sounding for longer portamento times, since it slows down and asymptotically approaches the destination pitch. A proper slew limiter (constant rate) might be better for general purpose use.
>>  	   		  
> 
> okay.. got one of them? 
> 
> [a schematic of something would be nice, all the "simple circuits" I've seen are just descriptions.]
> 

That'd be an integrator, like this:

http://www.electronics-tutorials.ws/opamp/opamp_6.html

Stick the cap in the feedback loop of an op-amp, use the resistor to alter the current flowing into the cap. Since it's inverting, you probably need a second op-amp and a couple more resistors to reinvert, but it's still just one 8 pin DIP.

T.