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

[Harry Bissell]

You need to couple the integrator with a comparator or it will run to the rails. You put the input signal to one
side of the comparator (non inverting), the integrator output to the inverting comparator input. The comparator will
bounce from rail to rail when it is locked (tracking), it would be potentially a very electrically noisy circuit.

You can also use the same RC network (cap to ground) with the comparator (assuming you have high input impedance
opamps like the TL07X series) and have a quasi-linear signal. For small voltage changes it looks pretty linear, but if you
go near the rails you can see that its really an RC time constant.

Watch out for the TL07x if you plan on voltages of more that maybe -7V on the integrator scheme, you can exceed the common mode
voltage range and it can hang up...

H^) harry

----- Original Message -----
From: Tom Wiltshire <tom at electricdruid.net>
To: Todd Sines <sines_list at scale.gs>
Cc: synth-diy at dropmix.xs4all.nl
Sent: Wed, 13 Jul 2011 13:23:24 -0400 (EDT)
Subject: Re: [sdiy] super simple portamento / slide / glide / slew limiting	circuit?


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.

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-- 
Harry Bissell & Nora Abdullah 4eva