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

[BrightBoy]

You could always build the gated slew circuit from the TB-303.

The circuit needs a few tweaks to work in the real world:

An series input resistor to the op-amp is needed since in the 
TB-303 the DAC is feeding the circuit a current rather than a
voltage signal.

You need to run the op-amp on a bi-polar supply so you can
actually achieve zero volts on the output.

Jeff

-----Original Message-----
>From: Harry Bissell <harrybissell at wowway.com>
>Sent: Jul 13, 2011 1:48 PM
>To: Tom Wiltshire <tom at electricdruid.net>
>Cc: synth-diy at dropmix.xs4all.nl
>Subject: Re: [sdiy] super simple portamento / slide / glide / slew	limiting	circuit?
>
>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
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