[sdiy] Glide Pitch Drop?

[xamboldt]

Thanks, Harry. I went and reread your cap FAQ, and it made more sense now
that I had a real-world understanding of how the leakage affected a module I
was making. I replaced the 10K pot with a 1Meg, and the 10uf electrolytic
cap with a .1uf mylar (that was all I had other than ceramic in that value).
There was still a little droop, so I measured the pot to see at which point
in the rotation the droop started, and put a resistor of that value in
series with the pot (about 100 ohms). So rather than getting rid of the
droop, I just made it so it was always there. If you can't beat 'em, join
'em.

Maybe on my next mouser order I'll get a better .1uf cap, but for right now
this solution should work for me...

Thanks for the help,
Chris

On 9/2/05 5:47 PM, "Harry Bissell Jr" <harrybissell at prodigy.net> wrote:

> Its likely you have a 10uF electrolytic, and it
> has some leakage.  I'd use a much larger potentiometer
> and a much smaller cap. Maybe a 100K and a 1uF or
> (if you have one) a 1M pot and a .1uF capacitor. Once
> you get to a .1uF you could get a polystyrene or
> polypropylene cap, which would be MUCH better in
> leakage etc.
> 
> Its possible to use a Tantalum if you NEVER have
> negative voltages. If you do, avoid tantalum like
> the plague.
> 
> slight possibility there is a bad TL074...
> 
> H^) harry
> 
> 
> 
> --- xamboldt <xamboldt at earthlink.net> wrote:
> 
>> Hi Everyone,
>> 
>> I'm modding a sequencer to add a simple glide out,
>> so I copied the glide
>> section from John Blacet's old "Digital Pattern
>> Generator":
>> 
>> http://www.blacet.com/dpg1.jpg
>> 
>> I didn't use the 50k output attenuator, just took
>> the CV out from the
>> sequencer and fed it through the glide circuit
>> exactly as shown in the
>> schematic. I'm using a TL074 for the opamps.
>> 
>> If I have the glide set to 0, then the voltage out
>> of the glide CV out is
>> the same as the non-glide CV out. The problem is,
>> once I turn the glide up a
>> bit, the CV out drops a little. Not the greatest
>> thing to happen if you get
>> a sequencer set up to the right pitches, and you
>> just want to add a little
>> portamento, but in order to do so you have to reset
>> all the sequencer
>> controls to compensate for the voltage drop.
>> 
>> Any ideas on how I could fix this? Or is a different
>> circuit my only hope?
>> 
>> Thanks,
>> Chris
>> 
>> 
>