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Simple Glide/Slew/Lag/Portamento..
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j.dilisio



Joined: May 19, 2009
Posts: 186
Location: baltimore

PostPosted: Tue Jun 30, 2009 3:28 pm    Post subject:  Simple Glide/Slew/Lag/Portamento..
Subject description: Should this work?
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Here's a beginner question...
Someone gave me the following schematic for a simple glide circuit.
Should this work?

I tried it and found that while it does add some Lag to a CV signal, it also attenuates it.
I'm using a 100k pot and a 1uF cap just because that's what I had lying around so there's not much lag effect.

I've also attached an image of my attempt to test it.

Any ideas?


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Tim Servo



Joined: Jul 16, 2006
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PostPosted: Tue Jun 30, 2009 4:03 pm    Post subject: Simple Glide/Slew/Lag/Portamento... Reply with quote  Mark this post and the followings unread

Hey JD,

Well, that circuit is really close. What you need to do is add an op-amp buffer to the input, and another one to the output. The idea behind the buffers is that they isolate the circuit. Otherwise, the load that the glide circuit places on your CV source changes a lot depending on what the glide setting is.

What you're looking for is a "voltage follower" or "unity gain buffer." The circuits are REALLY simple, and you can get a single 8-pin IC that contains the two op-amps you'll need. Of course, you're going to need a power supply, but that's something you'll need for almost any synth circuit. Do a Google search for those buffers and I bet you'll find a ton of useful info.

Tim (sometimes useful) Servo
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synthmonger



Joined: Nov 16, 2006
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PostPosted: Tue Jun 30, 2009 6:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm not sure how you have your jacks grounded but they don't look like they have wires tied to ground. Don't forget those!
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j.dilisio



Joined: May 19, 2009
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PostPosted: Tue Jun 30, 2009 6:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

well heres another question..
If this works I'm planning on ultimately using Banana jacks hense the lack of ground to the jacks.
I've never tried Bananifying anything before, but thats how it works right?
You just don't ground the jacks?
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synthmonger



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PostPosted: Tue Jun 30, 2009 6:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right. Though it never hurts to have a banana to 1/4" 1/8" inch jack module. ;D If you do plan on running the banana output to a computer/amp or whatever then you must have a common ground obviously.
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j.dilisio



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PostPosted: Tue Jun 30, 2009 6:58 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok, thanks,.
I think I'm going to go with the glide circuit that's attached.
It's taken from Ken Stone's Psycho LFO.
This one makes more sense right?


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widdly



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PostPosted: Wed Jul 01, 2009 7:50 am    Post subject: Reply with quote  Mark this post and the followings unread

not quite. The first opamp is non-inverting, and the second opamp is inverting. So you end up with an upside down cv. If you ditch the 100k pot and wire the first opamp like the second you will be in business.
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fonik



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PostPosted: Wed Jul 01, 2009 8:50 am    Post subject: Reply with quote  Mark this post and the followings unread

widdly wrote:
The first opamp is non-inverting, and the second opamp is inverting.

just the other way around Very Happy

the 1st OpAmp is set as inverting amplifier to enable multiple inputs.
the 2nd OpAmp is set as non-inverting voltage follower.

if you set the 1st like the 2nd, you cannot use multiple inputs (mix). however, i think you are not after mixing multiple inputs anyways.

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j.dilisio



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PostPosted: Wed Jul 01, 2009 9:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the help.
One last question..
Is it the capacitor value or the potentiometer that would increase/decrease the range of glide? or both?

*edit. I just saw fonik's post. I'll probably just be using one input. Is it better practice to do it the other way with both inverting?


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Last edited by j.dilisio on Wed Jul 01, 2009 9:13 am; edited 1 time in total
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synthmonger



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PostPosted: Wed Jul 01, 2009 9:12 am    Post subject: Reply with quote  Mark this post and the followings unread

The cap size controls how long the sampled voltage or 'glide' will last while the potentiometer just fine tunes it. With a 1M pot and that cap size you'll have a nice range.
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fonik



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PostPosted: Wed Jul 01, 2009 2:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

j.dilisio wrote:
*edit. I just saw fonik's post. I'll probably just be using one input. Is it better practice to do it the other way with both inverting?

IMHO no, it would just need resistors. OTOH with inverting configuration you could very easily add more inputs later...

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haxster



Joined: Feb 01, 2006
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PostPosted: Thu Jul 02, 2009 12:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I like this one, it's very simple
This one has (2) outputs.
You could just use (1)

http://electro-music.com/forum/topic-32272.html
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widdly



Joined: Jun 25, 2007
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PostPosted: Thu Jul 02, 2009 10:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

Why do you need an opamp buffer for each output? I would have thought you would be better off using one of those buffers on the input.
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Dave Kendall



Joined: May 26, 2007
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PostPosted: Fri Jul 03, 2009 2:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi guys.

The one below from Osamu Hoshuyamas "lunchbox synth" has worked well for me. It's buffered with voltage followers both on input and output, and is non-inverting. R2 doesn't have to be 1K2. 1K is fine. I didn't wire up or test the switch, but it looks useful. Smile

cheers,
Dave

(edited because *ahem* I just checked, and the lockbox synth is a Scott Bernadi synth, Sam's is a lunchbox modular.... Oh well....it was a nice day when I posted, I had a beer ...
Glad the circuit was of use to you Creekree - it was my first ever perfboard circuit, used to fix up a paia midi2CV8's CV zipper noise, which it did nicely using a 62K resistor instead of a 1M pot... Smile )


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creekree



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PostPosted: Fri Jul 03, 2009 12:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Dave,

thanks for posting that.
I quickly soldered it on stripboard - works like a charm!

Chris
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j.dilisio



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PostPosted: Sat Jul 18, 2009 2:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm having a little trouble getting this to work.
The CV signal I'm feeding it ranges between .5 and 3 volts.
The output from the first op-amp(pin1) is around 10.8V and stays around there for the rest of the path so the output frequency is really high.

I figure there's either something wrong with both of the LM358's I've tried,. or I've most likely made a really dumb mistake with the wiring.

I've attached a picture of the breadboard.
Any suggestions?


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haxster



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PostPosted: Sat Jul 18, 2009 6:23 pm    Post subject: Reply with quote  Mark this post and the followings unread

From looking at the schematic above, you have the inversions wrong. (-)inv should be pin 2, pin 3 is (+)non-inv. Op-amp (B) has the same label error. Also you do not have a freedback resistor or jumper on Op-amp (A).
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Tim Servo



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PostPosted: Sat Jul 18, 2009 6:28 pm    Post subject: Simple Glide/Slew/Lag/Portamento.. Reply with quote  Mark this post and the followings unread

Whoops, you've got that first op-amp wired as a comparator. When the input goes just a teeny bit above or below ground, the output will jump between (about) +12 and -12V. No in between for the output of a comparator. If you look at the diagram above, you'll see there's a feedback path on the op amps from the output back to the "-" input. What you want is to have the first op-amp wired as a buffer or "voltage follower."

Tim (just a bit above ground) Servo
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j.dilisio



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PostPosted: Sat Jul 18, 2009 7:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for replying so quickly!
It looks like I forgot to switch the + and - when I switched the numbers on the first op-amp. The second one should already be correct.

So all I'm missing is the feedback jumper.
Which of the following two schematics is right?
Does the jumper always go back to the - or whichever is the input?


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j.dilisio



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PostPosted: Sat Jul 18, 2009 7:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

I just noticed that pin 4 is marked as ground on the data sheet.
Should I go by that or does it matter?
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j.dilisio



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PostPosted: Sat Jul 18, 2009 8:42 pm    Post subject: Reply with quote  Mark this post and the followings unread

After some fiddling around I got it working.
I'm using a linear pot right now but it seems like a log pot will make a world of difference in controlling the subtle effects.

One last question..
I'm still getting a slight change in pitch when I turn the glide up.
It seems like the effect is too heavy for the CV and pulls it down about a quarter tone.
Are there any fixes for this?


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Tim Servo



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PostPosted: Sat Jul 18, 2009 8:58 pm    Post subject: Simple Glide/Slew/Lag/Portamento.. Reply with quote  Mark this post and the followings unread

Okay, good work, you're really close now. What you need to do is remove that connection to ground on the + input of the first op-amp. My guess is that's what causing the glide circuit to load down whatever is hooked to its input and mess up the output. Also, the LM358 can be powered by +V and Ground or +V and -V. My choice would be +V and -V (or "bipolar supplies") because then the glide circuit will be able to process any negative CVs that come its way.

Tim (wasn't there a dance named "The Glide"?) Servo
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j.dilisio



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PostPosted: Sat Jul 18, 2009 9:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well now its gliding along just fine.. Very Happy
Thanks for your time Tim.


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LetterBeacon



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PostPosted: Wed Oct 07, 2009 12:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm thinking about building that circuit above - when the Glide pot is turned completely CCW, does that mean there is a 0 amount of glide, or is there still a little bit of glide going on?

Thanks!
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j.dilisio



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PostPosted: Wed Oct 07, 2009 2:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

LetterBeacon wrote:
I'm thinking about building that circuit above - when the Glide pot is turned completely CCW, does that mean there is a 0 amount of glide, or is there still a little bit of glide going on?

Thanks!


There's no glide when the pot is all the way down.
There's also a dual glide board available from Bridechamber for cheap, $2 i think.

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