Adding A Portamento Circuit...

[Paul Marossy]

to an old pre-MIDI analog keyboard. Is it as simple as adding a little circuit on the output as on this page?
http://charlieslick.blogspot.com/2012_08_01_archive.html

It seems like that is just too simple. There must be more involved than that.

Wouldn't the input and output need to be connected to Vref if powered with a 9V battery? And that 10uF cap, would that go to ground or Vref?

[Mark Hammer]

Yes, sort of, but portamento to what?  To the pitch control voltage coming off the keyboard?

Go to the MFOS website, scroll way down on the synth-DIY menu, and look at the old single bus keyboard controller.  Once you look at the schematic, you'll see that the portamento in that circuit is exactly as you show: op-amp buffer, R/C lag circuit, op-amp buffer (IC4a and IC4b in this instance). But you'll also recogize that the basic lag circuit that provides slowed down charge-up and discharge needs a certain infrastructure to be inserted into, which may or may not be available in your case.

[Paul Marossy]

Yes, sort of, but portamento to what?  To the pitch control voltage coming off the keyboard?

Well, ideally I'd like to use it with my Korg Polysix as an outboard device. This blog I linked above makes it sound like all he had to do was stick it on the output and voila! Seems too simplistic to me...

[Gurner]

Yes, sort of, but portamento to what?  To the pitch control voltage coming off the keyboard?

Well, ideally I'd like to use it with my Korg Polysix as an outboard device. This blog I linked above makes it sound like all he had to do was stick it on the output and voila! Seems too simplistic to me...

That circuit is just adding slew to say a fast changing control voltage input (so rather than move imm ediately between say 1V & 3V, it'll slowly move between the two). The output of that circuit needs to feed something that can be controlled by a voltage - therefore voltage controlled oscillator, voltage controlled filter, voltage controlled amplier etc.

[Paul Marossy]

That circuit is just adding slew to say a fast changing control voltage input (so rather than move imm ediately between say 1V & 3V, it'll slowly move between the two). The output of that circuit needs to feed something that can be controlled by a voltage - therefore voltage controlled oscillator, voltage controlled filter, voltage controlled amplier etc.

Yeah, that's what I thought. The Korg Polysix has a VCO, a VCA and a VCF. All three can be used simultaneously, but not all patches use all three. So where would a portamento circuit go in that kind of environment?

[frequencycentral]

The Polysix is polyphonic and has a digitally scanned keyboard. You would need to add six slew circuits. If it were easy/simple/possible I would know about it.

[Paul Marossy]

The Polysix is polyphonic and has a digitally scanned keyboard. You would need to add six slew circuits. If it were easy/simple/possible I would know about it.

Yeah good point. I wasn't even thinking of it being polyphonic when I asked the question. Oh well, it was just a thought.

[space_ryerson]

There may be a few clues in the Juno-106's service manual, since it's a six voice polysynth that has portamento.

edit: after a quick look...no dice

[Paul Marossy]

There may be a few clues in the Juno-106's service manual, since it's a six voice polysynth that has portamento.

True. I'd rather have a second Polysix to mess with than to screw up mine, though.

[Paul Marossy]

Here's something I found that will give you a quasi-portamento, but it's not really that great sounding IMO.
http://tubbutec.de/wordpress/?tag=polysix

[wavley]

There may be a few clues in the Juno-106's service manual, since it's a six voice polysynth that has portamento.

edit: after a quick look...no dice

That was the same thing I thought and hoped I might visualize it differently than you (sometimes it takes more than one set of eyes).

But, you're right.  I thought was going to be so simple, my juno 106 has portamento... that looks like to me is microprocessor controlled.

[Paul Marossy]

my juno 106 has portamento... that looks like to me is microprocessor controlled.

Makes sense since it's a polyphonic synth.

[R O Tiree]

I used to have a four-note analogue polyphonic synth that had portamento - one unit for each channel.  You had to be careful how you fingered chord changes so that chords would smoothly slide up or down and notes didn't go "through" each other on the way (untidy).  You had to kind of rapidly "roll" each chord so that the notes would slide in their respective places.  How does the Juno behave?  Does the microprocessor figure out what chord you're playing and then assign portamento to the relevant channels or do you still have to roll the chords?  Either way, I guess you'll need to think in terms of as many portamento circuits as you have channels.

[wavley]

I used to have a four-note analogue polyphonic synth that had portamento - one unit for each channel.  You had to be careful how you fingered chord changes so that chords would smoothly slide up or down and notes didn't go "through" each other on the way (untidy).  You had to kind of rapidly "roll" each chord so that the notes would slide in their respective places.  How does the Juno behave?  Does the microprocessor figure out what chord you're playing and then assign portamento to the relevant channels or do you still have to roll the chords?  Either way, I guess you'll need to think in terms of as many portamento circuits as you have channels.

No, I don't think too many things in 1984 were smart enough to think about what chord you're playing, you have to pay attention to how you play, and that's why I tend to only use it for ambient things or lead lines.

[space_ryerson]

Also, the Jupiter 8 and Jupiter 6 are 6 voice VCO synths (the Polysix is VCO, while the Junos are DCO), so maybe there's some clues in those service manuals? I kind of doubt it...but just throwing it out there.

[aron]

Korg didn't even put portamento in their digital versions of the Polysix!

[Paul Marossy]

Korg didn't even put portamento in their digital versions of the Polysix!

Yeah. I wonder why? I guess they weren't into it. I think it's a cool effect, though.

[space_ryerson]

Even the Kiwisix upgrade doesn't add portamento! Sheesh.

[Paul Marossy]

Even the Kiwisix upgrade doesn't add portamento! Sheesh.

That would have been a nice feature for them to include.

Anyway, I just found a patch on my Yamaha keyboard that does portamento. So that will satisfy me for the moment.

[ElectricDruid]

Even the Kiwisix upgrade doesn't add portamento! Sheesh.

The Polysix uses a pretty unusual multiplexed-CV linear VCO scheme which would make adding portamento pretty difficult, and the linear VCOs would make it sound pretty weird too.
Although the Kiwisix replaces both the uPs in the Polysix (the main board one, and the voiceboard's 'key assigner' one) any Portamento would have to be added *after* the CVs are demultiplexed - that involves hacking the signals coming out of a '4051 1-to-8 switch IC on the voice board.
So it's possible in theory, but it ain't easy, and it's certainly not possible with a firmware update/replacement, even to both processors.

HTH,
Tom