Really simple portamento/slide circuit

Pastedgraphic-1I’ve wanted to include a simple slide in my silly CSQ-100-style sequencer, and I’ve just got this circuit from a post at electro-music working, using a (probably not ideal) LM358 as a buffer running off a single +12v supply, and using a 1M pot rather than the 100k.

Glide4_457

Here’s how it sounds on an MS20, with varying amounts of drunken slide.

The 1M pot is too big, I need to change the range to about 200k or so. From what I’ve read, I’d be better off with a log pot but I’ve only got linear ones to hand. I’m thinking I’ll switch the slide in and out of the circuit from the sequencer using a 4066 switch, that’s the next step.

Update: Here’s the MS20 being triggered by the sequencer, using a 4066 to bring the slide capacitor into circuit on 5v triggers from the sequencer, so the portamento only happens on certain notes. Initially I was trying to power the 4066 off +12v and switch it from +5v – If I’d have read the datasheet I would have realised it needs Vdd to switch, duh. Got there in the end.

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9 comments

  1. 19th April 2020Cabralia says:

    Hi! Do you happen to have the schematics implementing the switch? Sounds really nice!

  2. 20th April 2020ua726 says:

    I rarely drew anything out back then. I think it was literally just putting the 4066 inbetween the opamp input/pot and the capacitor – so opamp input/pot > 4066 pin 1, capacitor on 4066 pin 2, and then the trigger on pin 13.

    On my 100M clone I used the slide from the MC-202, adapted for an external signal – looks like this:

    Adapted 202 slide schematic

    I can’t remember why I chose to run the 4066 off 10V (its absolute max is 20V, rated for 15V), maybe something to do with the trigger voltage.

    Anyway it sounds like this:

    MC-4 > 100M, sawtooth with portamento switched from MPX

    The circuit could be made single-sided with an LM358 or something, but in that case it would struggle to get to 0V.

  3. 20th April 2020ua726 says:

    Should also say that it’d be worth tying the unused inputs on the 4066 to ground

  4. 13th May 2021Mike says:

    And this MC202 circuit – is it fixed speed or fixed time? If fixed time – its a development from the TB303 slide which you cannot vary the slide time – right?

  5. 13th May 2021ua726 says:

    To be honest the constant speed/constant rate thing has always confused me, I’m not sure. The circuit above (basically the 202 slide with the trigger input changed slightly to handle an external trigger) is slightly different from the 303 slide, but looking at it I can’t think it should act any differently if it’s set to the same RC value using the pot. There’s every possibility that I could be wrong.

    The 202 was used as a 303 substitute to some extent back in the day, so it’d make sense.

  6. 13th May 2021Mike says:

    Surely the 4066 having such a large supply voltage range could be triggered direct from a microcontroller without the need for the extra trigger circuitry? If the Vcc was 5v and the digital output was 5v?

  7. 14th May 2021ua726 says:

    Sure yeah, like I say the example schematic in my comment was showing the 202 slide circuit adapted to take external triggers. I made it to go in the base of my 100M clone – mostly it gets run off my MC-4, but I wanted it to be flexible enough to take a variety of input voltages.

    One day I might restart work on the sequencer I was working on in the first post, although I’d probably just do the slide in software now.

  8. 14th May 2021Mike says:

    I visit here a lot over the years. I started programming a step sequencer on Teensy this year.
    Very inspired by your step sequencer
    So far its got 4 voices with 4 patterns each. Total 1000 notes per voice (which is more than you’ll ever need haha)
    Legato but not slide yet
    And 2 types of offset timing. One global for each voice so you can make one voice lazier against another etc. And one Legato compensation delay – which is basically when you have slow attacks on a voice the delay brings in the next pitch change slower so sounds more realistic.
    I’d also like to get some kind of memory so you could turn it off and recall what you were last doing when you start it up

  9. 17th May 2021ua726 says:

    Excellent, glad to hear someone else is having a go at making a sequencer!

    If you’ve got four voices and you want to add slide to all of them, I guess you’d be adding four lots of a circuit like this one – or, like I mentioned, you could do it in software, and save all that. You’d just have to be updating the CV outs on a regular enough basis to make the pitch slide seem smooth tho.

    Chip Audette mentioned adding portamento to a Monopoly here http://synthhacker.blogspot.com/2013/04/portamento-voice-spreading-from-monopoly.html – I borrowed that equation when I added portamento to my ongoing sawn-off JP-4 clone, and it sounds alright.

    On the remembering-patterns bit, when I was twiddling with a home made sequencer I was trying to get it so that patterns could be edited and saved on the fly without having to stop the track playing, but also to avoid any timing problems caused by waiting for slow memory to update. This was before asynchronous SPI libraries were developed, so that might help these days for saving out to EEPROM, which tends to be a be a bit slower.

    If you’ve got a 3.6 you could save to a micro SD card, and that’s pretty simple, otherwise I think they have some flash masquerading as an EEPROM, although I don’t know how long that would last with repeated writes.

    My other plan was to use external SRAM and have a battery-backup, which seemed rather old-fashioned, but it’d be faster to update.

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