Baby 8 step sequencer schematic

I try to make schem for an old school Baby 8 seq with a CD4017, with some mix of several schem, and i’m not sure that my mix holds the road .

with some on/off/on switch you can on each step select, on/off cv & gate out or choose this step as reset step.

i use this part of schem for the external clock in, but only the up part (not the gate to trigger one) and i don’t really know what doing with the pin 2 of opamp, in my schem i only connect it to 100k then +12V

here’s my test on paper,plz if some expert eye can help me
thank you in advance

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The opamps are used in comparator: they will toggle their output at +12V or -12V, depending on the input (+12 when V+ (pin 3) > V- (pin 2) and -12 otherwise). So you need a reference voltage to compare to. One the first schematic, this reference is made with R17 and R22, and you should do the same on yours.

Also, you should put some kind of buffer at the outputs, at least for the CV output.

Besides that, everything seems fine!

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Thanks @telec16, i add the 15k to gnd and surely change TL071 by a 72 to buffered the CV out like you propose or a 74 for gate and cv out …
like this ?

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Very interested in your final schematic. I’ve built 3 baby8s and each was different. I like the way you’ve incorporated many later mods.

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me too i 've built many baby 8 (all different too) it’s a cool chip, but all in a boxe on 9V, this one is a project for my modular a small seq 10 cm for my case 5
i like Sam seq but it’s a big big one

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i just see 2 errors in my schem, when zero switch is select for reset step, pin 9 of cd4017 must be connected to reset to have 8 step.
and the step 9 don’t need to go to cv and gate out

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Coincidence? Today i was also working on a baby 12 extension for my Korg SQ-10 (the John Lee Hooker of step sequencers :grinning_face_with_smiling_eyes:)
I use a rotary switch as reset selector btw.

Also did some modding on the SQ-10 with on/off/on switches to be able to mute steps.

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nice work !
i find the switch on/off/on tip a good thing to minimize the panel side, i really want a small one.

it will look something like this

the schem with corrections

and i try a stripboard layout

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if I had more space I would surely add that (someone might be interested in it)

CV ajust (range & offset)

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If space is the issue could you use a dual concentric potentiometer?

Mouser have these but there are shorter ones available

If you need different values then you’ll need to open them up and swap the wafers. I did this for a stereo guitar that needed a volume/pan knob.

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thx i know and i have some double pot like that, but that mean one pot for 2 CV control maybe not very usefull. and i have not enough place for other add like range or offset CV because my layout panel is allready very full for 10 cm.

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Dual concentric pots would give you 2 independent controls in the same space as a single pot. So in your faceplate sketch tuning pot 4 could have an additional inner knob that’s for cv range and would work independently.

Or a fader pot up the middle or across the bottom :smiley:

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One warning. Finding knobs for those concentric pots can be tricky. That was what led to me buying a resin printer over the summer. A project with concentric encoders…and the only decent knobs only being available with a minimum order of something like 1,000 pieces :laughing:

It was easier to get a resin printer and design my own knobs than to try to deal with getting manufactured knobs.

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ok I did not identify the potentimeter you were telling me about, I understand better now.
I prefer to add nothing more and keep the layout panel that I did with 8 pot for CV.
thx

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i have another question about my schematic.

with +12V for powering the CD4017 , is there a risk to have a too high signal on the CV output ?
Gate out ? (even there’s a 10k for the gate)

edit : i put again my drawing maybe more simple

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Indeed it will be up to 12V on the CV output.
You can place a resistor before the pot to lower that voltage:
image
(assuming that you have a 100k potentiometer and that you want 5V max, you need a 140k resistor)
More info: https://old.telec16.fr/?p=pratique/utils_elec

Also, if you have only one gate out, you may want some sort of retrig signal too, because two consecutive gates will be seen as one long gate.

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thank you a lot @telec16 !!!

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Minus a diode drop, but yes.

Also up to 12 V minus diode drop on the gate out. There you can add a resistor to ground before the jack, for instance 680R gives you a little less than 5 V, or higher values to give you larger output.

Another option is to AND the gate out with the clock, though that might shorten the gate more than you want.

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so i add this complet schem for the trigger out

and now i have gate and trigger out jack

add a 140K resistor on CV pot for decrease the cv signal out to 5V

and add a 680R on the out gate

can i do the same (680R) to trigger out jack now

this the complet schem that i take for some idea
it’s strange here there are no resistor at all with 15V for the output voltage

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I guess Stone and Herrmann’s synths are designed to allow gates that large. And ideally all synths should be, too, but not everyone protects their inputs that well.

Also ideally all synths should set a low threshold, a volt or two, for gates, but some insist on higher.

The Kosmo spec topic says

and I’m surprised I haven’t started an argument about that. (So I just did.) 4 V minimum is way too high.

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