SH3a CV issue.

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3hands
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SH3a CV issue.

Post by 3hands » Tue Mar 24, 2020 1:13 pm

I have an SH3a with CV/gate in done using optical jacks and I’m triggering it with an Arturia BSP. For some reason, it won’t drop below the mid range of the osc. It’s a killer synth for basslines, but I simply can’t get either machine to get low enough to pull off a Bassline. Any ideas? It was a 3rd party who installed the mod, and I was told it’s +\- 5v, so technically, it should work. Would love to get this thing doing basslines!

Thanks in advance!
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oldgearguy
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Re: SH3a CV issue.

Post by oldgearguy » Tue Mar 24, 2020 2:32 pm

Looks like the BSP sends 0 -> 10v and your SH-3a mod is looking for -5v -> +5v, so you're not able to go lower than mid-range unless you get the SH-3a mod input range changed or figure out how shift the BSP output into the negative range.

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3hands
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Re: SH3a CV issue.

Post by 3hands » Tue Mar 24, 2020 4:33 pm

oldgearguy wrote:
Tue Mar 24, 2020 2:32 pm
Looks like the BSP sends 0 -> 10v and your SH-3a mod is looking for -5v -> +5v, so you're not able to go lower than mid-range unless you get the SH-3a mod input range changed or figure out how shift the BSP output into the negative range.
Hmm shit.

Here’s the million dollar question... where is a good place to start investigating shifting the output down? Sorry that seems like such a stupid and simple question. Could I do it by somehow stepping down the voltage in stages?
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KSS
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Re: SH3a CV issue.

Post by KSS » Tue Mar 24, 2020 4:54 pm

3hands wrote:
Tue Mar 24, 2020 4:33 pm
Here’s the million dollar question... where is a good place to start investigating shifting the output down? Sorry that seems like such a stupid and simple question. Could I do it by somehow stepping down the voltage in stages?
There are two steps to solving your situation. The first is verifying that shifting is the solution to the problem. This does not need to be small, economical, or robust. It only needs to show the result. After that, the second step is to address the problem. Which will have several possible answers which DO depend on things like ease, cost, durability and size.

For the first step use a mixer. Put a DC voltage on one input and the BS output on the other. Feed the mixer output to your SH3a. Since any DC -even a negative voltage- added to the mixer will effect a shift, and the mixer levels will change the amount of shift, you can see whether this is the problem.
Depending upon what other gear you have in your studio will determine whether you can easily add a negative voltage to the BS output to check directly. But you likely do have positive DC voltage available, if only a battery. Does this added positive voltage raise the floor SH3a frequency in volt per octsave fashion?

What to do after that will depend on if you want to mod the SH3a, the BS or use a 3rd independent device to translate between the two.

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commodorejohn
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Re: SH3a CV issue.

Post by commodorejohn » Tue Mar 24, 2020 7:30 pm

Yeah, this was one of the reasons I gave up on using a Keystep as a cheap CV converter.
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ricko
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Re: SH3a CV issue.

Post by ricko » Tue Mar 24, 2020 8:57 pm

What do you mean by "optical jacks", please?

I installed CV outs on my Sh-3A, though I have never used them, actually.

The 3A VCO design only needed to support 3.5 octaves of good tracking, one keyboard span, the range shifting being done by clock division not voltage control. So there is no reason to expect it does support a wider range with good tracking (but it may...) And similarly the "saw" waveshape is pretty much a constant shape for each note and transpose octave of a footage, being derived from the square. So I would not expect it to necessarily support a full range of MIDI notes well. So it might be happier for you to just accept only generating 0v to +5V and work with that.

(My guess is that you might have to transpose your midi keyboard down a few octaves, and press the lowest key on the 3A keyboard to get access to the same range as the keyboard, then use the 3A transpose and mixer to get the octave you want, and limit youself to 3.5 or so octave ranges of notes for any part. This may be wrong advice, just my expectation. )

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