Odd UniPulse Issue With Hammond AutoVari 64

[Anonymous]

Hi guys–

So I am setting up the unipulse to work with my Hammond Auto Vari 64. I have a 25V supply feeding the voice board and the UniPulse. They both seem to work, but I’m having a strange issue– the sounds fade in and out as they are struck, and then stop.

So, using the “test” button on the configurator, the first hit works, then the next 4 or 5 hits are lower in volume, and then nothing. When I plug it back in to the original setup — no tubbutec, afro-cuban-buttons version– it works okay.

I am using the open rect, 14V, etc. as specified in the page dedicated to this machine on the Tubbutec site.

We are tapping the “hi freq out” and “lo freq out” on the voice card to listen to.

Attached is the pertinent schematic and also a pic of the setup as it is, which is a crappy pic, but all i have at the moment.

Any ideas why this might be happening?

M

[Anonymous]

Oh also worth noting. If I turn everything off and on, it will work again for a few secs as described. This behavior is on the bass drum. The behavior on the snare is a little different but similar– it seems to more change tone over time than completely disappear.

[tubbutec]

Do you have the GND of your power supply attached to GND of the autovari?

[Anonymous]

tubbutec wrote:
Do you have the GND of your power supply attached to GND of the autovari?
You can see how it’s done in the pic in my original message. We connected OUT- of the PSU to the ground of the hammond, also the tubbutec board. Did we do that right?

Thanks!
Matt

[tubbutec]

looking at your pic, I realize that your issue might come from the fact, that you are only driving the voice board.
On each trigger point, try putting a resistor (100k – 470k) to ground.

[Anonymous]

Thanks I’ll look into this.

[Anonymous]

Actually, just for curiosity’s sake– why would this matter? Just trying to learn something here. Thanks!

[Author]

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