Odd UniPulse Issue With Hammond AutoVari 64

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mattwa1sh
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Odd UniPulse Issue With Hammond AutoVari 64

Post by mattwa1sh » Mon Mar 11, 2019 3:34 pm

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
Attachments
setup as it is now
setup as it is now
4783CC78-0BA3-4372-A40C-6DC6B9B4EEB5.JPG (1.91 MiB) Viewed 402 times
autovari-voice.pdf
schematic of voice board
(5.01 MiB) Downloaded 10 times
Last edited by mattwa1sh on Mon Mar 11, 2019 3:40 pm, edited 1 time in total.

mattwa1sh
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Joined: Tue Aug 30, 2016 4:28 pm
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Post by mattwa1sh » Mon Mar 11, 2019 3:35 pm

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.

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tubbutec
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Post by tubbutec » Tue Mar 12, 2019 4:25 am

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

mattwa1sh
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Post by mattwa1sh » Fri Mar 29, 2019 3:11 pm

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

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Post by tubbutec » Mon Apr 08, 2019 2:02 am

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.

mattwa1sh
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Post by mattwa1sh » Mon Apr 08, 2019 2:12 pm

Thanks I'll look into this.

mattwa1sh
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Joined: Tue Aug 30, 2016 4:28 pm
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Post by mattwa1sh » Mon Apr 08, 2019 2:13 pm

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

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