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 Forum index » DIY Hardware and Software » The layout factory
808 Bass Drum Clone Eagle PCB & CNC Gcode
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jbeuckm



Joined: Nov 30, 2008
Posts: 165
Location: Stockholm
Audio files: 9

PostPosted: Sun May 08, 2016 1:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

That sounds good for accents. What about triggers? Also, do you have any experience with multi-channel sample & hold ICs? eg. SMP08FPZ
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elmegil



Joined: Mar 20, 2012
Posts: 2057
Location: Chicago
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PostPosted: Sun May 08, 2016 6:17 pm    Post subject: Reply with quote  Mark this post and the followings unread

I apologize, I suck at keeping context on threads that spread out over time.

Hm.....

The real 808 has a master clock that actually has the variable high trigger signal combined with it. Any given voice is enabled by its individual gate, but the trigger (going into the "Accent" part of the circuit as they are often labelled when made separate) is what made it actually sound. The microprocessor on the 808 runs on 5V, so that gate has to be a 5V gate, and could be driven directly by whatever MCU you plan to use.

This doesn't let you have separate accent per voice, but I'm sure part of why they did it this way is related to the same problem you're running up against.

May not help with your MIDI part of the project, but just some thoughts....
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jbeuckm



Joined: Nov 30, 2008
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PostPosted: Sun May 08, 2016 6:38 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think you are saying that the signal through 22K to the first NPN's base on each voice is a 5V gate. In that case, I just keep that line at 5V and operate the voice with the "accent" 4-14V pulse, correct?
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elmegil



Joined: Mar 20, 2012
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PostPosted: Sun May 08, 2016 7:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

If you leave it always on, then you're still going to have to solve the problem of triggering voices individually. Whereas if you do like the original does, and only gate the voices you want to sound on a given step, that can be handled by the MCU directly or with minimal buffering, and leave you to only need one set of circuitry to generate the 4 - 14V pulse.

If I'm not making any sense, I would recommend reading through the 808 service manual, it's actually pretty well described there.
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jbeuckm



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PostPosted: Sun May 08, 2016 8:26 pm    Post subject: Reply with quote  Mark this post and the followings unread

In this MIDI version, there is no concept of steps and I am always triggering voices individually. Our 12 channel DAC or set of sample and hold circuits solve the problem of individual triggers, correct? So I could keep all gates at 5V and just send 12 separate scaled pulses for the instruments that should play.
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elmegil



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PostPosted: Sun May 08, 2016 10:06 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's worth trying Smile
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jbeuckm



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PostPosted: Mon May 09, 2016 7:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I guess the only signal that matters for separated voices is what happens at the collector of the PNP. I wish I thought of that before I built every single voice board with the gate circuit. Oh well head banging monitor
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jbeuckm



Joined: Nov 30, 2008
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PostPosted: Tue May 10, 2016 11:27 am    Post subject: Reply with quote  Mark this post and the followings unread

It does seem that keeping the gate at 5V allows the instruments to be triggered with a single scaled accent pulse. I want to make sure the always-open gate is not allowing signal bleed, but I'm probably going this way for the 12ch interface... separate power+trigger distribution board that sends these accent pulses via 12 euro-power connectors.

UPDATE: Layout and DAC code verified. I still need to build the power distro boards.


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jbeuckm



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PostPosted: Tue May 24, 2016 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread




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RyBowk



Joined: Nov 25, 2018
Posts: 9
Location: England

PostPosted: Thu Jan 10, 2019 5:09 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, this is an amazing project, and the fact that you have made your hard work available to the public is just pure class!
I’m new to all of the synth building but I do love it and I’m learning every day.
Can I just ask a simple question? So the 6 pads x 2 that are on the midi - cv board, do they connect to the power distribution board to supply each module with cv and gate?
Sorry but I need to ask the silly questions to move forward 😊 many thanks Ryan
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