MB808 Accent Circuitry

[fabreeze]

I have been trying to make a prototype and I have had troubles with the Accent circuit.

So far, the individual drum triggers work (1ms pulse), but when I try to add an accent circuit it gets a little confusing.

Maybe I am misunderstanding what I read at MidiBox.

From the MidiBox MB808 page:

"The concept is simple, we still use a pot connected as a voltage divider between the 5v and 15v rails to get our accent voltage but a simple transistor can be used to shunt the voltage of the wiper to the 5v rail when it is turned on. If we invert the common trig signal in code so that it is active low we only need the single transistor ;) It should be noted that the original schematic has 2 47uF capacitors as local resoviors for the common trig line. Testing on the beta unit showed that the current draw on the common trig line could sometimes be high enough that these caps are needed to keep the voltage from sagging."

Does anyone have a schematic for this simplified Accent schematic?

It would be very helpful.

Also, I tried using the schematic from the MB-808 Accent here:

accent

It didn't seem to work. I am writing my own code for it, sending 1ms pulses for Accent and Trigger.

I have tried all combinations of inverting or non-inverting the pulses from the 2 lines.

Still, it doesn't seem to work properly. I do know that my code is fine.

I can tell that pulses are coming out of the CPU as intended, but when they go through the circuit,

I only get the Trigger pulse, not the Accent pulse. So when I turn the Accent pot down, I get all unaccented sounds.

When I turn it up, I get all accented sounds. There is no variation. Kind of annoying. Anybody got a clue about this?