Boss DR-110 Clap Pulse Generator (trigger adapter)

Here's a circuit I came up with a while back. I had a DR-110 with a dead digital board. The digital board is responsible for generating all the triggers in the system, and it generates some very specific triggers for the clap circuit. 

CPI is three 1ms long pulses, every 10ms (100hz).
CPII is a separate pulse also 1ms long, that falls 10ms later.

I re-implemented this in the following circuit.
Traces from top to bottom are CPI, CPII, and Trigger in.

The traces are from a simulation of the circuit, that you can play with in real time here.

Breaking down the circuit, we start at C8 and R11. These form a hipass filter for the incoming trigger. This ensures that long triggers will be handled the same way as short triggers.

IC6A & B are schmitt NAND gates and they form an SR latch. It is set by an incoming trigger, and is reset by the CPII pulse. The output is used to enable the generation of the CPI signal.

IC6C is the core of an oscillator that can be enable/disabled from pin 8. It works by charging and discharging C9.
R14 sets the charging rate of C9, and determines the low time between pulses.

R15 and D4 set the discharge rate, and determine the length of the pulses.

R12 & R13 help bias C9 near the threshold voltage of IC6C. This ensures that the first pulse will be close in length to the following pulses. If C8 had to charge all the way up from ground, the first pulse would be much longer.

IC7 is a counter, and is keeping track of how many pulses have been seen on CPI.
Once the end of the third pulse is counted, output QC goes high. This resets the SR latch, disabling the oscillator, and very quickly stopping the fourth trigger.

Output QC is also used as our CPII signal. To limit it to 1ms in length, we use it to charge C7 through R9. After about 1ms, C7 has charged enough to trigger the CLR pin of the counter. This causes output QC to go low again and discharge C7.

So, with some simple tweaking, this circuit can generate different lengths, rates, and numbers of pulses.

Boss DR110 Modifications

Here's one from the archives, a set of changes I made to a Boss DR110. Here's the finished product, rehoused in a gun case.

Here is a version of the schematic that includes the modifications. It's pretty rough, as I never intended to share it, but here it is.


Most of the modifications are simple pot-for-resistor swaps and are already well documented. I scraped a few together in my notes:

Kick Pitch - R70
Kick Decay - R86
Kick "Oomph" - R70(add 10uF) 

Snare Tone - R80
Snare Body Pitch - R76/ R75
Snare Snappy Mix - R81
Snare Snappy Decay- C52/R84 

HiHat Tone - R14
Open HiHat Decay - R20
Closed HiHat Decay - R53
Cymbal Decay/Tone - R47/R44 

Clap Pitch/Mix - R114/R115
Clap Decay - R113/C50

 Also included is the standard DINSync mod that uses a 74*74 as a clock divider.





At the top is a simple replacement for the built in cymbal/metallic oscillator. It allows you to change each of the four frequencies. I designed a more complicated one that involved a kind of ring-mod, but it ended up inducing its signal into the other voices and causing a constant hum.

A large chunk of the circuit is devoted to buffering the voices for separate outs. I wanted them to be fully separate so that they could be added to/removed from the main mix and its accent VCA. 

The trick is that all the voices are interconnected and load each other in a way that affects the sound. This means you have to add a resistor and/or cap onto each voice to simulate the load of other voices that are now disconnected. The values for these components are up to the user's preference. They affect things like volume, decay and sometimes tone.

At the bottom is the second snare oscillator. It's a clone of the standard oscillator, but it's pitched a bit higher. It's similar in tuning to the 808's snare oscillators(depending on revision). Included is a mix adjustment between the original and new.

The last part is not pictured. It's an AVR that provides MIDI and trigger input functionality. It ties into the 110's button matrix and watches as it scans. Once the correct column is being scanned, the AVR controls the rows to simulate buttons being pressed. This leaves the original CPU to generate the triggers.

Here is the button matrix:


I designed an alternate way to provide trigger ins. You can add some tri-state buffers and use the column scanning signals to gate your triggers into the button matrix. The triggers come in the left side and pass through (when gated) to the right, pulling the rows low through diodes. Note, protection diodes are needed to make this tolerant of modular trigger levels.

DR-110 Schematic and PCB

I'm working on some DR-110's and needed a nice, clean schematic and board layout that I can pull up in eagle. I decided to redraw the two from the service manual.

I've corrected some small inconsistencies between the schematic and board. It's mostly limited to incorrect part names and swapped positions. Also, there are at least two versions of the board, both of which have test points that conflict with the schematic. I've compromised on these.

I've routed the board so that it's very similar to the original. The audio jacks have been omitted due to a lack of proper footprints, and some tweaks have been made with the potentiometers.

Images below, .sch and .pcb are available on my Github here.