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Help with "Semi modular" DIY Drum Machine
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Monkeproggs



Joined: Jul 27, 2020
Posts: 3
Location: Sweden

PostPosted: Mon Jul 27, 2020 2:05 am    Post subject:  Help with "Semi modular" DIY Drum Machine
Subject description: Need pointers on how to build this drum machine
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So I've got a crazy idea to build a drum machine. I've started breadboarding separate pieces and found them to work but I can't breadboard the whole thing. I must have tried at least 25 differnt setups for sounds before deciding on these.
So I thought maybe I can get some pointers from some experts.

The setup is quite simple:
I've got a NE555 as clock (with obvious Clock in coming, it's not on the shematic yet) driving a CD4017.
This 4017 I want to sent to a matrix of 8x4 patchpoints. Every step is sent to a row of 4 outputs.
Output1>---XXXX
Output2>---XXXX
et cetera et cetera
Drummaschine Matrix_schem.png
These outputs are then patched into another matrix where the signal is sent to the various sounds of the drummachine.

XXXXXXXX---> SNARE
XXXXXXXX--->Bass Drum
XXXXXXXX--->High Hat
XXXXXXXX--->Woodblock
Like so

So in effect you can "program" it by connecting cables to each step and the corresponding sound. If you'd like you can play all sounds all the time.
Will also be adding a Clock divider so you can get sounds to play every 2,4,6,8th time it's triggered.
This is my intention.

I Have a basic layout that I'm working on, and would like som input on the circuit.
A few questions have come up:
Do I need to "buffer" the output from each step if I'm going to send it to multiple inputs? and how?
Do I need to put a Diode on every input?
Do i need to put a diod on every output (in the matrix)?
Will it work?

Thankful for any pointers given and any correction. I'm more of an enthusiast than electrician so my knowledge has limits.
Posting a schematic for it too (it's big).
Drummachine_schem.png
Thank you
/
Monkeproggs


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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Mon Jul 27, 2020 12:29 pm    Post subject: Re: Help with "Semi modular" DIY Drum Machine
Subject description: Need pointers on how to build this drum machine
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welcome party!


Quote:
A few questions have come up:
Do I need to "buffer" the output from each step if I'm going to send it to multiple inputs? and how?

Not necessarily, but it depends a bit on if you want to use it as is or want to patch it to other devices in the future.
But there is something else to consider first. With the way the inputs of the drum circuits are currently configured
their sound depends on both the input level and to a lesser degree the pulsewidth as well. This can be useful to
shape the sound a bit more but only if you have a sequencer that has settings for this. You could add some buffers
to the inputs or even better something that gives a constant pulsewidth so that no matter what you feed it they will
always sound like you want them to sound.

If you have buffers on the inputs you don't really need buffers on the outputs of the sequencer but it's not a bad thing
to add anyway. Especially if you want to connect it to some other gear aswell. The advantage is not only a bit more
current but (depending on what you use) a stable output voltage and short circuit protection. Personally I like to add
opamps configured as voltage followers as most modern opamps can handle shorts pretty well. And if you have a
circuit running on 12V but want a 5V output you can just add a voltage divider before the opamp, so that it doesn't
limit the current. At the very least I would add some resistors to the outputs since with most connectors a short to
GND is not unlikely to happen.

Also increase the resistor value for the LEDs,. I would say at last by 10X as the output voltage will drop if the current
is too high. You could also use some transistors or maybe a convenient transistor array like the ULN2804.

Quote:
Do I need to put a Diode on every input?
Do i need to put a diod on every output (in the matrix)?

It's a choice, either the outputs or the inputs (or both) In this case I would add the diodes to the inputs so that you
can plug in multiple sources without having to worry that they might get shorted together. In my lunetta system I use
diodes and resistors on all outputs so I can connect as many to any input as I like. Downside is that the outputs can't
pull an input to GND if they have diodes on them.

Quote:
Will it work?

I haven't looked at every detail of the schematic but in theory it should work.
However. if you would connect 2 consecutive steps of the sequencer to an input it will only be triggered once (at the
first step). A simple trick is too use an AND gate on every output that is also connected to the CLK signal. This way the
outputs will only be high for the duration that the CLK is high. Sometimes this leads to double triggers thogh so you
might want to take a look at the 'Little Gate' sequencer.

I am not sure if making it patchable is the most practical thing to do. It does give you the most flexibility
but performance wise using switches is much more convenient, this can get more costly though.

Something else is that instead of using 1 sequencer to control 4 voices you can do a lot more interesting things with 4
seperate sequencers and with a gate sequencer that doesn´t require that much more components. You can use the same
CLK for all of them so they are in sync but also use different ones or divisions. Where it really shines though is if you use
different sequence lengths, Instead of having only 8 steps (or max 10 with the 4017) it can now take a lot longer before
the sequence repeats and you get some nice variations within the sequence.

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Monkeproggs



Joined: Jul 27, 2020
Posts: 3
Location: Sweden

PostPosted: Tue Jul 28, 2020 3:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
How do you mean? do you mean that the 4017's triggers will overlap? i.e that there is no "low in between them? cause i've noticed that sometimes in the baby 10 sequencers, that the gate signals can get rather muddy unless there is a difference in voltage.
So by adding an AND gate between the 555 (or clock in) and each output of the 4017 I would cut the duty cycle of the 4017 to the lenght of the 555?

yes exactly. The outputs of the 4017 stay high untill the next step so you wiould never get a pause in between steps.
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Monkeproggs



Joined: Jul 27, 2020
Posts: 3
Location: Sweden

PostPosted: Wed Jul 29, 2020 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

So something like this?


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