CD4031 tap looper...

[nathanxl]

Hi. Ive been away all summer(winter for you in the north).
The workshop is now cool enough to work in.

Ive just bought a bunch of MC14557 chips and want to try out this circuit.
While Im waiting for them to arrive, could you smart fellows perhaps shed some light on whats going on.?..

Using all of the 64bits how many gate will this get me?
Am I correct that it will allow me 64 gates passing through it and then loop them?

Sorry if this is a silly question.

[noto]

check out the mc14517 too. when i saw this concept for the first time, it blew my mind! i used it to build a four part programmable drum machine for a circuit bent yamaha PS-3. my schematic is probably unreadable to anyone but me, but if you'd like, i can redraw it..
http://2.bp.blogspot.com/-LqcYmi9hPuo/Uds4K7_vvlI/AAAAAAAAAxY/JlDh9VtwXmE/s1600/Picture+074.jpg
more info on the PS-3 build
http://www.noystoise.com/2013/07/yamaha-ps-3.html

[billsship]

Is there a way to clear the 4031's 'memory' quicker than holding down normally-on button for the duration of it's cycle?

I'm wondering if cutting off pin 16 (+V) momentarily would help it forget.

The reason being, if feeding slower clocks into this thing, 64 steps might take a while to cycle through.

[noto]

for mine, I used a 'step-erase' switch to delete steps incrementally, and a 'quick-erase' switch that opened the loop while switching the input clock to another one that was set to a significantly higher frequency. one short press and the whole sequence is gone. if you just turn the power off, some of the bits will still be stored when you power back up. I found it necessary to build an 'initial-clear' circuit and a flip flop to keep the loop open upon power up, but then closed when a 'write' signal is sensed.

[billsship]

[roglok]

this is really interesting! is there a way to reset the loop sequence?

[SUGARAT]

No reset or inhibit pin on the 4031. That's too bad because there is plenty of room for one. As stated above the quickest way to clear the loop is probably to switch the clock to a really fast one while keeping data low. Sort of like erasing a tape loop. You hit record and turn up the motor speed.

Also, with enough stages you should be able to loop audio not just control signals, no? you would just be limited to as many cycles as there are stages in the shift register. also frequencies above the clock frequency won't playback properly.

[PHOBoS]

I finally got my hands on some CD4031s to built my own TAP looper. But there was one thing I didn't really like about the original circuit;
the not so standard Normally Closed switch, and the fact that it is placed within the data line so it can't be controlled by other logic. But after
studying the datasheet I figured out a way to use a more standard Normally Open switch. And because it is connected between GND and a pin
of the CD4031 it can now be controlled by other logic. The discrete OR gate (diodes + resistor) add the WRITE signal to the output so you can
directly see/hear what you are doing.

I also designed a deluxe version which has a nicer output in the form of an actual logic gate and it also sends the ERASE signal through to the
output. The spare NOR is used to drive an LED.

And I designed a stripboard layout for the deluxe version for those who like to use that.

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[dk]

Just a quick question... to debounce the switches on these, would it be as simple as strapping a cap (100nF?) over the switch contacts?

[PHOBoS]

hmm, the circuit somewhat debounces itself unless you run it at a very high frequency because bits are only added/removed on
a low-to-high transition of the clock. However because it also routes the switches to the outputs bouncing can occur here.
A simple capacitor can sometimes improve things but can also make it worse. With these digital circuits you want transitions
to be as fast as possible, so no rising/falling slopes. Ideally you would use an RC low pass filter followed by a schmitt trigger or
comparator with hysteresis after the switch. It depends a lot on the switches you use though and what you are triggering with
the output. Something like a drummodule or envelope generator will be more forgiving than a clock input.

[dk]

Ah yes... the 4031 doesn't seem to mind my switches, but one of the cool things about your setup with the switches passing through to the output, so when I'm not using the looper, I can still use the switches as a manual trigger. Sometimes they can be a bit wonky this way

I take it, then, that the best way to resolve this is with a similar setup to the one you added to someone else's design here: http://electro-music.com/forum/phpbb-files/button_gated_oscillator_127.gif ?

[PHOBoS]

yep, the configuration used in the 'button gated oscillator' should work. Here's a version which has the RC low pass filter,
drawn by Scott/JovianPyx. Having a resistor in series with the switch is also a bit better for the switch and the cap otherwise
you are shorting it out to GND. Not really a big problem which such tiny caps but it could prolong the life of those components.

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[dk]

Cool, thanks for posting that!

[cyclic]

What am I missing here?

How the hell is this not as well known as the baby8 or APC etc as a super simple beginner circuit. It seems to achieve functionality vs size beyond either of those two as well.

Is there some major weakness which I've missed?

[PHOBoS]

heh, there are a lot of interesting simple circuits posted on this forum that aren't well known, especially in this 'lunetta' section.
It might be because this forum isn't visited enough for them to spread and personally I don't really hang out anywhere else.

As for this circuit in particular the 4031 can be difficult to get.
The 4089 is another very interesting CMOS IC but also hard to obtain.

[cyclic]

I'm doing an order soon and mouser has the 4031 at $2.50 which is...ok..so I reckon I'll get one.

Have you Daisy chained them ever for 128 steps? I can see how it seems to be used at a high rate and is only nominally 64steps for our use, and I assume this means max 32 square gates with an on Off cycle, which is then run pretty fast for long/multiple gates. So I figure 128 doubles the resolution if not the functional number of gates.
If it's trivial I'd get 2 and design a PCB for them...

And 4089: subharmonics by the note rather then octave? Eg subharmonics 5th?

[PHOBoS]

yes, you can chain them. I was actually working on a version that could switch between 2 seperate 64 step ones or one 128 step one.
The design I have needs a 4-throw switch so I ordered a rotary switch for it but by the time I got it I was already working on some other
things so I never tested it.

The frequency you use depends on how you want to use it. The orginal idea is to run it at a high frequency so the timing will be close to the
'rhythm' you tap. So yes, if you use 128 steps (and double the frequency) you will get a higher resolution. It can also be used at slow
frequencies though and you could 'program' the sequence step by step. (wasn't that a 90's TV show ?)

I don't think the outputs of the 4089 are musical/tonal although I didn't check if there is a fifth in there. But it is great for creating interesting
rhythms. (see also this circuit)

btw. if you order from mouser I would order at least 1 extra in case you blow it

[cyclic]

Re: the 4031, so did you ever get a confirmed schematic? If you've got an eagle file I'll work on a PCB for it. I AM trying to do all PCBs not protoboard these days because my synth has to survive being strapped on the front of my bike and vibration breakages have occured most inopportunely...

Re: the 4089, nah I looked at the ratios and since its a /16 the only true harmonic ratio it will do is a perfect 4th and suboctave. So sounds better for patterns and weird noises than chords. Not that I'm at all against patterns and weird noises!

[Top Top]

[cyclic]

[Top Top]

[PHOBoS]

[cyclic]

So Tip Top,

I'm trying to understand. <And>

Your 8 key entry pad isnt 8 notes, it's just 8 buttons that each are encoded into 3 bits as high or low. Which means in practice you can encode one step across all 3 4031s with a single key entry.

And this combination then is the data input for another shift register which has 8 individual outputs? Does the 4051 then just give a single output based on the inputs <aaaah> So.... This process encodes those 8 switches to 3 bit binary which is saved as a 64 gate sequence by 3 4031s which then sends their 3 bits back to the 4051 which decodes it back to the 8 pots for cv output...

Did I get it?

Cheers
Lance

[Top Top]

[PHOBoS]

neat idea with the triple looper + mux
If you add a priority encoder in front you can use 8 buttons.