Bug-Crusher -- Sample Rate Reducer DIY

[bugbrand]

Hey, I should have posted this last week, but timetimetime:::::

I made a hardware bit-crusher style effect - actually its a sample-rate reducer - audio rate Sample&Hold using the AD781 (available as a free sample from http://www.analog.com - Analog Devices website)

Here's the super simple version: http://bugbrand.co.uk/images/circuits/r ... _proto.gif

And the Voltage Controlled version:
http://bugbrand.co.uk/images/circuits/v ... educer.jpg

Note:: these are built for a modular system so run on +/- 12v bipolar power supply.
Oh yeah and there's a 5v regulator in there to for the 40106 gating.
Last week I built the VC one into a stomp pedal (with preamping and then level reduction at the end so as not to overdrive the guitar amp input) plus a modulation tri/sqr LFO::::


And, DAMN, it sounds freaking amazing.!.
Guitar
TR505
Voice
Whistling

WhoooHooo! Plenty of people already very interested -- I'm probably going to start production building of them in July - but if anyone wants to DIY then I can confirm its an ace sounding project (and not too complex at all if yr up to modular works)

[expanoncolin]

Pretty cool and very simple!  I had always thought of doing the bitcrusher with ADC/DAC with an external clock in.  But this makes a lot of sense, too.  Did you use the same clock oscillator for the CV in one  (IE still a inverter based astable?)

-Colin

[birt]

what are all those pots that are not in the schematic?

[DiscoFreq]

Thanks Birt for showing me this )

[z1]

that sounds amazing!
hope i'll be able to build it one day...

[bugbrand]

Pretty cool and very simple!  I had always thought of doing the bitcrusher with ADC/DAC with an external clock in.  But this makes a lot of sense, too.  Did you use the same clock oscillator for the CV in one  (IE still a inverter based astable?)

-Colin

HiHi Colin

Yeah with a few tweaks -- the AD781 requires really narrow pulses otherwise its track&hold - actually, I changed C2 in the first schem to 22p as this stopped the clocking signal from bleeding through (by making the pulses really really narrow). The 781 just allows a fast s/h with minimum fuss (and free samples! (not to be confused with sample&hold though!))

YES! S/H is super simple but very effective. Don't know if this has really been done like this before - wanted to do it digi for ages, but I just never get around to really figuring what the best ADC/DACs to use and micros are forever on my to-do list.

[bugbrand]

what are all those pots that are not in the schematic?

The top pots are the modulation - simple Sqr/Tri LFO - I chose to have independent Sqr and Tri modulation depth controls but this is somewhat overkill..

Then below is preamp level input (need to tweak this a little 'cos for guitar it really needs to be fully up always) - this brings the lowlevel guitar (or other source) up to suitable levels for the circuitry. The other silver knob is the output level and the big knob is the main Sample Rate control

Oh yeah, I forgot to say - 'cos this is a CV controlled effect I added a foot control input on the back (standard volume style foot control) - so you also can attach a volume pedal to adjust the sample rate nice'n'easy while playing - from no effect to total sonic disintigration.!.

[bugbrand]

Oh yeah - and hoping to finish something even more exciting tomorrow.... (along different more modular lines) .....more details then...

Cheers All!

[birt]

it's funny i was searching for a way to incorporate a guitar input into some kind of synth using the CD40106.
 

i don't really understand the CV part though ... i have no experience with that

[para]

so i've got my AD781 chips in and im getting the rest of the parts together now but im not sure what to use for the power supply. i think its about time for me to start slowly building a modular so im looking for something on the cheap that can hang in there with me through like 20 - 30 modules or more if possible. how do i tell if a supply is bipolar, does that just mean its AC? and how many amps am i going to need for a mix of analog and digital stuff? and anything else i might need to know.

also is there a supply that can run some modules at +/-15v and +/-12v

[expanoncolin]

Most people who build synths, myself included, use PowerOne supplies.  YOu want bi-polar DC, not AC.  As far as amps go, for 30-40 modules you may want to consider a bigger one, but you probably will only need the 1 amp model.  Why do you want both 12 and 15?  Most 12's will run on 15.  And if it won't, you can just use regulators.

-Colin

[para]

thanks colin, i'm just now trying to learn this stuff after much bending and avoidance. i was under the impression that i might run into some things that want 15v, and i just wanted to prepare ahead of time (my feet already have enough holes in them). i still don't understand this whole bi-polar thing, is there someplace online you can point me to that can explain it. i did some searching but it was fruitless. also how would i tell on used supplies if they are bipolar like on ebay or something. what am i looking for. i already searched for power-ones after reading a suggestion on this board and they don't say if they are bipolar. and what’s a switching supply in contrast?

[expanoncolin]

Power supplies vary very much, as so many different kinds of people use them.

In my synth, I am using an HAA15-0.8-A.  It's a +/-15v, .8 amp power supply.  I am running maybe 6 +/-12v modules with it.  Many modules use op amps, which don't depend too much on the supply voltage.  You will run into modules that run on +/-12, 15, even +5 sometimes.  But regulators will answer when you can't just run it with your power supply.

Voltage is a bit of a strange thing to understand.  To begin, we will first define "ground" as 0v.  Ground is the earth outside, it is where all electrons go to die.  It has no potential.  It is just this huge conductor where current can flow to and essentially dissapear.  Now that we have a reference, we can give values to things.  What we are giving value to is the flow of current...  You can thing of voltage as a source of electrons.  More voltage means there is more in the "source".  Negative voltage means that this source isn't really a source, but it wants electrons.  So really you are just measuring how much and how the current flows.  A battery is a source of electrons with 9 volts, but if wired backwards, it is a drain that wants 9 volts.  So why create this drain?  Because alternating voltages, which is what sounds are, vary from a high voltage to a lower one.  And since ground is a very standard reference, you may as well make that the middle point of this varying voltage.  In order to create a wave that varies from a voltage lower than ground, to a voltage higher than ground, you need the voltage in the first place!  Then you can make it move to suit your needs.  A bipolar supply provides this voltage-positive and negative.  You could oscillate from a higher voltage to a voltage above ground (this is what happens in stompboxes and anything with a single battery), but synthesizers use the standard grounda s the reference point, so you need a bipolar supply.

Switching power supplies use a method that allows a smaller, cheaper transformer to be used.  They are generally cheaper and more noisy.  Linear power supplies use a very standard approach, but require big transformers, and are expensive.  I have never heard of anyone using a linear power supply in a synth.

-Colin

[para]

so then the stuff im going to run into relies on the fact there is a positive, negative and ground but is not technically "AC" because its not actually alternating. its constant at both + and -. and not moving back and forth across 0v like a sinewave? and i should think of the bipolar supply as two separate supplies with one of them backwards running - and the other + and they share a common ground?

as much as i've read about voltage and current it still hasn't sunken in. can you use an actual audio signal running through a mixer or something as a metaphor for me. would voltage be "volume" and current like the "frequency spectrum" from 20 to 20k or the “stereo field” or do i have it all wrong. i'm trying to visualize it somehow so this makes more sense?

what does a switching supply switch between? does it simulate a true bipolar by clicking back and forth between + and - ? and does so poorly i would assume?

again what info on a used supply would tell me its bipolar or would it say straight out?

[para]

or is more like the number of instruments playing at once filling the frequency spectrum and the tempo put together.  like filling a river full to the top and having it move really fast would be high current/amps? and having the river with just a little slow moving water is low current or is it just speed and not the mass?  

my understanding is that it is mass (of electrons) and the time they take to move that = current

 right?