Sonic Reducer - my take on the analog bitcrusher

[Freppo]

Here is my take on the analog bitcrusher.

I fixed the carrier bleedthrough issue with the original circuit and also added a "resolution" pot. It changes the width of the pulse oscillator. Wider pulses lets more of the clean signal through the sample and hold, so it almost functions as a blend.



More info, vero layout, pcb layout and schematic at my blog: www.parasitstudio.se

cheers
/ Fredrik

[Travis]

This is awesome! Do you think a TL074 should work or do I just need to order an LM324?

[Freppo]

I'm afraid that the LM324 is crucial in this case

[Silver Blues]

Fredrik, I notice you're really into the weird, funky modulation effects. Where did you learn to design circuits like this? Theory on design of overdrives/distortions/preamps/EQ, etc. (even tremolos) are common but once you cross into the realm of envelope filters/ring mods/delay/reverb/flange/phase, etc. there's little to be found IME.

Also, I think it would be an interesting experiment to have the option to control the sample rate with an expression pedal.

[Freppo]

Yes. :) That's a though question to answer.

I have just tried to learn as much as I can about the fundamental stuff, how op amps operate, cmos logic ect. It helps alot to think outside the "guitar effects design-bubble" and just read up on general theory insted of theory behind guitar effects specifically. For example, if you are designing a phaser, learn about the all-pass filter, and so on.

Other then that I think the most fun way to learn is just to borrow bits and pieces from other schematics (don't have to be guitar effects), breadboard them, tweak ever resistors and cap to see what happens and keep notes. For the oscillator in this bit crusher, I just googled "pulse oscillator op amp", and found and tried a few different ones (that were totally unrelated to guitar effects) until I settled for a combination of two and tweaked it to suit the needed frequency range. At first I tried to modify the original oscillator, but changing the pulse width also changed the frequency. This new oscillator is much better for this application imho. :)

Often you can find good starting points in the datasheets for cool circuits or building blocks. For example, the LM13700 datasheet has perfect examples of oscillators/LFO's, envelope controlled lowpass/highpass and bandpass filters, ring modulator (four-quadrant multiplier) sample and hold (bit crusher), PLL ect. All that can be easily adapted for guitar effects use. :)

I recommend these books:
The CMOS Cookbook (Don Lancaster)
The Active Filter Cookbook (Don Lancaster)
Handmade Electronic Music (Nicolas Collins)
Make: Analog Syntesizers (Ray Wilson)

Elliot Sound is a great resource:
http://sound.westhost.com/

I often also get ideas and inspiration from synth stuff.
I recommend the electro-music forum

That said, I still consider myself a newb at all this. My designs probably have alot of flaws to the eye of a seasoned engineer. But hey, as long as it works and makes sounds right. :)

Sorry about the long post.. You hit a weak spot lol
Cheers / Fredrik

[Synsound]

This just made the short list!
Any chance a J201 would work or any other common subs instead of the 5457?
Thanks for sharing

[Freppo]

A J201 will work fine aswell :)

[Synsound]

Great. I don't know why I stocked up on 324s but I'm happy abot it now. And I have the 201s that saves me a wallet raping at the local shop. I really do need to buy a bunch of 5457s I have been putting it off for a while.
Since you're here,
I had a question about your ugly face.
(Ha that's a funny sentence)
I built mine with a Tayda ldr and ultra clear blue.
Do you think that installing the specified Bactria would smooth out the sweep of the filter?

[Synsound]

The reason I asked is because in your demo vid the sweep in the LFO seems very symmetrical. On my build it will sweep in then back out quickly then no filter then repeat. I forgot toe toon that when o posed the question.

[Freppo]

Haha, yes that is a funny sentence.. :)
Yes, I guess it is worth a try.
I measured a few of the Tayda LDR's and they varied alot so..

[Freppo]

Silver Blues wrote

Also, I think it would be an interesting experiment to have the option to control the sample rate with an expression pedal.

That should be an easy mod since the sample rate pot is just a variable resistor. :)

[Silver Blues]

Thanks

[Synsound]

Great Work. I just teasted it with the J201 and it sounds great.
About the expression input, where would the CV + connect?

[Freppo]

Thanks! That was fast :)
Regarding the expression input, I don't know for sure. I have never added a expression pedal input to any pedal. But the expression pot would have to be the same value (B500K) and replace the sample rate pot (maybe make it switchable) so that could require a dedicated expression pedal since most I have seen have either 10K or 100K pots. I will research on it further when I have more time.

[lucas abela]

just built this sonic reducer and i'm getting nothing wondering if anyone can see my mistake

it kind of just makes a high pitched oscillation or something and dosn't let any signal go through (unless bypassed)

all the pieces seem to be in the right spot and i checked meticulously for solder bridges as i built her

[lucas abela]

thought maybe the LT072 was in the wrong way and turned it around only it have it cook so it wasn't that

i assume the LM324 is in correct as that had the small little indicator U at one end

[Synsound]

Looking at your bypass switch, assuming that where your LED cathode connects is lug 1, your input is coming from the jack to lug 9 and also jumps to lug 4. That looks correct, but it looks like that jumper wire fro 9 to 4 may be touching or connected to lug 5 as well. If that is the case then you have a problem there. Lug 5 ( the center lug)  should only connect to the input of the board and nothing else.
I apologize if this is not the case it can be hard to tell from photos.

[Freppo]

Hi Lucas
Sorry to hear that you have problems with your build.
It's very hard to tell from the picture if there is an error.
I would unbox it and maybe use an audio-probe to see where the signal gets lost or where the oscillation starts. I hope you manage to solve it.
/ Fredrik

[MAndrews]

Hi Freppo
I have just built this and I can get some great sounds out of it. What role does the transistor do in the circuit? Will biasing affect the sound made? Mine sounds as if it goes to more extremes than yours - yours sounds more 'playable' through the knob ranges.

Thanks a lot for share all your designs. I know we all really do appreciate it.

Regards
Mark.

[Freppo]

Hi Mark,
Thanks. Glad you like it :)

The transistor only acts like a switch, so type of JFET or biasing makes no difference in this case. It closes/opens at the same frequency of the oscillator. When it's closed, the signal that came through at the last open state gets stored in the 47nF capacitor, until it opens again. This is called Sample & Hold and in this circuit it basically works like a crude analog to digital converter / sample rate reducer.



Maybe your oscillator goes alittle lower in frequency, that would explain why it would sound more extreme.

Cheers
/ Fredrik