Sonic Reducer - my take on the analog bitcrusher

[Synsound]

Just thought I would share my completed build. Thanks again!

[Freppo]

Great psycadelic artwork! :)

[johnk]

Hi Fredrik,
I just etched and built one today. it works, but it has a constant high pitch whine in the background that varies in frequency with the sample rate pot. the gate trimmer doesn't gate the whine on mine but rather turns the effect on or off and has to be nearly fully counterclockwise in order for the circuit to work at all. is that how it's supposed to be?

[Freppo]

Hi John,

That doesn't sound right. For me the trimmer is set about halfway and the whine is only heard faintly when playing, and with the sample rate turned up (fully cw) it should be just clean signal as the oscillator goes above the hearing range.

However, alot of people has been having problem with this circuit. It's super sensitive and require grounded input/output and pot wires. The LM324 is a must aswell. Seems like you might have some other problem though.. :/

I noticed a huge difference between my stripboard build and my dual layer PCB. The stripboard build suffered from bleedthrough from the rectifier gain stage making it sound a bit dirty, but the PCB goes from totally clean (is this thing on?) to very crushed. I'm going to write about it in my blog and put up sound examples.

/ Fredrik

[Synsound]

Interesting. When I tested mine on its own I had the same slightly dirty results. When I put it in the middle of my effects chain, which is quite long, it works perfectly.

[johnk]

Freppo wrote

Hi John,

That doesn't sound right. For me the trimmer is set about halfway and the whine is only heard faintly when playing, and with the sample rate turned up (fully cw) it should be just clean signal as the oscillator goes above the hearing range.

However, alot of people has been having problem with this circuit. It's super sensitive and require grounded input/output and pot wires. The LM324 is a must aswell. Seems like you might have some other problem though.. :/

/ Fredrik

hmmm.I went over my pcb and build a bunch of time so I know that I built it correctly. still has the same problem with the gate  trimmer's position and still whines . it also whines when in bypass unless my instrument's volume is turned down.

I also tried a couple of different brands of LM324N's and they both sound the same.

[Freppo]

I have built both the pcb and the vero without any problem. If it still whines in bypass it means that there is something wrong around the gainstage/envelope follower. Have you tried a buffer in front to see if it helps?

You can buy the dual layer PCB from me if you want a safe and noise free build.. ;)

Synsound wrote

When I put it in the middle of my effects chain, which is quite long, it works perfectly.

That's interesting. Thanks for letting me know your findings! The circuit would probably benefit from having the envelope follower gainstage after input buffer. I'll probably make a MKII with a few small changes when I have sold out my PCB. The problem seems to only happen to the vero so..

cheers / Fredrik

[M. Spencer]

I was having issues with my build where the board was passing effected signal, but the dry to wet signal ratio was too high. When you turned the pots you could hear the faint oscillator change pitch, but if wasn't sonically reducing like in the demo video.

After all the usual debugging it still wasn't firing right. I traced it to the 2n5457. I swapped in two others but got the same results. Then I remembered some folks using a j201...and bingo, the effect works great. (And I love the sound!)


So...did I just grab 5457s that had undesirable hFe? Why did the 201 do the trick?

[Silver Blues]

Not sure but I'd like to point out that hFE is not a concept that is applicable to field effect transistors, because it refers to current gain and FETs are voltage controlled devices.

[johnk]

after spending some time away from it, I finally got mine working. my PCB had an open trace where the 10u cap connects to the 100R and 2K2 resistor.
it works perfect now.

[Freppo]

M. Spencer wrote

Why did the 201 do the trick?

That's a good question. As Silver Blues wrote, hfe can't be the issure here. In this circuit the transistor is only used as a switch and pretty much any JFET will work. I guess you either had a faulty 2N5457 or one with a different pinout. I have noticed that both 2N5457 and J201 can have different pinout depending on manufacturer. Very confusing.

[Freppo]

johnk wrote

after spending some time away from it, I finally got mine working. my PCB had an open trace where the 10u cap connects to the 100R and 2K2 resistor.
it works perfect now.

I'm glad to hear you got it working :)

[M. Spencer]

"FETs are voltage controlled devices."

Noted. Thank you for the correction.

[johnk]

Freppo wrote

I'm glad to hear you got it working :)

although mine works, it doesn't seem to have the same range as yours. I only get the more drastic bit crushing when both pots are counterclockwise.