Analog "bitcrusher" circuit: schematic questions and "improvements"

[iainpunk]

so, if i understand correctly, you can see the crushed signal on the scope, but can't get it past the output jack? is it possible you didn't wire it right? i have a feeling that you connected the output to the ring, instead of the tip? inserting a mono cable would short out the output signal that way, maybe you want to re-check that?

cheers

[NoahMeurer]

So apperently it's all wired up right. I checked it again and the opamp buffered version did work before (besides the opamp getting too hot), I definetly don't have it connected the wrong way. I'd describe it like this: As soon as I'm connecting my amp to the output jack the crushed signal collapsesn and I can't hear a thing. However, when I disconnect the speaker/amp, the crushed up signal reappers on the output jack. Thats why I tried the buffering and so on...

Regards, Noah

[PRR]

> got really warm (all of a sudden it immediatley drew 50mA).

+ and - power reversed?

(I know how HOT a 8088 CPU gets with backward power.)

[NoahMeurer]

Got warm compared to room temp. Doesn't seem to be a big deal and I'll just ignore the current draw.
Now there are two problems left: First one is that I've got still some clock noise on the output (@PRR which diode should I use?) If I'm now connecting a 1N914, the sound of the circuit just is VERY low. In addition, it changes the shape of the sound.
And the second one is, that the effect only works at a certain sound level. If that specific level isn't reached I just don't hear a thing at all.

I really think about giving up at the moment.

I'm going to draw a new version of this circuit for everyone who is confused (I'd be, too!), perhaps this evening.

Best regards, Noah (my workbench looks like a battlefield)

[iainpunk]

i don't condone giving up, but i do support starting over.
re-check the pinouts, pull out all components and start with an empty breadboard.

cheers, Iain

[anotherjim]

I don't see any power supply decoupling. The 555 version had some, but probably not enough unless the original developer used battery power that might have disguised it.
With the JFET biased at 4.5v, how low does the control need to go before -Vgs is enough?
What is the duty cycle of the new oscillator? Does it allow the JFET to turn on long enough to hear anything?

[NoahMeurer]

I just built the parasitestudio bitcrusher on my breadboard and it sounds really decent!
Here's the ressource: https://www.parasitstudio.se/uploads/2/4/4/9/2449159/sonic_reducer_pcb.pdf
However, the signal is after being processed only at 1/2 of it's volume. I just can't find what I've connected wrong. (Any suggestions?)
If I have fixed this I'm done with the circuit stuff

regards, Noah

[iainpunk]

you might want to reduce the negative feedback (=increase the gain) on the amplifier before the Jfet, give it some make-up gain to match volumes. bit-crushers can suck some volume in general, especially when they are analog! you can also throw in a smaller capacitor and check if your volume increases

cheers

[ElectricDruid]

<pedant mode>

Strictly the stuff we've seen so far is more of a sample rate reducer than a bit crusher. E.g. It reduces the signal in the horizontal direction rather than the vertical. Imagine sampling a signal with a 24-bit ADC, but at 2000Hz - that's sample rate reduction. Now imagine sampling at 192KHz, but with a 6-bit ADC (or an 8-bit ADC with the lower two bits ignored, more likely). That's bit crushing. They don't sound the same, since bit crushing introduces harmonics by turning the waveform into something more steppy and staircase-like, but sample-rate reduction introduces enharmonics by virtue of heavy aliasing becoming audible. Both of these things are strictly digital, so what we're doing here is a like an "analog simulation" of a digital artefact.

Technically, the ParasitStudios circuit is a track-and-hold circuit, which can be adjusted to be a sample-and-hold circuit at very short 'track' times.

</pedant mode>

[iainpunk]

or, in other words, its a Nyquist distortion...

*symon and garfunkel start playing*
>> hello Nyquist my old friend
>> a pain to hear from you again...

cheers, Iain

[garcho]

Oops, I just replied to the post at the end of page 1 

[iainpunk]

Oops, I just replied to the post at the end of page 1 

wdym? were still on page one

cheers

[NoahMeurer]

Back again, adding a resistor from the negative input to the output of the opamp before the JFET didn't change a thing and it had the same volume. Tried values from 1M to 10k.
I don't know how I should use a cap with an opamp. Also, do I want to create inverting or non-inverting gain?

Regards

[PRR]

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wdym? were still on page one

Dig into your Profile Settings, Look and Layout:

[iainpunk]

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wdym? were still on page one

Dig into your Profile Settings, Look and Layout:

i know, i like 50 better

Back again, adding a resistor from the negative input to the output of the opamp before the JFET didn't change a thing and it had the same volume. Tried values from 1M to 10k.
I don't know how I should use a cap with an opamp. Also, do I want to create inverting or non-inverting gain?

Regards

i think non-inverting is better here, since the circuit kinda needs the near-infinite input impedance of the opamp to function.
the capacitor i mean is the one after the Jfet, before the opamp.
what type of opamp do you use? i believe this type of circuit works best with Jfet input opamps for the buffer stages! tl072, or tl074

cheers

[duck_arse]

postimg.cc is currently down again.

[NoahMeurer]

Okay I now tried literally everything that came into my mind on how to increase the opamps gain. However, the volume always stays the same. I tried positive and negative feedback, different resistors, differnt ratios, different caps and nothing seems to work.
I used values from 1k to 1M and I'm a *tiny* bit frustrated. But I don't think that the laws of electric circuits stopped working for me. There must be something I'm missing out on. The opamps that I use are LM358P's, the 2opamp/ic version of the LM324, the quad opamp that Parasitestudio is using. His circuit needs a tl072 but he only uses it for the clock + voltage buffer.

This is a though one
Regards, Noah

[garcho]

You need an input resistor for inverting op amps, and a voltage divider at the inverting input for non-inverting. If you don't know what I mean, ask. A feedback resistor on its own won't work.
For sure you don't want positive feedback.
You're going to get this, be patient.

[NoahMeurer]

Thank you for your answer! This is really helping me.
So if I understand you correctly I should build Nr. 3, right? (the one at the bottom)

And if so, which values should I choose? Or: how is the gain being calculated?
I watched a couple of videos about the opamp but I'm still kinda clueless and randomly changing resesitors won't make it any more unfortunately.

Best regards

[ElectricDruid]

Both the second and third one include a voltage divider R1/R2 which reduces the negative feedback and thereby sets the gain. In the case of number one, all the output is sent back to the input irrespective of the value of R1 (that would affect the current, but we're not much concerned with that for the voltage gain). So the number one circuit acts like the typical op-amp buffer - R1 might as well be zero, a wire.

Neither number two or number three show any biasing for the op-amp. Depending where they're being fed from and what the rest of the situation is, this might not matter, but more likely it matters a lot. This is the difference between "textbook" op-amp circuits and practical ones. The practical ones have to worry about details like the power supply and the biasing. Textbook ones mostly ignore those details, since they vary from circuit to circuit. This has the unfortunate side-effect that if you try and build a textbook circuit as drawn, it mostly doesn't work!

Have you got a schematic of what you've got on the breadboard at the moment? Can we have a look, please?

If you haven't, I really recommend that you get into the habit of keeping track of what you've done and any changes you've made on the breadboard by drawing a schematic and keeping it up to date with tweaks. Doesn't have to be tidy, just legible! It's extremely easy to start swapping out this bit and that bit on the breadboard and then it doesn't work, and you have no idea why or even what you're looking at any more. A slightly more positive outcome is if you finally do get something you like, then you find you've no idea what it is. And then you have to trace out your own circuit from a load of breadboard spaghetti - which is a horribly error-prone process, as I've found to my cost. It's *easier* in the end to keep track of things as you go along.

HTH