Bitshuffler? - modified Digital Fuzz

A code-less bitcrusher, inspired by this old DIY design from Experimentalists Anonymous.

Schematic

My circuit ditches the DAC chip, opting instead for a resistor ladder DAC. I'm told the ADC in the original should be labelled as "ADC0804", so that's what I've used. A couple of simple mods make this thing a lot more stable, tying pin 9 to an external VREF (2.5v) and using a voltage divider at pin 6, the input. Together these changes will bias your input signal, vastly improving audio quality.

I'm powering the entire circuit from +5v (my schematic shows a 5v regulator) so as not to overload the ADC. It might be better to use a rail-to-rail op amp and take advantage of every last whisker of resolution, but I'm not too fussed personally.

The main challenge with this circuit is how to change the bit depth. I'd envisioned a pot tied to 7 comparators. As the pot is turned the comparator outputs switch off one by one. The comparator outputs control CMOS switches that disconnect the bits. This example shows 4 of 7 comparators/switches that would give you a 1 bit to 8 bit pot:

But that's a lot of parts for just one pot. The original schematic appears to show a dip switch, which would be great if they were easy to mount to enclosures. My solution is to have 8 outputs (from the ADC chip) and 8 inputs (to the DAC), ideally connected to mini 3.5mm jack sockets (the type you see on modular synths). This way we can turn the bits off in any order (i.e. bit-masking) and send the bits to different inputs, jumbling them up to make weird waveforms.

Technically these wires should be connected to ground to switch them off, but it doesn't make an audible difference in a whole lot of settings.

I've also added an input buffer, output mixer with dry and wet volumes (these aren't included in the video prototype), a stupidly wonderful tone control, a drive (pre-gain) pot and changed the sample rate knob to a more usable range.

Stripboard