Welcome to Robot Dialogs. This is a place where I will record my progress, mistakes, errors, failures, lessons learned and hopefully occasional success in my designs and implementations of robots and other technical endeavors. I will try to make it as educational, informative and entertaining as I can...

Sunday, July 10, 2022

Eurorack Noise Generator v1

When I bought the AS3310 chips from Electric Druid for the polyphonic envelope I also bought a few other chips to experiment with. One that I expected to be a pretty straight forward project to set up for a module was the Noise2.  

The chip is just an 8 pin PIC preprogrammed to output white and pink noise. There's a thorough writeup on the development of the firmware here.

Only 4 pins on the Noise2 are used and it's all 0 to 5V so interfacing is pretty easy. I wanted both filtered and unfiltered white noise and a pink noise output all buffered to prevent undo current draw on the Noise2 chip and amplified to 0 to 10V in my setup which required 3 op-amps. That left one op-amp available so I also have an inverted filtered white noise. With 4 outputs the jacks on the module could be on top and bottom and support the PCB properly.

The filter in this case is a simple RC low pass filter straight off the data sheet.

I went about simulating the circuit and then breadboarding it to confirm my schematics.

Simulation of the filter and output buffer with inversion: see it live

 

The PCB design went fast relative to some other designs. Having 3d models for parts and a template worked out for starting designs has helped speed up the work. I used TL072s instead of a TL074 (as shown in the breadboard) mainly because I have more of them available.

  
Assembly is pretty quick with so few components:
  1.  Surface Mount Resistors
  2.  Ceramic caps first, the solder points are below sockets on the top side.
  3.  IC Sockets
  4.  Diodes and Ferrite Beads
  5.  Polarized Caps
  6.  2x5 Power Socket
  7.  7805 Regulator
  8.  Jacks, aligned to panel
Testing went well, there haven't really been too many surprises on this design. The only potential problem I thought I had was a -6V spike on the unfiltered white noise output's falling edges, but I haven't observed that when the output is connected, only when it's floating, so I'm not going to stress about it.

Here are a few scope images showing the outputs:
Unfiltered White Noise and Filtered White Noise
Unfiltered White Noise and Pink Noise
Filtered White Noise and Inverted Filtered White Noise (with math adding them together there in the middle).

Power consumption of the module is 21mA on the +12V rail and 7mA on the -12V rail.



Once again I had a friend with a mill help me with some front panels with engraving. The width is 4HP (20.32 mm).

 


The depth is ~32mm but can be improved with a lower profile 5V regulator... something to change in v2.

Other thoughts for a v2:

  •  Use better footprint for polarized caps.
  •  Add alternate 7805 footprint for T0-92 or surface mount.

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