Buchla 265 Source Of Uncertainty

I did not build this 265 Source Of Uncertainty but repaired and modified it.



This scope image shows the Random Voltages with a mid probable rate of change.


This scope image shows the Stored Random Voltages with a high correlation.  The pulse threshold for the left input was 7.5V and the threshold for the right was 5V.


The noise source uses a zener diode followed by a high gain transistor and op-amp the same as the 212 Dodeca module.  Similar to the Dodeca module the noise source isn't very good.  It picks up hum and sometimes oscillates which is probably a combination of circuit design and PCB layout.  You can see the hum "bars" in this scope image of the three noise outputs.




I found it easier to replace the original noise circuit with the Electric Druid Noise IC similar to my modifications for the 212 Dodeca module.  I epoxied a 8 pin socket on top of some PCB insulating material in the upper left corner for the noise IC.  I removed the parts associated with the zener diode and transistor amplifier and modified the circuit for the high noise output only.  I added a 78L05 regulator since this board does not use +5V and didn't want to run an extra power wire.  The yellow capacitor at a slight angle is a 1 uF capacitor on the output of the 78L05 regulator.


I just ran a single ground wire on the rear of PCB2.


The noise outputs sound much better.


265 Noise Modifications

I wrote these after doing the mod so they are unconfirmed.  Contact me if you did this modification to confirm it is correct.

  1. Remove or do not install Z1, Q1, C1, C3, C6, C8, R4, R11, R12, and R19.

  2. Replace R16 with a wire link.

  3. Replace R17 with a 24K9.

  4. Replace R13 with a 10K resistor in parallel with a 470 pF capacitor.

  5. Replace C9 with a 220 nF but only insert one lead into the top hole.  Leave the other lead unconnected.

The Electric Druid IC requires +5V.  You can either run a separate power wire to the +5V or you can add a local regulator from +15V.  I chose to add a local regulator.

  1. Add a 78L05 regulator.  I chose to connect the input to the cathode of Z1, the output to the anode of Z1, and the ground to the left pad of Q1.  This pad is floating so you need to add a ground wire on the rear to the bottom pad of R11.

  2. Add a capacitor on the output of the 78L05.  I chose a 1 F ceramic.  You can mount it to the middle pad of Q1 and the right pad of C6.

I mounted a socket for the Electric Druid Noise IC.  I used an 8 pin DIP socket and cut off pins 2, 4, 5, 6, and 7 and  folded out pins 1, 3, and 8.  I cut a piece of blank PCB material slightly larger than the socket and glued this with epoxy in the upper left corner as an insulator.  Then I glued the socket with epoxy to the insulator.

  1. Wire pin 1 of the socket to the output of the regulator which is the anode of Z1.

  2. Wire pin 8 of the socket to ground.  I chose the bottom pad of R11.

  3. Wire pin 3 of the socket to the unconnected lead of the 220 nF capacitor C9.