Buchla 257

 The Buchla 257 is a really useful module.

The front panel is a bit intimidating, but once you decipher the symbols and letters its not too hard to understand.

[Va * K ] + {[Vb*[1-M]] + [Vc*M]} + Voffset = Vout

 A great module for mixing, scaling, and processing Control Voltages. (the 257T can also be used with audio voltages)

There are 3 inputs: Va, Vb, Vc.

There are 3 knobs: K, M, Voffset

You can add, subtract, scale, invert & multiply voltages.

The above equation can be simplified to:

K + M + V = output

Va * K (Attenuverter): Inverts/attenuates and scales the voltage from input Va.... allows for -10 to zero to +10V control of whatever is plugged into Va

{[Vb*[1-M]] + [Vc*M]}: blends inputs "Vb" and "Vc" . 

The voltages Vb & Vc can be crossfaded with the M knob 

or a CV at the banana input between Va & Vc

There is a switch that when turned on, will apply +0.5-1V (depending on your calibration) directly to the Vb input

V(Offset):  Adds a DC offset to the final output.

                   The V knob when increased will output 0-10V.

                   (with NOTHING plugged into the module, if you turn the V knob to 50% ,you

                   would have +5V show up at the output).

How I like to imagine this module is as a way to sum 3 voltages in creative ways.

Remember that you have two voltage processors. You can combine these.

For comparison see the Buchla 254v,  Buchla 256 & 156.

254v (buchla format)

Buchla 256

The Buchla 256 is a evolution from the Buchla 156 .

Its a voltage processor. 

The official Buchla name is "Dual control voltage adder".

There are two identical circuits.

The offset allows you to add 0-15V to whatever is 

plugged into any of the 4 inputs. 

(I've calibrated mine to 0-10V)

The 4 inputs are identical Attenuverters.

They invert/attenuate the voltage at the inputs.

eg if you plug +5v into a jack you will get +5V at the output

with the knob turned fully clockwise, and -5V at the output

with the nob fully anticlockwise.

At 12 O'clock it will be 0V

Allows for -10 to zero to +10V control of whatever is plugged into 

the corresponding jack.

Other Buchla CV processors:

+ 254v (buchla format)

+ 257  Control Voltage processor

DOBOZ - Touch Sensing Note Memory - Buchla format 4U --- part 1

These are my build notes for the DOBOZ TSNM module

 I like the compact format.

Its a sequencer +

 

Here are some pics of the raw PCBs

 

There are two versions of this module .

One uses a teensy 3.2, and a second uses a teensy 4.0

i bought this board many years ago when teensy's 3.2 were plentiful.

I recently received a NOS 3.2, so thought I'd finish this build.

My board is from 2017. rev 1.0

MPR121 breakout board.

Links

+ Official site

+ BOM 

+ official build notes

SEMICONDUCTORS first

Orientation of IC1-IC5 and IC7, Q1, D1 and D2 is clearly designated on the PCB. 

74HC595 2 IC3, IC4 - shift registers

mouser 595-SN74HC595DR

 

 

OPA171

IC5 

SOIC-8 operational amplifier 

mouser 595-OPA171AIDR

TL072

 IC1 

SOIC-8 dual operational amplifier 

mouser 595-TL072CDR

 

 

ADP150-3.3V 

IC7 TSOT-5 linear voltage regulator 

Mouser 584-ADP150AUJZ-3.3R7

 

"The trickiest part may be the DAC8560 (IC2), it’s a VSSOP-8 device. 

This is hand soldered

 

Use lots of flux , a fine soldering tip and fine solder.

... and a steady hand

--------------

MMBT3904 

Q1 SOT-23 NPN bipolar transistor 

Mouser ;512-MMBT3904

I didn't have this exact transistor.

I used this instead:

Encoder: ordered and arrived.

Mouser No:

858-EN11-HSM1BF20

Mfr. No:

EN11-HSM1BF20

Mfr.:

TT Electronics

 

 

Resistors..

Some of the resistors need to have 0.1% tolerance

2 x 100K, (R1 & R15)

1K x 1, 

27k, 

33k, 

teensy 3.2

mouser

coco.