246 Buchla Format Build notes - 3

This is part 3 of my build notes for the Buchla format 246 module.

It's a replica of the Buchla 246 sequential voltage source.

 

Above is a photo of a vintage one.

 My earlier posts can be found here:

       Roman 246r - Buchla Format - build notes 1

       Roman 246r Sequential voltage source - buchla format - part 2  

 

 These are just my personal build notes.

I'm not a pro technician. 

These pics and notes as just to help me trouble shoot should I run into any problems.

 

The 246 can be built without modifications. I have one of these which works well.

This particular build uses the Modular Synthesis mods.

 + Modular synthesis

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Don't install

 R279, R280, R281, R282, R283, R284, R285, R286, R287, R302, R303, R304

I've marked these with a white pen

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Clock Waveshape

 

According to Dave from Modular Synthesis:

"The waveshape is similar to the 245 but the baseline sits at 4V, not 2V (I believe) due to the number of stages. When all the stage pulse output resistors were changed to 6K8, the module would no longer advance."

To fix this issue adjust the clock waveshape trimmers until it functions reliably.

 

 

 This is the waveshaper section on PCB2.
Change R301 to a 10K trimmer.

PCB2
Change R306 & R315 to a 20K trimmer (wiper at the node connecting R306 & R315).

 

Photo x 2 *

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Diodes

Looks like they are all standard 1N457 

D1, D2, D3, D4, D5, D6, D7, D8, D9, D10 

mouser 512-1N457

10K resistors first

1K resistors, etc etc

 

 

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

 

100K trimmers

mouser 858-25PR100KLF

 

I used a different footprint one on TR2

still 100k

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Time to install the transistors

Don't install Q75, Q76, Q77, Q79.

These are 2N3906

Connect the base to the collector with a link on Q75, Q76, Q77, Q79.

 

 

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The waveshaper section is completed

 

-------

Q5 is a JFET

.... a junction field effect transistor.

 

 

+ JFETS - matching for synthesizers   

 

 

-------

LS312 

package: TO-78

This is a TIGHTLY MATCHED, MONOLITHIC DUAL transistor

 

...

 

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Replace IC31, IC32, IC33, IC34 with LT1637.

These are Precision Amplifiers

 

..

 

 

We need to swap pins 2 and 3 of IC31, IC32, IC33, IC34.

 

That is the input & output pins are reversed. 

Ive modified the back of the PCB

...

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LM311 

IC7, IC9, IC10, IC12, IC13, IC15, IC16, IC18, IC19, IC21, IC22, IC24, IC25, IC27, IC28, IC30

photo*

 

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LM741 

IC2,

photo