Buchla format 208p build guide

Build guide for Portabellabz 208p Electric Music Easel DIY module

created by Steffen Ahmad

 

Disclaimer

The PCBs are sold unpopulated and need to be stuffed by yourself. Advanced electronic skills are needed to build this module.

You can follow this build guide to build your own 208p Electric Music Easel DIY module but please note that we will not take any responsibility for damages or injuries when building and running this module.

Thank you for your understanding.

Caution

This DIY module build requires you to solder a lot of components. Please note that solder fume can cause serious damage to your health.

Please do NOT solder without a fume extractor or at least ventilation that prevents breathing toxic solder fumes. If you have ever cleaned a fume extractor filter you will never ever again solder without fume extraction or at least proper ventilation.

Stay safe !

Introduction

Thank you for purchasing Portabellabz 208p PCBs. 

Don’t have the PCBs and panel yet and wonder where to get them ? Click here

This guide will help you building a clone of the legendary Electric Music Easel by Buchla. With Portabellabz PCBs you have a spot on recreation of the vintage 208 PCBs once used by Buchla. The PCBs come with additional soldermask and silkscreened reference designator though to make you life easier.

The soldermask will prevent you from bridging 2 nearby pads when soldering for example and it will also prevent any corrosion when you work in environments with high humidity. The soldermask comes in 2 colours – blue and black.

The silkscreened reference designator on the other hand will make it super easy to find the right spots for all components to be soldered. Not only reference numbers are noted on the PCBs but also the values to be used – like 10K 1% for a 10K resistor with 1% tolerance.

Now lets have fun – happy building !

 

The right tools

In this build I have used the following tools. Those are just suggestions and you can sure use whatever you are used to.

The Knipex 35 32 115 will be used to bend the lead of components and with the Knipex 78 13 125 leads will be snipped off after soldering. 

My preferred solder wire is Kester 24-6337-6417. It is a water soluble solder and flux can be washed off under rinsing water with ease. The results are fantastic – super clean solder joints with no flux all over the place. Make sure to wash the PCBs thoroughly after using water soluble solder and make sure not to wait too long because the flux of water soluble solder is corrosive and can damage your traces after a while. Thats why in this build guide there are multiple “parts / steps” for placing, soldering and washing the PCBs.

Kester 24-6337-8800 NO-CLEAN solder will be used later for all parts that cannot be washed – like trimmers & potentiometers.

Knipex 35 32 115
Weller WSD81i SE
Hakko FR-410
Knipex 78 13 125
Weller T0053638699N.
Siglent SDS2104X
Knipex 12 62 180
Kester 24-6337-6417
Fluke 87V
Kester 24-6337-8800

Part 1 – Card 1 to 12

Placing diodes & resistors (22R – 10K)

The 208p build uses different lead spacings for the components. Before placing a diode or resistor check the lead spacing before bending the legs of those parts. For diodes about 4mm legth from the body should be fine. Bend carbon resistor legs (brown) about 2mm away from their body and for most metal resistors 5mm should be fine. Again – please check before bending the leads.

Once you have seated a component – press it with one finger against the PCB and bend the leads on the solder side of the PCB. This will hold the component in place until it is soldered.

To make life a bit easier I made pictures after installing parts of a specific value so you basically have an easy to follow parts placement map. In “Part 1” of this guide I started with the 1N457 diodes all the way up to 10K resistors. In most of my builds I start pupulating PCBs with the most flat parts. This way you can put the PCB on a flat desk and the components will be pushed against the board while soldering.

For Part 1 I will not place any component on the “SOT” designators. “SOT” stands for “select on test” and I will later put tulip headers in most of the “SOT” spots.

Click on the thumbnails below for high resolution images.

After all the pictured diodes and resistors (22R – 10K) have been placed you can start soldering them.

To make sure you do not overheat components please only solder one side of a component and then move on to the next one. Once you have finished soldering one side of each component move on with the other side of each component. Once you are done your PCBs should look like on the following pictures.

Click on the picture for a high resolution image.

After soldering snip off all component leads.

It is important to WASH your soldered PCBs. If you have used my recommended water soluble solder from Kester take your PCBs to your bathroom and wash them thoroughly under water for about 3 minutes. After that please use a hairdryer and thoroughly dry your PCBs. If you have used regular solder please wash with isopropyl alcohol or flux cleaner. From my experience I get the best looking results with water soluble solder. Once you are done your PCBs should look like this:

Click on the pictures for high resolution images.

Part 2 – Card 1 to 12

Placing resistors (12K – 100K)

Repeat the procedure from Part1 – this time with 12K – 100K resistors.

Click on the thumbnails below for high resolution images.

After all the pictured resistors (12K – 100K) have been placed please solder them.

Again – to make sure you do not overheat components please only solder one side of a component and then move on to the next one. Once you have finished soldering one side of each component move on with the other side of each component. Once you are done your PCBs should look like on the following pictures.

Click on the picture for a high resolution image.

After soldering snip off all component leads.

Please wash your PCBs again or if you have plenty of time – move on with Part 3 and wash afterwards. Just make sure you don’t put the PCBs away for a few days with solder flux on the boards if you cannot proceed. Once you are done your PCBs should look like this:

Click on the pictures for high resolution images.

Part 3 – Card 1 to 12

Placing resistors (120K – 13M)

Repeat the procedure from Part1 – this time with 120K – 13M resistors.

Click on the thumbnails below for high resolution images.

After soldering snip off all component leads and wash the PCBs. If you can proceed with the next step the same day – wash after Part 4.

Click on the pictures for high resolution images.

Part 4 – Card 1 to 12

Placing capacitors

Repeat the procedure from Part1 – this time with ceramic and film capacitors.

Click on the thumbnails below for high resolution images.

Part 5 – Card 1 to 12

Placing Semiconductors and ICs.

I will begin with Q1 – the 2N1711s on card 3, 4, 10 and Q2 on CARD 11. I’d like to have a bit of clearance between the bottom of the 2N1711 and the PCB so I used a film capacitor to offset them a bit from the board. I immediately soldered them in place after pushing against the 2N1711 and bending the leads on the solderside of the PCB.

Proceed with the 2N2907 (CARD3 / Q2) and LS352 (CARD6 / Q4).

2N2907
LS352

Place the 2N3565 and the selected 2N4339 (CARD8 / Q1). The 2N4339 needs to be selected for an IDSS value between 0.8 and 1.2mA for a proper sine waveshape. A regular non-selected 2N4339 will be installed on CARD6 / Q5. 

2N3565
2N4339

Place 2x 2N4340 (CARD10 Q2 + CARD11 Q1) and 2x 2N4341 (CARD6 Q1 + CARD7 Q1)

2N4340
2N4341

Then there’s the DG200BA (CARD9 IC3). To make this part fit the board you’ll have to cut off pin 7 as shown below. 

And finally before installing all the DIP sockets to the boards – I will place the LM380 ICs on CARD12. The LM380s produce a lot of heat and to add some cooling there’s a ground plane on CARD12 fo those. To allow for a better heat transfer please solder them directly to the board – without DIP sockets. You may adjust the location of the inductor on CARD12 a bit to free up some space for IC3. 

Now solder all DIP sockets in place. I usually only solder 2 pins of a DIP socket to hold them in place. Once the boards have been populated with the sockets – flip over the boards and finish soldering all parts with water soluble solder or whatever you prefer. I will leave pins 8 & 9 unsoldered as I will later apply Dave Browns CARD 5 mod and will use NO-CLEAN solder for those pins. 

After all DIP sockets have been soldered I took the chance while soldering with water soluble solder to include the mods on the sequencer CARD1. I have added 9x 0.1uF ceramic caps to prevent erratic behaviour on the sequencer. You can see the mods on the pictures below.

This should be the result of the previous steps:

Before I proceed with NO-CLEAN solder I will break apart all cards from both PCBs and add pin headers for the pA726 card by Portabellaz to CARD 6 and CARD 7. This card will replace the obsolete uA726 and using this replacement does not change the change the sound of the 208. I will build the pA726 once I’m done with CARDS 1-12 and the Mainboard.

I will also add all the Molex connectors to the card using water soluble solder.

Now I’ll add the Molex connectors to CARDS 1-12 and wash each CARD thoroughly. This is the last time I’ll be using water soluble solder on CARD 1-12. Make sure to dry all cards with a hair dryer and put them in a warm dry room or outside if you live in a sunny spot of this world. Let them rest for a day to make sure they’ll get dry as fast as possible.

Washing and drying the PCBs is time consuming but at the end of the day you will be rewarded with super nice and clean looking solder joints.

Part 6 – Card 1 to 12

Adding “SOT” (selection on test) components & trimmers.

I may have to change SOT parts multiple times later when testing the unit. Thats why I’m going to solder tulip headers to the “SOT” spots. It will make the selection process easy as I don’t need to unplug the cards all the time to solder in a new resistor value for example for testing. Once we have all the values needed we can desolder the headers and solder the correct values in place. 

Tulip headers will be placed on CARD5 (R29), CARD6 (R5, R58), CARD7 (R3, R14, R44), CARD10 & CARD11 (vactrols).

Place resistors after installing the tulip headers. I will use the following values for initial testing and will stick with the 1.2V/OCT calibration values recommended by Portabellbz.

CARD5 (R29) – 18K -27K (difference in the CO output amplitude between AM and FM)

CARD6 (R5) – 91K |  (R58) – 390K (MO 1.2V/Oct calibration)

CARD7 (R3) – 1.8K Timbre folding | (R14) | 44K (120K + 68K in parallel) & R44 – 150K (CO 1.2V/Oct calibration)

Add trimmer as noted in the BOM to CARD5 (20K), CARD6 (100K), CARD7 (100k), CARD8 (20K), CARD9 (100K).

Part 7 – Card 1 to 12

Vactrols & ICs

I will now add the vactrols to CARD5, CARD7, CARD8, CARD10 & CARD11.

It is mandatory to match the single vactrols on card 5 – even if Dave Brown’s CARD5 mod will be applied. The dual vactrols I’ll be using on the LPGs (CARD10 & CARD11) however should be matched for a good decay time. Thats why I have installed tulip headers for vactrols on CARD10 & CARD11. The 208p FULL KIT from SAmodular comes with matched vactrols for card 5 and the LPGs.

At this stage I will also install the ICs on all cards

LM301AN: CARD6 IC3 | CARD7 IC3 | CARD9 IC5, IC6 & IC7

LM380: already soldered to CARD12

LM3900: CARD1 IC1 | CARD2 IC3 & IC4 | CARD3 IC4 | CARD6 IC1 | CARD8 IC3

CD4001BE: CARD1 IC2, IC3 & IC4 | CARD3 IC6 | CARD4 IC3

CD4009UBE: CARD1 IC9

CD4011BE: CARD1 IC8

CD4012BE: CARD1 IC5

CD4013BE: CARD1 IC6 & IC7

CD4015BE: CARD2 IC5

CD4016BE: CARD8 IC2

CD4025BE: CARD3 IC5

CD4066BE: CARD2 IC1, IC2 & IC6 | CARD3 IC2 & IC3 | CARD4 IC4 | CARD5 IC2 & IC3 | CARD6 IC5 | CARD10 IC3 | CARD11 IC1 & IC4

RC4136: CARD3 IC7 & IC7 | CARD4 IC1 & IC2 | CARD5 IC1, IC4 & IC5 | CARD6 IC2 | CARD7 IC1 & IC2 | CARD8 IC1 & IC4 | CARD9 IC4 | CARD10 IC1 & IC2 | CARD11 IC2 & IC3 | CARD12 IC1

LM311P: CARD6 IC6

MC846P: CARD9 IC1 & IC2

LM741: CARD3 IC8


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