208p build thread (papz's PCBs)

papz · Post by **papz** » Thu Jan 11, 2018 10:02 am

FAQ
Buildnotes and calibration
Parts layout
Schematics

Happy building !

The new black or blue silkscreened revision is available from SAmodular.

The blue bare tracks "vintage" revision is available from me as long as stock lasts.

the bad producer · Post by **the bad producer** » Thu Jan 11, 2018 11:11 am

papz · Post by **papz** » Thu Jan 11, 2018 6:10 pm

I updated the cards pics with components layout and values and the build notes.
The C5 47µF tantalum cap mentioned in the BOM works fine in the CO instead of the 56µF.
R45 100k instead of 20k eases tracking calibration.

Karl71 · Post by **Karl71** » Thu Jan 11, 2018 6:22 pm

this is gonna be good.

looking forward to a thread of well documented success stories.

papz · Post by **papz** » Thu Jan 11, 2018 6:30 pm

Me too for sure !

beautyofdecay_ · Post by **beautyofdecay_** » Sat Jan 13, 2018 1:29 pm

I started my build today and populated the motherboard.
I have to wait for the cards components before I can continue...

papz · Post by **papz** » Sat Jan 13, 2018 4:43 pm

papz · Post by **papz** » Wed Jan 17, 2018 12:57 pm

Some extra infos added in the build notes.

It's better to match the vactrols on boards 10 and 11, or use dual VTL5C3/2.

Vactrols VT4 and VT2 on board 5 need to be selected on test for proper AM performance.

On board 7, R3 should be selected on test, a value between 3k8 and 12k, depending on the vactrol, to set the desired timbre amplitude. I find 4-5 folding is good, as shown on http://modularsynthesis.com/buchla/208/buchla_208.htm but others prefer more foldings. It's up to the builder to select what best suits his needs.

On board 8 the 2N4399 needs selection on test for proper sine waveshape.

I think this depends not only on the part itself but on the other parts in the circuit as well, therefore I use to select parts on test directly in each circuit.

pathein · Post by **pathein** » Thu Jan 18, 2018 7:03 am

thanks for the updates

I have just received the pcbs and panel. Got to say that the panel is really looking good. Next up will be waiting for the various parts to arrive, cant wait to start working on it

papz · Post by **papz** » Thu Jan 18, 2018 10:54 am

Thanks for the feedback

pathein · Post by **pathein** » Thu Jan 18, 2018 6:12 pm

hi papz, some questions regarding the pA726 board. For the electrolytic, is it necessary to get at least 35v rating type or 25v type depending if its +-12v/+-15v?

for tab 1/1tab, it will be populated with male pin header?

for the resistors, will 1/10w rating be ok or stick to 1/4w type?

papz · Post by **papz** » Thu Jan 18, 2018 6:38 pm

25V is ok for the electrolytics, these are between each +15V/-15V/+10V rails and ground. But higher voltage is ok, I generally use 50V since I mostly stock these, are the same size and price as 25V and can do more. Also, the higher the voltage rating, the longer the life expectancy.

I'd rather use 1/4W resistors.

The DIP10 emplacements are to connect the pA726 to the boards, vertical one to 6 and horizontal one to 7.
I'm not sure the holes are large enough for headers.
I simply use thick components legs, there are much more than needed when building a 208.

"1" shows the µA726's pin 1, "tab" the µA726's tab/pin 10.
The trimpot should be on the same side as the other trimpots, this way you can't be wrong.
More details and pics on http://www.portabellabz.be/pa726.html

pathein · Post by **pathein** » Thu Jan 18, 2018 7:31 pm

Cool, thanks for the info, much appreciated!

heapish · Post by **heapish** » Sat Jan 20, 2018 6:56 pm

Has anyone done a mouser cart for this?

beautyofdecay_ · Post by **beautyofdecay_** » Mon Jan 22, 2018 2:24 pm

papz wrote:Some extra infos added in the build notes.

It's better to match the vactrols on boards 10 and 11, or use dual VTL5C3/2.

That's a good idea.
I think a VTL5C3/2 should work like this? The vertical blue line is a wire link.

The wires of the original VTL5C3/2 are long enough to connect the vactrol this way. I don't know about the current clones however...

papz · Post by **papz** » Mon Jan 22, 2018 6:03 pm

Or this way.
Legs can be extended with wire if needed.

sanemalkavian · Post by **sanemalkavian** » Tue Jan 23, 2018 9:59 am

Hi everyone. I am new at this, so not sure how good it is.

I compiled a Mouser project based on the BOM lists from PDFs. Mouser project has all the components that can be found based on those BOMs, so parts that are rare and cannot be found on mouser, including sliders, pots and hardware parts are not included.

I also included everything needed for pA726 except for CA3046 and two pin header.

In the attachment are all Excel files generated from PDFs, including a compiled mouser cart, where all parts that are not in stock are replaced with other part number. Compiled Excel doesn't include parts needed for pA726.

I hope this will help.

Mouser project 208

beautyofdecay_ · Post by **beautyofdecay_** » Tue Jan 23, 2018 12:44 pm

I think there is a mistake in your BOM (I made the same mistake...

)
You should order CD4016, not CD4066!

The original BOMs from Roman specifies the CD4066. Check the PCB layout pictures from papz (or the original Buchla schematics). There only 4016s are used.

EDIT: checked the datasheets and the 4066 can be used also as it is an updated version of the 4016... Sorry for the confusion!

sanemalkavian · Post by **sanemalkavian** » Tue Jan 23, 2018 1:21 pm

Thank you for the info. I used the recommendations from papz, as he says that 4066 can be used, except for card 8, where 4016 is recommended for IC2, so BOM contains 1 4016.

papz · Post by **papz** » Tue Jan 23, 2018 2:44 pm

Thank you sanemalkavian

Some 4016 may cause problems indeed, which can be avoided using 4066 instead. I now use 4066 in all my 208 builds.
In case some wonder whether this affects the sound, the answer is no, these ICs are used to voltage control switches.

papz · Post by **papz** » Fri Jan 26, 2018 1:12 pm

Some builders ask me about this on the promo PCBs card 8.

The trace touched the eyelet and was rectified at last minute, but the solder mask wasn't rectified.
So no worries, it is ok and can be used as is.

beautyofdecay_ · Post by **beautyofdecay_** » Wed Jan 31, 2018 10:45 am

Making progress...

Card 1, 2, 3 and 4 are up and running

papz · Post by **papz** » Wed Jan 31, 2018 11:29 am

[video][/video]

trimix · Post by **trimix** » Sat Feb 03, 2018 1:44 pm

Since I can't seem to find anyone offering panels for the 208 right now, I was wondering if anyone has drawing files (especially drilling centres) for the 208.
Formats can be .svg .ai .dxf ... anything editable.
I'm not looking to make a clone... I actually want to customize the look of the panel for myself. But of course the locations of the hardware must remain the same.
anybody???

delayed · Post by **delayed** » Sat Feb 03, 2018 2:05 pm

https://electricmusicstore.com should have both panels and a drill sheet

MOD WIGGLER

MOD WIGGLER

208p build thread (papz's PCBs)

208p build thread (papz's PCBs)

Panel files for 208