Build a buchla 208 rev2

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Synesthesia
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Post by Synesthesia » Tue Dec 19, 2017 7:58 am

I remember using 2 trimmers on my first 208, which i did manage to calibrate well.

so - do you mostly use TR8, and front Tr2 ?

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Post by boops » Tue Dec 19, 2017 10:15 am

Yes , once I ve implanted a pin resistor in the bad hole,and impossible to tune,then check each parts

Synesthesia wrote:I remember using 2 trimmers on my first 208, which i did manage to calibrate well.

so - do you mostly use TR8, and front Tr2 ?
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
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Post by astroschnautzer » Tue Dec 19, 2017 10:24 am

Dual vactrols work well for the lpg (card 10 & 11). No need for matching.


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Post by boops » Wed Dec 20, 2017 3:57 am

Yes , once I ve implanted a pin resistor in the bad hole,and impossible to tune,then check each parts

Synesthesia wrote:I remember using 2 trimmers on my first 208, which i did manage to calibrate well.

so - do you mostly use TR8, and front Tr2 ?
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

Ernst Bitter
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208 on on on switches

Post by Ernst Bitter » Sat Jan 27, 2018 8:24 am

Hi,

anybody tried building the 208 with these switches?

https://www.taydaelectronics.com/mini-t ... on-on.html

I did but I have several issues and the suspicion that these are one of the causes of my problems. Wrong choice?

The BOM says DPTD on on on but the suggested switches from digikey are actually SP3T.

Does anybody know an alternative switch which is less expensive?

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Post by cygmu » Sat Jan 27, 2018 10:25 am

An SP3T switch is typically a DPDT on-on-on wired in a certain way -- see the info sheet on the digikey product page to see what I mean.

The trouble is that there are two different kinds of DPDT on-on-on, and no way to tell f the Tayda ones are the right type without testing them. With the switch in the middle position, looking at the pins from the bottom, on the digikey swtiches , the middle right pin will be connected to the top right, and the middle left to the bottom left.

If your tayda ones are like this, they should be ok. If they are the other way around (middle left pin to upper left and middle right pin to bottom right) then they won't work, so that could be your issue.

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Post by boops » Sun Jan 28, 2018 3:07 am

Small bear switches are cheaper then nkk/ckk (apem are really good too)it’s not the same quality ,but work fine ,if you are a furious tweaker with your 208 ,use best quality ,it will take time to change a switch if one one fails
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
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Post by papz » Sun Jan 28, 2018 5:28 am

C&K switches are unduly expensive and not worth the expense.
Several ones proved faulty and I've had to unmount a few builds to replace on-on-on switches although brand new :bang:
They also feel wonkier than the Taiway ones available from Small Bear, whose pinout is ok.
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Post by Ernst Bitter » Sun Jan 28, 2018 2:20 pm

Thank you very much for the answers,

ordered the Taiway ones, looking forward to finding out if it solves most of my 208 issues...

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Post by Ernst Bitter » Mon Mar 05, 2018 4:06 pm

hello again,

after successfully changing the on-on-on-switches, I have 2 problems left:

-the reverb doesn't´t work -I get some kind of ugly distorted ringmod-sound when I turn it up (did the mod with the shielded wire directly to card 12).

-the Modulation Oscillator doesn't respond to the keyboard although i switch it to keyboard in. It only reacts when I plug the keyboard cv directly in the freq modulation input and also the moving of the trim pot has absolutely no effect on the scale.

Maybe someone has an idea where I should start looking for errors? Already checked the resistors etc. and changed RC4136...

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Post by papz » Mon Mar 05, 2018 4:49 pm

For the keyboard CV to the MO, check the switch and trimpot.

For the reverb, check your wiring connections : signal to IC1 pin5, shielding to 0V. The trace on the rear of board 12 going to IC1 pin5 should be cut.
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I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
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Post by sines » Tue Apr 03, 2018 11:36 am

Hi Don,

Wondering, should all the 1n5228's be replaced with 1n5236's in the entire 208 v1 build, or just for card 5?
Don T wrote:
haceka wrote:Thanks a lot Don T

Image

Image
Well, all the resistor stripes are the correct colors 8-) , but that doesn't mean there isn't a defective one someplace. I do not see any obvious solder bridges on the back or the front of the board.

However: If you have not already done so, replace the 1N5228 zener diodes with 1N5236! 1N5228 will definitely make IC's 2 and 3 get hot, if indeed it hasn't already killed them :deadbanana: (The part numbers are pretty much impossible to read in the photo.)

After that, I would definitely wash all the flux residue off the back of the board. Some of it looks a bit toasted, and may have begun to leak a bit of current.

Good luck, keep us posted!

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Post by keninverse » Tue Apr 03, 2018 2:17 pm

sines wrote:Hi Don,

Wondering, should all the 1n5228's be replaced with 1n5236's in the entire 208 v1 build, or just for card 5?
D3,4 of card 5 are the only 7v5 zeners. Check Dave B's site.

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Post by Don T » Tue Apr 03, 2018 7:26 pm

sines wrote:Hi Don,

Wondering, should all the 1n5228's be replaced with 1n5236's in the entire 208 v1 build, or just for card 5?
Just Card 5

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Post by Ernst Bitter » Tue May 01, 2018 3:11 pm

changed switch and trimpot an checked tracks near by. Didn't´t help :despair:
papz wrote:For the keyboard CV to the MO, check the switch and trimpot.

For the reverb, check your wiring connections : signal to IC1 pin5, shielding to 0V. The trace on the rear of board 12 going to IC1 pin5 should be cut.

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Post by papz » Tue May 01, 2018 3:20 pm

Next suspect is Q1 on board 6. Also check R3, R4, R5 solder joints and value.
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Post by Chaotic » Sat Jun 02, 2018 4:18 pm

Hi I'm on my way to build papz version of the 208, but in the meantime I have a friends Roman ver. 2 208/218 on my workbench for troubleshooting. My first Buchla but I have built eight Serge panels.
The first major problem for him was no functional random. Swapped the 4016 to 4066. Ok
Next was that the fm did not work. Also swapped the 4016 to 4066. The fm seems to work but the index pot does not work on fm. Only on am.

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Post by boops » Sun Jun 03, 2018 2:21 am

Use all the infos here or modularsynthesis to build your papz pcb ,there are the same,perhaps some light mods to do like missing ,track ,pads etc
Good built
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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Post by Chaotic » Sun Jun 03, 2018 3:27 pm

boops wrote:Use all the infos here or modularsynthesis to build your papz pcb ,there are the same,perhaps some light mods to do like missing ,track ,pads etc
Good built
Thanks.
The problem was my friend´s Easel. Not my papz version.
And it seems that you have built it. Its marked Boops on the psu in the 218. Maybe you only have built the 218?
I have looked at the schemas and found out that the signal to the fm goes through the vt5 and ic2 on card 5. And since I have fm then I found the vt5 had to be the guilty one.
I have no vactrols in stock and had to make my own to test.
Now the index pot works for fm too :banana:
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Post by boops » Mon Jun 04, 2018 2:00 am

Ah ok,i ve built only the case.

Chaotic wrote:
boops wrote:Use all the infos here or modularsynthesis to build your papz pcb ,there are the same,perhaps some light mods to do like missing ,track ,pads etc
Good built
Thanks.
The problem was my friend´s Easel. Not my papz version.
And it seems that you have built it. Its marked Boops on the psu in the 218. Maybe you only have built the 218?
I have looked at the schemas and found out that the signal to the fm goes through the vt5 and ic2 on card 5. And since I have fm then I found the vt5 had to be the guilty one.
I have no vactrols in stock and had to make my own to test.
Now the index pot works for fm too :banana:
Image
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

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Post by boops » Mon Jun 04, 2018 2:01 am

Ah ok,i ve built only the case.

Chaotic wrote:
boops wrote:Use all the infos here or modularsynthesis to build your papz pcb ,there are the same,perhaps some light mods to do like missing ,track ,pads etc
Good built
Thanks.
The problem was my friend´s Easel. Not my papz version.
And it seems that you have built it. Its marked Boops on the psu in the 218. Maybe you only have built the 218?
I have looked at the schemas and found out that the signal to the fm goes through the vt5 and ic2 on card 5. And since I have fm then I found the vt5 had to be the guilty one.
I have no vactrols in stock and had to make my own to test.
Now the index pot works for fm too :banana:
Image
FS :custom buchla 203 style càbinet ,skiff new design,boat ,hardware for diy cabinet ,easel case ,new 1u to 10u to 56u and more. / New 208 buchla card 12 /
HQ small case buchla psu PCB
https://www.muffwiggler.com/forum/viewt ... 93#3118393
https://www.muffwiggler.com/forum/viewt ... highlight=

Ernst Bitter
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Post by Ernst Bitter » Thu Jun 07, 2018 7:36 am

papz wrote:Next suspect is Q1 on board 6. Also check R3, R4, R5 solder joints and value.
Changed Q1 and the resistors are ok (changed R5 to 68k for having 1V / oct).

My transistor tester tells me "NJFET, Vgs=1,6V, I=2,3mA", so should be ok?

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Post by papz » Thu Jun 07, 2018 7:54 am

Swap IC6 on card 2 just in case.

On the MB check continuity between
- the keyboard voltage in socket and the MO "trim" trimpot's left pin looking from the rear
- the trimpot's central pin and the top pin header of card 6
- the keyboard switch low pin and R57 (next to it) top leg
- the keyboard switch central pin and card 3's pin header 4 (+13.5V)
- R57's bottom leg and edge connector bottom row pin 24 and card7's top pin header

Also check R57 is well 390k.

Do you have keyboard CV via a program card with a 200k resistor in "MOD key" ?
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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Post by ghostcode » Fri Jun 08, 2018 10:27 am

I revisited working on some of the slight bugs in my build. There are two things that I'm currently working out:

- Volume adjust scratchiness when outputting a low frequency sine wave
- A very tiny glitch in the complex oscillator sine wave


For those with completed 208s, how clean is your sine wave output from the complex oscillator? Mine has an extremely small glitch that seems to line up with the square wave output. It's so small that I can almost not see it on the scope, but large enough to add in an audible click when a low frequency sine wave is being output.

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Post by papz » Fri Jun 08, 2018 12:16 pm

Not sure what you mean by glitch but fine tweaking of the timmers on card 9, CO timbre and CO waveshape may help.

The former lowest frequency of CO is 55Hz, lower, instability might occur.
For a lower frequency range, a mod is detailed on Dave Brown's page.
Finest EMS gear service and Music Easel/208 goodies

I'm not a synths dealer and I'm not aware of an inexpensive Synthi secret market, please don't ask me if I know one for sale.
I don't offer support of any kind to people attempting to build clones of EMS equipment.

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