208p build thread (papz's PCBs)

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papz
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Post by papz » Thu Oct 24, 2019 8:26 pm

Typical troubleshooting routine : double check all components and solder joints, check and swap ICs in their socket etc.

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Post by xahdrez » Thu Oct 31, 2019 6:33 am

Finally got to testing my 208, and all is working really well (great build btw!)

Only thing I'm struggling with is the reverb. Based on comments above, it seems likely it is the tank that has been damaged in transit/installation as I'm experiencing similar symptoms (spring is being driven but no reverb sound returning). Could some one tell (or show!) me where I should be taking readings across to check the coil isn't broken? I'm a bit confused, and I can't tell if it is because my multimeter isn't accurate enough or I'm probing the wrong places!

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Thanks! :tu:

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Post by papz » Thu Oct 31, 2019 7:31 am

Looks like you didn't connect the reverb with a shielded cable as explained in the build notes. If so, it's normal it doesn't work.
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Post by xahdrez » Thu Oct 31, 2019 7:44 am

Oh wow, would that stop it working all together? I had assumed that it would just affect the quality of the reverb return signal/introduce bleed, not kill it all together? I just did it as a quick test (got the shielded cable but it was in storage, so I hooked up with regular wire between house moves to verify it was working). Will swap over and see what happens. Thanks!

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Post by papz » Thu Oct 31, 2019 7:55 am

http://www.portabellabz.be/208pcbfaq.html wrote: The reverb output is via a shielded cable only to avoid the MO bleed common issue, it won't work otherwise, the related trace on board 12 was removed.
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Post by xahdrez » Thu Oct 31, 2019 8:58 am

papz wrote:
http://www.portabellabz.be/208pcbfaq.html wrote: The reverb output is via a shielded cable only to avoid the MO bleed common issue, it won't work otherwise, the related trace on board 12 was removed.
Thanks - I totally took a more liberal interpretation of that line! Will swap it over and see how I get on. :tu:

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Post by xahdrez » Sat Nov 02, 2019 1:47 pm

Sadly the shielded cable hasn't fixed the reverb, but it has made me more aware of the bleed! Reading posts above it seems like I've got the same issue as others (complex oscillator bleed, exacerbated by timbre, mostly rectified by "groundhack" detailed a few pages back). Going to do a bit more digging and see what I can come up with before my replacement reverb tank comes! Just need to stop playing with it long enough to actually fix it!

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Post by sanders » Sun Nov 03, 2019 1:10 am

posted this in other thread, but maybe belongs here:


I just finished assembling my 208, built with the discounted introductory PCBs.

I’m pretty stunned to find most everything working altready. VCOs and Timbre need trimming. My LPGs were a little wonky sounding but I wasn’t sure if maybe it was wonky source audio giving that impression.

Before I could figure it out for sure, the LPG2 LED went dark.

I was examining board 11 and decided to replace the 4340 with a J201. This made a world of difference in sound. LPG2 sounds and works great, better than LPG1 (w original 4340). But the LED is still dead. I tried a brand new 2n1711, but no dice.

The LED is getting +5v, it’s oriented right (it was initially working). I wouldn’t have thought it possible, but, could the actual LED have failed somehow?

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Post by papz » Sun Nov 03, 2019 4:37 am

Sometimes LEDs happen to fail. You can test it with a multimeter in diode position.

Reverb tanks are fragile. You can measure the coils resistance : input should be about 25 ohms, output about 900 ohms. Infinite resistance means the coil is broken and the tank needs replacement.
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Post by boops » Sun Nov 03, 2019 3:04 pm

xahdrez wrote:Sadly the shielded cable hasn't fixed the reverb, but it has made me more aware of the bleed! Reading posts above it seems like I've got the same issue as others (complex oscillator bleed, exacerbated by timbre, mostly rectified by "groundhack" detailed a few pages back). Going to do a bit more digging and see what I can come up with before my replacement reverb tank comes! Just need to stop playing with it long enough to actually fix it!
which psu do you use ?
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 /
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Post by papz » Sun Nov 03, 2019 3:11 pm

Did you well connect the cable shielding to ground on board 12 ?
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Post by xahdrez » Sun Nov 03, 2019 4:11 pm

boops wrote:
xahdrez wrote:Sadly the shielded cable hasn't fixed the reverb, but it has made me more aware of the bleed! Reading posts above it seems like I've got the same issue as others (complex oscillator bleed, exacerbated by timbre, mostly rectified by "groundhack" detailed a few pages back). Going to do a bit more digging and see what I can come up with before my replacement reverb tank comes! Just need to stop playing with it long enough to actually fix it!
which psu do you use ?

Using the 60W Bicker power supply which comes with the samodular case.

Shielding of reverb cable is well connected to card 12 ground.

It seems two other users experienced similar (Chaotic & tombet) and the additional ground cable definitely helps - but I feel like there might be something else at play. Will have to check through for shorts or any other issues, but would definitely welcome more ideas!

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Post by boops » Mon Nov 04, 2019 3:57 am

Check the isolation between each rails with an ohmmeter power off
a value under 200 ohms is suspect
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HQ small case buchla psu PCB
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Post by xahdrez » Mon Nov 04, 2019 5:09 am

Thanks Boops - will try tonight and see what I find!

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Post by papz » Mon Nov 04, 2019 6:32 am

I - and other people such as Captnapalm - noticed 208 issues related to Roman's 211 board, that is not best design and is used by SAmodular, as reported in older posts of this thread.
Replacing it with the PSU solution that I offer based on a Mean Well PD2515 + Mini Distro Board fixed them all... :party: http://www.portabellabz.be/distro.html
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Post by xahdrez » Mon Nov 04, 2019 8:58 am

papz wrote:I - and other people such as Captnapalm - noticed 208 issues related to Roman's 211 board, that is not best design and is used by SAmodular, as reported in older posts of this thread.
Replacing it with the PSU solution that I offer based on a Mean Well PD2515 + Mini Distro Board fixed them all... :party: http://www.portabellabz.be/distro.html
Thanks - I had a feeling that might be the best route forward! Out of interest, have you (or has anyone else!) tried using a 211 board with a Meanwell GSM60A12-P1J 12 volt 5 amp Medical Adapter (Mouser 709-GSM60A12-P1J) as per Dave Brown's suggestion here:

https://modularsynthesis.com/roman/211_ps/211_ps.htm

Tempted to try that first out of curiosity, but will give it a miss if this is a well trodden path! :tu:

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Post by papz » Mon Nov 04, 2019 11:19 am

The issues are caused by the 211, not by the brick that powers it.
Having designed my own Mini Distro Boards and being happy with, I had no reason to try other solutions.
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Post by sanders » Mon Nov 04, 2019 3:36 pm

I replaced a blown LED (confirmed by diode test) in LPG2, and now everything’s basically functioning. However, aside from calibration, there are still a few things that could use some tweaking. Hoping to get some advice.

1. LPGs sound and work fantastic. But all of the volume increase happens in the lower quarter of the slider travel. So, it goes from 0 to 10 in the first quarter, and from there the signal increases saturation for the rest of the travel. This is not the intended behavior, is it? It’s like this on both LPGs.

2. the timbre sliders behave the same. My timbre is way too strong to begin with (and I’ll follow the instructions to deal with this). But I believe the control is a separate concern.

I’m sure I bought linear sliders, so I don’t believe it’s the sliders at fault (man, I hope not!!)

3. I used low intensity LEDs, as discussed here, however, these are still way too bright for my taste. I would love to get my sequencer, envelope and pulser LEDs to light at the intensity of the LPG LEDs when they’re just barely indicating signal. You know? Just so they’re visibly lit, but not lighting up the whole panel

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Post by sanders » Mon Nov 04, 2019 3:42 pm

sorry if this paragraph is double posting, it’s not showing up when I submit it:

Can anyone recommend a higher value current limiting resistor (and is it prudent to change the values for the sequencer LEDs)? They’re “currently” 220R. I don’t think there are resistors used on the Pulser and Envelope indicators. Wondering if it would be ok to use limiting resistors here.

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Post by tarandfeathers » Tue Nov 05, 2019 7:59 am

sanders wrote:sorry if this paragraph is double posting, it’s not showing up when I submit it:

Can anyone recommend a higher value current limiting resistor (and is it prudent to change the values for the sequencer LEDs)? They’re “currently” 220R. I don’t think there are resistors used on the Pulser and Envelope indicators. Wondering if it would be ok to use limiting resistors here.
The only way to be sure is to work it out for the specific LEDs you have used. I use superbright ones for all my builds to reduce current consumption and anything over about 1.5mA is blinding. The best thing is to determine the current you want empirically by driving an LED of the same type you used from a fixed voltage with an adjustable limiting resistor, measuring the current at the brightness you want and then working out the appropriate resistor for the different voltages from there using ohm's law.

The current limiting resistors for the envelope and pulser (and LPGs) are on the associated cards (3, 4, 10 and 11) in the emitter of the driving transistors. The envelope and pulser are run from the 12V rail whereas the sequencer and LPG LEDs are run from 5V so you will need different values for each.

As for the clipping/saturating behaviour of the LPGs, I would hazard a guess that this is to do with the output FETs. If you bought these from utsource/ebay/aliexpress/whatnot I'd try something from a more reputable supplier.
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Post by jonen » Tue Nov 05, 2019 5:17 pm

Does anyone know what other factors influence the stability between the two oscillators of the complex oscillator? I can only get it stable with a specific setting of MB TR4 (Timbre), MB TR7 (CO Waveshape) and Card 9 R5 (Low freq tracking). However, I want to have more wiggle room for the timbre trimmer since I want to properly set the folding behavior ( the one I end up with is not the best). I specifically want it to be stable for low frequencies.

I already tried out a few different 2n4339, however, with little success.

Any idea, where else to look or what to try?

Maybe it does have to do something with the vactrols on card 7? I am trying to understand the schematics, but coulnd't really figure out, what they exactly do on card 7. Any ideas?

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Post by papz » Tue Nov 05, 2019 6:35 pm

Don't hope too much for a CO stable below 55Hz, its design has its limitations.

The timbre behaviour depends on R3 and VT1 on board 7.
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Post by boops » Wed Nov 06, 2019 2:41 pm

With my experience of the 208.for debugging
often ,we believe that all is fine ,on each card,but with a simple 4016
shorted,a flux short,a real short,a bad connection,etc somewhere in the 208,small problems appear,like a click in the env,an osc no stable etc.
use the schematic,trace the signals with an osilloscope ,if possible,isolate the bad function using only the card needed.take off some parts if needed,
be sure all the actif and passive parts are fine.
example ,the Mo can not be tracked by a keyboard without the card 7,there are the key controls on it.plenty of little details/functions ,that you can discover with the schematics.learn slowly but learn ;)
with the good psu ,and clean cards,no bleed,osc stables ,tracking excellent with the ua726(i didnt try the other solutions)but dont expect 7 octaves,the 208 is not noisy .
a tube amp ,yes .

DB:

The BOM specifies R3 as 1K8 while the original schematic shows 10K. Increasing R3 to 10K significantly increases the timbre folding. I ended up selecting R3 to be 8K2 for best performance


jonen wrote:Does anyone know what other factors influence the stability between the two oscillators of the complex oscillator? I can only get it stable with a specific setting of MB TR4 (Timbre), MB TR7 (CO Waveshape) and Card 9 R5 (Low freq tracking). However, I want to have more wiggle room for the timbre trimmer since I want to properly set the folding behavior ( the one I end up with is not the best). I specifically want it to be stable for low frequencies.

I already tried out a few different 2n4339, however, with little success.

Any idea, where else to look or what to try?

Maybe it does have to do something with the vactrols on card 7? I am trying to understand the schematics, but coulnd't really figure out, what they exactly do on card 7. Any ideas?
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 » Wed Nov 06, 2019 2:58 pm

boops wrote:With my experience of the 208.for debugging
often ,we believe that all is fine ,on each card,but with a simple 4016
shorted,a flux short,a real short,a bad connection,etc somewhere in the 208,small problems appear,like a click in the env,an osc no stable etc.
After having debugged some 208 that you built and sold, I can only confirm this. :mrgreen:

R3 value depends on both the VT1 vactrol tolerance and the final user's own preference, therefore it should be selected on test as explained in the 208p build notes.
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Post by kristop » Wed Nov 06, 2019 4:16 pm

So, what is the best way to test/debug these things? I am just finishing up everything. Last night I powered up my MB. Tried adding a few cards, up to the pulser. I could get the single trigger light to fire when I flipped to toggle, but couldn't get the sequencer to run. Is that normal though? Do I need all the cards in for things to work? Tonight I hope to finish the pA726 cards and get them mounted, then I can put the rest of the cards in but in the meantime, I'm just curious if things should be working differently so far. It's been a fun build and I'm stoked that with 4 cards in, no blue smoke yet.
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