Build a buchla 208 rev2

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search64
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Post by search64 » Sun Sep 29, 2019 11:16 am

Post a picture of what you changed.

jonen
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Post by jonen » Sun Sep 29, 2019 12:19 pm

Actually, I just noticed that I used a wrong capacitor. For IC1 I used 51pF and for IC6 I switched in 100pF right now, which dramatically improved. Now, only the stage 4 in the stage 4 setting is sometimes not triggered. Will try to find a 51pF capacitor for IC6 too tomorrow and report back!

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Post by jonen » Mon Sep 30, 2019 2:41 pm

Unfortunately, I do have another problem with my build. My complex oscillator doesnt work properly. I do get oscillation but the output is weirdly distorted and is very unstable, and also decreases with higher frequencies. It gets more stable when I add some timbre. I tried to solve this by calibrating following dave's suggestion, however I suspect its a bigger issue.

I checked the output of card 8 which should be a triangle on pin 15, correct? I do get a solid and stable triangle wave there. When I try running it without card 9 I get a stable undistorted wave for square wave and pulse. Though the sine and triangle is missing which comes from card 9 I guess.

When I check the output of card 9 (card 9 pin 5) it looks quite odd:
Image

Is this something I can fix by calibrating?

I tried replacing the RC4136 with no effect. Unfortunately, I dont have any more lm301 to try out. Could it be the DG200BA or the MC846P? I also checked all my solder joints but couldnt find anything odd.

Here is my card 9:
Image
Image

Any ideas what I can try to fix this? Maybe replacing the MC846P with 74LS03?

jonen
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Post by jonen » Sun Oct 06, 2019 9:54 am

I was able to fix my complex oscillator problem by replacing the two MC846 which I got from utsource with two 74LS03 and additional pullup resistors as described by Dave. It worked perfectly.

However, now I noticed a different problem. My am modulation doesnt seem to work correctly, it is really noisy. The signal coming in from the mo on pin 2 is a perfect triangle (in setting triangle of course) however, on pin 2 of IC4 it is really distorted, like so:
Image

I also noticed that IC4 and IC5 on board 5 get warm, not quite hot but notably warmer than other ics. They are not supposed to be even warm, right?
I tried switching all the chips on the board but without luck. I already checked all resistor values and looked at every solder joint, however everything seems to be fine. Any idea what else to try?

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boops
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Post by boops » Tue Oct 08, 2019 10:23 am

Some aop can be a little hot,but you can always put and leave your finger on them,try to trace,isolale the issue,use only the card needed to test.

jonen wrote:I was able to fix my complex oscillator problem by replacing the two MC846 which I got from utsource with two 74LS03 and additional pullup resistors as described by Dave. It worked perfectly.

However, now I noticed a different problem. My am modulation doesnt seem to work correctly, it is really noisy. The signal coming in from the mo on pin 2 is a perfect triangle (in setting triangle of course) however, on pin 2 of IC4 it is really distorted, like so:
Image

I also noticed that IC4 and IC5 on board 5 get warm, not quite hot but notably warmer than other ics. They are not supposed to be even warm, right?
I tried switching all the chips on the board but without luck. I already checked all resistor values and looked at every solder joint, however everything seems to be fine. Any idea what else to try?
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=

jonen
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Post by jonen » Thu Oct 10, 2019 3:20 pm

Managed to find the error, it was a solder bridge. I guess a lot of trouble with this build is saved by looking at all cards with very good lightning and a magnifying glass.

I still have some trouble with the AM though, it looks fine on my scope but just doesn't sound good yet. Will try to calibrate a bit more. For reference I am looking at this video: at around minute 2. Mine doesn't sound nowhere as good. Does anyone else's sound like that?

Does anyone know what the timing capacitors on card 8 and 9 do, dave mentions on his page, when he shows the picture of his entire build? Can't seem to find them mentioned anywhere else on his page.

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ilya.n
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Post by ilya.n » Fri Oct 18, 2019 7:54 am

I have a problem on a v2 208. Maybe someone could give me a hint...

The Gate2 routing switch doesn't seem to make any difference (at least noticable), in routing. The effect is always as if main vco goes > gate1 >gate2.

I tried to swap card 11 from a working easel, didn't make a difference.

The toggle itself seems to work fine.

Thank you.

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boops
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Post by boops » Sat Oct 19, 2019 3:10 am

Check your mother board,for a missing resistor or a bad solder

ilya.n wrote:I have a problem on a v2 208. Maybe someone could give me a hint...

The Gate2 routing switch doesn't seem to make any difference (at least noticable), in routing. The effect is always as if main vco goes > gate1 >gate2.

I tried to swap card 11 from a working easel, didn't make a difference.

The toggle itself seems to work fine.

Thank you.
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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boops
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Re:

Post by boops » Wed Apr 15, 2020 1:56 am

boops wrote:
Tue Dec 09, 2014 3:45 pm
Really deep sound ....an audio demo very soon.... :bananaguitar:

I hope to upgrade the circuit around the rev ...or someone else perhaps...
new card 12 pcbs are available,forget to note here.

viewtopic.php?t=211862
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=

finlayshakespeare
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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Wed Jun 17, 2020 8:48 am

Blegh. I need some help with my Card 9 - I finally got around to building my 208 over lockdown, it was fully working, then I went to install some of Dave Brown's mods and managed to insert my Card 9 board up or down a pin on the motherboard. Since then, the Card 9 oscillator hasn't worked, meaning I get no signal from the Complex Oscillator when the Timbre slider is at zero.

Scoping around the card, there is no triangle wave being produced at pin 5. Pin 4 of the RC4136 is low, sitting at around -10V. Pin 1 of the DG200 is receiving the processed pulses from Card 8's oscillator. I'm a little unsure where to go next though - I have replaced all the ICs (DG200, RC4136, SN74LS03, LM301s) to no avail, and I'm beginning to think the problem lies either elsewhere, or there's a problem with the PCB (though I have already tested continuity many of the traces and all seems well). I have more DG200s and SN74LS03s on order, though I'm really doubtful this is the problem - I've just tested the last DG200 I had in there on breadboard and all seems to be working. Also, the SN74LS03s have the pull-up resistors installed.

Any pointers would be very much welcome - I'm really stumped with this one and very much regret tinkering with what was otherwise working pretty well :bang: :cry:

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Re: Build a buchla 208 rev2

Post by Karl71 » Wed Jun 17, 2020 3:34 pm

Have you tried replacing the 4016 on card 8.?

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Thu Jun 18, 2020 5:39 am

Karl71 wrote:
Wed Jun 17, 2020 3:34 pm
Have you tried replacing the 4016 on card 8.?
Good shout, but I did replace this and it made no difference. All the waveshaping is working as expected, by the way - it's simply that card 9 will not oscillate, and the timing cap is being pulled down towards the negative rail. It actually hits -15V if I remove card 8, though this may be normal as the cap doesn't have anything to drive it... right...?

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Re: Build a buchla 208 rev2

Post by Karl71 » Sat Jun 20, 2020 12:35 pm

finlayshakespeare wrote:
Thu Jun 18, 2020 5:39 am
Karl71 wrote:
Wed Jun 17, 2020 3:34 pm
Have you tried replacing the 4016 on card 8.?
Good shout, but I did replace this and it made no difference. All the waveshaping is working as expected, by the way - it's simply that card 9 will not oscillate, and the timing cap is being pulled down towards the negative rail. It actually hits -15V if I remove card 8, though this may be normal as the cap doesn't have anything to drive it... right...?
What mods did you carry out on the card?

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Re: Build a buchla 208 rev2

Post by Karl71 » Sat Jun 20, 2020 12:40 pm

Have you checked the solder joints on the interconnects between the motherboard and the card. I fractured one one time removing and replacing card 8.I took a long time to find. Make sure you have all voltages on the interconnects.

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Mon Jun 22, 2020 5:07 am

Karl71 wrote:
Sat Jun 20, 2020 12:35 pm
finlayshakespeare wrote:
Thu Jun 18, 2020 5:39 am
Karl71 wrote:
Wed Jun 17, 2020 3:34 pm
Have you tried replacing the 4016 on card 8.?
Good shout, but I did replace this and it made no difference. All the waveshaping is working as expected, by the way - it's simply that card 9 will not oscillate, and the timing cap is being pulled down towards the negative rail. It actually hits -15V if I remove card 8, though this may be normal as the cap doesn't have anything to drive it... right...?
What mods did you carry out on the card?
I was changing the capacitor values in order to shift the pitch of the oscillators up a bit - taking the 15nFs on both card 8 and card 9 to 10nF.

I'll check the board interconnectors, but through scoping cards 7 - 9 out, all the correct voltages seem to be present in the relevant parts of the circuit. Supply voltages are certainly all good, and the timing/sync pulses for card 9 are there too.

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Mon Jun 22, 2020 7:51 am

OK, so scoping around and I've found a somewhat bizarre thing. -15V is present at R4, then completely "disappears" on the other leg, where I can only scope around 0V. Does anyone know what's going on at this part of the circuit? Surely some current from -15V can flow through D2 and D3...

I ask mainly because I've managed to get card 9 to oscillate by strapping resistors across from pin 2 of the DG200BA to the junction between (T)R5 and R6 -AND- from -15V to pin 6 of the RC4136. However, the oscillation is limited to a tiny section of the Pitch range, and is also not really very triangular.

The control signal (from card 7) at pin 6 is at 0V at the lowest pitch, and spans up to 1 - 2V.

Schematic attached for reference...
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Re: Build a buchla 208 rev2

Post by tele_player » Mon Jun 22, 2020 8:16 am

Are you sure that R4 hasn't failed OPEN?

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Mon Jun 22, 2020 8:55 am

tele_player wrote:
Mon Jun 22, 2020 8:16 am
Are you sure that R4 hasn't failed OPEN?
Alas R4 is all good - I even tried strapping another 100k on top to see what would happen, but absolutely no change. R4 also makes good continuity with the two cathodes of D2 and D3.

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Re: Build a buchla 208 rev2

Post by tele_player » Mon Jun 22, 2020 9:16 am

Baffling. Maybe replace R4 with 2x47K in series, then measure the voltage in the middle? I expect that will be about -7v.
Since R4 is not open, the fact that the voltage is different on the two legs means current IS flowing.

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Mon Jun 22, 2020 12:15 pm

I've strayed away from that area of the schematic now... I can understand if there's some current-related thing going on that wouldn't allow me to scope around R4...

What I think the problem is now - the LM301s that I've bought to replace the ones I thought I had fried seem to be fakes. Pin 8 isn't doing anything when it should be limiting the output swing. Because the output goes well above +5V here, these fake LM301s then fry the logic gates. So, in essence, swapping the ICs has actually caused further damage.

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Tue Jun 23, 2020 12:32 pm

FIXED IT! It was, indeed, fake / broken LM301s purchased from Nikko Electronics on eBay. :foul:

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Re: Build a buchla 208 rev2

Post by blinosynth » Wed Jun 24, 2020 3:21 pm

is it a difficult build? you guys think is it possible for a first project?

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Re: Build a buchla 208 rev2

Post by Don T » Wed Jun 24, 2020 8:23 pm

blinosynth wrote:
Wed Jun 24, 2020 3:21 pm
is it a difficult build? you guys think is it possible for a first project?
Depends upon your current knowledge of electronics and electronic troubleshooting skills. There is plenty of good advice in this and the 2.1 (blue) build thread. The 208 is so complex that rarely will everything work properly when completed, either due to a bad part or a mistake. Even after sorting out all the errors and getting it working 100%, something is likely to fail in the future. Example: The sequencer that I documented a fix for early in this thread, that would only sequence 2, 4, and 5 steps, and getting it to behave by adding decoupling caps on one of the CMOS chips, it has reverted to 2, 4, and 5 steps again as opposed to 3, 4, and 5 steps. It worked well for a year, and suddenly started misbehaving. I still haven't figured out what's wrong.

Also, you'll need to have the proper tools on hand, with the knowledge to use them well. Good soldering and DESOLDERING equipment (you WILL make mistakes), and very good DMM, and an oscilloscope are requirements, not luxuries.

So, I won't say that you shouldn't do this as a first project, because I don't know your skill level. That said, I'd not recommend it as a first project. I had been doing electronic repairs for quite a few years, and had built quite a few other Buchla clones before tackling the 208, and I still found it a challenge.

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Re: Build a buchla 208 rev2

Post by OrganFixer » Wed Jun 24, 2020 9:09 pm

blinosynth wrote:
Wed Jun 24, 2020 3:21 pm
is it a difficult build? you guys think is it possible for a first project?
Also, it is expensive and you need to source some hard to find rare parts.

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Re: Build a buchla 208 rev2

Post by finlayshakespeare » Thu Jun 25, 2020 3:24 pm

blinosynth wrote:
Wed Jun 24, 2020 3:21 pm
is it a difficult build? you guys think is it possible for a first project?
I would very much not recommend this as a first project. I've been building synth equipment for more than a decade - several of those years now as a full-time professional - and I found this project pretty nasty. Fault finding is particularly difficult to do with the 208 due to the positioning of the cards in situ. What I would say, however, is that it's very much worth it and, like many other great "monosynths", it's far more than just the sum of its parts. :sb:

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