Buchla 208r V2.1 (Blue) Build Thread

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auxren
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Post by auxren »

What is the best way to get individual oscillator outputs from the 208 to interface with the rest of my Buchla system? I saw that there is no audio broken out to the program card.
I'm thinking of replacing the to/from prog banana jacks with tinijax with vco 1 and vco2 out.
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Post by davebr »

auxren wrote:What is the best way to get individual oscillator outputs from the 208 to interface with the rest of my Buchla system? I saw that there is no audio broken out to the program card.
I'm thinking of replacing the to/from prog banana jacks with tinijax with vco 1 and vco2 out.
The MO output is on the banana. It is just level shifted to be unipolar. Personally, I would change one of the signal output jacks to stereo and put both the MO and CO on that. Then you just need a splitter cable to separate the stereo to two mono. That way you don't eliminate any functionality and there are no holes drilled.

Dave
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Post by auxren »

davebr wrote:
auxren wrote:What is the best way to get individual oscillator outputs from the 208 to interface with the rest of my Buchla system? I saw that there is no audio broken out to the program card.
I'm thinking of replacing the to/from prog banana jacks with tinijax with vco 1 and vco2 out.
The MO output is on the banana. It is just level shifted to be unipolar. Personally, I would change one of the signal output jacks to stereo and put both the MO and CO on that. Then you just need a splitter cable to separate the stereo to two mono. That way you don't eliminate any functionality and there are no holes drilled.

Dave
I like that solution! I'll scope it out. Thanks Dave
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Post by we_squirm »

Don T wrote:
we_squirm wrote:Where did y'all source the coloured caps for the sliders? I found Mammoth has ones for the switches but can't find the slider guys anywhere!
They are one and the same! Seriously. Warm the caps up (I heat mine up in a strainer over boiling water) and slide them down on top of the sliders.
Thank you!
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Post by Sammus »

I have a couple of questions about caps on the BOM:

1) There's a couple of 5% ceramic caps on card 12:

140-50S5-101J-RC
140-50S5-471J-RC

that are marked obsolete on mouser, and there don't seem to be any substitutes with the same characteristics (5% tol, 5mm lead spacing, ceramic disc).

How important are those characteristics? Can I just replace them with any ceramic disc or mlcc 100pf and 470pf?

2) there was recently a post on the JML synth page about some errors in the 208r BOM without many specifics:
their's some wrong diodes that are for making the 12volts +/- to 7.5volts the diodes specified makes the voltage to high and it fries the chip. Also he has stated 10000pf caps code# 104j but they are supposed to be 910pf code# 911j
Are these diodes the known 7.5v zeners mentioned in this thread that are in the v2.1 BOM? And also what about the 10,000pf vs 910pf caps??

Thanks for any help!
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Post by tarandfeathers »

Sammus wrote:I have a couple of questions about caps on the BOM:

1) There's a couple of 5% ceramic caps on card 12:

140-50S5-101J-RC
140-50S5-471J-RC

that are marked obsolete on mouser, and there don't seem to be any substitutes with the same characteristics (5% tol, 5mm lead spacing, ceramic disc).

How important are those characteristics? Can I just replace them with any ceramic disc or mlcc 100pf and 470pf?
Yes, I did my whole build with TDK 5% C0G ceramics, it's not important, just the value and voltage tolerance, but ceramics with less than 40/50V capability are unusual and the biggest voltage difference in the 208 is 30V.
2) there was recently a post on the JML synth page about some errors in the 208r BOM without many specifics:
their's some wrong diodes that are for making the 12volts +/- to 7.5volts the diodes specified makes the voltage to high and it fries the chip. Also he has stated 10000pf caps code# 104j but they are supposed to be 910pf code# 911j
Are these diodes the known 7.5v zeners mentioned in this thread that are in the v2.1 BOM? And also what about the 10,000pf vs 910pf caps??

Thanks for any help!
This is a reference to the previous V2 BOM. If you are building from the V2.1 BOM then the correct zeners are specified.

I'm not aware of anywhere that 10,000pF caps were specified in place of 910pF, but 1000pF are used throughout wherever 910pF were used in the original. For some reason Don Buchla barely ever used 1000pF caps, I suspect he must have got a deal on thousands and thousands of 910pF caps in the late 60s/early 70s and spent the next 10 years trying to use them up, haha. At any rate, it's not important. None of these are used in critical timing applications so 1000pF is more than close enough.
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Post by Sammus »

Awesome thanks.
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Post by Don T »

tarandfeathers wrote: For some reason Don Buchla barely ever used 1000pF caps, I suspect he must have got a deal on thousands and thousands of 910pF caps in the late 60s/early 70s and spent the next 10 years trying to use them up, haha. At any rate, it's not important. None of these are used in critical timing applications so 1000pF is more than close enough.
There are a couple 910pf caps in the filter section of the lo pass gates (Cards 10 and 11), and I usually make sure I use 910pf in those positions at least.
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Post by we_squirm »

How's it going with the Motherboard? It's the only card we haven't seen finished, correct?
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Post by Don T »

Don T wrote:
davebr wrote: However, I believe a 74LS03 will work fine with 5 pullups on the two chips. That is a more direct plug-in solution.

Dave
I've added a few 74LS03 to my next Mouser order, will report results here as soon as available!
Sorry, meant to post results earlier:

Image

Thanks to davebr for his advice on this. Yes, the above works. It works incredibly well in fact. The sound is indistinguishable from the original chip, and probing around the circuit in various points with the scope while sweeping the Timbre control also confirms that performance is identical to the original chip. So, if you can't find MC846P, give 74LS03 a try! I used 2.7K pull up resistors.
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Post by we_squirm »

Don T wrote:Some progress, and perhaps a solution to a common problem should anyone else want to confirm.

I have worked on many different pieces of gear, and have noticed almost all of them that use CMOS chips have a decoupling cap across the Vdd and Vss (or ground) pins of most, if not all the CMOS chips. The original 208, as well as the 208r V2 and V2.1, have NONE. Most of the stability issues in the 208r are CMOS-chip-related, and I happened to run across a deal on these really nice machined-pin sockets that have decoupling caps built-in. I figured it may be worth a try, and at the very least it should do no harm...

Since I'm not an expert (at all) on CMOS-related things, I ran the idea by davebr. He gave me a thorough and educational response (Dave, feel free to jump in, or I can share your response here if you'd like) that basically said it may be a good idea in the sequencer, but perhaps putting them on every CMOS chip would be overkill. He mentioned that he tends to put one decoupling cap for every three CMOS chips. Dave also cautioned to make sure that any additional caps would not add enough capacitance to allow a charge to be stored in a voltage regulated circuit large enough that it would reverse-bias a voltage regulator, unless the regulator has protection diodes installed. Think of it as a "back flow" if you will, especially when powering down.

So, with basically a "go for it", I installed the sockets on my sequencer board. The decoupling cap can be removed without too much trouble, so I pulled it out of the socket for the LM3900:

Image

In my previous post, I mentioned the trouble I had been having with my first 208's sequencer LEDs, and the solution, which involved replacing what I assumed was a faulty CD4009, which is the LED driver for this circuit. As an experiment, I placed the new 4009 in one of those decoupled sockets to see if there would be a result, plus you can see above that I didn't use sockets at all on my first build, which tends to slow things down a bit if you need to replace a chip...

Here's that part you've been waiting patiently for, hoping I would shut up and just get on with it:

Before installing the decoupling socket, my first sequencer card displayed the common behavior of only doing 2 steps with the Stages switch set to 3. It would do 4 and 5 steps normally, but not 3. Well, after installing that socket with the decoupling cap, and no other modifications done, that same sequencer card now reliably switches between 3, 4, and 5 stages as designed! :nana:

The new, blue sequencer card, which you can see above has decoupling caps everywhere except the LM3900, and no other modifications, also switches reliably between 3, 4, and 5 steps as designed.

Being a firm believer in "Correlation Does Not Imply Causality" (unless confirmed), I am not going to declare the decoupling solution as the fix for the 2, 4, 5 step sequencer bug until someone else confirms. All one needs to do is solder a 0.1uf cap (ceramic will do nicely) on the back of IC9 on their sequencer (Card 1) between pins 8 and 16. Please share your results here!

Right now, all I'm going to tell you guys is that I have two otherwise-unmodified sequencers that behave as intended!

Image

And yes, the sockets just happened to be blue! :nana:
Just to clarify as this is a bit new to me, which legs on the IC socket do you solder the decoupling cap to? and as for value (again just to clarify as I prefer to over state it instead of making a mistake) you're using a 0.1uf monolytic cap?
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Post by Don T »

we_squirm wrote:
Don T wrote:Some progress, and perhaps a solution to a common problem should anyone else want to confirm.

I have worked on many different pieces of gear, and have noticed almost all of them that use CMOS chips have a decoupling cap across the Vdd and Vss (or ground) pins of most, if not all the CMOS chips. The original 208, as well as the 208r V2 and V2.1, have NONE. Most of the stability issues in the 208r are CMOS-chip-related, and I happened to run across a deal on these really nice machined-pin sockets that have decoupling caps built-in. I figured it may be worth a try, and at the very least it should do no harm...
Just to clarify as this is a bit new to me, which legs on the IC socket do you solder the decoupling cap to? and as for value (again just to clarify as I prefer to over state it instead of making a mistake) you're using a 0.1uf monolytic cap?
Yes, a 0.1uf cap is used, and it is soldered across pins 7 and 14 of a 14-pin CMOS chip, and pins 8 and 16 of a 16-pin CMOS chip. Just the CMOS chips mind you, those marked CD40xx.
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Post by davebr »

Don T wrote:Yes, a 0.1uf cap is used, and it is soldered across pins 7 and 14 of a 14-pin CMOS chip, and pins 8 and 16 of a 16-pin CMOS chip. Just the CMOS chips mind you, those marked CD40xx.
I only solder decoupling capacitors across the CMOS parts on Card 1. I don't on any of the other cards. FYI.

Dave
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Post by Don T »

davebr wrote:
Don T wrote:Yes, a 0.1uf cap is used, and it is soldered across pins 7 and 14 of a 14-pin CMOS chip, and pins 8 and 16 of a 16-pin CMOS chip. Just the CMOS chips mind you, those marked CD40xx.
I only solder decoupling capacitors across the CMOS parts on Card 1. I don't on any of the other cards. FYI.

Dave
Yes, forgot to mention they don't ALL need decoupling caps. I added one to all of Card 1 as well, plus I did one CMOS chip per card, and only on the cards that had CMOS chips.

But, definitely do Card 1, I found that it stabilizes the sequencer and allows it to run as intended. When first built, mine had the common problem of running in 2, 4, or 5 steps only. If the switch was set for three stages it would only do two. With the decoupling caps added it works without a glitch.
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Post by cnicht »

Can anyone tell me the dimensions of the 208r front panel please?

Thanks
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Post by captnapalm »

cnicht wrote:Can anyone tell me the dimensions of the 208r front panel please?

Thanks
It should be exactly 7" x 17"
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Post by cnicht »

Thank you
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Post by Karma »

hey guys!!! are there any alternative for the toggles switch? C&K are a way too expensive, i wonder if the mountain switch fits, like this http://www.mouser.fr/ProductDetail/Moun ... NxBJT50%3d for the spdt on off on or other reference
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Post by we_squirm »

Where did y'all source your Accutronics 1bc2e reverb tank? The only link I found online was tube amp doctor, which is in Europe. I'm in Canada so something in North America would be great.
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Post by Sammus »

we_squirm wrote:Where did y'all source your Accutronics 1bc2e reverb tank? The only link I found online was tube amp doctor, which is in Europe. I'm in Canada so something in North America would be great.
The only place I found was to order directly from belton/accutronics in korea. I think it ends up being about 25usd delivered.
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Post by we_squirm »

Sammus wrote:
we_squirm wrote:Where did y'all source your Accutronics 1bc2e reverb tank? The only link I found online was tube amp doctor, which is in Europe. I'm in Canada so something in North America would be great.
The only place I found was to order directly from belton/accutronics in korea. I think it ends up being about 25usd delivered.
Awesome thanks! ALSO: where did y'all get the 22 x sliders for the mother board? Farrell (the place listed on the BOM) is out of stock and has an estimated delivery time of mid-November :S
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Post by Sammus »

we_squirm wrote:
Sammus wrote:
we_squirm wrote:Where did y'all source your Accutronics 1bc2e reverb tank? The only link I found online was tube amp doctor, which is in Europe. I'm in Canada so something in North America would be great.
The only place I found was to order directly from belton/accutronics in korea. I think it ends up being about 25usd delivered.
Awesome thanks! ALSO: where did y'all get the 22 x sliders for the mother board? Farrell (the place listed on the BOM) is out of stock and has an estimated delivery time of mid-November :S
I'm seeing around 4000 available?
http://uk.farnell.com/alps/rs4511150k/p ... dp/1191730
or

http://au.element14.com/alps/rs4511150k ... 5-00001622
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Post by we_squirm »

Sammus wrote:
we_squirm wrote:
Sammus wrote:
we_squirm wrote:Where did y'all source your Accutronics 1bc2e reverb tank? The only link I found online was tube amp doctor, which is in Europe. I'm in Canada so something in North America would be great.
The only place I found was to order directly from belton/accutronics in korea. I think it ends up being about 25usd delivered.
Awesome thanks! ALSO: where did y'all get the 22 x sliders for the mother board? Farrell (the place listed on the BOM) is out of stock and has an estimated delivery time of mid-November :S
I'm seeing around 4000 available?
http://uk.farnell.com/alps/rs4511150k/p ... dp/1191730
or


http://au.element14.com/alps/rs4511150k ... 5-00001622
Same, BUT when i placed the order they sent me an email saying expected delivery of November. Super weird.
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Post by davebr »

Karma wrote:hey guys!!! are there any alternative for the toggles switch? C&K are a way too expensive, i wonder if the mountain switch fits, like this http://www.mouser.fr/ProductDetail/Moun ... NxBJT50%3d for the spdt on off on or other reference
Let me offer my advice where none was asked. I do restorations at the vintageTEK museum and I restore vintage radios and music electronics as a part time business. The most unreliable parts in a 208 are the electromechanical parts - switches, potentiometers/sliders, and sockets. My advice is with the $$ you are going to put into it for parts and your time, you don't want a cheap switch to fail early. I have repaired 208s with crummy sockets and bad switches. The sockets are easy. Replacing a switch is not and you risk damaging the PCB without proper desoldering equipment. If you choose something other than the C&K, make sure they are very reliable.

Dave
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Post by we_squirm »

For Card 9, when installing the DG200BA apparently you have to cut leg 7 off so the IC fits in the socket. There's a photo and description of that here: http://modularsynthesis.com/roman/buchl ... 08spss.htm

My question, is the photo taken from the top down, or from the bottom up? It may seem silly but I just want to clarify before cutting a leg off. What is the orientation of the photo?
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