Buchla 208 Random PCB

[bf]

I'd be interested in a few depending on the final options and price.

[Danno Gee Ray]

I would be interested in a pcb as well.

[TheAncientOne]

Fascinating circuit! Amazing the way he used a 3900 to synthesize the Exclusive-Or function. The 1/4 4016 could be replaced with a switching FET, it only provides a clock level translator - my guess is it was spare on the 208 main board, and was used for economy

I'm going to breadboard this up when I get a minute, and see if it can be done with a 4070 instead of the first 3900, (since they are getting rare), and perhaps a 40106 schmidt as the input shaper and 1 injector. that would leave 4 Schmidts over to make a clock oscillator, and perhaps a random-ish clock based on Ken stones 'Psycho LFO'.

Interesting too that Don didn't use the classic maximal length sequence for 8 bits, which has taps from stages 4, 5, 6, and 8. Can't remember enough theory to work out the length for this one off the top of my head, but I'll see if I can work it out. Since the circuit hasn't got a tap from the 8th bit, it can't be longer than 127 steps.

Hmmm - a thought. I wonder if a mixture of the stage output voltages, summed through pots could be used to trip a Schmidt trigger and inject more random 1's into the Exclusive-Or stack. Trouble is, there is always a danger of lockup. For n stages you can have (2^n)-1 steps, with exception of the 'all ones' state, or the 'all zeros' state. Randomly injecting 1's can lead to a sequence that terminates. Some lighting systems use LFSR's and used to have gating to get them out of the lockout state.

DaveMoog said he was getting a problem like this - it could either be power line noise, he could have mixed up a couple of resistors on the 2900 doing the logic gating, or maybe the cap on the 1's injector is a bit low.

I've been in love with these circuits as sources since I built my first one as a kid. I need to get back on the bench soon, and do more work on the LFSR add-on for my Klee. Which gave a sort of Klee arpeggiator effect, on my first experiments, (though with 16 steps, the max length is 65535!), and would, in fact let the Klee act like a big version of the circuit we're discussing, but with only one output.

(Edit: for some reason I wrote '2900' rather than '3900' - corrected)

[pcp2020]

Any word on another PCB run for this or is it dead?

[J3RK]

I made an Ares layout based on this one, and was going to send it out and get a few made. (small proto run)

If it works, and I didn't make any major mistakes, I can make the file available for people to get some done themselves.

[DGTom]

did you look at removing the 4016 J3RK?
i always assumed that was part of the 208s preset thingy(?)
wasting 3 switches made me grimace, I think when I get back to it I'll mod that section,

that being said, I have a spare board here - from bbobs run - if anyone should want it.

[J3RK]

No I didn't actually. I just turned that drawing into a 2 bit BMP, and loaded in as the background in Ares, and built the same thing 1:1 over top of it.

Since this board was fairly simple, I used this as a test for doing this sort of thing. The next one I did was Mark Verbos' DIY Buchla 258 VCO, which other than a few errors (like not mirroring it back, flipped SSM orientation, etc.) turned out pretty well.

I've had a lot of practice since then, so I could probably rework it to remove the 4016 at this point. I'll take a look at it soon. I'm just wrapping up another project, so I might be able to get to this by next week sometime.

[J3RK]

It's been a little while since I've looked at this. There are a few things I'm fixing right now while I have a little spare time. I did a few shortcuts like just putting pads instead of a resistor screen when the length was shorter than res40, and other such. I'm fixing these now. I also pulled the 4016. I have one question. I routed pin 4 of the LM3900 directly to the 100K resistor at the bottom. I'm not sure if this was the correct thing to do here.

Previously it went through another 100K, through the 22pF cap that's was on the 4016, then down to the one I routed it to directly now.

It may not be necessary at all now. I don't have schematic. Maybe I'll look back in this thread to see if there is one there. It also wouldn't take very long to put this in ISIS, and simulate it really quick. Maybe I'll do that.

[J3RK]

Based on a quick look at the schematic, I think my edit should be fine. Still might be a good idea to simulate it though, just in case.

[J3RK]

Eek, I don't have an LM3900 model in ISIS...

[J3RK]

After all that, I went and read the post above on this page. I think since 4016s are what 60 cents? that just leaving it there might be better for now. Could always find a use for the extra parts later.

So, I'll just use the old file, and fix some of the shortcuts I mentioned earlier.

[DGTom]

i'd be surprised if the LM3900 couldn't just drive the resistor / cap, then the 4015, maybe easier to breadboard than simulate, been awhile since I looked at the schem tho, I might dig mine out tomorrow, pull the 4016 & try a jumper.

a re-designed board could be alot smaller, but yeah, the real estate is prob only worth as much as the IC _shrugs_

[Peake]

Would a 555 on a 15V rail be able to actuate this circuit? Straight out of pin 3, that is.

[J3RK]

I've got all the necessary bits including a CMOS 555. I could try this out after I fix a problem I'm having with my current project.

[Peake]

Two of these circuits on a single PCB will fit behind a Buchla panel, so I have a pair of the artwork set up side-by-side and linked the ground, jumpered the rails, and moved the end bits to provide space for a 555 clock on each...but I don't know if the 555 will fire this circuit as many Buchla trigger ins look for 10V. Okay, Google'd it:

The high output level of the 555 timer is 1.7 volts less than the supply voltage.

That's plenty. The only issue would be needing normal'd/interrupting banana jacks...I see Conrad has them, gotta find out...end stream of conscsiousness posting...

[J3RK]

Nice! Good to know, because I'd like to get a few boards made when my short backlog is out of the way. (1.5 projects to go.) Of course I do have a ton of 4016s laying around.

[fluxmonkey]

make sure you use the cmos 7555... the standard 555 is notorious for dumping power spikes onto the rails

for myself, i not sure i see the musical utility of doubling up this module... 4 independent synched random voltages is plenty for most purposes. thinking about it, one possibility would be to clock the second one at a division of the first clock. in any event, i'd keep at least an option to separate the inputs.

b

[pcp2020]

[Peake]

[bubzy]

I didnt actually look through the whole thread(so sorry if it's already been done), but i always find a BOM useful to see if i have everything required for the build, so i made one up for this board.

in non image format too because downloading bmps is so passé

IC's Quantity
CD4016 --1
CD4015 --1
LM3900 --2

Capacitors
22pf --1
470pf --1
0.1uf --5
10uf electrolytic --2

Resistors
10 or ferrite bead --2
1k --5
68k --1
82k --2
100k --2
150k --4
330k --4
680k --9
1m --5
2.2m --4

edit : i put 2xcd4016. sorry. now fixed, will do the bmp later

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buchla 208 BOM.bmp
Description:		Download
Filename:	buchla 208 BOM.bmp
Filesize:	228.59 KB
Downloaded:	2344 Time(s)

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[Tasmanian Alkaloid]

I built 2 of these & they both freeze up when clocked fast.
They will only resume functioning after powering down & back up.
Does anyone else have the same problem?

[TheAncientOne]

[davemoog]

I'm getting no lock up with mine until well above audio frequencies (that I can hear - not quite sure what frequency that is, but pretty high , However one observation is that if I don't use a pulse waveform with a very, very narrow pulse to clock the random generator then the lockup will happen at somewhat lower frequencies. Also it does not need power of-on to restart operation- just bringing the frequency lower will restart the unit. I was monitoring operation of both the random unit and the clock pulse on a scope.
dave

[Tasmanian Alkaloid]

Thanks guys.

-Prof, i don't have a scope, so can't verify your troubleshooting ideas. But thanks- i will keep this in mind should the problems continue.

-Dave, sounds like we have the same problem! I'd been clocking mine from a Wiard Noise Ring's clock output (i'm not sure how narrow the pulse is, it may even be a full square wave). When it first started locking up (after a few uses of working fine), it would start up again by adjusting to a lower speed. But eventually that no longer worked, & it needed repowering.

I now have a VCO with variable pulse width, so i will try a narrower pulse & see if i get a better result. I haven't tried them since getting the VCO- they've been waiting for panels as well & sitting on a shelf.

cheers

[TheAncientOne]