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 Forum index » DIY Hardware and Software
Buchla 208 Random PCB
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TheAncientOne



Joined: Dec 26, 2006
Posts: 146
Location: United Kingdom

PostPosted: Tue Jan 25, 2011 11:31 am    Post subject: Reply with quote  Mark this post and the followings unread

Just had another thought about this unit. Perhaps someone more expert in things Buchla could chip in here.

I seem to remember that Buchla used 1.2V/Octave in his synths, making some setups easier at 100mV/Semitone, rather than the 0.08333 in the Moog format.

If that's the case, maybe a change in the output scaling and cross coupling might be a possible modification for most current synths. I know one can always adjust the modulation depth control, but in certain areas I feel that may not quite be enough, because the cross mod from the 680K output to input cascade is acted upon by the gain of each output current amplifier.

Dammit! I'm just going to have to build one now.

(edited for missing '0' c- for maths today!)

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Last edited by TheAncientOne on Tue Jan 25, 2011 5:26 pm; edited 1 time in total
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Peake



Joined: Jun 29, 2007
Posts: 1109
Location: Loss Angeles
Audio files: 3

PostPosted: Tue Jan 25, 2011 4:59 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey Prof!

I believe that the 200e use 1.2V/8va; the vintage oscillators (258) were 2V/8va.

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Tasmanian Alkaloid



Joined: Jun 29, 2008
Posts: 116
Location: Isle De Mort

PostPosted: Wed Jan 26, 2011 3:11 am    Post subject: Reply with quote  Mark this post and the followings unread

TheProf wrote:
Tasmanian Alkaloid wrote:
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.



A cheap logic probe, (Cue original 'Tron' line "Bring on the logic probe!"), might help. They can be obtained quite cheaply on ebay. Testing the clock input and the stage outputs of the register will tell you where the failure point is. I'd look to see if the clock input was 'blocking' - locking up, or the shift register. My bet is on the shift reg, due to the power cycle needed to clear it.

If you use a test meter on a shift register output, this will tell you if it's locked at 1's (voltage high), or 0's, (voltage low). Looking at the design, it would seem Don Buchla was protecting against the all 0's condition, (see diagram note around U4D). If you let it lock, then reduce the clock speed to where it would run, you could probably inject some 1's by temporarily grounding the junction of U4 pin 1 and R23, via (say) a 1K resistor. If the pattern re-starts then you have at least cut your problem search down to the shift register and feedback part.

Hope this helps



Thanks! Totally fascinating. I'll revisit the schematics & have a closer look at the modules.
-Matt
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303monkey



Joined: Mar 11, 2008
Posts: 59
Location: NODNOL

PostPosted: Fri Jun 10, 2011 3:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

I'm in for two boards if a run is made.
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tlu



Joined: Feb 26, 2011
Posts: 5
Location: Pacific Northwest

PostPosted: Thu Aug 18, 2011 11:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

RERUN???? Count me in please.
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inlifeindeath



Joined: Apr 02, 2010
Posts: 315
Location: Albuquerque, NM

PostPosted: Fri Aug 19, 2011 2:30 pm    Post subject: Reply with quote  Mark this post and the followings unread

On the issue of the CD4015 locking up...
I built a circuit based on one of my favorite Lunetta patches using 40106 oscillator and a 4015 SR. I had issues getting it to work like I wanted it to because it kept locking into the same sequence. Once I added a voltage starve pot, it would create insane freak out sequences but then once it got back to full 9v supply it would lock up again. I don't quite remember how I hook up the data and clock inputs but I thought it was interesting to see it happening in a Buchla (clone) module. Going to have to throw one of these together.
Here's a video of the device in action
http://youtu.be/gM4IZ28ccEI

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LFLab



Joined: Dec 17, 2009
Posts: 191
Location: Rosmalen, Netherlands

PostPosted: Sat Sep 17, 2011 2:35 pm    Post subject: Reply with quote  Mark this post and the followings unread

Etched a board for the 208 random a while back. I added a doepfer power connector, onboard cliff jacks and perf area for an on-board clock. Didn't feel like finishing one of the other 500 or so projects in progress, but felt like starting something new. Plonked all components in and started it up, had a monster of a short in the psu connector so it didn't work on first startup, but when the short was removed it worked like a charm! Good thing regulators survive shorts, or at least mine seem to have.

Quite a bit of output, so these will need a divider, not sure if I want to put in fixed ones or panel mounted pots, seems a bit overkill for such a simple thing.

Haven't tried clocking it really quickly.
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ShapeSorter



Joined: Aug 16, 2014
Posts: 2
Location: Cleveland

PostPosted: Sat Aug 16, 2014 10:50 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, I know that this is necromancy, and a newb question:

I have noticed that people have mentioned making eurorack modules out of this pcb. Are they changing resistor values when providing +/-12v or just leaving the circuit as is?
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bubzy



Joined: Oct 27, 2010
Posts: 555
Location: United Kingdom
Audio files: 62

PostPosted: Sun Aug 17, 2014 1:56 am    Post subject: Reply with quote  Mark this post and the followings unread

Doesn't look like theres any reason to change resistors for 12v to me, give it a go, its not gonna explode Smile

Nothing wrong with a bit of topic necro Smile especially for this nifty unit!

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ShapeSorter



Joined: Aug 16, 2014
Posts: 2
Location: Cleveland

PostPosted: Sun Aug 17, 2014 8:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Awesome! Does anyone know the output level, so I may incorporate fixed dividers into my PCB?
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Snaper



Joined: Feb 28, 2014
Posts: 65
Location: Hungary

PostPosted: Tue Aug 19, 2014 12:45 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, a bit to big for euro...
Anybody did a smaller layout? (around 80x80 or something like this?)
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LFLab



Joined: Dec 17, 2009
Posts: 191
Location: Rosmalen, Netherlands

PostPosted: Tue Aug 19, 2014 7:41 am    Post subject: Reply with quote  Mark this post and the followings unread

My rack is deep enough, so I just have the PCB perpendicular to the panel. Even added a eurorack IDC power header.
Didn't add a divider, but did add a simple lfo as a means of a clock source.
Not sure if it's on 12v or 15v (I have both in my rack).
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Snaper



Joined: Feb 28, 2014
Posts: 65
Location: Hungary

PostPosted: Tue Aug 19, 2014 7:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Then I have to redraw it in eagle:(
My rack is 115 mm deep, the panel is around 125 :S
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