dual 281 project [build related stuff only!]

[zthee]

Checking the schematics - Shorting it would probably result in that you can with one pot control both attack and decay.

[toppobrillo]

extra "summing" nodes for those who wish to implement "both" control

[waveselector]

Just cleared this up with Topp:

You need to add a resistor, 2.2k to 4.7k, in series with the end-of-release pulse output. This resolves an issue where if patching from the pulse out to another module while in cycle mode the cycling would halt. Not a problem for banana jacks, but if using 1/4" or 1/8" jacks you should add the resistor.

[emdot_ambient]

[toppobrillo]

[djg]

[SubG (deactivated)]

Not easy to attach the boards where they belong to be attached,but am good...

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[roman_f]

1) anyone knows how to wire the OP's (peak) knob? i see only the peak out jack on the wiring scheme

2) should i connect all the B+s into one hole @ the pcb?

3) not sure about pots
where G, B+ and Green connections go?
(related to the attached picture - 1-2-3 from left to right)

4) how can i attenuate PULSE out for 10V?

5) what does LED show? the ENV cycle or PULSE?

thank you

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[mph]

Hi Roman

1/ you've got the knob related to the peak out on the wiring diagram, it's called "B AMNT" because it is used to attenuate the B signal when merged to the A out to create the Peak output.
You only have one B AMNT pot per pcb if you use the dual version.

2/ the B+ pads on the pcb are linked. So you do what you want; I would take one wire from the pcb, then make all the connections between the pots like a daisy chain.

3/ According to the diagram:
Pin1: ground
Pin2: green wire for Dec pot for example (it's wired on the taper of the pot)
Pin3: B+ for both ATT & DEC pots.

4/ you could simply put a resistor or a trimmer just before the output socket.

5/ If I'm right the LED acts the same as in a ADSR, so it will follow the status of the AD enveloppe. If you're in cycle mode it will flash at the same rate as the cycle itself.

Hope this helps
Cheers.

[roman_f]

[mph]

Hi Roman

I havn't finished this module yet, so I can't tell you precisely. I still don't know what method is the best to reduce peak out to 10V.
First method could be a trimmer or resistor. For this one you could begin to solder a 15K trimmer in series with the pulse out jack, then take a measure of what is going out and adjust your trimmer. If you want you can keep it like this, or simply remove the trimmer carefully and measure its resistance, then you'll only have to replace it with a fixed resistor of the same value.

Second method would be using a voltage divider, like this one:
http://www.electronique-radioamateur.fr/elec/schema/calcul-diviseur-tension.php
If VCC is 15V, then R1 is 820ohm, R2 is 1K5... this would set output voltage to 9,69VCC this allow the use of common resistor values.

I'd love someone to tell me what is the best to do here too.


Concerning the peak out resistor, yes, it should be soldered between the jack tip and the pcb (best would be to solder the resistor directly onto the jack socket and run a wire from the resistor's second leg to the pcb).


The onboard trimmers seem to set up the range of the module in cycle mode; quoting Topp talking about the previous version:
"if you set the trimmer where you get nice long rise and fall times [10 sec. by pot control alone] and control the slopes with an external source, you can get up to around 2500 Hz with -5V CV [into both]. i haven't measured exactly, but the cycle will die out somewhere not too far above that [maybe around 4k?] as the end pulse disappears, so perhaps you could find a compromise somewhere in there. the range of this circuit is pretty incredible."


Edit: found the docx compilation from Russma (thanks a lot) concerning the previous version but most of information applies to the Dual version too:
http://dl.dropbox.com/u/168766/281_notes.docx

[SubG (deactivated)]

Just missing the 4016,damn

btw,i have two kits on offer (panel,knobs,populated pcb's).

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[roman_f]

i've done the assemble, but something is wrong
the pcb is fully assembled
i've wired A-part (knobs, jacks and switches), didn't wire b-jacks/pots + peak + quadrature

it's like working all the time without an external trigger - the led always lights
and the filter which is connected to the 281 - it just makes the freq pot fully opened

what may be the reason? where should i have a look?

[roman_f]

it seems that the power was shortened with a trig-in
upd:

4016 was put in a wrong way
fixed it - now just hear the silence

[beautyofdecay_]

Finally wired one of the 281 dual boards and got some funny results...

The OR (peak) section is working OK.
However, sustain mode does not work for the A section. Cycle mode, one shot mode and end pulse work fine.
For the B section one shot mode and sustain mode works fine and cycle mode does not. I also do not get an end pulse from section B.

Also, in quadrature mode section A does not work correctly: the attack phase is immediately followed by the decay phase without sustaining the signal until section B's attack phase has finished.

I've been staring at the schematics but can't figure out where to start debugging these problems. Maybe someone can give me some pointers?

[beautyofdecay_]

Finally found the problem: The 1N4148 diode between the two TL062's (in between the 10k and 20k resistors) in section B was soldered the wrong way round...

I corrected it and now all works as it should.

This is a great module!

[roman_f]

[roman_f]

got it working

post were wired reversed
regular pot would just work (but reversed)
in that case as soon as 2 pins are shortened by a resistor - it doesn't work properly
voltage on 4016 never drops below 0.2V so it's constantly opened

thanks everyone

[beautyofdecay_]

Congrats!

I had my pots also wired wrong at first (reverse action) so also had to rewire...

[J3RK]

One of my boards is working perfectly. The other is behaving slightly oddly. It seems to function correctly, but the LEDs are acting funny. I haven't had time to check the wiring yet though. As an example, if I set them both to cycle, one slow, one fast, both LEDs fade slowly, but pulse a bit with at the faster pace. (so like they're being blended between CHA and CHB) This doesn't happen on my other board. If I switch the quadrature mode, they pulse in the correct phase relationship. Odd... I'll debug this once I get a few other things done, and post back in case it helps someone else.

[camelneck]

I'm looking for a pair of unpopulated PCBs for the Buchla 281. If anybody has 2 PCBs that they want to sell, please send me a pm. Please include your asking price.

Thanks.

[ATOM]

Here one of my two 281 modules.
What a great module.

Thank you Toppobrillo

ATOM

[camelneck]

That looks great ATOM. I'm also considering adding extra pots to regulate the amount of "Attack CV" and "Decay CV". I also plan to use "switching jacks" for the "Attack CV" and "Decay CV" inputs. This way I can wire them up so that the "output of the EG" is wired to the Attack CV and Decay CV inputs when a patch cord isn't inserted into these jacks. You can then use the pots to reshape the output of the EG from a linear-type envelope output to an exponential-type envelope output.

Did you wire your module up in this manner? If so, how does it work. (Some scope shots would be wonderful!)

[ATOM]

[emdot_ambient]

Very nice design ATOM. What knobs are you using on the Attack and Decay pots? I don't recognize them.