[build] dual 281 boards

djs · Post by **djs** » Thu Jul 25, 2013 10:56 am

also- is there a schematic available? I see there's ones for the older boards, but I don't know if that is valid or not for the newer dual board?

logicgate · Post by **logicgate** » Thu Jul 25, 2013 1:21 pm

Can someone please post a very simple sketch of the wiring? I mean, for noobs

I find it easier when thereÃ‚Â´s the rear view of the pots

Thank you

logicgate · Post by **logicgate** » Thu Jul 25, 2013 4:41 pm

Another question:

Can someone please confirm if this ferrite bead is ok for this project?

http://www.newark.com/panasonic/exc-els ... 20Products

Cheers!

djs · Post by **djs** » Thu Jul 25, 2013 6:57 pm

logicgate wrote:Another question:

Can someone please confirm if this ferrite bead is ok

Looks ok to me. I wouldn't be too picky about the ferrites, other than if they physically fit.

valis · Post by **valis** » Tue Feb 04, 2014 1:47 pm

Greetings all,

I'm building a 281 into a buchla style 281 panel and have two questions:

1. In the "Peak" section (which is sometime called the "Or" section), what do the two knobs do? Do they just attenuate the Peak output from 0v to the peak output?

2. My second question has been asked before and involves how one wires the second LED/quadrature indicator. Would this work best running a buffered LED indicator from the quadrature switch or can I run an LED straight from the switch? Am I missing something?

djs wrote:
toppobrillo wrote:
the buchla-format (RSFC) panel has 2 LEDs per set of function generators... but the topobrillo board only has a single? what a folks feeding to the second LED?
that 2nd LED is the quadrature indicator- as I understand it on the original, when A and B are in quad, both LEDs will light at A and B. you could of course only install one LED and use the other hole to mount a standoff..
any idea how to wire this? I could see doing something with the quadrature switch, but i don't know if the led current draw would mess that circuit up somehow?

Thanks for your time!

David

Ginko · Post by **Ginko** » Fri Apr 11, 2014 11:51 am

Nearly done:

pre55ure · Post by **pre55ure** » Fri Apr 11, 2014 3:32 pm

Lookin good!

I just finished the first of mine a few days ago.

Wiring the Led's is what actually prompted my soldering wire to wire thread.

davidschwan1 · Post by **davidschwan1** » Fri Apr 11, 2014 10:45 pm

Hope to start building mine soon.

Ginko · Post by **Ginko** » Sat Apr 12, 2014 1:45 am

Annoyingly, I just bought like 50 knobs to fit spiked shafts, then realised that every potentiometer I have bought recently has a round shaft

Ginko · Post by **Ginko** » Sat Apr 12, 2014 2:43 pm

Alright, finished! Seems to be working great as well

Two questions:

The pulse out, when does the pulse happen in the cycle? Is it at the start or at the end of the attack?

WTF does B Level do?

Ok three questions, does the envelope behave differently in response to gate and pulse signals?

EDIT: ok I found answers to question one and three, the pulse happens at the end of the cycle and yeah gate / transient mode makes sense now.

I still don't get what B Level is for???

FetidEye · Post by **FetidEye** » Mon Apr 14, 2014 7:04 am

i have a question:

I'm populating the (new) board. In the BOM it says 15 x 4.7k resistors (3 x external). I can only find 10 on the PCB. > see attachment
Am i blind?

eolianmollisol · Post by **eolianmollisol** » Mon Apr 14, 2014 7:14 am

this could be a stupid idea...but, perhaps, some of the 4.7M is supposed to be 4.7K, and it is a typo, considering they are so close on the computer keyboard. Could be a possibility

Ginko · Post by **Ginko** » Mon Apr 14, 2014 10:03 am

I would be very interested to know if this is the case!! I also found that I was short of 2 47ks or 4.7ks from the bom (can't remember which, maybe both). I used two 4.7M on the board for those two at the top...

keninverse · Post by **keninverse** » Mon Apr 14, 2014 2:48 pm

Any off board resistors?

FetidEye · Post by **FetidEye** » Mon Apr 14, 2014 4:19 pm

yeah 3 , that's what i meant by externals.. so i'm missing two 4.7k places.

Ginko · Post by **Ginko** » Tue Apr 15, 2014 2:18 am

With mine built according to the PCB though, I'm not sure there is anything wrong. I was a bit surprised by the attack / decay time though, I thought you would be able to make them a lot longer, the attack and decay seems to go to about 2 seconds or so when the knob is at 95% but then jumps to something a lot longer (possibly locks) if turned to 100% - not sure if this is normal or not.

I still can't figure out what BLevel does by the way

Ginko · Post by **Ginko** » Tue Apr 15, 2014 2:51 am

toppobrillo wrote:right the 1K* spots- 1.2 to 1.5K is OK, I went 1.5 on my newest boards, just increases the control range to about what It whould be,, the actual ideal value would be around 1.35K i think- you should be able to trim it for 1mS at min and around 10S slope at max [w no CV in] I dont thnk I ever posted a ref. designator picture of the board, as it really doesnt have any perse, but the ones w the asterisks are the ones..

Ah, just got this from page one of the thread, I tweaked the envelope to around 2ms at fully CCW, but although I may get 10S at fully CW, I don't get a smooth transition between those times - I wonder if I got the wrong value parallel resistors on the pots?

regenbot · Post by **regenbot** » Tue Apr 15, 2014 3:06 am

Ginko wrote:
I still can't figure out what BLevel does by the way

I think it's the amount of B out of peak out

Ginko · Post by **Ginko** » Tue Apr 15, 2014 3:45 am

regenbot wrote:
Ginko wrote:
I still can't figure out what BLevel does by the way
I think it's the amount of B out of peak out

Ok cool. That is probably the one thing I didn't try!

I had a little wiggle this morning and yeah, in the attack/decay time I get about 8-9 seconds at a full turn, but millimeters before on the turn I am on like 3 seconds!! The curve is a bit sucky. Is it like this for anyone else? Any idea what might cure that?

pre55ure · Post by **pre55ure** » Tue Apr 15, 2014 4:28 am

My curves seems to feel pretty good

Maybe you inadvertently used log pots instead of linear?

Do you have the wiring diagram that shows the 4.7k resistors across the pot input and wiper?

Ginko · Post by **Ginko** » Tue Apr 15, 2014 6:29 am

Yeah I have the diagram and installed the resistors, I don't think I installed log pots instead of lins but I have a bad feeling I may have used 47k instead of 4.7k for the parallel resistors...

Ginko · Post by **Ginko** » Tue Apr 15, 2014 10:32 am

Having looked at the wiring diagram, it shows that 47k resistors should be used across the pots - am I looking at the same thing as you? I am going to double check them with a multimeter and check the pots are linear!

Ginko · Post by **Ginko** » Tue Apr 15, 2014 11:12 am

Riiiiight OK, I double checked and the build documentation that I have for the dual board shows a 47K resistor being used as the parallel across each pot. I measured across the resistors I had soldered to the pots and I was getting a reading of around 4.33k with the pot fully CCW- I thought that was odd as I was expecting something around 22 - 24k - at first I presumed that I had used 4.7K resistors by mistake and began desoldering them, but then realised that the 47K resistors I was pulling out the draw had exactly the same colour bands...

So, on a hunch I tried soldering a 4.7K resistor across the pot terminals and upon testing - it works much much better!!

So... I apologise for confusion and misinformation added to this thread, but there definitely is an error in some versions of the build documentation

Use 4.7K resistors across the pot terminals!!

EDIT: I would also say, in response to the earlier question, just solder up all the resistors you can see, you will have a few left over from the BOM - this is almost certainly an error, your 281 will work fine

pre55ure · Post by **pre55ure** » Tue Apr 15, 2014 2:05 pm

Ok well now I'm totally confused. I actually did use 47k resistors across the pot terminals as stated on the wiring diagram. So my apologies for making this potentially more confusing for others to follow along with.

Anyway, even with the 47k resistors across my pots I still don't find the curves to be weird. I'm not measuring it with anything except my ears and eyeballs (through the O'tool) but it seems to have roughly the same pot response as my Quad slope or maths.

Oh well, alls well that ends well right?

Ginko · Post by **Ginko** » Tue Apr 15, 2014 2:13 pm

pre55ure wrote:Ok well now I'm totally confused. I actually did use 47k resistors across the pot terminals as stated on the wiring diagram. So my apologies for making this potentially more confusing for others to follow along with.

Anyway, even with the 47k resistors across my pots I still don't find the curves to be weird. I'm not measuring it with anything except my ears and eyeballs (through the O'tool) but it seems to have roughly the same pot response as my Quad slope or maths.

Oh well, alls well that ends well right?

Hmm, very weird

- what value pots did you use? It definitely made a big difference for me - I used 50K pots

EDIT: I should probably say that Toppobrillo has now confirmed that the documentation IS CORRECT. So 47K is the right value to use. There must be some other cause to the problem in my build, but meh... It works exactly as described so I won't be poking it anymore... At least until I decide to do the capacitor cycle self-trigger mod...

MOD WIGGLER

MOD WIGGLER

[build] dual 281 boards