[build] dual 281 boards

bsmith · Post by **bsmith** » Fri Nov 09, 2012 11:46 pm

There are another 4 x 47k off board, 1 each for the attack and decay pots x 2 - another 4 more for good 47k morale perhaps?
http://www.sdiy.org/toppobrillo/DOWNLOA ... %20PDF.pdf

rowman · Post by **rowman** » Fri Nov 09, 2012 11:51 pm

I just doubled the quantities from the single 281 board BOM.

hpsounds · Post by **hpsounds** » Fri Nov 09, 2012 11:57 pm

bsmith wrote:There are another 4 x 47k off board, 1 each for the attack and decay pots x 2 - another 4 more for good 47k morale perhaps?
http://www.sdiy.org/toppobrillo/DOWNLOA ... %20PDF.pdf

I've counted also them. Doesn't matter, a few more resistors can always be useful.

Other question : this MOUSER reference (581-08055C104M) is a SMD/SMT component ?

Sorry for my "newbee" questions ...

HÃƒÂ©di K.

rowman · Post by **rowman** » Fri Nov 09, 2012 11:59 pm

There's a few smd 100nF caps for power decoupling to the ICs, you don't have to put them on if you don't want to, from memory.

lessavyfav · Post by **lessavyfav** » Sat Nov 10, 2012 12:03 am

The 47ks get lonely. I stuffed and soldered the board resistors and diodes. Got a +-12v power supply board from MFOS to use for my new testing set up. The board is well organized between the A half and the B half- nice Toppobrillo. I put 20ks in place of the 100k* resistors - the notes suggest 22k for "smoother" LED response. I love smooth. I hope to finish stuffing on Monday. Then debate hand wiring the whole thing on a card stock panel or waiting for the panel/daughterboard to happen.

BSmith- do you dare post images of your progress?

marvkaye · Post by **marvkaye** » Sat Nov 10, 2012 12:27 am

Got my dual 281 PCBs just about completely populated, only missing the 7810 regulators... it's always something...

There are 2 circles with 3 pads in them just above the "A" and "B" at the end of the board...

They look like placement marks for something in a TO-5 package but there's no legend or mention of them on the schematic or wiring diagram... anyone know what they're for?

<marv>

lessavyfav · Post by **lessavyfav** » Sat Nov 10, 2012 9:02 am

Marvkay- I think those might be 20-50k trim pots. I just now looked at the old v.3 single board documentation for clues. Could be wrong though, I am not there yet.

bsmith · Post by **bsmith** » Sat Nov 10, 2012 10:03 am

lessavyfav wrote: BSmith- do you dare post images of your progress?

*gulp*

embarrased to post this one, much tidying needed!....

I think I used 33k on that led resistor and it's fine - didn't compare to other values though. Used 50k's on those A and B trims. I did end up doing a couple resistors in series to get 1.35k there where he says to use 1.2k - 1.5k in place of the 1k* for 12v operation - I like the range here.
One thing that was a booger for me that I was bonking on initially due to newbishness, and the daughter board will be helpful for this especially, was those resistors that go between the lugs and the B+ for the A and D pots. Have my other board standing by, so when the panel and board happen I'll rip this dude apart gladly - that panel george did up is amazing how much it packs into that space, in what looks like a pretty damn ergonomic manner!

lessavyfav · Post by **lessavyfav** » Sat Nov 10, 2012 1:56 pm

"Plex" appeal.

lessavyfav · Post by **lessavyfav** » Mon Nov 12, 2012 6:03 pm

I just finished populating my board and found that in the Rowman's BOM linked above that the 2 .1uF "high quality" caps per board mentioned above were missing. I'm not sure how to update Rowman's BOM but in the board order thread Consumed mentioned the below which I'm gonna order....

consumed wrote: here's another "high quality" .1uF cap. this is not polypropylene or polystyrene, but c0g mlcc
double check the lead spacing on the board if this is a concern (i dont have mine in front of me)

Mouser part: 810-FK26C0G1H104J

Also, cribbing shamelessly off Rowman, I went with these high voltage super caps mentioned here:

rowman wrote: Also in my personal spreadsheet I've changed my 47nF film caps to these polypropylene ones instead of polyester

Unfortunately they have a bigger footprint then the board want's to accomodate. I just kinda left mine sitting over the neighboring resistors, hopefully that isn't a problem. There is a 250v version which seems like it would fit normally. Anyone know if that would be a better choice?

CHUBBY CAPS

rowman · Post by **rowman** » Tue Nov 13, 2012 12:13 am

lessavyfav wrote:Unfortunately they have a bigger footprint then the board want's to accomodate. I just kinda left mine sitting over the neighboring resistors, hopefully that isn't a problem. There is a 250v version which seems like it would fit normally. Anyone know if that would be a better choice?

Sorry about that, I didn't realize they could be too wide!
The ones you've linked are 470pF with a 7.5mm lead spacing, these are 47nF and might be a bit narrower, though it says they won't be in stock for 5 days.

Also for the .1uF high quality caps, try these, slightly cheaper then the C0G caps. They are in the BOM though, just after the electrolytics.

And good on you for keeping the first post up to date, it will help a lot of people myself included.

lessavyfav · Post by **lessavyfav** » Tue Nov 13, 2012 10:37 am

Thanks for the info Rowman. Those .1 caps were there after all. Got tired at the end of the day. I'll correct the opening post. Notably those are also wide fellas. I checked some other caps I had and 2.5mm wide x 7.2 long x 6.5 high seem like the proper case size FWIW. On Mouser different products seem to assign LWH to different sizes but these look like the right size for the .1uF and then
for the .047uF this seems like the right size

do these seem good? Why some cost .33 and some cost .25 is a mystery to me. I usually go with the one with the highest stock for these ida parts assuming herd mentality. Unless someone knows better I'll update the first message comments... I'll also order so for my second board to make sure they work...

bsmith · Post by **bsmith** » Tue Nov 13, 2012 10:47 am

hey just chiming in - I did try some c0g ones there on my other board and it worked fine.

negativspace · Post by **negativspace** » Tue Nov 13, 2012 5:11 pm

lessavyfav wrote:Marvkay- I think those might be 20-50k trim pots. I just now looked at the old v.3 single board documentation for clues. Could be wrong though, I am not there yet.

Nope, you're correct.

marvkaye · Post by **marvkaye** » Tue Nov 13, 2012 7:39 pm

Thanks, guys... I see them now. I even managed to have some 20Ks in my parts bin that fit.... how cool is that?

<marv>

rowman · Post by **rowman** » Tue Nov 13, 2012 10:55 pm

lessavyfav wrote:Thanks for the info Rowman. Those .1 caps were there after all. Got tired at the end of the day. I'll correct the opening post. Notably those are also wide fellas. I checked some other caps I had and 2.5mm wide x 7.2 long x 6.5 high seem like the proper case size FWIW. On Mouser different products seem to assign LWH to different sizes but these look like the right size for the .1uF and then
for the .047uF this seems like the right size

do these seem good? Why some cost .33 and some cost .25 is a mystery to me. I usually go with the one with the highest stock for these ida parts assuming herd mentality. Unless someone knows better I'll update the first message comments... I'll also order so for my second board to make sure they work...

Those will fit much better, but for the 0.1uF 'high quality' caps, toppo recommended using polypropylene which is apparently better spec the polyester. I had the idea to just use polypropylene everywhere since it only adds up to a few extra dollars per build, but they don't fit! It's probably the best to just use c0g 0.1uF caps.

Here's a BOM with C0G caps instead of the chubby polyprops:
https://au.mouser.com/ProjectManager/Pr ... c7098677f5

edit: and I've attached the spreadsheet I've been working from, in case anyone wants to make their own changes and import it to Mouser, it's pretty easy.

camelneck · Post by **camelneck** » Mon Dec 17, 2012 11:48 pm

I just started building my Buchla 281 clone. Unfortunately, I couldn't find any of the Dual 281 PCBs so I'm using two version 2 and two version 3 Single 281 PCBs.

So far I have finished installing FG #1 and it appears to be running just fine. In order to get the 281 to cycle (or behave as an LFO), I have to apply a pulse to the trigger input jack in order to "jump start" the FG.

I heard that if the FG's mode switch is in the cycle (or loop) position when the 281 module is powered up, the FG will begin cycling automatically. (When I say "automatically", I mean no trigger pulse is needed to "jump start" the cycling.).

QUESTIONS (in order of importance):
1) If the FGs are in cycle mode when the module is powered up, are trigger pulses still needed to jump start the FGs so they will begin to cycle (like an LFO)?

2) I've heard that there is a modification for this looping problem. Does anybody have any info or details that they can share regarding this modification?

3) Could someone tell me how to adjust the trim pot? (I have a scope in case one is required.)

4) In the dual 281, it appears like Topps has changed the value of one of the 100K resistors in the 2N3904 (LED) circuit to a value of 22K. Could someone take a meter to this 22K resistor and tell me if one end of the resistor is connected to ground. (Once I have this information, I'll be able to determine which resistor this is in the rev3 schematic--R30 or $31--since only one of these is connected to ground.)

Thanks.

lessavyfav · Post by **lessavyfav** » Fri Mar 08, 2013 10:16 pm

So, I'm finally gonna do this! Hardware in the mail from Mouser! and I finally stopped hoping for the euro panel! I quote myself from the panel thread:

lessavyfav wrote:Since you've been gone. We are never ever ever getting back together. I can get another man like you in a minute. Etc.

I am over you thread! No more late night stalking , no more shameless begging , no more faux casual "how you doin' thread?" , and best of all no more pitiful bumps ! [Mordor] no more! [Mort d'amour] no more!

....unless you guys are about to have the Daughterboard done

I got a pack of water-slide decals coming from Amazon with this lil puppy's name written all over it!

hank · Post by **hank** » Sun Jun 23, 2013 12:12 am

Hi folks,
I'm having some trouble with my 281 (2010 dual board) build. I can get it to go from 0v -- 10v, but I can't change the attack and decay times.

As it stands, I can get it to act as a LFO or one-shot function generator but the cycle time is around 1 minute, somewhat limiting it's usefulness

This affects both sides of the circuit, which leads me to believe that I've messed up the panel wiring somehow.

Does this ring a bell?

Also if anyone happens to have a picture of their panel wiring I would love to take a peek.

Thanks!

hank · Post by **hank** » Sun Jun 23, 2013 2:23 pm

For future reference and for my own humiliation, I had mistakenly used a CD4001 instead of a CD4016(!).

toppobrillo · Post by **toppobrillo** » Mon Jun 24, 2013 9:46 pm

I just started building my Buchla 281 clone. Unfortunately, I couldn't find any of the Dual 281 PCBs so I'm using two version 2 and two version 3 Single 281 PCBs.

So far I have finished installing FG #1 and it appears to be running just fine. In order to get the 281 to cycle (or behave as an LFO), I have to apply a pulse to the trigger input jack in order to "jump start" the FG.

I heard that if the FG's mode switch is in the cycle (or loop) position when the 281 module is powered up, the FG will begin cycling automatically. (When I say "automatically", I mean no trigger pulse is needed to "jump start" the cycling.).

QUESTIONS (in order of importance):
1) If the FGs are in cycle mode when the module is powered up, are trigger pulses still needed to jump start the FGs so they will begin to cycle (like an LFO)?

2) I've heard that there is a modification for this looping problem. Does anybody have any info or details that they can share regarding this modification?

3) Could someone tell me how to adjust the trim pot? (I have a scope in case one is required.)

4) In the dual 281, it appears like Topps has changed the value of one of the 100K resistors in the 2N3904 (LED) circuit to a value of 22K. Could someone take a meter to this 22K resistor and tell me if one end of the resistor is connected to ground. (Once I have this information, I'll be able to determine which resistor this is in the rev3 schematic--R30 or $31--since only one of these is connected to ground.)

Thanks.

this is old, so apologies, but I feel like I already answered it in the main thread? perhaps not so I will again-

1) yes they do, tho often mine power up cycling if the switches are in cycle mode. I never knew and still don't whether the original 281 had any additional mods or peripheral circuitry to 'fix' this. I kind of like having to send a trigger to initialize cycling, but YMMV.. which brings me to
2) I posted about this for sure. Roman has designed a 281 board for his series of 200 clones. he messaged me a while back about a mod he grifted from the 208's pulser schematic, this involves a "start capacitor" of sorts but I still haven't tested it and it doesn't seem like it would work very well or reliably.. ? duno I posted the drawing he sent me in the other thread..
3) the trim is to trim to the Buchla spec for panel control range, ie 1mS to 10S per slope over the travel of the knob, or as close as u want to get to it..
4)I cant recall the part number but 1 end is connected to ground yes

fluxmonkey · Post by **fluxmonkey** » Sat Jul 06, 2013 10:58 am

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?

toppobrillo · Post by **toppobrillo** » Sat Jul 06, 2013 2:43 pm

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..

fluxmonkey · Post by **fluxmonkey** » Sun Jul 07, 2013 10:41 pm

for the attack/decay pots, does 10v go to the full-clockwise end of the pot? or the anti-clockwise end.

why, yes, 2 years later i am just getting around to building these.

djs · Post by **djs** » Mon Jul 22, 2013 12:44 pm

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?

MOD WIGGLER

MOD WIGGLER

[build] dual 281 boards