[build] dual 281 boards

bezier · Post by **bezier** » Fri Apr 18, 2014 5:23 am

Hi everyone,

I "think" i have my mouser cart almost together by now, but i'd much appreciate a little help with two parts.

First, i couldn't find the semiconductors "PN4393, MPF4393" on mouser, which are used instead of "MPF-102"s.

Also, i am confused by the IN914/4148 Diode, as it says "SILICON DIODE" on the BOM sheet, but my parts don't seem to bear the term silicon anywhere. Would this part be correct: http://de.mouser.com/Search/ProductDeta ... 2-1N914BTR

Any help would be highly appreciated. My questions might be dumb as this is my first self-sourced project, but i can't solve these last things on my own unfortunately...

FetidEye · Post by **FetidEye** » Fri Apr 18, 2014 5:26 am

yes that diode is fine

and here:
http://de.mouser.com/ProductDetail/ON-S ... w88rBT8%3d

bezier · Post by **bezier** » Fri Apr 18, 2014 5:37 am

FetidEye awesome, thank you!!

Navs · Post by **Navs** » Sat May 03, 2014 3:14 am

Just finished one of two 281 boards - I like these! The peak out, especially when cross-modulating, is loads of fun. I'll post some build pics and thoughts soon, but first have a question regarding the auto-loop mod.

I followed Camelneck's scheme, as per this post:

viewtopic.php?p=1021533#1021533

Because of the way I'd wired my module, I made the capacitor connections directly on the switch lugs that offered the relevant connections. So, one end of the 47nF to the cycle contact of the mode switch and the other connected to the lug carrying 10V on the quadrature switch.

This works for a while after initial power-up. After about 10 minutes - regardless of whether it's engaged or not - it ceases to have an effect. To get it going again I have to apply a trigger.

Any ideas why? Is it because of the circuit in general or because of the way I've wired it i.e. there's some unwanted interaction? As you can see in the bottom of my pic, I anchored the capacitor to the unused lugs of the dual pole 'mode' switches I used (didn't have any single pole to hand). Could that be disturbing the circuit or is the mod itself, as Josh suggests, not ideal? If it's the latter, I can live with it, else I'd undo the mod.

Thanks!

Emalot · Post by **Emalot** » Sun May 04, 2014 9:28 am

I don't know if ot's the good place to ask this but...
I 'm making 1/2 of 281 with toppo rev3 PCB.
I ask me what's the J2, J3, J3 etc in these boards ???
I also found only 6 1N4148 in each board, no 9 like Toopo write in the BOM...
Somebody built this rev 3????
Thank you very much.

Navs · Post by **Navs** » Wed May 07, 2014 1:31 pm

Navs wrote:... question regarding the auto-loop mod ...

Lil' bump for any ideas

It seems triggering the envelope after it ceases to auto-loop can reset its ability to self trigger. Not immediately and not every time, but sometimes

bkbirge · Post by **bkbirge** » Wed May 07, 2014 7:01 pm

Where did you guys get the pn4393's for your builds? Mouser is out of 'em. Almost done with a pair of these and getting the euro specific parts together.

Edit: nevermind, saw the link to the Deutschland mouser earlier in the thread, here's the part number for USA mouser if anyone needs it...
863-MPF4393RLRPG

bkbirge · Post by **bkbirge** » Wed May 07, 2014 8:03 pm

In progress pics, my smt soldering sucks balls but no bridges so hopefully it's ok, just waiting on parts to finish, I'm going to change out the large alpha pots with some minis...

Arnoid · Post by **Arnoid** » Thu May 08, 2014 3:51 am

I skipped the smd decoupling caps the module is working so I guess they're not needed ?

bkbirge · Post by **bkbirge** » Thu May 08, 2014 8:54 am

Arnoid wrote:I skipped the smd decoupling caps the module is working so I guess they're not needed ?

Probably not as I think they are just power supply filtering caps for the IC's but I wanted the practice soldering smt.

Emalot · Post by **Emalot** » Thu May 08, 2014 10:18 am

SOmebody knows what's the PI/PO in the board Rev3?
And the ARI/PKO? (they look like OUTput but what's difference?)

Navs · Post by **Navs** » Thu May 08, 2014 2:24 pm

Emalot wrote:SOmebody knows what's the PI/PO in the board Rev3?
And the ARI/PKO? (they look like OUTput but what's difference?)

viewtopic.php?p=1550769#1550769

bkbirge wrote:Where did you guys get the pn4393's for your builds?

I got my MPF4393 and other parts from http://www.uk-electronic.de/onlineshop/index.php/

It was the first time I'd shopped with them and I was very happy with the turnaround

Now, has anyone got an idea why camelneck's self-starting loop mod is intermittant or whether it might be disturbing the circuit?

viewtopic.php?p=1546581#1546581

Third time lucky, eh?

Emalot · Post by **Emalot** » Tue May 13, 2014 6:01 am

When you put the Cycle mode, do you need one first TRig/gate to make Cycle or not? Because mine need this first trig/gate.
BUt i feels like when i built only one channel, it worked in Cycle mode without first trig...

Arnoid · Post by **Arnoid** » Tue May 13, 2014 7:28 am

Emalot wrote:When you put the Cycle mode, do you need one first TRig/gate to make Cycle or not? Because mine need this first trig/gate.
BUt i feels like when i built only one channel, it worked in Cycle mode without first trig...

Yes it needs a trigger to cycle but somtimes it cycles when powering up

Emalot · Post by **Emalot** » Tue May 13, 2014 7:47 am

...OK. Somebody knows why in DUSG Cycle doesn't need a trigger to cycle, and why inthis 281, it needs one?

bkbirge · Post by **bkbirge** » Tue May 13, 2014 8:30 am

Emalot wrote:...OK. Somebody knows why in DUSG Cycle doesn't need a trigger to cycle, and why inthis 281, it needs one?

They are different circuits. The 281 is based on a Buchla circuit, the DUSG is a Serge design. According to Ken Stone's site about the DUSG "If the TRIG IN jack is connected to the TRIG OUT jack, the DSG will oscillate with a waveform and frequency set by the RISE and FALL knobs."

Navs · Post by **Navs** » Thu May 15, 2014 12:07 pm

Emalot, have you read the thread?

I think part of the difference is that the End Out of the Serge DUSG/ VCS is a gate, whereas the Pulse on the 281 is a trigger. So, if you 'miss' the pulse, the EG will not loop. On a Serge End Out, this is high for as long as the EG is idle i.e. you can't miss it.

This might also explain why camelneck's cap fix doesn't work reliably ...

I have now de-soldered what I outlined here. I found that when looping with these caps fitted, the 281 outputs trapezoids not triangles. Maybe it was just the way I'd wired it.

My new solution was to tap the 10V, as before from the quadrature switch, and to wire it via a momentary button/ switch and 10K resistor to the switching contact of A + B's trigger input jacks. Basically, I wired a manual gate to both jacks. This means I can fire both envelopes or get them looping. Ideally, I would like external triggers to also be 'multed' to both EGs in a switching scheme, but I think this is no longer possible

Anyway, now I have a new question

The 281 stops responding to external triggers after a certain frequency. Can someone suggest why e.g. is there a HP filter/ gate-to-trigger converter at work and, if so, do I need to make that trigger shorter? I have a hunch this is what it is. After all, when looping, the 281 runs at 500Hz, triggered by its own End Pulse, right?

bkbirge · Post by **bkbirge** » Sat May 17, 2014 1:05 pm

Finished up a pair of these today, here's some detail pics. One has blinding white led's and one has mellow red led's that's the only difference. Great module, the effort is worth it.

Getting better at wiring, things are more organized, could trim some slack but the length is good for unfolding the board and troubleshooting...

Wires all connected from underneath...

Obligatory front side...

Inside...

Here's a little detail of the B+ buss I made, you can see above the B level pot, all the B+ connections meet there, from the LED's and the attack/decay pots, so only one wire needed to go to the PCB.

twospartans · Post by **twospartans** » Sat May 17, 2014 1:26 pm

blbirge,

looks nice!
really excited to get started on my pair!

bezier · Post by **bezier** » Sat May 17, 2014 4:48 pm

bkbirge thank you for uploading photos, really helpful. I see you stuffed the L+/L- pads as well, are those ferrite beads? I'm just curios for i couldn't find any information in the docs, but have some spare beads i could use.

bkbirge · Post by **bkbirge** » Sat May 17, 2014 5:22 pm

Yeah those are just ferrites.

bezier · Post by **bezier** » Sat May 17, 2014 6:48 pm

bkbirge thanks, will put them in right now

davidschwan1 · Post by **davidschwan1** » Sun May 18, 2014 12:21 pm

I used to think ferrites were overkill until I started doing wireless design at work. I'm a firm believer in ferrites, they kill any unwanted RF signals.

Navs · Post by **Navs** » Mon May 19, 2014 4:04 pm

Tidy, bkbirge

I'm glad to see I wasn't imagining things with the Greyscale panel, though - it's too small for all-16mm-Alphas, right? I went with 9mm.

Now that I've used mine for a while I think the panel led me astray on another point too: the 281 really wants a couple of attenuverter/ mixers per channel too to give you contour plus VC length. A manual gate is pretty much essential too given the non-selfstarting loop mode and unreliable cap mod.

It's lovely to have & behold, but was there some poll to keep it at 16HP or something?

pre55ure · Post by **pre55ure** » Mon May 19, 2014 5:08 pm

Navs wrote:Tidy, bkbirge

I'm glad to see I wasn't imagining things with the Greyscale panel, though - it's too small for all-16mm-Alphas, right? I went with 9mm.

Actually, for anyone else wondering- I did mine with 16mm alphas and they fit just fine.

MOD WIGGLER

MOD WIGGLER

[build] dual 281 boards