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 Forum index » DIY Hardware and Software
Euro 281 -- Double Dual Function Generator
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AlanP



Joined: Mar 11, 2014
Posts: 499
Location: New Zealand
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PostPosted: Fri May 25, 2018 2:37 pm    Post subject: Euro 281 -- Double Dual Function Generator
Subject description: Buchla 281 QFG euroclone
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Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Posted Image, might have been reduced in size. Click Image to view fullscreen.

I have, on the way, some PCBs for a Buchla Quad Function Generator clone. Hopefully I've done this right. Eurorack format, rather cramped, though.

I've just straight swapped the 15V supply for a 12V one -- seemed to work with the Source of Uncertainty, albeit with some component value changes.

For the 10V supply to some of the ICs, I've used a LDO voltage regulator -- the TL750L10 or something similar. I'm also going to test whether I can just run 'em on 12V or not. The panelpcb has a trace added for either 10V/12V for some switches.

The pads on the dual opamps are smaller than I like, but I wanted routing flexibility for this circuit.

For the Engineboard A trimpots, I put them close to the edge so that right-angle trimpots (Bourns type) can be used, or kludge some other one into place.

For the FETs, I'm going to try a few substitutes.

The 100nF caps in the core of the circuit, I've worked up so that either a 5mm box cap can be used, or a 10mm fancycap. (Polystyrene probably won't fit, but you can try if you want.) There are more traces around these than I like, but I'm working within size constraints.

Yes, this is four function generators (hence DoubleDual) like the original, not two function generators like most Euro adaptations!
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AlanP



Joined: Mar 11, 2014
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PostPosted: Mon May 28, 2018 11:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Right, PCBs turned up, so I populated just the B engineboard. The two engineboards are independant, and the B one has the rear of the board exposed (along with power header) when the module is assembled, so I can probe it under power.

I tried my luck with 12V going to all sections (including the 10V section.) Nothing blew up, but nothing worked correctly, either. (I was pretty sure this would be the case, but nothing ventured...)

TL750M10 regulators are on order, they just won't be in my grubby little paws for a week or two. I'll perf up a TL071 10V source at some point. I'm also going to have to order some more LM13700's, so that my Jerkster build can have it's OTAs back. I have a horrible feeling that even with 10V added, I'm going to have to troubleshoot.

As you can see, the panel is going to be pretty damn cramped. I tried to give the Attack and Decay pots some vertical finger room (there is no horizontal room), but even so... the price we pay for a 3U synth size, I guess.


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LFLab



Joined: Dec 17, 2009
Posts: 470
Location: Rosmalen, Netherlands

PostPosted: Tue May 29, 2018 5:52 am    Post subject: Reply with quote  Mark this post and the followings unread

Looks nice Alan! But yeah, troubleshooting is part of making your own PCB's
Density doesn't look too bad, right? You could switch to SMT IC's and the smaller submini switches (APEM TL36 or similar).

Thinking about PCB sandwiches as well, but I am wondering about exactly which parts in Eagle to use.
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AlanP



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PostPosted: Tue May 29, 2018 9:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

The stock pinhead.lbr is what I use -- be VERY careful about location and orientation between PCBs you are connecting.
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AlanP



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PostPosted: Wed May 30, 2018 2:04 am    Post subject: Reply with quote  Mark this post and the followings unread

Perfed up a TL071 with 100k, 20k, and 1k resistors for a 10V source, and that is now flying-wired to the back of the module. (See, Dave, I can do wires. I just don't want to, when possible Razz )

The module is now working, but one channel has a 5V offset (why, I have no idea...) and the attenuator for the Peak is affecting one of the channels (my suspicion is a solder bridge somewhere.) The quadrature switch is also strongly, strongly affecting the circuit, more than it should, and I think I'll have to cut some normalization traces I've done.

I'll look at this more tomorrow. Troubleshooting during week nights is... not optimal.
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AlanP



Joined: Mar 11, 2014
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PostPosted: Thu May 31, 2018 8:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

Found the offset problem -- two resistors were tied to ground, not the negative rail.

Also, found there were no 1k output resistors. I'm an idiot. Also, wrong cap value on the input switch.

Think I might get a new PCB set done. Annoyed with myself at this.
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LFLab



Joined: Dec 17, 2009
Posts: 470
Location: Rosmalen, Netherlands

PostPosted: Sat Jun 02, 2018 4:54 am    Post subject: Reply with quote  Mark this post and the followings unread

With modern opamps, you do not really need those 1k output resistors anyway.
An alternative would be to simply break the output tracks and tack on 0805 SMT resistors.
The other two resistors one could probably scratch through a track or two and hook them up to V-?

Meh, not enough to be annoyed with yourself about, it is quite a bit of circuitry, and one ecannot make an omelet without breaking some eggs.

Let me know if you'd like to get rid of a surplus set of those boards, totally do not mind crushing those particular bugs (we could do a trade again, I have a few boards you might be interested in).
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AlanP



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PostPosted: Sat Jun 02, 2018 12:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

I need to get panels made anyway Smile
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AlanP



Joined: Mar 11, 2014
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PostPosted: Sat Jun 02, 2018 10:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Worked up a front panel.

I also found that the Attack and Decay controls are reversed on my v0.2 boards. Aiyaiyai.

For the v0.3 boards, I added a set of pads for a TO220 package TL750M10 regulator, as well as the TL750L10.
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MapacheRaper



Joined: Feb 15, 2018
Posts: 40
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PostPosted: Sun Jun 17, 2018 10:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

You are doing a fantastic work!

If you plan to sell PCBs when they are ready please put me in the list. This module is like a 2x version of Maths, more or less, isn´t?

flower
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AlanP



Joined: Mar 11, 2014
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PostPosted: Sun Jun 17, 2018 10:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Maths still confuses the hell outta me. The front panel design is willfully obtuse and hard as hell to understand.
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LFLab



Joined: Dec 17, 2009
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Location: Rosmalen, Netherlands

PostPosted: Mon Jun 18, 2018 6:49 am    Post subject: Reply with quote  Mark this post and the followings unread

MapacheRaper wrote:
You are doing a fantastic work!

If you plan to sell PCBs when they are ready please put me in the list. This module is like a 2x version of Maths, more or less, isn´t?

flower


Maths also has 4 attenuaverters, voltage control over cycling, analog logic, and summing signals. But yeah, it is a start Smile
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g.gabba



Joined: Nov 29, 2008
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PostPosted: Mon Jun 18, 2018 8:53 am    Post subject: Reply with quote  Mark this post and the followings unread

As you are talking about,
would it be to much to ask for a description of what it is doing?

ahoi, gabi
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AlanP



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PostPosted: Mon Jun 18, 2018 2:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's a copy of the Buchla Quad Function Generator. It's set up in two pairs of two.

Each Function Generator requires at least a trigger to get going (even in Cycle mode.) You can control the attack or decay slopes (like a VC Slew), and there is an Output, and an End Of Cycle output trigger. There are three modes -- Sustained (ASR, basically), Short (AR, no decay, no sustain), and Cycle (the EOC trigger goes to the input gate and sets the whole thing off again at the end of each cycle.)

Each pair of function generators has a Quad switch, and a Peak Out (with the B output going through an attenuator before the Peak Out.) Quad Mode means that when A finishes rising, B is triggered to start, and when B finishes it's rise time, A is triggered to decay.
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MapacheRaper



Joined: Feb 15, 2018
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PostPosted: Wed Jun 20, 2018 3:47 am    Post subject: Reply with quote  Mark this post and the followings unread

Yeah, that´s quite similar to and Maths module. If you cange the attenuaters for attenuverters and do some OR fusion with the two ones you basically get an Maths. Both are great.

Will you sell PCBs once you get it finished?
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g.gabba



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PostPosted: Wed Jun 20, 2018 11:10 am    Post subject: Reply with quote  Mark this post and the followings unread

thx man! salut

some questions:

is the" cycle" on the frontplate an inputut/ output / switch or pot?
i would guess a switch.

when in cycle mode ASR is also working or is it then automaticly AR?

when in cycle mode it only needs one trigger to let it go around and let it cycle endlessly? later trigger is then recognized?

"Quad Mode means that when A finishes rising, B is triggered to start, and when B finishes it's rise time, A is triggered to decay" --> that means it is kind of ASR then? A can only decay when B is finished its attack?

Is it the VC over attack AND (/OR?) decay that makes the thing so interesting or is it more the whole concept?

thx again,
gabi
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AlanP



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PostPosted: Wed Jun 20, 2018 1:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

g.gabba wrote:
is the" cycle" on the frontplate an inputut/ output / switch or pot?
i would guess a switch.


Yep, a switch (on-off-on). The middle position (off) is sustain mode.

g.gabba wrote:

when in cycle mode ASR is also working or is it then automaticly AR?


In cycle mode, the channel will with no gate/trig input keep cycling. If a gate comes in, then the output will stop cycling and stay high until the gate stops (Sustain mode out, basically), at which point with no more gate input it will go back to cycling (a very odd triangle/saw.)

g.gabba wrote:
when in cycle mode it only needs one trigger to let it go around and let it cycle endlessly? later trigger is then recognized?


After the initial trigger, it self-triggers from the end of cycle, in cycle mode, if that's what you mean.

g.gabba wrote:
"Quad Mode means that when A finishes rising, B is triggered to start, and when B finishes it's rise time, A is triggered to decay" --> that means it is kind of ASR then? A can only decay when B is finished its attack?


I think so (I need to stop answering these when I wake up.)

g.gabba wrote:
Is it the VC over attack AND (/OR?) decay that makes the thing so interesting or is it more the whole concept?


The whole concept. The VC attack and decay are separate control voltages in. If you patch the output back into either of them, you get an exponential response Smile

Dave Brown has some scopeshots here -- https://modularsynthesis.com/roman/buchla281/281_qfg.htm
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g.gabba



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PostPosted: Fri Jun 22, 2018 3:07 am    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for taking the time,
i guess i really got a picture now how it works,
before it was always a mistery!

good luck with the pcbs,
cheers
gabi
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AlanP



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PostPosted: Mon Jun 25, 2018 2:26 am    Post subject: Reply with quote  Mark this post and the followings unread

Got the bugger.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

Posted Image, might have been reduced in size. Click Image to view fullscreen.

The only issues I had with this version:

Engineboard A rev 0.3 has some vias insanely close to solder pads, as in be VERY careful in some places to not get solder bridges.

The Atk and Decay voltage inputs need attenuators. Too sensitive right now, I might change some resistors.

Silly me forgot to include the LEDs in the panel, so I had to nip 'round to Dad's shed to drill four 3mm holes for them. ("If that's the only issue I have, I'll be glad," I said while drilling.)

Otherwise, she's a good 'un.

Oh, and the B Attenuator on the Peak Out is more a B Level (ie, it's in reverse.)
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MapacheRaper



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PostPosted: Mon Jun 25, 2018 7:25 am    Post subject: Reply with quote  Mark this post and the followings unread

So sexy!. It only need some minor tweaks and is ready. Cool. jackson dancing
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g.gabba



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PostPosted: Mon Jun 25, 2018 11:38 am    Post subject: Reply with quote  Mark this post and the followings unread

like we say at home: Glückwunsch Alter! --> Gongrats dude!
thumleft thumright

(is there a meaning behind left and right thumb? better put both!)
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AlanP



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PostPosted: Mon Jun 25, 2018 12:32 pm    Post subject: Reply with quote  Mark this post and the followings unread

The original Buchla used 180nF timing caps. Roman's schematic used 100nF timing caps.

With 100nF timing caps, with maximum decay and minimum attack (a saw waveform), the trimmer meant to adjust for 10sec decay time had a minimum decay time of about 18sec.

I had a bag of 47nF WIMA caps lying around (is this a sign I have a problem?), and so bunged them in, in place of the 100nF caps. Now, I can adjust the maximum decay for 10sec Smile

The Atk and Decay cv inputs are still pretty responsive, but now are not insanely touchy. That seems to have fixed that problem Cool
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LektroiD



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PostPosted: Sat Aug 11, 2018 5:41 am    Post subject: Reply with quote  Mark this post and the followings unread

This looks like a really nice project. I'll definitely be interested in a PCB & black panel when it's all ready...

Excellent work!

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AlanP



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PostPosted: Sun Aug 12, 2018 2:35 am    Post subject: Reply with quote  Mark this post and the followings unread

How many people would be interested in a pcb/panel set for this?

I need to do a new revision of the Engine A PCB (there are some vias that are insanely close to solder pads), and the panels I have are missing the LED holes (I can drill them out myself, but if I'm ordering more Engine A PCBs anyway...)
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LektroiD



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PostPosted: Sun Aug 12, 2018 3:18 pm    Post subject: Reply with quote  Mark this post and the followings unread

AlanP wrote:
How many people would be interested in a pcb/panel set for this?

I need to do a new revision of the Engine A PCB (there are some vias that are insanely close to solder pads), and the panels I have are missing the LED holes (I can drill them out myself, but if I'm ordering more Engine A PCBs anyway...)


As stated above, I'd absolutely love a set, maybe two, depending on cost (my wallet has been hit pretty hard of late with vintage purchases)... I really like that black panel though...!

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