Dunnington 258D build thread

From circuitbending to homebrew stompboxes & synths, keep the DIY spirit alive!

Moderators: lisa, luketeaford, Kent, Joe.

Post Reply
tarandfeathers
Wiggling with Experience
Posts: 334
Joined: Wed May 07, 2014 3:02 pm
Location: Leeds, UK
Contact:

Dunnington 258D build thread

Post by tarandfeathers » Fri May 29, 2020 6:03 am

I announced these in the Buchla subforum but I thought it would be worth having a thread for folks to discuss building these modules.

First off, full docs are at https://github.com/DunningtonAudio/258D

As per the notes, for hand assembly it's best to solder the lowest profile/finest pitch parts first, and work up to the highest profile parts. I had a query about selecting MMBFJ201s - fortunately this is not really any more difficult than selecting a THT J201, you just need an adapter socket. I use one of these:

https://www.peakelec.co.uk/acatalog/pca ... sot23.html

But similar ZIF sockets (mostly for SOT-23-6) are available on Aliexpress, there is also this place in the US that stocks a similar adapter: https://www.waveshare.com/sot6-to-dip6-b.htm, or you can google for SOT 23 programmer/socket/adapter etc. and find lots of similar devices.

Looking forward to seeing how people get on with these, any feedback on buildability etc. is definitely welcome.
Dunnington Audio - Various Buchla format accoutrements available

tarandfeathers
Wiggling with Experience
Posts: 334
Joined: Wed May 07, 2014 3:02 pm
Location: Leeds, UK
Contact:

Re: Dunnington 258D build thread

Post by tarandfeathers » Tue Jun 02, 2020 4:55 am

Peake wrote:
Mon Jun 01, 2020 7:12 pm
I'm looking at the 258D and see it =appears= instead of hard-wiring for saw or square one could wire those connections out to a 3PDT switch for square/saw selection per oscillator...the question is then, depending upon what sort of PCB-mount pots you use, is there 15mm between the front panel and PCB as in most Roman builds (and would even that be enough for a 3PDT switch)...or a small STST wired to +V going to control a daughterboard with a DG202 or similar...
You could fit a switch. The mechanical side of that would be up to the builder in terms of how to mount things. I used 14mm standoffs with lockwashers between the standoff and panel, which is perfect for the right angle 16mm pots when you fit a lockwasher on those - there is actually some lead coming through the PCB to solder to, which you don't really get with 15mm standoffs. If you make the gap too big, the fine tune pot won't come through the panel far enough to give a decent user experience. I debated switchable waveforms when I was doing the layout but 1) it's another hole in the panel and I didn't want to deviate any further from the standard drill file on top of the V/O jack and 2) I have three other 258 type oscillators in another system that I built with the switch and I found that I basically never use it and I'd rather not have it cluttering things. For the rare occasions I want to change it I'm happy to take the module out of the case and move the jumper. As for the calibration thing - true you can do a "lowest common denominator" calibration of the shape zero but then you always have a dead spot at the start and reduced overall range of control for the saw setting.

But fundamentally yes, if you wanted to build it with a switch, the pads are there to do it quite easily.
Dunnington Audio - Various Buchla format accoutrements available

User avatar
Peake
I'm in ur DIY. Filling cases with Buchla
Posts: 6933
Joined: Fri Nov 07, 2008 10:00 pm
Location: Loss Angeles

Re: Dunnington 258D build thread

Post by Peake » Tue Jun 02, 2020 12:16 pm

My experience is that the alt waves are at their greatest usefulness at maximum level but everyone uses things differently. Thanks for the info. Apologies for the distraction. Support and best wishes for your projects.
This is not the place I'd imagined it to be.

tarandfeathers
Wiggling with Experience
Posts: 334
Joined: Wed May 07, 2014 3:02 pm
Location: Leeds, UK
Contact:

Re: Dunnington 258D build thread

Post by tarandfeathers » Tue Jun 02, 2020 3:10 pm

Peake wrote:
Tue Jun 02, 2020 12:16 pm
Apologies for the distraction.
Not at all! These are kind of close to my ideal 258s but I know they won't be everybody's. I'm definitely interested in feedback and ideas to make the board more flexible, so although I wouldn't build one with a switch it would be cool to see other people do it. It should be relatively straightforward, so long as you pick a switch that will fit.
Dunnington Audio - Various Buchla format accoutrements available

User avatar
cygmu
Super Deluxe Wiggler
Posts: 1498
Joined: Mon Feb 15, 2016 3:33 pm
Location: UK

Re: Dunnington 258D build thread

Post by cygmu » Wed Jun 10, 2020 12:34 pm

tarandfeathers wrote:
Fri May 29, 2020 6:03 am
I had a query about selecting MMBFJ201s - fortunately this is not really any more difficult than selecting a THT J201, you just need an adapter socket. I use one of these:

https://www.peakelec.co.uk/acatalog/pca ... sot23.html

But similar ZIF sockets (mostly for SOT-23-6) are available on Aliexpress
I ordered one from AliExpress which arrived today. Sad to say it is essentially useless, at least for this purpose. It does not make proper contact with the transistor pins at all. Well, one time it did, out of about 100 attempts. There may be others on Ali which work ok or it may be that I am just an idiot and can't put the device in the socket properly, but for now I'd advise caution with the Ali ones.

tarandfeathers
Wiggling with Experience
Posts: 334
Joined: Wed May 07, 2014 3:02 pm
Location: Leeds, UK
Contact:

Re: Dunnington 258D build thread

Post by tarandfeathers » Mon Jun 29, 2020 8:11 am

cygmu wrote:
Wed Jun 10, 2020 12:34 pm
I ordered one from AliExpress which arrived today. Sad to say it is essentially useless, at least for this purpose. It does not make proper contact with the transistor pins at all.
That's a bummer to hear. I can absolutely vouch for the Peak test jig linked above, I have tested hundreds of transistors with mine and it works like a charm.

I made a couple of updates to the project files today:

1. Added a note in the notes and BOM to pay attention to the orientation of Q102/Q102/Q201/Q202 - these do not have a symmetrical pinout, which caught someone out on a 281D build.

2. Changed the main timing capacitors C101/C201 from 4n7 to 2n2 in the schematic/BOM - I've found that this extends the range of good tracking at the high end by at least a couple of octaves without compromising the low frequency tracking at all so this ought to be the standard rather than an option.

3. Changed TR103/TR203 from a 3314J-1-101E to a 3224W-1-101E in the BOM - 3224W will fit on the 3314J footprint and gives 12 turns of adjustment for setting the V/O tracking so makes calibration significantly easier. Note that the direction of rotation is reversed compared to the 3314 type so I have updated the calibration procedure with a note to this effect.
Dunnington Audio - Various Buchla format accoutrements available

jimfowler
Veteran Wiggler
Posts: 560
Joined: Mon Feb 22, 2016 1:13 pm
Location: New York
Contact:

Re: Dunnington 258D build thread

Post by jimfowler » Mon Jun 29, 2020 9:55 pm

Good call on the multi-turn trimmer. Thanks for the update.

Post Reply

Return to “Music Tech DIY”