Dunnington 258D build thread

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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.
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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.
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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.
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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.
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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.

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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.
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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.

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Re: Dunnington 258D build thread

Post by CliffordMilk » Fri Nov 13, 2020 3:30 am

In the BOM, the order code for the MMBF5484s is listed as 512-MMBF5485.

Is this correct or should it be 512-MMBF5484?

Or is either part valid?

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Re: Dunnington 258D build thread

Post by tarandfeathers » Fri Nov 13, 2020 4:22 am

MMBF4584 might work but my builds were done with MMBF5485s, so those are tested and known to be good. I've amended the documents on github to correct this, thanks for pointing it out!
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Re: Dunnington 258D build thread

Post by discomicke » Mon Dec 21, 2020 9:03 pm

Hi, a quick question to try to save myself some troubleshooting time. All seems to work well with my 258D except that I can't get the 1.2V/Oct scaling to work well on either VCO. Top VCO is just short of a full octave regardless of TR103/203 settings and bottom VCO overshoots. The CV-summing network seems to work well but even with identical voltages at pin2 of TR103/203 I get wildly different frequencies. This is leading me to think, does Q101 need to be selected as well ?

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Re: Dunnington 258D build thread

Post by tarandfeathers » Tue Dec 22, 2020 12:23 pm

discomicke wrote:
Mon Dec 21, 2020 9:03 pm
Hi, a quick question to try to save myself some troubleshooting time. All seems to work well with my 258D except that I can't get the 1.2V/Oct scaling to work well on either VCO. Top VCO is just short of a full octave regardless of TR103/203 settings and bottom VCO overshoots. The CV-summing network seems to work well but even with identical voltages at pin2 of TR103/203 I get wildly different frequencies. This is leading me to think, does Q101 need to be selected as well ?
Odd, I haven't experienced or heard of this before. I don't believe there should be any requirement to select Q101. Did you use the 3224W 12 turn trimmers for tracking adjustment? What voltage source are you using to calibrate, and how far short is "just short"? If you set TR103 at its halfway point, and take external control out of the equation, do you get a sensible range of adjustment from the frequency controls? What is the maximum frequency from the coarse control if you trim the offset for ~5Hz at the low end with the fine control centred?
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Re: Dunnington 258D build thread

Post by discomicke » Tue Dec 22, 2020 5:22 pm

Thanks for the response.

The range of the coarse know was another thing I which was suspicious to me. It's now goes from 2hz to 60k, which is a bit excessive for making music. I'm using 150K for R103/203.

I'm using an Ornaments & Crime module for calibration and the 12 turn 3224W for tracking adjustment (with R105/205 at 120K). Setting the top oscillator to 16.5hz at 0V gave me right under 500hz for at 6V. This can be calibrated a few hz up using TR103 but still far from 523 where it should be.

What voltage swing should I ideally have coming out of pin 2 of TR103? Would be nice to know if I have an issue before or after the expo converter.

Just want to add that overall this was a really fun build. I hope there are more Dunnington boards coming.

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Re: Dunnington 258D build thread

Post by ikkini » Mon Mar 15, 2021 4:19 am

Hi,

I have a question concerning the BOM, sorry if my question is stupid, I've built a few SMD modules and never had to use that.
In the BOM, a thermally conductive adhesive is listed (https://www.mouser.fr/ProductDetail/590-8329TFF-25ML), what is it for ?

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Re: Dunnington 258D build thread

Post by tarandfeathers » Mon Mar 15, 2021 10:26 am

discomicke wrote:
Tue Dec 22, 2020 5:22 pm
What voltage swing should I ideally have coming out of pin 2 of TR103? Would be nice to know if I have an issue before or after the expo converter.
Sorry, missed this before - I've just measured a fairly well calibrated unit - with the coarse frequency control at minimum, fine control centred, I get 130mV at the wiper of TR*03 on the top oscillator and 110mV on the bottom oscillator. With the coarse frequency control at maximum I get -65mV on the top oscillator and -90mV on the bottom oscillator. These numbers will vary depending on the value of R*03, although the low end should be in the same ballpark if the offset trimmer is adjusted to give ~5Hz.
Just want to add that overall this was a really fun build. I hope there are more Dunnington boards coming.
Thanks! There will be more in due course...
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Re: Dunnington 258D build thread

Post by tarandfeathers » Mon Mar 15, 2021 10:31 am

ikkini wrote:
Mon Mar 15, 2021 4:19 am
Hi,

I have a question concerning the BOM, sorry if my question is stupid, I've built a few SMD modules and never had to use that.
In the BOM, a thermally conductive adhesive is listed (https://www.mouser.fr/ProductDetail/590-8329TFF-25ML), what is it for ?
There is a note next to this line in the BOM - you can apply the epoxy over the top of the PNP transistor pairs and PTC thermistor which will help to keep the parts at the same temperature and reduce the effect of any airflow over the parts inside the case for better stability. It's optional - I don't apply this myself as I have found the stability to be adequate without and it will make the board harder to repair if either of those parts fail.
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Re: Dunnington 258D build thread

Post by ikkini » Mon Mar 22, 2021 6:00 am

Thanks for your reply ! :)

One more question, how do we get polarity of the SOT-363 ? Which side goes to the long line ?

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Re: Dunnington 258D build thread

Post by tarandfeathers » Mon Mar 22, 2021 10:23 am

No problem! Pin 1 of all the SO packages is positioned where the long line on the silkscreen is. This is marked by a dot or line on the package, depending on the manufacturer of the part. For the SOT-363 packages from Diodes Inc, the dot is very small - from memory, the dot should be towards the sprocket holes on the tape, but it's a good idea to check this under good lighting/magnification if necessary.
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Re: Dunnington 258D build thread

Post by haceka » Thu Apr 08, 2021 4:49 am

i buy 60x MMBF201 from mouser and i never get one with a Idss between 0.7 to 1.2mA i just get 0.2 to 0.6mA
i will order maybe 100x other to get the good one's :confused:

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Re: Dunnington 258D build thread

Post by CliffordMilk » Wed May 12, 2021 5:47 am

I have all the components in place apart from the J201s. Is there away I can measure vgs off without investing in a DCA tester? I don’t mind £25 for the adaptor. I’m sure when I built a 258J I got by with a multimeter and a 9v battery, measuring idss.

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Re: Dunnington 258D build thread

Post by tarandfeathers » Wed May 12, 2021 6:00 am

CliffordMilk wrote:
Wed May 12, 2021 5:47 am
I have all the components in place apart from the J201s. Is there away I can measure vgs off without investing in a DCA tester? I don’t mind £25 for the adaptor. I’m sure when I built a 258J I got by with a multimeter and a 9v battery, measuring idss.
You can also measure VGS(off) with a 9V and a multimeter (needs to be from a fairly reputable manufacturer so that you can trust it will have a 10M input resistance). Have a look at this page for a schematic: https://stompville.co.uk/?p=112. You'll see that it's similar to the technique for measuring IDSS but using a voltmeter in the source rather than an ammeter in the drain. The two paramaters are related, so you can use the IDSS method for selection, but the relationship is not 1:1 and the critical characteristic of the JFET in the M & R sine shaper is VGS(off) as this determines how the triangle is clipped which is why I specified that rather than IDSS that Buchla used to select parts for the circuit.
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Re: Dunnington 258D build thread

Post by CliffordMilk » Wed May 12, 2021 8:20 am

Very good to know. Thank you. I shall give it a go :)

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Re: Dunnington 258D build thread

Post by CliffordMilk » Thu May 27, 2021 6:52 am

Does it sound plausible that I’ve measured over 100 J201s from three different suppliers and the closest vgs(off) reading I get is around -0.87? I tried two completely different DMMs and got the same results.

I’m trying the following circuit:
8C6BFA2E-9877-46DE-9E77-7DA3AE3B8A12.jpeg
D6891CFB-0D57-4FAE-AFF9-92012AF469C2.jpeg

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Re: Dunnington 258D build thread

Post by tarandfeathers » Thu May 27, 2021 10:07 am

CliffordMilk wrote:
Thu May 27, 2021 6:52 am
Does it sound plausible that I’ve measured over 100 J201s from three different suppliers and the closest vgs(off) reading I get is around -0.87?
Unfortunately, yes. It's the same with the through hole versions, they tend to congregate at the low end of the spectrum. I did buy a few hundred MMBFJ202s as well as there is some overlap according to the spec sheet but they were all much higher. I would try with the highest ones you found - you'll probably get an okey shape but the level of the sine output might be a bit lower than average.

Edit just to add: I don't recognise the DMM you're using there but it looks fairly cheap/generic - are you confident it has a true 10M input impedance?
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Re: Dunnington 258D build thread

Post by CliffordMilk » Thu May 27, 2021 12:44 pm

Ah - well I did try a different DMM with that in mind but it too is probably cheap and generic. I’ll see if I can test one with the other :)

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Re: Dunnington 258D build thread

Post by cygmu » Thu May 27, 2021 3:02 pm

You could put a large resistor in series with the DMM probe to guarantee that only a tiny current flows.

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