Make Cheap but quality Stepped pot

[zayance]

Hi there,

I've been using, as most guys around here when going stepped, those that Uraltone sells as seen here:
http://uraltone.com/kauppa/product_...--2x24.html&XTCsid=qmeg0cc5g0cvbe2j9v6foqpke3
And as most know it's a time killer and a PITA to solder those resistors around, get the right values within 0.1% if need precision etc....
So the day i came across them i also saw that some evilbay sellers were proposing some already assembled with smd resistors one...Pin to pin soldering, doable, but needs some care....
And it got me thinking why not make a pcb that would help soldering those 0805 0.1% resistors onto the pot itself. EDIT: maybe 1206 size resistors
The idea would be to first solder the resistors on the PCB, dismantle the pot, solder the round pcb to the pins and voila, wire directly on pins also...
Of course people that are afraid of those Evil SMD parts would backup, but it's actually faster to solder 0805 and even simpler for 1206 ones compared to thrue hole when you get your marks. And 0.1% gets that matching job away...


But anyway, i've designed a PCB that would fit the pot, i'm still checking some things to do, but i'll be ordering a couple just for my needs i think, more if people could be interested? and this will actually maybe help me think of finalising the Stereo Sontec in a more "Mastering" level, using all 0.1% resistors ala goldpoint, but you can call this cheaperpoint haha...
Well didn't get into the numbers still, but it could be cheaper than Goldpoints.

It would be a 1.2mm thick PCB, there is a little triangle marking place, where it's possible to write down the configuration of the resistor net to keep track before soldering them in place.

What do you think?
Any ideas or comments are welcome.




LINK TO SOME PICTURES: (Sorry for late update for the lost pictures)
https://drive.google.com/drive/folders/1zGdTFAMMRt3AyrUj6HaDQcWR__p0bEZj

 

[mrclunk]

Sound like a great idea.

Not sure i understand how the resistors are fitted.
Is the red pad the smd resistor and the green pad the link to the switch solder lug? Blue being the pcb traces?

Also what about if the pcb was in two pieces so we wouldn't have to disassemble the switch?
It could clasp round the switch with a couple of links.

 

[zayance]

Not sure i understand how the resistors are fitted.
Is the red pad the smd resistor and the green pad the link to the switch solder lug? Blue being the pcb traces?

The red pad is the pad for soldering the Pot pins to it.
The green pad is a Via inside this red pad that allows connection of the SMD resistors fitted at bottom/Back of PCB, you can see two blue pads under the big rad one, that's the 0805 resistor.
EDIT: Actually maybe 1206 size resistors, bigger ones....
And yes blue is the PCB traces.

Also what about if the pcb was in two pieces so we wouldn't have to disassemble the switch?
It could clasp round the switch with a couple of links.

Yes that was my first drawing actually, But the pot is so easy to disassemble and assemble that it's cleaner i think this way, and avoid any links to add etc....
But yes it's possible... could add a couple of drills to make it possible to separate if needed....


EDIT: And one important point to keep in mind, is that those stepped pots, don't have any stop pins, so if you want to make a stop anywhere before the 24steps (23effectively), you'll need to drill a hole and add a resistor leg or so, add some crazy glue and done. As Dagoose had done for making his stepped pots for his Sontec Mastering Version.
It's seems hard but it's really simple with some care (can show some pictures of how to), that's why since people might add a stop, then that means disassemble all the pot and reassemble etc... so.....
At the end not a plug and play type of pot, but hey, you can't have all options cheaper in this world hahaha

 

[JohnRoberts]

I don't know if I have the old data sheets but I vaguely recall alps making a commercial part using a rotary pot wiper to tap a resistor divider string.. this was decades ago long before SMD was common and IIRC more than 30 steps. .

I would consider using the larger R's (1206?) as some small Rs have been found to exhibit measurable distortion.

JR

 

[zayance]

I would consider using the larger R's (1206?) as some small Rs have been found to exhibit measurable distortion.

Yes i actually had corrected my post saying , maybe better go for 1206 size. AND it Would be even more DIY friendly.
Thanks for feedback.

 

[volker]

Cool idea! Even though I must say I quite enjoy the match-and-solder-meditation most of the times .

 

[12volts]

Tony I'd like to commit to buying 10+ boards, any estimates on price??


Frank B.

 

[zayance]

Cool idea! Even though I must say I quite enjoy the match-and-solder-meditation most of the times .

Thanks. Well it's still possible to buy 1% resistors hahaha, cheaper also....

Tony I'd like to commit to buying 10+ boards, any estimates on price??

Well i'm on it, depends on the total number as always, but maybe 3 - 4 Euros max, but gotta make sure all this.
Don't want to make it too expensive for spending the money on the important things.
I might jump and do a bigger run, i was going to make 40 for me, for getting price down, so.....
If people could be interested, then drop a line here, and so i can have a better idea of all this.

The PCB now has 1206 resistors, will tweak a couple of things and i'll put my order i think.


EDIT: For getting a better idea of a total cost of a DIY pot.

Here is the list of 0.1% Vishay TNPW series resistor, they are most at 0.7Euros (0.9$)
http://fr.mouser.com/Search/Refine.aspx?FS=TRUE&N=4294759685+12549316+4294578029+4292707030+4292893182+4292586304+4292870952+4294741774+1323043

Or IRC brand resistors (same brand used in Golpoint switches):
http://fr.mouser.com/IRC/Passive-Components/Resistors/Surface-Mount-Resistors/Thin-Film-Resistors/_/N-7h7z1?P=1yzvlkuZ1z0vpm5Z1z0znqlZ1z0wdws&Keyword=IRC&FS=True

The pots are sold by Uraltone as on my first link, so you have their price there... (i remember getting them cheaper with an Evilbay selller i can't find anymore :/)

Would give a total of about 30Euros for a switch with one deck fitted, about 50Euros with the second deck.
That's way less than Goldpoint, the switches are not Elma's of course, but they're not bad...
Fitted with 0.1% resistors. Can still use 1% ones, would be cheaper, up to you and your Zen 


Thanks.

 

[zayance]

I did some mods and corrections on the PCB, i think it's good to go.

Anybody other than me and Frank (maybe)  might be interested?

EDITED: Center coin is now a Try out space, 1206 on one side, 0805 on the other, added 0603 AND 0402 for those who would like to play a little hahaha  ,
Anyway this would help you get your marks before soldering those expensive resistors, just use cheap 1% ones there.....

 

[zayance]

Depending on quantity, but it would make 2.5 Euros for a board for one deck.

Will wait a couple of days, and if no interest, i'll order the ones i needs and some spares.



Thanks.

 

[zayance]

Got the PCB's.

They look as expected.

I have some spares, so If some would be interested let me know by PM.

I forgot to mention that they have a Max Diameter on Pot of 40mm sharp, so i guess would fit in 1U, but tight, could be possible to file a little of the edges if needed,
Didn't wanted to make the ring to sit too tightly on the pot so.....




Overview, front and back, with front having blank Corners for writing specs.

Resistor Soldering, center coin try out, used 1206, and some 0603 ones i had in hand.

Dismantling center coin by carefully twisting it, or cut and file the excess to make a nice round shape.

Marking Step 1 Of Rotary Pot using Continuity check on DMM

Dismantling rotary Pot

Adding Rotary Disk on PCB, Step 1 previously marked going to Step 1 of PCB

Soldering the Rotary Disk Legs, NO TURNING BACK HERE!!, so must Double check

Reassembling Switch with Correct PCB Resistor net made, and on the Step 1 Mark.

Rotary Overview Fitted front, you can cut the corners at the end.

Rotary Overview Fitted Back

 

[Marcocet]

They look great!

 

[kazper]

Message sent, great idea.

 

[zebra50]

Hey Tony,

This is great work, and a good budget alternative to the goldpoint switches. Nice!

 

[radiance]

Splendid work!

 

[Sylvain D.]

Whoa Zayance,

Quelle idée!

Well done!

 

[zayance]

Merci Messieurs  .

 

[rafafredd]

speechless! Quality DIY!

 

[dagoose]

Brilliant!
And i think that the thing we talked about (outer size) will not be much of an issue really. I thought that it would stick out more then it actually does.

 

[kato]

Recently came across this post that might interest:

DIY Stepped Attenuator Volume Control.  Prebuilt for $18. Seems impossible.

BTW Nice design Zayance, yours is infinitely cooler.