Make Cheap but quality Stepped pot

[zayance]

Thanks again for the kind words.

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.

Yes i tought so also, not much outer size added, the strict minimum.

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.

There is also tons of offers on Evilbay like this, it's actually one of them that made me think of this PCB, some had the SMD resistor soldered across the pot legs, tricky but doable...
This helps you get a "budget" goldpoint switch in a way, use 0.1% resistors and there you have it, and has a "practice facility" imbedded , and it's way easier to solder, believe me .
Since it's DIY friendly, you can make yourself precision log pots with values of your choice and you can also add stops, drilling a hole and adding a Resistor leg and a drop of crazy glue, will show some pics of how Dagoose came with this nice idea as well.
Of course the overall price is more than 18$ for a Stereo pot, but you'll use higher quality resistors, well if this is an important factor for you?

 

[kato]

No comparison. I just happened upon that post the same day I read this thread and mistakenly thought it was a newly available thing. (I'd looked at Goldpoints before.)

Even the author who wrote that blog post says the resistors are not closely matched, so if I were going to build a pair, I'd choose yours even if they were twice the price. Sorry I shouldn't have posted that. I assume it goes without saying a DIY community project trumps cut rate chinese crap any day of the week.  :-X

 

[Sylvain D.]

No comparison. I just happened upon that post the same day I read this thread and mistakenly thought it was a newly available thing. (I'd looked at Goldpoints before.)

Even the author who wrote that blog post says the resistors are not closely matched, so if I were going to build a pair, I'd choose yours even if they were twice the price. Sorry I shouldn't have posted that. I assume it goes without saying a DIY community project trumps cut rate chinese crap any day of the week.  :-X

Ditto 

 

[zayance]

No comparison. I just happened upon that post the same day I read this thread and mistakenly thought it was a newly available thing. (I'd looked at Goldpoints before.)

Even the author who wrote that blog post says the resistors are not closely matched, so if I were going to build a pair, I'd choose yours even if they were twice the price. Sorry I shouldn't have posted that. I assume it goes without saying a DIY community project trumps cut rate chinese crap any day of the week.  :-X

Hey no prob man, you can post whatever you want, freedom of speech, and i wasn't taking this as an offense or whatever really.
I was just giving an answer  8)

 

[druu]

Bump!

 

[gswan]

Note that the Johnson noise from SMD resistors will be higher for the same value of a good metal film leaded component. Not a problem for line levels, but if you use one of these stepped switches in a high gain mic pre then the difference will be audible.

 

[pasdesignal]

Note that the Johnson noise from SMD resistors will be higher for the same value of a good metal film leaded component. Not a problem for line levels, but if you use one of these stepped switches in a high gain mic pre then the difference will be audible.

What evidence is there of this?

 

[gswan]

Note that the Johnson noise from SMD resistors will be higher for the same value of a good metal film leaded component. Not a problem for line levels, but if you use one of these stepped switches in a high gain mic pre then the difference will be audible.

What evidence is there of this?

Sorry, should have said excess noise, not Johnson noise. Johnson noise is dependent on R value, the higher the R the greater the noise. Excess noise is dependent on the resistor material characteristics, and is proportional to any DC voltage across it. Carbon composition are the worst, and wirewound have none. Good leaded metal film resistors have approx 0.05uV/V, whereas thick film SMD resistors have 1-10uV/V.

 

[zayance]

I propose using Thin Film not Thick film, i guess these are better.
Reply#7

 

[gswan]

Yes, or metal foil. You can also get wirewound SMD resistors too, for ultimate luxury, but I'm not sure of the resistance range available or the size.

 

[Rochey]

Note that the Johnson noise from SMD resistors will be higher for the same value of a good metal film leaded component. Not a problem for line levels, but if you use one of these stepped switches in a high gain mic pre then the difference will be audible.

What evidence is there of this?

Sorry, should have said excess noise, not Johnson noise. Johnson noise is dependent on R value, the higher the R the greater the noise. Excess noise is dependent on the resistor material characteristics, and is proportional to any DC voltage across it. Carbon composition are the worst, and wirewound have none. Good leaded metal film resistors have approx 0.05uV/V, whereas thick film SMD resistors have 1-10uV/V.

Where do you get rthose values from, datasheet? What spec?

 

[gswan]

Where do you get rthose values from, datasheet? What spec?

Data sheets.

 

[zayance]

You have a current noise graph on the TNPW series datasheet, the 1206 package beeing better in performance.
No graph on the IRC ones tough, but i guess similar or maybe even better.

 

[Ptownkid]

Wow...pretty impressive Tony! Well done.

 

[zayance]

Allright sometime ago someone over here asked for some pictures of how to add a stop pin to these pots
as i previously mentionned doing it going with the nice idea that the forum member "dagoose" had posted before, thanks to him.

Anyway here it is for who would be interested, it's not much complicated and it's pretty much something you could figure out yourself,
but here is how i'm doing it, it just needs a little care........

I'll make a pot to Stop at position 21 (if you count first step all the way down).

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Tools needed:

1x drill
1x Vise
1x HSS bit, i used a 1.5mm bit that was the smallest one i had in stock
1x Crazy glue
1x Diode leg preferably of the same size as the drill, so the stop pin seats tightely in the hole.

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1- You need to check which pin is number 1 as seen on picture, and draw a long line including all discs blue and white with it (helps assembly)

2- Then dismantle the pot, adding discs on sandwish right next to it, if you're afraid to loose track

As you can see on the blue rings (white ring as well) there is little round dots, one on each opposite sides, this gives you direction of assembly.

Now what if this little Sliding pin gets out of the inner white disk?
Well you got to understand that the sliding pin has two sides, one has two dots (as seen on picture) the other one is at about 35 - 40° up when assembled.
The double dot side goes on the plain disc, while the other angled one goes on the dented disk as seen on picture below (right side).

3- After all disc dismantled you should be left with this part (picture below).

As you can see i've marked for the sake of the pictures the first step, wich is all the way down, and the 20th step, where we need to drill our hole.
For identifying step 20, well the pot still has its steps, so count to 20 turning the pot, or count to 21 if you include the step all the way down.
After that add a small dot right after the little metal finger as seen on picture, NOT BEFORE!!

And here is where we're going to drill our hole  8)

For drilling this, use a vice, and try to drill slowly and as vertical as parralel as possible to the axis.
You'll likely drill a trench on the white plastic, but that's ok, as it will help keeping the stop pin in place.
Here is our hole at right position now.

Take your Diode leg, and cut its length for making it enough to be in the trench and right at the metal finger inside the pot,
don't have to go further the finger or the white plastic on the other side, as seen on here:

Add just little dots of crazy glue in the trench NOT MUCH, as plastic doesn't like much crazy glue, and fit your Stop pin,  making sure it doesn't go too far in the inside of the pot.
Press the pin on the trench a couple of seconds, and make sure that the crazy glue got the pin tightly fitted and you're done.

VOILA, our stop pin is installed and at correct position.

AND if you were to use the SMD Mounting PCB's then you would leave 3 resistors OUT for this example.

T.

 

[pasdesignal]

G'dday Zayance,

Do you think it is possible to implement a certain variation on this design?

I was thinking an improvement would be a version which uses smaller resistors and doesn't extend the diameter of the switch beyond the original pins? So that means a slightly smaller pcb, and resistors obviously stepped down a size to accommodate this change.

I'm not asking you to do it, but interested in your thoughts of how hard that would be.

A 1U enclosure can have as little as 38mm clearance height internally. Its a squeeze just to get these switches in as they are, thats what has prompted my query.

Interested to hear you thoughts....

 

[dandeurloo]

very cool!

 

[zayance]

G'dday Zayance,

Do you think it is possible to implement a certain variation on this design?

I was thinking an improvement would be a version which uses smaller resistors and doesn't extend the diameter of the switch beyond the original pins? So that means a slightly smaller pcb, and resistors obviously stepped down a size to accommodate this change.

I'm not asking you to do it, but interested in your thoughts of how hard that would be.

A 1U enclosure can have as little as 38mm clearance height internally. Its a squeeze just to get these switches in as they are, thats what has prompted my query.

Interested to hear you thoughts....

That was my first drawing, using 0805 resistors, and diameter was a little less. But as mentionned earlier and as i had noticed, noise is a little more on those 0805.
NOW it's still possible to use 0805 package on the PCB, the 1206 pads are big enough to accomodate them.
So theorically you can use 0805 here and file or cut the excess on the extrems (beeing carefull not to cut the track) for allowing it to pass in a 1U configuration. Just an idea...

But as i said earlier, i didn't wanted the PCB to sit too tight on the pot, so..... it would be possible to shring the thing a little more, jut by orienting the
resistors so that the ring could be a little less width. When the PCB's i have in stock will be used and out, i could redesign this thing just taking like 3mm away (well try),
and fab these, will see....


T.

 

[zayance]

I'll be ordering some shrinked out board for me to fit 1U or whatever tight space,
they'll have 37mm diameter, wich is the diameter of the pot itself including the solder eyelets.
They'll use 1206 resistors as well.
Will post some pics when here for if curious.


T.

 

[zayance]

So smaller version, 37mm Max diameter. (small mistake on the silk, but nothing catastrophic)
Have some stock for these, and a little left for the other if some would be interested.