Pot numbering/connecting woes

[znowman]

hi people, just built my second pedal (a rat from ggg.com), and im having pot troubles...

i assumed as you are looking at the pot (with the knob pointing skywards) that the numbering is left to right, as this:


http://hidebehind.com/2C682A

the volume is fine, but the other 2 are working in reverse...

a friend of mine who built the same pedal about a week ago, had exactly the same issue, but after reversing the connection of one of the pots, it cured both of them.  this makes no sense to me, so can anyone please explain (in newbie terms) how this is possible.

ive resoldered one of the pots, but  now i dont get any sound at all, looks like i need to order another few pots from the usa

any help much appreciated as im totally confused - thanks

           

[R.G.]

Quit numbering pot terminals.

IMHO numbering pot terminals is a little silly. What you need to know about pot terminals is:
(a) which terminal is the wiper
(b) which terminal is the contact the wiper contacts when the shaft is rotated fully clockwise (or up for sliders)
(c) which terminal is the one that the wiper contacts when the shaft is fully counter clockwise (or down).

It happens that many pots are standardized these days, so a numbering system makes quasi-sense.

However, there seems to be some movement to call the clockwise pin 1 (or 3), the wiper 2, and the counterclockwise one whatever's left. That's OK if everyone's in on the convention.

But why not simply call them clockwise, wiper, and counterclockwise? Simple, direct, easy to figure out with a DMM, and it calls the pins what you need to know them as.

I habitually use "hot" for clockwise, as in audio signal use, the end the wiper contacts at full clockwise is where the biggest signal is; "cold" for the grounded or counterclockwise end of the pot, and wiper for wiper. It makes no difference to me what the mechanical position of these pins on the pot are at all. I only want to know where the wiper is when it's fully clockwise or counterclockwise.

It used to be common to use a small arrow on the wiper in the schematic to show the direction the wiper moved when turned clockwise (up). That seems to have disappeared in a welter of 1/2/3s that add one more layer of misdirection between you and what you need to know.

But that's just my opinion.   

[Alex C]

Hello, and welcome to the forum!

I'm assuming you're looking at the Rat ("Rodent") schematic here (PDF), and the GGG layout file here (also PDF).

It seems that the layout shows the back of the pots, so as you look at the image, picture the shaft pointing directly away from you on the other side.  When you assemble the circuit, the pot will be upright with the shaft up and the lugs facing you, like in your picture.  In this case, that which is labeled "1" in the layout is counter-clockwise, "2" is the middle/wiper, and "3" is clockwise, which is how they are labeled in the picture you posted as well.

R.G. makes some very good points.  Conventions are great if everyone is aware of them and agrees upon them, but it can often just cause more confusion (much like "A/B" for lin/log pot designations).

-Alex

*EDIT* Now that I look at it, there may be an error in the DRIVE and FILTER connections. The VOLUME control is shown correctly, but DRIVE and FILTER look like the wiper (center lug) is connected to the wrong outer lug. As shown, with the DRIVE control in the counter-clockwise position, the signal sees a high resistance in the feedback loop of the opamp, and with it in the clockwise position, the wiper connects to "3," and there is little resistance, allowing more of the signal to flow around the opamp instead of through it.  This is the opposite of how the control should work; you want more distortion as you turn the control CW.

On the DRIVE and the FILTER pot, connect the wiper/center lug to whichever lug it is not connected to at the moment.

[znowman]

thanks for the reply, so you are basically saying that pots are manufactured to different standards ?

another question i now have is - how can i identify from the ggg.com layouts which is the wiper/clockwise and anticlockwise terminals ?   is it a case of going to the schematic ?

i will read through your reply again tomorrow when ive had some sleep,

thanks again

[znowman]

hi alex, and yes, ive been using that rodent layout (not the schematic)

i originally built the pt-80 delay, and connected the pots up using my assumed theory of numbering left to right (with shaft pointing skywards), the thing that was confusing me was that 2 of the controls worked fine, with only the 'repeats' knob being backwards

now when ive built the rodent, 2 of the controls are backwards and 1 is working correctly

im gonna ignore the numbering on layout drawings from now on

[znowman]

On the DRIVE and the FILTER pot, connect the wiper/center lug to whichever lug it is not connected to at the moment.

i tried that, but now im getting no sound at all      i think i must have cooked the pot and need to order some more.

[Alex C]

thanks for the reply, so you are basically saying that pots are manufactured to different standards ?

Not all pots are manufactured with labeling printed on the terminals; in fact, most are not.  The fault lies not so much with the manufacturers, but with those who design schematics and layouts, and are not mindful of the differences in labeling and numbering standards.  Imagine a car's owner's manual using the term "driver's side door."  If your country's standard is to have the driver on the left, but this vehicle was manufactured in a country where the opposite is true, how do you know which side is being described? Do you go by where you are, or by the standard in the manufacturer's location?

another question i now have is - how can i identify from the ggg.com layouts which is the wiper/clockwise and anticlockwise terminals ?   is it a case of going to the schematic

If the numberings are correct and consistent among all the GGG files, you could associate "1" with CCW, "2" with wiper, and "3" with CW.  But this is not always reliable, as seen here.  A search of the forum turned up several threads noting the mislabeled wiring on the Rodent layout.

If you can understand what each control is doing in the circuit, it's better to look at the schematic first, and think "when I turn this volume control CW, the output sees less resistance to the effected signal, and more resistance to ground.  The output will be higher when I turn the pot CW."

[znowman]

after looking at the diagram for a while, im still unsure about the whole thing, ive marked the schematic with what i think is correct:



does this look ok, or am i still getting this confused

thanks

[Mark Hammer]

It is always possible to figure out which lug should go where by asking yourself "If I move the wiper towards <here>, will there be more, or will there be less, resistance in the way of the signal?"

Also, consider that when a pot is used to adjust gain of an op-amp, the direction that you want to increase resistance will depend on where the pot is located.  When gain is adjusted by resistance in the feedback loop, you want the resistance to increase as you go clockwise.  When gain is adjusted by the resistance to ground from the inverting pin, you want the resistance to decrease as you go clockwise.  So, in the first case, the wiper moves away from the lug where the other connection is, and in the second case it moves towards the lug where the other connection is.

When you use a pot to adjust the corner frequency of a lowpass filter, as in the Rodent/Rat or with the SWTC, decreasing the resistance will raise the frequency where the filtering begins (i.e., let more treble remain in the signal), so you'll want to wire the pot so that rotating it clockwise decreases resistance.

Of course, the tricky part is really more one of imagining the front of the pot while looking at the back of it to solder the wires.

[theundeadelvis]

My method has always been wire the pot the "wrong" way first and then have to switch the outer two wires. Never intentionally, but it always seems to work this way.  I need to adopt RG's method of testing the pot first. 

[DougH]

I never understood the use of a numbering "convention" for this either, especially when it's not consistent. And when it's not consistent, it serves no purpose other than to confuse. Learn to buzz out your pots with a meter, as R.G. mentioned. Then wire it up using common sense (when you turn the volume/gain up all the way, the wiper should touch the "hot" or "clockwise" lug). No need for numbering conventions or arrows (although arrows can be helpful)- Done. Another hint- Alpha 24mm and 16mm pots (which a lot of people use in their diy pedal builds) are consistent as to which lug is which. Once you figure one out you can pretty much follow the same convention for the rest of your build.

[culturejam]

My method has always been wire the pot the "wrong" way first and then have to switch the outer two wires. Never intentionally, but it always seems to work this way.

This is my method as well. Works every time. 

[znowman]

ive worked in the electricity industry for over 10 years now, so im used to having standards on how everything is done, for example, when im looking at a panel of switches, things are labelled left to right - i need to get these conventions out of my head

now ive got the idea of not thinking of the lugs as numbered in any way, my only problem is following the signal path.  i need to study more about how electronic circuits work i rekon        

in my job, system diagrams are part of my daily job, but open points are the only interest we have in electrical flow (but i only work on 11kv upwards)

anyway, thanks again for the help, i will get there in the end