Tone reversed on DIY Fulltone OCD

[justfine99]

Hi guys

First post on here and I'm done trying to figure out what I did wrong 

Basically my OCD clone came out pretty darn good and sounds amazing, although I have one small issue, the "tone" knob is working in reverse, in other words when I turn it clockwise I get the high cut instead of the high boost and vice versa when turning counter clockwise.

Any idea what I did.wrong?

Any advice will be appreciated

[GibsonGM]

Swap the outer wires on the tone control pot, and it will work the opposite way from what it's doing now. 

Welcome to the forum!   

[justfine99]

Thanks GibsonGM

But I tried that and it did exactly the same thing... so I'm pretty mind boggled at this stage

[Kipper4]

According to this schematic

http://www.wiringdiagrams.org/wiring/fulltone-ocd-version-1-4-schematics.html

The tone pot is wired as a variable resistor.

So if you wired the outside lug to the centre(wiper) try it wiper wired to the other outer lug.

Welcome.

[justfine99]

Hey Kipper4

I was thinking about trying that so will give it a go

Will keep you updated!

[Mark Hammer]

The tone pot and cap form a lowpass filter according to the formula Freq = 1 / (2 * pi * R * C).  The smaller either R or C gets, the higher the frequency of the roloff point.  So what you want to do is wire the pot such that its resistance always gets smaller as you turn clockwise.

One of the traditional practices when wiring up a pot as simply a variable resistance is to connect the wiper to one of the outside lugs.  This is done asa sort of failsafe practice, for reasons I won"t get into now.  But the implication is that if your tone pot was wired up that way, it would still work "opposite", unless youchanged where the wiper was connected to.

As an aside, the Proco RAT has their tone controlwired up so that it works "opposite", rolling off more ighs as you go clockwise.  I'm guessing that's why they decided to legend it as "Filter", sothat customers wouldn't expect it to work like "normal Tone controls usually do.

[Ben Lyman]

Kipper nailed it, when a pot is wired as variable like that but operates in reverse of that which is desired, just connect the wiper (middle) to the other outer lug...
or simply label it "FILTER"  and leave it as it is
welcome aboard!

[justfine99]

Hi All

Once again for everyone's advice!

I went to go have a look at the manual of the OCD and it is actually meant to work in "reverse"
So as Mark explained, it is actually a "filter" and not a traditional "tone" knob.

I did gain some valuable knowledge though knowing now that if I connected the wiper to the other outer lug it would change
to the more traditional setting.

Thanks to everyone that cleared things up for me!

[GibsonGM]

LOL, the version I found was the "Super OCD".  Totally different tone control.   Obviously the schematic Kipper posted was the correct one.

Check this out:  http://1.bp.blogspot.com/-mdmZKzXJusA/T00EjAPiDyI/AAAAAAAABA8/gwhJo9nX90Y/s1600/briggs_super_ocd.jpg

My bad, I assumed it would be similar, and it's not.  Doh.   

[justfine99]

No stress GibsonGM 

[anotherjim]

I found one variation where the tone pot was the only one with the direction drawn in a clockwise=brighter fashion. Gain and Volume were both shown backwards!

Sometimes though, backwards is deliberate to suit a log taper pot to save the cost/bother of buying in anti-log taper. Call it a "Tone" control and not a "Treble control". It isn't lying then if clockwise don't mean more treble.
The true cowards/cheap way out is to use ordinary linear taper and live with a lack of response in part of the controls sweep.

[Mark Hammer]

ALL "tone" controls are filters of one kind or another.  The two most omnipresent distortion pedals when the RAT came out were likely the TS-9/SD-1 and the Big Muff, both of which tend to emphasize treble at one end of the Tone.  The Rat Filter conrol doesn't emphasize anything; it merely allows all, or amounts less than all, of the treble to reach the output.  That's why I think Proco chose to call it "Filter".  Wiring it so that it rolls off more as you rotate clockwise, OR so that it opens up as you rotate clockwise, doesn't change what it actually does, just the direction you need to turn to get what you want.

Where direction does matter is the extent to which it complements the taper of the pot used for the tone control.  You want the pot taper and wiring of the pot to work with each other not against.

[Kipper4]

Kipper nailed it, when a pot is wired as variable like that but operates in reverse of that which is desired, just connect the wiper (middle) to the other outer lug...
or simply label it "FILTER"  and leave it as it is
welcome aboard!

A trick I learnt from you my friend.

[highwater]

Kipper nailed it, when a pot is wired as variable like that but operates in reverse of that which is desired, just connect the wiper (middle) to the other outer lug...
or simply label it "FILTER"  and leave it as it is
welcome aboard!

That same trick works if you can't find a 1Meg reverse-log pot for a Distortion+ - wire a normal 1Meg log backwards and label it "Clean".