Tone Control U/S

JezWynd · May 2023

Recently picked up an old EKO bass and I find that the tone control is having no effect at all. Can the likely cause of the fault be diagnosed from this pic - Tone control is the pot in the centre and it rotates smoothy and evenly.

Any tips or advice gratefully received.

ICBM · May 2023

Is the cap lead on the right touching the edge of the pot casing?

stickyfiddle · May 2023

ICBM said:

Is the cap lead on the right touching the edge of the pot casing?

That was my first thought. Otherwise could just be a dead pot

JezWynd · May 2023

ICBM said:

Is the cap lead on the right touching the edge of the pot casing?

No, it's not. It's very close and I've eased it further away from pot but still no Tonal adjustment possible. I notice that when I sweep the Tone pot I get a small amount of amplified scratch noise, would this indicate that the pot is working and it must therefore be the capacitor at fault?

ICBM · May 2023

JezWynd said:

I notice that when I sweep the Tone pot I get a small amount of amplified scratch noise, would this indicate that the pot is working and it must therefore be the capacitor at fault?

No - if the cap is faulty you would most likely get no noise, since then the tone pot would be out of the circuit. The cap can't be shorted either, since then the tone would act as another volume.

First check the solder joint to the cap on the volume pot that we can't see, since that's a possibility.

If that's OK, try shorting from the right lead of the cap to the ground wire - ie bypassing the tone pot - if that works, the cap is OK and the pot is dead. You could try soaking some contact cleaner into it - even though it's an enclosed type, they're not well sealed and it will penetrate.

JezWynd · May 2023

ICBM said:

JezWynd said:

I notice that when I sweep the Tone pot I get a small amount of amplified scratch noise, would this indicate that the pot is working and it must therefore be the capacitor at fault?

No - if the cap is faulty you would most likely get no noise, since then the tone pot would be out of the circuit. The cap can't be shorted either, since then the tone would act as another volume.

First check the solder joint to the cap on the volume pot that we can't see, since that's a possibility.

If that's OK, try shorting from the right lead of the cap to the ground wire - ie bypassing the tone pot - if that works, the cap is OK and the pot is dead. You could try soaking some contact cleaner into it - even though it's an enclosed type, they're not well sealed and it will penetrate.

Thanks for the suggestions. I've tried some contact cleaner without any improvement and the solder joints all look good. I think it may be the pot that is the problem - it has a much less drag on it than the identical volume pot (which works fine). I've ordered a 250k linear as a replacement (can't see any ident on the original). I'm uncertain as to how I should solder the replacement as the three contacts are very different in the replacement. Is there a common order for the three legs? Looking at the original it looks as if I just need to know which is the ground leg on the replacement, as the other two are linked together.

ICBM · May 2023

You need a Log pot for tone, not linear. It will still work, but all the range will be at the bottom end.

It’s wired slightly unconventionally with the two legs joined, but you can do it like any standard tone control. The one that needs to be grounded is the right hand one if you’re looking down onto the back of the pot with the terminals facing you.

JezWynd · May 2023

ICBM said:

You need a Log pot for tone, not linear. It will still work, but all the range will be at the bottom end.

Oh dear! I ordered it from an eBay site where they stated - The Log A pots are usually used as volume controls and the Linear B pots are usually used as tone controls.

I'll use this one for now and if it's too noticeable I might get the matching volume pot and replace both. Thanks for the info re the legs.

Funkfingers · May 2023

Linear (B or, sometimes, D) taper tone controls are what I associate with budget SE Asian instruments. Where there is any brand name marked, it is often CorTek.

ICBM · May 2023

JezWynd said:

Oh dear! I ordered it from an eBay site where they stated - The Log A pots are usually used as volume controls and the Linear B pots are usually used as tone controls.

Unfortunately that misinformation is repeated in many places on the net, and it’s forgivable for you to have been tripped up by it.

Tone controls should always be Log for proper operation*, volume can be Log or linear depending on your preference for how it rolls back from full-up to halfway - in fact for bass where you’re almost always using it as an actual volume control rather than an overdrive control for an amp, Lin is often better.

(*Unless you deliberately want all the range in the bottom quarter turn for a ‘hand wah’ type effect.)

JezWynd · May 2023

ICBM said:

JezWynd said:

Oh dear! I ordered it from an eBay site where they stated - The Log A pots are usually used as volume controls and the Linear B pots are usually used as tone controls.

Unfortunately that misinformation is repeated in many places on the net, and it’s forgivable for you to have been tripped up by it.

Tone controls should always be Log for proper operation*, volume can be Log or linear depending on your preference for how it rolls back from full-up to halfway - in fact for bass where you’re almost always using it as an actual volume control rather than an overdrive control for an amp, Lin is often better.

(*Unless you deliberately want all the range in the bottom quarter turn for a ‘hand wah’ type effect.)

I have to confess to being very confused about Log vs Linear. I presumed that linear means an even variation in Tone and Volume over the entire travel of the pot while Log refers to a variation that is greater at one end of the travel. If this is so then Linear seems to make sense for Volume and Tone for bass; or is it that we perceive the two things differently. I'll have to do some. reading up to get a better understanding.

ICBM · May 2023

JezWynd said:

I have to confess to being very confused about Log vs Linear. I presumed that linear means an even variation in Tone and Volume over the entire travel of the pot while Log refers to a variation that is greater at one end of the travel. If this is so then Linear seems to make sense for Volume and Tone for bass; or is it that we perceive the two things differently. I'll have to do some. reading up to get a better understanding.

It's not as simple as that - yes, linear is an even change in resistance as you turn it, and Log is progressively faster as you go up - but the way they interact with the circuit and your hearing means that Log gives what sounds like an even taper for tone. For volume, 'audio taper' (a type of Log) was originally designed for hi-fi volume controls since that's also how the ear perceives volume changes in a full-programme sound, but it doesn't work as well for an individual instrument volume - although it comes into its own when you're using it to control the *gain* of an overdriven amp.

The 'Log for volume, Linear for tone' thing is quite widespread, but all I can say is that anyone who has ever tried it both ways round will agree that Log is best for tone

. Volumes can definitely be both, it's a matter of preference and application, but I would generally say that for bass or clean guitar, linear is better.

JezWynd · May 2023

ICBM said:

JezWynd said:

I have to confess to being very confused about Log vs Linear. I presumed that linear means an even variation in Tone and Volume over the entire travel of the pot while Log refers to a variation that is greater at one end of the travel. If this is so then Linear seems to make sense for Volume and Tone for bass; or is it that we perceive the two things differently. I'll have to do some. reading up to get a better understanding.

It's not as simple as that - yes, linear is an even change in resistance as you turn it, and Log is progressively faster as you go up - but the way they interact with the circuit and your hearing means that Log gives what sounds like an even taper for tone. For volume, 'audio taper' (a type of Log) was originally designed for hi-fi volume controls since that's also how the ear perceives volume changes in a full-programme sound, but it doesn't work as well for an individual instrument volume - although it comes into its own when you're using it to control the *gain* of an overdriven amp.

The 'Log for volume, Linear for tone' thing is quite widespread, but all I can say is that anyone who has ever tried it both ways round will agree that Log is best for tone . Volumes can definitely be both, it's a matter of preference and application, but I would generally say that for bass or clean guitar, linear is better.

Thank you, that makes sense.

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