NBD ends in tears... how do I fix the volume pot?

[polvo]

Just picked up a second hand bass, tested it out and it was all working fine. And then I went into idiot mode. 

I decided to switch out the volume knob, but the knob was really stiff and hard to lift off the bass (me being an idiot, I only noticed the little screw in the side afterwards). I managed to get it off... but something has come loose and now there's no sound coming from the bass at all.

A few other symptoms...

The volume knob just keeps turning now, it has no minimum or maximum.

The internal part of the volume knob (don't what this bit is called) can now lift up or push back into the bass. I'm assuming it should just be staying pushed down?

 

 

 

The volume pot inside the bass has also come a bit loose. All the wires still seem to be connected but it has a bit of wiggle which none of the other pots have.

 

I think I must have just pulled something loose... any ideas how to fix this?

I'll take it to a tech if I have to, but would like to have a go at fixing it myself. If this is a risky procedure I have a crap £10 guitar I can experiment on first...

 

 

 

 

 

 

 

 

[PaulThePlug]

New pot... simples.

Have the cover of the back and see what it is? A250k vol log pot, solid shaft... what make Guitar and Pot?

Full Size or Mini? Post a pic of the gubbins inside the cavity.

Edited January 3, 2023 by PaulThePlug

[polvo]

Just now, PaulThePlug said:

New pot... simples.

Have the cover of the back and see what it is? A250k vol log pot, solid shaft... what make Guitar and Pot?

 

 

All it says on the back is 'A'

 

 

 

The bass is a Cort Artisan B4, so I'll do some digging online and see if I can find any specs about what kind of replacement pot I need.

 

 

 

 

[PaulThePlug]

Alpha, made in Korea.

If you undo the nut on the top, and push it thru, should have the value on the underneath... Active with Mk1 Barts? Similar to Ibanez SR500/600...

 

B500K ?

Edited January 3, 2023 by PaulThePlug

[polvo]

32 minutes ago, PaulThePlug said:

Alpha, made in Korea.

If you undo the nut on the top, and push it thru, should have the value on the underneath... Active with Mk1 Barts? Similar to Ibanez SR500/600...

 

Sweet, got it, thanks!  It's a B250. Now just need to figure out if it's short/medium/long shaft length, but I'll check with the ebay seller about that.

 

On another note, the ebay advert says "I would check what pots you have installed first before you choose your replacements. Most bass guitars are actually fitted with all A250K pots as with an audio taper the treble is decreased much later in the turn of the knob proving more useful for bass players". I'm curious what basschatters think... is there any advantage to the taper instead of linear? I would have thought linear is better - I'd rather my volume knob only controls volume, so I can EQ separately.

 

 

 

 

 

 

[SamIAm]

A B250 is a linear 250KOhm pot, where your ebay seller talks about the treble changes they are referring to a passive tone pot so is not applicable here (your bass has active EQ with 3 separate tone controls).

 

As your pot goes through the body of the guitar, I'd guess it to be a long shaft pot, but measure the length of the bit that has a screw thread on it and it will likely be about 10mm (short) or 19mm (long) and get a replacement that has the same length ... also worth checking the diameter of the threaded section is the same.

 

Also make sure you get a smooth shaft rather than a grooved shaft.

 

Thomann have a quite good article about pots

 

S'manth x

[tauzero]

It seems odd that it's a B250 as that's a linear pot, so not very good for volume control (the sensitivity of the ear has a logarithmic response). Although the schematic for the B4 shows it as a B500:

 

 

Unless this is one of the revamped B4s (Element?) in which case looking at Bartolini's circuit diagrams might be more useful.

 

[polvo]

I've ended up buying a logarithmic pot as a replacement, from what I've read online that sounds like a better choice for me. 

 

Decided to stick with 250, since that's what was in it originally (unless the previous owner replaced it at some point).

 

35 minutes ago, tauzero said:

It seems odd that it's a B250 as that's a linear pot, so not very good for volume control (the sensitivity of the ear has a logarithmic response). Although the schematic for the B4 shows it as a B500:

 

 

Unless this is one of the revamped B4s (Element?) in which case looking at Bartolini's circuit diagrams might be more useful.

 

 

This is really useful, thank you! Where did you get this from? And which model is this for specifically?

 

Mine is a B4 Plus AS RM.

 

 

[itu]

2 hours ago, tauzero said:

It seems odd that it's a B250 as that's a linear pot...

 

If it is a linear:

https://www.alphapotentiometers.net/html/taper_curves.html

 

A means audio except B means logarithmic depending on the manufacturer. European and American companies use same alphabets - and every now and then different meanings. Standard would be very nice, but we lack a global one.

[tauzero]

3 hours ago, polvo said:

This is really useful, thank you! Where did you get this from? And which model is this for specifically?

 

Mine is a B4 Plus AS RM.

 

Just did an image search for "cort b4 schematic" - I use DuckDuckGo but Google should get the same. I think that the list in the top left corners is the list of instruments that it's applicable to.