Help needed re tone control misbehaving when volume is not on full throttle

prudd

Hi all,

I have a small issue with my PRS Bernie Marsden. when using either pickup and with the volume (s) on full, the tone control works a treat, however when you roll off the volume (even by the smallest amount) the tone control goes into a sort of secondary volume control mode, losing its tone changing capabilities and just reducing the volume.
I have looked at the wiring and it looks to be OK
I have had this happen on 3 other PRS USA guitars in the past which makes me think it is supposed to happen, all the guitars in question were built from 2008 onwards, never had it on earlier models.

Any ideas and suggestions would be welcome 

ICBM

Can you post a pic of the controls? I would be surprised if they’re meant to do that... but PRS sometimes have some strange ideas!

(Like the deliberate complete lack of shielding for the coil split wiring on some pickups, for example.)

All the PRS guitars I’ve owned or played worked normally, but I haven’t actually come across that many very recent ones.

Rowby1

Isn’t that what a treble bleed cap does? That’s been my experience on all guitars with treble bleed. That’s why none of my guitars have that.

prudd

here you go @ICBM ;

https://i.imgur.com/fuGVzyY.jpg
https://i.imgur.com/XVujQCX.jpg
https://i.imgur.com/qiSlGI7.jpg
https://i.imgur.com/asBgBVm.jpg

thanks for your help.

@Rowby1 ;  

I do remember reading something way back about PRS introducing treble bleed caps, I have had 2  305's and a 2008 Experience 24 that all had the same thing going on. So I might have to look into making changes to the cap.

thank you for your input

ICBM

That does appear to be wired right - although I'm not sure why there appears to be a snipped-off ground wire on the tone pot - but I can see that the cavity is shielded with paint, and there appears to be very little gap, if any, between the pot terminals and the paint. If the one the tone cap is soldered to is touching the paint, even slightly, then it will do what you're describing. (In fact, if it was making a really good contact it would act as a volume even when the volumes are full up.) I would take the tone pot out temporarily and see if the problem stops - just leave it hanging, don't unsolder it - if it does, put pieces of masking tape on the body under where the three pot terminal boards are, volumes as well just to head off any potential issues there, and that should fix it.

prudd

Hi
the snipped-off wire would have originally gone to the bridge as a ground judging from a wiring diagram I found for a Bernie M, the ground to the bridge now comes off of the neck volume pot, not sure why that was changed.
I will give that a go with the tone pot.

cheers

prudd

Took the tone pot out and no different, had a good look around all the wiring and any dodgy contact points, could not see anything that was noticeably wrong. Maybe as @Rowby1 said, it is to with a treble bleed cap, though not sure how to deal with that scenario.

Appreciate your help thus far @ICBM ;

ICBM

There's no treble pass (not "bleed") cap on these.

Can you see what value the tone cap (which is actually a treble bleed...) is? It's not visible in the pic. It will say something like 223 or 473.

Funkfingers

In photographs 1 and 3, the third (normally unused) terminal of the tone pot has solder filling the loop. Within that solder, there is a spiky bit that resembles the end of a wire. Is anything connected to that terminal? If so, where is the other end connected?

Headphones

Is the tone capacitor shorted?  Either by something bridging it or the cap having failed short circuit? 

ICBM

Headphones said:

Is the tone capacitor shorted?  Either by something bridging it or the cap having failed short circuit? 

That would make it work as a volume control even when the volumes are up full. It would have to be only a partial short for it to do what's described, which would be very unusual with that type of cap, and virtually impossible for the exact same fault to exist on several guitars.

@prudd - what are you plugging it into?

sixstringsupplies

For me that solder joint on the volume pot looks cold/fractured. The tone cap looks like it is shorting but if the tone control is working when the volume is on full then this can't be the case.

The issue must be with the volume control. 

prudd

@ICBM  ;what are you plugging it into?........a Roland Blues Cube Artist, but the issue was the same with my old Fuchs ODS30

Thanks for all your comments chaps, I will delve deeper into it later and when I get the time  

Funkfingers

Please take another photograph, from a different angle, looking over the volume pots towards the tone pot.

In an attempt to differentiate between "graphite" paint and black cable insulation, use either flash, a piece of white paper or both.

I reckon that the signal to your tone control currently has two paths to ground when it should only have one.

prudd

Hi all, sincere apologies for not getting back to you, been a mad week.

@ICBM ;  the cap says 2a223j

@funkfingers here are some more pics of the pots, I have had a good look to see if any wires are touching and it all looks OK to me

https://i.imgur.com/299nbtN.jpg
https://i.imgur.com/kteWgoe.jpg
https://i.imgur.com/SwgHFel.jpg
https://i.imgur.com/CFzDvgl.jpg
https://i.imgur.com/p9jTxuf.jpg
https://i.imgur.com/keALE7w.jpg

thanks again for your input on this

ICBM

The cap value is correct.

If you've taken the tone pot out and it did the same, what happens if you take the volume pots out? I still wonder about some contact between the terminals and the shielding paint somewhere.

Funkfingers

Thank you.

You appear to have two white insulated wires going to the middle terminal of the tone pot. Where are the other ends of these two white conductors connected?

ICBM

Funkfingers said:

You appear to have two white insulated wires going to the middle terminal of the tone pot. Where are the other ends of these two white conductors connected?

They will be the switch and the jack. It's a 'Flying V' scheme.

This does have the inherent property that the tone control is downstream of the volumes ("50s" wiring) which can have this effect, but I wouldn't expect it to such a drastic degree as to be effectively a volume control.

Funkfingers

ICBM said:

They should be the switch and the jack. It's a 'Flying V' scheme.

FTFY.

ICBM

Funkfingers said:

FTFY.

Must be, or the rest of it wouldn't work properly.

Funkfingers

prudd said:

I have a small issue with my PRS Bernie Marsden

Q1) Have you owned the guitar from new?

Q2) Have you or any previous owner attempted a Fifties wiring mod?

I am still concerned about the solder in the third terminal on the tone control pot. I do not believe that PRS/World Guitars QC would permit a mistake like that to leave the factory. I reckon that somebody has been meddling.

The tone control should work as is BUT the Gibson Vee/Explorer circuit convention is to connect the capacitor to the centre terminal and the white in/out to the third terminal.