Treble bleed mod not as expected. Advice please.

neilgregson

Hi there,

I recently sold a Suhr Classic but loved the treble bleed it I’d as standard and wanted to replicate that circuit in other guitars. I contacted Suhr (whose customer service is amazing by the way) and they provided me with the following wiring diagram:

https://m.box.com/shared_item/https%3A%2F%2Fsuhr.app.box.com%2Fs%2Fr6blfr2e1pvd5ljzb5mxujperz9d703s

I passed this to my man who does my mods and he completed them as per the diagram, however it doesn’t sound right to me at all. 

I have a PRS S2 Singlecut with a SD 59 in the bridge and a Jazz in the neck. The problem is that as I turn the volume pot down with gain on (I play mostly rock) it doesn’t get cleaner like my other guitars, instead it stays almost as gainy until about 1 or 2 on the pot, but loses some high and low frequencies instead. For reference on my other guitars with treble bleed mod on the settings I use it would get edge of breakup clean at about 5 on the pot, but this just seems to get darker, not cleaner. 

If my description has made any sense, has anyone an idea of what might be wrong here?

Thanks for any help. I’m scratching my head. 

BillDL

Have you looked inside the control cavity to see whether the treble filtering resistor/capacitor combination are soldered to the correct lugs of the volume pot?  It should look like this, although a different looking capacitor might have been used:

https://www.northwestguitars.co.uk/sprague-orange-drop-treble-bleed-kit/

It should be connected across the lugs of the volume pot as shown in the diagram on that page, and interpreted from the viewpoint as you look down into the control cavity.

Modulus_Amps

Doesn't sound like "your man" has done it correctly. post a photo of the pots/wiring

borntohang

The circuit as drawn looks right, assuming that your guy has put it together correctly.

That said, treble bleed circuits are super dependent on the rest of your rig. The pickups, the buffer they're running into - even the length of the cable all have an effect on the taper and brightness of the roll off. It's not a one-size-fits-all circuit unfortunately so might be worth trying different cap/resistor values until you find one you like.

Funkfingers

Treble bypass! 

If people continue to make this error, I shall need heart surgery!

p90fool

Sounds like you have a linear pot too or maybe the resistor is messing with the taper. 

Personally I'd just ditch the resistor, start with a 330pf cap and adjust to taste from there. 

neilgregson

Funkfingers said:

Treble bypass! 

If people continue to make this error, I shall need heart surgery!

What do you mean? Is this a common error and if so what causes it? The incorrect lugs being wired as mentioned? 

Dave_Mc

Funkfingers said:

Treble bypass! 

If people continue to make this error, I shall need heart surgery!

Do you want people to stop or not?

 

neilgregson said:

Funkfingers said:

Treble bypass! 

If people continue to make this error, I shall need heart surgery!

What do you mean? Is this a common error and if so what causes it? The incorrect lugs being wired as mentioned? 

No it's just technically the wrong term for it. It's technically a treble pass, not a treble bleed. The problem is (much like vibrato bridges are almost always called tremolo) the name has kind of stuck by now, so using the name most people use makes more sense (to me) because it makes it easier to google etc.. 

I mean, chemistry still persists in using incorrect, obsolete terminology even though it's technically "wrong" now, and if it's good enough for something as useful, important and potentially really dangerous (not to mention mind-numbingly boring) as chemistry, it's good enough for guitar electronics...

Regarding your original question, I agree with @Modulus_Amps - it sounds like it hasn't been done right. From your description it actually sounds like you don't have a treble bleed at all. Maybe it's not corrected correctly.

ICBM

If it's drastically affecting the taper and acting as a midrange pass at lower volume, my first thought is that he's used the wrong cap value - too large, by a factor of 10 or even 100. (Or possibly even 1000!) Second thought would be the opposite, that he's used the wrong resistor value, too small by a factor of the same type. (But probably less likely.)

The correct cap value is 680pF, which could also be labeled as 681 (6, 8, followed by one zero). If he's used a 682, 683 or 680nF (also often labelled .68uF) then that would do what you're getting.

neilgregson

I’ve dropped some photos into this folder:

https://www.dropbox.com/sh/nl3omsqe1ahjmzb/AAAWCehyALxek48gl1tEUbQ8a?dl=0

ICBM

Aha - the cap and resistor values are correct, but the pots are wired backwards. This is sometimes called ‘independent’ wiring, but it’s basically wrong and doesn’t work properly - it shouldn’t normally be used unless it’s unavoidable because there’s no switch, eg in a Jazz Bass.

On both volume pots, the pickup is connected to the middle (rotor) terminal and the switch to the end (top of track) terminal. Swap these on both volume pots and it should work OK.

I expected it to be a single volume control like the Suhr diagram, I didn’t realise it was two-volume or I would have suspected it as the third possibility .

neilgregson

Aha! Thank you so much! 

Dave_Mc

ICBM said:

the pots are wired backwards

Noooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo! 

Apart from where it's unavoidable like you said, it's just horrible.

ICBM

Now I've seen it again I think PRS do actually wire the guitars like that as stock, it's not something your tech has done wrong - although if so, in my opinion he should have been aware of the problem, since 'independent' wiring is not really compatible with treble-pass, and especially not if there's a resistor as well.

Essentially, it's using the pot the wrong way round so that instead of dividing the signal voltage, it lowers the load resistance on the pickup (which is why it sounds middy and strangled) and adds a series resistance between the pickup and the amp to reduce the volume. With no treble-pass, this 'sort of' works, but with one, and especially with a resistor as well, too much signal gets past for it to make much difference to what reaches the amp.

The *only* reason for wiring the controls backwards like that is so that you can turn one right down to off without muting the other pickup - but if you have a switch, why would you ever need to do that? It's only necessary when there isn't one.

Rickenbacker also do it that way, and this thread has been a useful reminder that I need to rewire my bass! Since one of the other big problems is that when you turn the volumes down to mute the output, you get hum... which I noticed (again) at band practice this week.

Dave_Mc

ICBM said:

Now I've seen it again I think PRS do actually wire the guitars like that as stock, it's not something your tech has done wrong - although if so, in my opinion he should have been aware of the problem, since 'independent' wiring is not really compatible with treble-pass, and especially not if there's a resistor as well.

That's really weird... doesn't PRS use a treble bleed as well most of the time? I remember tearing my hair out trying to figure out what I'd done wrong wiring in treble bleeds in a couple of guitars, eventually I figured out it was the backwards-wiring thing. Basically the treble bleeds (I was using the PRS 180pF value and no resistor EDIT: Just to be clear, they weren't PRSes, I just use that value with humbuckers because it seems to work best for my ears and the way I play) didn't seem to do anything at all...

ICBM

Dave_Mc said:

That's really weird... doesn't PRS use a treble bleed as well most of the time?

I think they only use them on the single-volume-control models - and not on all of those either - although I could be wrong.

Dave_Mc

ICBM said:

Dave_Mc said:

That's really weird... doesn't PRS use a treble bleed as well most of the time?

I think they only use them on the single-volume-control models - and not on all of those either - although I could be wrong.

Oh I get you now, I thought you meant all of them. I'm guessing they did it on the 2V2T models so you can roll the volume to 0 and still get the sound of the other pickup? I agree with you, though, that's scant consolation for all of the other problems you get with it!

neilgregson

I forgot to mention that I replaced the stock pots because I didn’t like them; they were way too easy to knock out of place. As I remember these are CTS pots that are specific to PRS guitars, with a different shaft size I believe. Might that make any difference in how it’s wired? 

ICBM

Dave_Mc said:

I'm guessing they did it on the 2V2T models so you can roll the volume to 0 and still get the sound of the other pickup? I agree with you, though, that's scant consolation for all of the other problems you get with it!

Exactly. Being able to turn one pickup off using the volume control is pointless when you have a switch to do it.

neilgregson said:

I forgot to mention that I replaced the stock pots because I didn’t like them; they were way too easy to knock out of place. As I remember these are CTS pots that are specific to PRS guitars, with a different shaft size I believe. Might that make any difference in how it’s wired? 

No.

There’s no specific to PRS shaft size, they’re standard US 1/4”. The only difference might be the taper.

Dave_Mc

ICBM said:

Dave_Mc said:

I'm guessing they did it on the 2V2T models so you can roll the volume to 0 and still get the sound of the other pickup? I agree with you, though, that's scant consolation for all of the other problems you get with it!

Exactly. Being able to turn one pickup off using the volume control is pointless when you have a switch to do it.

Yeah.