Shift the mid spike

[WDeeGee]

Hi... the PGb sounds a bit harsh, I read that using a 250k pot lowers and widens the mid spike (it affects the resonant frequency?).

I always wonder if a similar thing could be done by sticking a little slab of brass or metal to the bottom of the pup, which would affect the inductance.

 

[beaubrummels]

I haven't tried those two. I went about it another way. I recently played around with a RLC network to slightly flatten/scoop the mids of a Custom Custom. Basically like a single setting from a Gibson Varitone. I played with different resistor, cap and inductor values to change the Q and the scoop.

 

[Masta' C]

Haven't tested it to verify, but I'd hazard a guess that a brass slab beneath the baseplate isn't going to increase the inductance to the degree you're expecting. It's essentially transparent in terms of ferromagnetism (it's basically identical to nickel-silver from a composition standpoint) and isn't the same as adding more copper/metal to the actual wound coils.

I suppose you could try swapping some iron or mild steel bar stock in place of the plastic/wood spacers on the sides.

You can also change the pole pieces (slugs and screws) for a different alloy, like 1010, but the change is very subtle.

FYI...the soft iron slugs DiMarzio uses between the actual poles for their "virtual vintage" technology (typically 6 slugs per pickup) only increase the inductance by 3-4%, so a fairly small amount, though it is perceptible in how it affects the response.

 

[WDeeGee]

Then how does a brass baseplate have so much effect? I notice the attack is softer, the sound more bass heavy... and yes, less note definition.

I figure it would be possible to achieve that effect in small doses by sticking a bras splate, say the size of a bar magnet but perhaps not as thick.

 

[Masta' C]

I don't want to get into the baseplate version of the "tone wood" debate. All I will say is that *nearly* every aspect of a pickup does contribute to the result. However, not equally and not always in a linear fashion. In the end, you've really got nothing to lose by trying it, so if you've got a slab of brass hanging around, I say give it a shot!

 

[Teleplayer]

Brass has higher electrical conductivity (high copper content), so it causes greater eddy-current loss. That is different to altering the inductance. Brass is used for most of the older generation Dimarzio humbuckers and is also popular with off-shore makers. Duncan humbuckers use "nickel-silver" base plates, which give the lowest eddy-current loss and brightest tone, the same as the original PAF humbuckers.

Steel base plates are sometimes used on *single coil* pickups to increase the inductance. That wouldn't work on a humbucker, as it would largely cancel out the magnetic field (the base plate being adjacent to the bar magnet). To increase inductance you would be better off to put some steel screws or slugs into the bobbins like a virtual-vintage modded pickup.

 

[Teleplayer]

The simplest way to change the resonance of the pickup is to wire a small ceramic capacitor across the outside lugs of the volume control pot. Personally I have used values around 68pF, 100pF, 150pF, which give a subtle effect and change the voicing of the mids. Other people have use larger values such as 470pF up to 1nF (1000pF), which IMO just make it sound muddy.

The capacitance of most instrument cables is 350pF to 500pF, so that puts the size of the capacitor into perspective. The capacitor across the volume control input is not the same placement as capacitance of the instrument cable, except for when the volume control is dimed at 10/10.

 

[freefrog]

Hi... the PGb sounds a bit harsh, I read that using a 250k pot lowers and widens the mid spike (it affects the resonant frequency?).

I always wonder if a similar thing could be done by sticking a little slab of brass or metal to the bottom of the pup, which would affect the inductance.

What Teleplayer said - I could have wrote the same things than him and I thank him to avoid me a long explanation ;-)... Added capacitance is exactly the trick that I've used decades ago to tame a PG in a too bright LP copy.

For the record, this trick was clearly evoked in the Seymour Duncan FAQ's, two decades ago. Excerpt:

228.
Capacitors can be used to reduce brightness in a pickup by soldering one side to ground and the other to the hot output"

 

[Clint 55]

Use a double thick A2. It deepens it and makes it less harsh.. Or not. Yes, 250k pots or a brass baseplate will also have a notice-able effect. Try a combo of all 3!

 

[Masta' C]

Brass has higher electrical conductivity (high copper content), so it causes greater eddy-current loss...Duncan humbuckers use "nickel-silver" base plates, which give the lowest eddy-current loss and brightest tone.

You're not wrong about the greater electrical conductivity of brass vs. nickel-silver. Nickel-silver has around twice the electrical resistivity of yellow brass, but this difference isn't just because of the relative copper content. Both nickel-silver and brass generally have a similar composition of copper at around 55-60%. Though, admittedly, some unique formulations of nickel-silver can dip a bit lower, but I doubt that's the case with most pickup baseplates.

Essentially, any additional metal placed within the magnetic field is going to have some influence. What type and how much impact it has depends on the metal, how much is used, and where it is distributed within/around/near the circuit that is generating the signal.


Yes, baseplate material and thickness can change the tone, but this change isn't always strikingly apparent. That said, I think the "slab of brass" approach could be interesting!

 

[WDeeGee]

It needs a 220k resistor parallel across the volume pot to tame the harsh top end. I tried a capacitor but it seems to muddy the sound.

I'll try and A8 mag, as I don't have double thickness A2.

 

[Clint 55]

I'll try an A8 mag, as I don't have a double thickness A2.

You have to buy them.

 

[freefrog]

II tried a capacitor but it seems to muddy the sound.

A cap of which value?

IME and IMO, some fine tuning is needed here: such a capacitor adds itself to other capacitive elements - like the cable between guitar and amp. And tts action is balanced or not by other factors - pots resistance but also coupling caps in the effect(s) and amp(s) used, not to mention the peaks and dips characterizing the louspeaker(s) played...

If the overall stray capacitance added in the guitar is too high, yes, it will sound muddy. Conversely, it will sound nice if it's properly tuned (for example: if it aligns the resonant peak of a pickup with a pleasing peak due to the loudspeaker).

In the early 80's, Pete Willis (Def Leppard) had something like a 2,2 nF cap in his Hamer Explorer: it worked as a mid enhancer without sounding muddy because he plugged in bright Marshall amps with low value coupling caps.

I have a 1nF capacitor in my main Strat, to emulate a warm Hendrix and/or hot SC tone with low inductance single coils. Not only it doesn't sound muddy but it works like a charm... with the rest of my gear.

BUT I had to try various caps to achieve that (and to measure capacitance as well as resonant peaks but that's another story since I know that most players don't have access to lab gear).



For the record, an average guitar cable measures 100pF to 150pF per meter. Plugging a too bright PG through 6m or 9m of cable might suffice to tune it nicely - and if the guitar is usually plugged through 3m of cable, an added cap of 680pF might suffice too. There's no need to overdo it, although the guitar might also require a higher or lower capacitance than this. Only repeated experiments can tell what is the "proper" stray capacitance to add for a given guitar and rig considered as too bright (same things with amps or effects: I do trials and errors process when it comes to adapt a drive circuit to a bright loudspeaker, for instance. Done this a few days ago with a Fender Hot Rod...).


BTW, Seymour was not the only one to evoke added caps back in the days. Bill Lawrence (RIP) was recommending low capacitance wires + a cap on a push pull to emulate the warming action of coily cables.

 

[WDeeGee]

For those who'd like to know, I put an A8 magnet in the PG and I like it very much!
The mids are a bit fatter, the high end still bitey but not nails on a chalkboard. I still might add a 500k resistor across the volume pot, though, to get a hint of a creamy sound going.
Of Course, the PG is a bit hotter now but it's still very dynamic and articulate.