The British Steelies Society

Why do some PSG,s have a small,low value pF, non-polarised capacitor, fitted across the pick up? What does it do? Does it do anything to enhance the tone? Interested to know the answer. Anyone?

Thanks Ken for that. Any more answers,anyone. Maybe the proffessor (Baz) might chip in ?

Perhaps this may help you:

The tone pot and capacitor comprise a low-pass filter, so, when you lower the pot, you lose treble and your tone gets darker. More interesting: as you substitute caps of higher value, you lose more and more highs as you lower the pot.

Thanks Ron. Seems a very sensible answer. Ron,you seem to have had some fun with ZB,s in the past. Mine has NOT got any caps fitted. Should it have or did they have one fitted? Or maybe only if a steel has a tone pot, which my ZB Custom doesn,t have.

If it has a tone pot and it still seems very 'trebly' it's worth a try.

How many pF is that capacitor? A 200pF cap at 10kHz (the upper limit of many adults' hearing range) represents a reactance of approaching 100k ohms, ten times that at 1kHz, 2 octaves above middle C. Difficult to imagine such a low value cap having any appreciable effect on the audible spectrum.

It does represent a lower impedance path to earth (i.e. low pass filter) for higher frequencies. It may have been to shunt away the likelihood of picking up AM broadcast signals in areas near a transmitter. All depends on the cap value.

Thanks again guys. Will,re your idea that maybe they block out AM signals. Well they do have high power AM radio stations in US. Not forgetting those good old buddies on them AM CB radios. Well 10-4 good buddy. Catch you on the flip flop.

The answer to your question is:- It is used to shift the self resonance frequency of the pickup. This capacitor and the lead capacitance combines and affects the centre frequency of the resonance peak or bump in the overal response. The guitar manufacturer, working with the pickup designer, has probably determined the optimin frequency and the gain or Q of the peak after many hours of listening tests. The temptation is to remove this capacitor, notice the sound gets brighter and consider it "better"! What you may not be aware of is the self resonance was set to reduce a particular frequency that tends to be emphasised by the mechanics of the guitar. The frequency that self resonance typically occurs is quite high, so Issues may not be immediately obvious.

Hope that helps
Mark

Thanks very much for that Mark. Couldn,t of got a better answer even from that Mr Google fellow ! Thanks again and best wishes for 2017. Regards Graham