250k pot with SH-2 Jazz

[blueman335]

Re: 250k pot with SH-2 Jazz

yes, that's the idea, but... I'm usin' tone control quite often

Another way to look at it: Many of us try to get the PU's sounding the way we want, without having to adust the tone controls. The pots on their own filter and change the signal's EQ (without even adjusting them). In a neck PU, you rarely have to turn down the treble, unless its a bright single coil. But in a bridge, treble reduction is often needed, in some manner. I'll put in a warmer magnet to take off excess treble. I find A4's to be very useful when a PU with an A5 is too bright. A4's have a balanced EQ that makes the mids more prominent, unlike A5's which have scooped mids & can seem very bright on some guitars (like a JB).

What you do is up to you, but if it were my guitar, I'd put an A4 in the bridge PU, and wire separate volume pots for each PU. I think necks require 500K's, and most bridge PU's can benefit from one or two 250K pots. I've got a Michael Kelly version of a double-cutaway LP, which has only two pots, that I did this re-wiring to. In fact, the two volume pots are push-pulls, so I can get the each of the PU's in single coil too (8 PU options, instead of the usual 3). Even with a bare-bones two-pot guitar, you can still do some creative wiring. All of this stuff is easy to do; the hardest part is learning to let go of the manufacturer's uninspired wiring, and starting with a clean slate to make the guitar fit your needs.

 

[uOpt]

Re: 250k pot with SH-2 Jazz

and why noise gets higher when you turn down your volume pot a bit? it's so nice to control drive with your volume knob, but then noise appears as you lower it...

The volume knob in a passive guitar goes not exclusively control volume.

In addition to controlling volume it adds resistance across the pickup, and that dampens the (height of) the resonance peak. For every - say - 10% of volume you kill you kill 30% of the resonance peak.

Noise, in particular the 50/60 circle hum, is located in frequencies not anywhere close to the resonance peak and hence in the above example you lower the hum volume by 10% but other important frequencies get dampend by 30%. Hence the noise appears higher in relation to the overall sound.

Note that this is "in relation". If the volume of noise actually goes up, then you have noise leaking into places that insert it into the output in certain potentiometer settings. That shouldn't happen, you need to shield the electronics cavity better, and potentially you have ungrounded junk trailing off one of the pots or something similar.

one more question: I've heard things like linear, audio and logarythmic potentiometers. what do they mean and which ones can be used with guitar? I know that one of them begins lowering immediately and one of them makes reasonable lowering only after reaching it's 50%...

thanks again, in advance

Normally, a linear potentiometer takes down volume linear. So 50% poti settings means 50% volume.

However, your ears are working logarithmic. Making a sound 2x as loud physically only appears to be slightly louder to your ears. To achieve an impression of 2x volume to your brain you have to give 10x the physical volume. Hence logarithmic potentiometers are generally used in audio applications to control volume, because for your ears that appears to do the right thing.

 

[Gustaff]

Re: 250k pot with SH-2 Jazz

"Normally, a linear potentiometer takes down volume linear. So 50% poti settings means 50% volume."

and what does the audio do?

which one is used for guitar? linear or audio potis?

 

[korus]

Re: 250k pot with SH-2 Jazz

... However, it should be worth experimenting whether lowering the frequency (not the height) of the peak is a more rewarding thing to do (that's the capacitor in parallel to the pickup).

Can you suggest values for those, maybe your experience with different pickups/magnets/woods/pot values ? Or just the approx. range (like 100pf-1000pf) ?

 

[jeremy]

Re: 250k pot with SH-2 Jazz

audio is a log taper which is more common in guitars but some people prefer linear.
audio taper is something like
50% pot setting 10% volume
90% pot setting 50% volume

 

[korus]

Re: 250k pot with SH-2 Jazz

Tone pots are always audio. I never heard of linear taper tone pots and it would not make any sense to have a pot with usable range from 0 to 2.

Volume pots are usualy audio, but e.g. Gibson puts linear taper vol pots in most of their current product range.

The issue is that most of audio tapers are realy just an approximation of logarithmic curve by using 2 or 3 linear ranges as shown/explained : http://www.geofex.com/Article_Folders/potsecrets/potscret.htm

One of the side effects on putting a RESISTOR in PARALLEL with treble bleed capacitor on vol pot is that resistor “flattens” audio taper a bit bringing it somewhat closer to linear taper, which is most of guitarists would find as optimal for guitar volume pot – audio taper slightly altered/”flattended” toward linear taper. That’s why these exist – custom taper pots:

http://www.rsguitarworks.net/rsstore/product_info.php?products_id=388
http://www.doctorvintage.com/drv1_controls.html
http://www.guitarcenter.com/DiMarzio,Misc-Guitar-Replacement-Parts.gc

Ofcourse, I am not affiliated with any of these ...

 

[uOpt]

Re: 250k pot with SH-2 Jazz

Can you suggest values for those, maybe your experience with different pickups/magnets/woods/pot values ? Or just the approx. range (like 100pf-1000pf) ?

For capacitors across the pickup to lower the frequency of the resonance peak I use values between 0.5 to 10 nF. Much smaller than the tone poti capacitor, you only want to notch off a little bit. Much smaller than the caps you use for the tone poti.

If you have a back-routed guitar you can just use crocodile clip cables to attach them for experiments without any soldering or de-stringing.

For advanced use, get a 12-position turn switch that has potentiometer dimensions and use that instead of a regular tone poti.

 

[korus]

Re: 250k pot with SH-2 Jazz

For capacitors across the pickup to lower the frequency of the resonance peak I use values between 0.5 to 10 pF.

While we're at it, I would like to ask you some more questions if it is not too much to ask :

1. your suggestions/experience for treble bleed : cap or cap & res PARALLEL or cap & res IN SERIES for single-coil / for humbucking ; what values ?

2. what is the net effect of "grounding" hot from pickup with such a small e.g. less than 100pF cap on resonance peak of the pickup ? it will certanly shave some of harsh treble on too bright bridge PU/guitar combo; (tried some simulations in SPICE but have to learn how to use it some more before any conclusions/usable chart&diagram for conclusion on this issue)

BTW, aligator clips + 12pos/6pos rotary switch or 5pos megaswitch is exactly what I use when I'm testing.

 

[uOpt]

Re: 250k pot with SH-2 Jazz

1. your suggestions/experience for treble bleed : cap or cap & res PARALLEL or cap & res IN SERIES for single-coil / for humbucking ; what values ?

I only have them in parallel.

You always have a resistor across the pickup - the poti. Even with the poti at 10 it is a resistor leading hot to ground. So adding a capacitor means you have a capacitor and a resistor in parallel even if you don't add your own resistor. If you add a resistor then you have one cap and two resistors in parallel.

I don't know offhand what happens with the resistor and the capacitor in series, I'll have to look it up at home.

2. what is the net effect of "grounding" hot from pickup with such a small e.g. less than 100pF cap on resonance peak of the pickup ?

Grounding like that is the same thing as having a capacitor in parallel to the pickup. It lowers the frequency but not the amplitude of the resonance peak.

it will certanly shave some of harsh treble on too bright bridge PU/guitar combo; (tried some simulations in SPICE but have to learn how to use it some more before any conclusions/usable chart&diagram for conclusion on this issue)

To simulate that with an EQ you would have to position a parametric EQ excactly at the frequency of the resonance peak. That might not be easy to do.

My rule of thumb is to use a capacitor to lower the frequency of the resonance peak when the guitar is too bright and use a less resistance poti (or a resistor) to lower the amplitude of the resonance frequency when the pickup is too bright. Of course that's a knee-jerk^10 assessment.

Let me know how this goes.

All this fiddling went a little but out of fashion with ebay. If you don't like your pickup, ebay it off and get a new one. But this kind of thing can be useful to direct your search and experiement a little bit with your particular guitar. It's pretty annoying that everytime you get a different guitar all your previous pickup experiments can be invalid.

 

[korus]

Re: 250k pot with SH-2 Jazz

Let me know how this goes.

Currently waiting for some RS Guitarworks stuff to be installed (Jensens,superpots..). It'll take some time, but I'll get back as soon as I have something new to add/share. Thanks for your time & effort.

 

[uOpt]

Re: 250k pot with SH-2 Jazz

I had mixed up pico and nano above. If you made a shopping list, please re-check.