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Adding a passive tone control to EMG circuit

atrapp

atrapp

Supporting Member
Dec 4, 2006
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Portland, OR
www.tobyrapp.com
#1
Thanks to Roger Sadowsky I am a huge fan of passive tone. I just received a 4 string Lull with an EMG system in it, the Lull is a rare bird with a P body and J EMG 40 pups.
I am clear on installing a passive tone pot and I have three holes Vol, Blend stacked T/B so I need to go with Vol/Vol stacked, Vol/Blend or Vol/Tone all easy enough, and IIRC EMG uses like 25K volume pots. I can get a Stacked 25k V/V pot from BBG, does it matter what value pot I use for passive tone - and where should it go in the circuit?

Thanks a lot
Toby
 
#2
Guts shot
PXL_20210316_004410335.jpg
 
#6
EMG's stuff is so modular these days, it can almost get to the point of being confusing! They tend to have very good documentation on their website, check it out if you haven't yet.
 
#9
yes it will work fine! I've used stacked 25k pots as a vol/tone for EMG pickups many times.

The volume pot you have in there now looks a little sloppy! Replacing it with a stacked pot will give you a chance to clean things up a bit.
 
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#11
atrapp said:
Thanks to Roger Sadowsky I am a huge fan of passive tone. I just received a 4 string Lull with an EMG system in it, the Lull is a rare bird with a P body and J EMG 40 pups.
I am clear on installing a passive tone pot and I have three holes Vol, Blend stacked T/B so I need to go with Vol/Vol stacked, Vol/Blend or Vol/Tone all easy enough, and IIRC EMG uses like 25K volume pots. I can get a Stacked 25k V/V pot from BBG, does it matter what value pot I use for passive tone - and where should it go in the circuit?

Thanks a lot
Toby
Click to expand...
Having had a few active EMGs wired up with passive controls, they recommend a 0.1uf capacitor for a bass tone pot and I definitely agree. That value is usually about the largest cap you’ll see used with passive basses (for a particular dubby sound with the tone rolled down), but with the EMGs it is comparatively mild.
 
#13
Balance, Master Tone, Master Volume could be a simple three knob solution at the expense of not having individual control of volume and tone for each pickup.
Neck Volume/Tone stacked, Bridge Volume/Tone stacked could give you a two hole solution and an extra hole.
Stacked tone (one level for neck, one level for bridge), balance, master volume would give you tone control for each pup.
These are the options that popped up in my mind.
 
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#14
Don't expect a typical "passive" sound with the passive tone control. Since the buffer preamp is in the pickups you don't get the same sort of resonant bump from the impedance load of the cable and amp input.

I've owned a few Steinbergers, all with the passive tone pot. While the pot works in rolling off the highs you never lose the clarity like you do with say a Fender.
 
#16
brianrost said:
Don't expect a typical "passive" sound with the passive tone control. Since the buffer preamp is in the pickups you don't get the same sort of resonant bump from the impedance load of the cable and amp input.

I've owned a few Steinbergers, all with the passive tone pot. While the pot works in rolling off the highs you never lose the clarity like you do with say a Fender.
Click to expand...

If you're not a fan of the rolloff you get in a Fender tone circuit, there are a myriad of other values that you can use for the capacitor in the circuit that will change how it works. By your description, I'd suggest a much smaller value capacitor Perhaps a tenth of what's in there at present) would be to your liking. The tone controls in mass produced instruments are designed to do obvious things - the treble rolloff on a Fender is pretty drastic if you dial it all the way down. You won't break anything by trying different values of capacitors - there is literally nothing (except your soldering iron) that can hurt you if you decide to experiment. I have built for myself or rewired for other people a few dozen basses - very few of them used a .047uF capacitor anywhere in the ultimate design.
 
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#17
micguy said:
If you're not a fan of the rolloff you get in a Fender tone circuit, there are a myriad of other values that you can use for the capacitor in the circuit that will change how it works. By your description, I'd suggest a much smaller value capacitor Perhaps a tenth of what's in there at present) would be to your liking. The tone controls in mass produced instruments are designed to do obvious things - the treble rolloff on a Fender is pretty drastic if you dial it all the way down. You won't break anything by trying different values of capacitors - there is literally nothing (except your soldering iron) that can hurt you if you decide to experiment. I have built for myself or rewired for other people a few dozen basses - very few of them used a .047uF capacitor anywhere in the ultimate design.
Click to expand...
All you have to do to eliminate that resonant “bump” at the bottom of any passive tone control is to solder a small resistor between the capacitor and its connection to ground (basically the same as only turning the pot 95% off). A lot of G&L tone controls are wired this way.
 
#18
sunbeast said:
All you have to do to eliminate that resonant “bump” at the bottom of any passive tone control is to solder a small resistor between the capacitor and its connection to ground (basically the same as only turning the pot 95% off). A lot of G&L tone controls are wired this way.
Click to expand...

Yes, but what value? Depending on the value of the capacitor, the impedance of the pickup(s), and wheter or not you want to hear some of the bump (when you use smaller vaues for tone caps, the bump is in a desireable range, not an awkward one), I've used anywhere between 15 kOhms and 470 kOhms. I characterize the pickup's impedance, buid an equivalent circuit, then simulate the tone circuits and other tricks that I use in my circuits - I can get myself pretty close to a circuit I'll like doing this, but there are always a few value tweaks to really dial things in.
 
#19
micguy said:
Yes, but what value? Depending on the value of the capacitor, the impedance of the pickup(s), and wheter or not you want to hear some of the bump (when you use smaller vaues for tone caps, the bump is in a desireable range, not an awkward one), I've used anywhere between 15 kOhms and 470 kOhms. I characterize the pickup's impedance, buid an equivalent circuit, then simulate the tone circuits and other tricks that I use in my circuits - I can get myself pretty close to a circuit I'll like doing this, but there are always a few value tweaks to really dial things in.
Click to expand...
I personally have no interest in it, after also experimenting with the idea in a few basses- just adding to the conversation (Changing the capacitor on its own only changes the frequency range of the resonant peak, while a resistor can minimize or eliminate it). The G&L L1000 I had used a 6.8k resistor and worked pretty well (that was a bass I often used with the Tone off, still thumps but not so “dubby” as would be typical). I used some larger values in a P-bass to good effect. These days I just use a standard tone control and turn it up a bit from the bottom if I want that sound. Works for me
 
#20
sunbeast said:
I personally have no interest in it, after also experimenting with the idea in a few basses. The G&L L1000 I had used a 6.8k resistor and worked pretty well (that was a bass I often used with the Tone off, still thumps but not so “dubby” as would be typical). I used some larger values in a P-bass to good effect. These days I just use a standard tone control and turn it up a bit from the bottom if I want that sound. Works for me
Click to expand...

You can also use a resistor in series with the capacitor to do kinda the same thing. The parallel resistor (the first scheme you mentioned) has the side effect of robbing a bit of level from the signal when the tne control is "off", even above the cutoff frequency of the filter. The side effect of the series resistor circuit is that the rolloff curve of the filter isn't as steep once you get well above the cutoff frequency.
 

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