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Trialing the effect of a passive tone control

A

-Asdfgh-

Apr 13, 2010
15,367
27,582
UK
#1
I have a Precision Player Plus. I'm blown hot and cold over it. It's my only bass with a 42mm width neck, for example. It came to me with fairly worn frets and although my fret level wasn't perfect it will take a 1.3mm action if I play very lightly or my standard 1.7 to 1.8mm (E, 12th fret) for more realistic playing.

The issue I have is the electronics. On other active basses, bar my Precision Lyte, I have a passive option with a traditional tone control and sometimes that gets the job done. But in the Precision PP, passive defeats all the tone controls. It's a mass of wires in there so I'm not sure how I'd wire up for the option of a passive path with regular time as every control seems to be linked to the circuit board as opposed to some set ups where it's traditional pots and values for volume and blend with more just active EQ.

So before I consider any butchery or wholesale replacement (I have a spare Glockenlang two band but I'm not sure I like the frequency centre points and Q), are there any (cheap) devices or plugins - filters with appropriate resonant peaks - that would allow me to trial the approximate effect of a passive tone control by plugging the passive output into it?

Many thanks.
 
#2
P.S. one of my options is actually building the Passinwind preamp which I have the parts for and ignore the passive nonsense entirely. That's a lot of soldering and I don't know if I'd like the end result. Plus I'm not very confident I could build it correctly, or even if it would fit.
 
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#3
-Asdfgh- said:
P.S. one of my options is actually building the Passinwind preamp which I have the parts for and ignore the passive nonsense entirely. That's a lot of soldering and I don't know if I'd like the end result. Plus I'm not very confident I could build it correctly, or even if it would fit.
Click to expand...
A Precision isn't the bass I'd typically recommend my designs for. Noll sells a dual section pot that can replace the treble pot in many onboard preamps, then giving you the passive TC option in bypass mode, but you still may also need a different push-pull volume pot with the right switching. We'd need to see the details of your current config to know. This can all work pretty well if the stars align, IME.
 
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#4
Why not just plug the passive output into an external pot + cap to ground, right outside the bass, to fiddle with and see how you like it? You could try different pot values, caps etc (though the cap value only makes a big difference when the tone pot is at or close to the minimum).

Or, of course, you could just buy my filter premp if you're not sure you could build Charlie's :)
 
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#5
Passinwind said:
A Precision isn't the bass I'd typically recommend my designs for.
Click to expand...
It's a PJ, But it was a passing thought (no pun inteded)

Passinwind said:
Noll sells a dual section pot that can replace the treble pot in many onboard preamps, then giving you the passive TC option in bypass mode, but you still may also need a different push-pull volume pot with the right switching.
Click to expand...
Luckily, the active to passive switching is via a toggle switch, but see below.

Passinwind said:
We'd need to see the details of your current config to know. This can all work pretty well if the stars align, IME.
Click to expand...


As you can see, everything seems to go via the PCB. So I am not sure I get any options. It's not like it's high value volume pot to high volume blend pot then to the switch and then to the PCB for 3 band EQ or if passive, straight to the jack socket. So I may be out of luck without dropping in the Glockenlang as an alternative. The Glockenlang has push pull for active/passive - what could I do with the additional switch hole? Series/parallel for the P pickup?). But it has bass centred at 40Hz and treble at 18kHz. I don't know what the Q values are, but that seems quite extreme for the active side.
 
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#6
-Asdfgh- said:
It's a PJ, But it was a passing thought (no pun inteded)


Luckily, the active to passive switching is via a toggle switch, but see below.




As you can see, everything seems to go via the PCB. So I am not sure I get any options. It's not like it's high value volume pot to high volume blend pot then to the switch and then to the PCB for 3 band EQ or if passive, straight to the jack socket. So I may be out of luck without dropping in the Glockenlang as an alternative. The Glockenlang has push pull for active/passive - what could I do with the additional switch hole? Series/parallel for the P pickup?). But it has bass centred at 40Hz and treble at 18kHz. I don't know what the Q values are, but that seems quite extreme for the active side.
Click to expand...
The Glockenlang was in something else, not a deliberate purchase. I know some people swear by them, but the bands didn't seem to be ideal for me. Maybe they'd work in the Fender, I am not sure.
 
#8
cut a guitar cord and put alligator clips on the conductors of the cut ends. clip it whatever you think might sound good, plug into your amp and hear what you got.
Screenshot 2026-03-15 at 2.04.43 PM.png
 
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#9
-Asdfgh- said:
It's a PJ, But it was a passing thought (no pun inteded)


Luckily, the active to passive switching is via a toggle switch, but see below.




As you can see, everything seems to go via the PCB. So I am not sure I get any options. It's not like it's high value volume pot to high volume blend pot then to the switch and then to the PCB for 3 band EQ or if passive, straight to the jack socket. So I may be out of luck without dropping in the Glockenlang as an alternative. The Glockenlang has push pull for active/passive - what could I do with the additional switch hole? Series/parallel for the P pickup?). But it has bass centred at 40Hz and treble at 18kHz. I don't know what the Q values are, but that seems quite extreme for the active side.
Click to expand...
I recently did an RTA sweep test on the two and three band Glock preamps I have here, the “center” frequency is actually much lower than that, albeit still relatively high IMO. It appears they spec at the top shelf knee, where treble boost just starts to level off. There is no universal standard for spec’ing shelving EQ controls, and they apparently go with one textbook way of doing that, as we might expect a good German engineer to do. I am of Swiss-German heritage myself so no disrespect implied. ;)

Just FYI: Preamps similar to Glockenklang?
 
#10
Passinwind said:
I recently did an RTA sweep test on the two and three band Glock preamps I have here, the “center” frequency is actually much lower than that, albeit still relatively high IMO. It appears they spec at the top shelf knee, where treble boost just starts to level off. There is no universal standard for spec’ing shelving EQ controls, and they apparently go with one textbook way of doing that, as we might expect a good German engineer to do. I am of Swiss-German heritage myself so no disrespect implied. ;)

Just FYI: Preamps similar to Glockenklang?
Click to expand...
Interesting. It goes lower (on treble boost and cut) than I imagined, but I still find that circa 80Hz and 8kHz work better for me.
 
#11
Looking at the connections diagram from Fender, it would be fairly someple to add a passive tone control. The pickup leads are connected to the blend pot and the output of that pot goes to the switch than sends the signal either to the preamp or to the output jack. Solder a wire to the switch where the output from the blend is and send that to a 250Kohm pot center lug. On the left lug of the pot solder a .047mfd cap and solder the other end to the pot case. Then solder a wire from the pot case to ground. Job done. The passive tone control works in both active and passive settings. Very useful. I should add that this will work with any active bass where the pickups are passive and are fed to a switch that directs the signal alternatively to the preamp or the output jack.
 
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#12
-Asdfgh- said:
Interesting. It goes lower (on treble boost and cut) than I imagined, but I still find that circa 80Hz and 8kHz work better for me.
Click to expand...
If you only boost halfway you are probably actually at somewhere nearer that ballpark, but I get what you mean and I don't necessarily disagree, especially for Fender-ish instruments.
 
#13
Turnaround said:
Looking at the connections diagram from Fender, it would be fairly someple to add a passive tone control. The pickup leads are connected to the blend pot and the output of that pot goes to the switch than sends the signal either to the preamp or to the output jack. Solder a wire to the switch where the output from the blend is and send that to a 250Kohm pot center lug. On the left lug of the pot solder a .047mfd cap and solder the other end to the pot case. Then solder a wire from the pot case to ground. Job done. The passive tone control works in both active and passive settings. Very useful. I should add that this will work with any active bass where the pickups are passive and are fed to a switch that directs the signal alternatively to the preamp or the output jack.
Click to expand...
Thank you!

I couldn't make sense of the diagram from Fender, and there are a lot of wires in there when I looked and I sort of ran away in panic... But that sounds positive from what you say and more what I would have expected.

Having the passive tone in there works for me and reminds me of my old Westone Thunder 1A.

So the question becomes, do I add a mini trim pot internally to set a suitable point for the mid control and sacrifice the knob on the front to add the passive tone or get a stacked and keep the mid control? I have a source (if I find it) for fairly arbitrary stacked pot values. I suppose given that the frequencies will have been chosen for three bands then the latter probably makes most sense.

I tested out the overall likely sound by using a two pole resonant low pass filter and some signal analysis to get a rough match to a "typical" passive tone knob in various positions and then played recordings of the bass live and passive though it. It sounded how I'd want it to sound.

Thanks for the help, everyone.

I'll add this modification to the soldering queue :). I'm putting in some series-parallel-single switches to a couple of basses first. That's something I understand better, I just hate soldering which is why I still haven't built those Passinwind preamps!
 
#14
Passinwind said:
If you only boost halfway you are probably actually at somewhere nearer that ballpark, but I get what you mean and I don't necessarily disagree, especially for Fender-ish instruments.
Click to expand...
Sometimes I want to make radical changes, like maximum treble cut. Ok, I typically use outboard effects and can do it with those, but the option to do so when going direct is useful. As long as it's musical.
 
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#15
-Asdfgh- said:
Sometimes I want to make radical changes, like maximum treble cut. Ok, I typically use outboard effects and can do it with those, but the option to do so when going direct is useful. As long as it's musical.
Click to expand...
I get that. If a two pole LPF can get you where you want to go there are more and more commercial solutions out there these days, and for mostly hard cuts any of my DIY designs back to the very first one can do a pretty good job of that too. Getting big boosts right took quite a bit longer, and for those of us who need that my newest ones are a bit better, for sure.
 
#16
Passinwind said:
I get that. If a two pole LPF can get you where you want to go there are more and more commercial solutions out there these days, and for mostly hard cuts any of my DIY designs back to the very first one can do a pretty good job of that too. Getting big boosts right took quite a bit longer, and for those of us who need that my newest ones are a bit better, for sure.
Click to expand...
I went through an active bass fallow period from 2006 to about 2023 so I'm probably doing it wrong :).
 
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#18
And my first bass was active, but the tone control was passive and active was just a signal boost and a slight baked-in bass and treble boost. Then it was a Cowpoke which I'd probably like now but I had a love-hate relationship with the preamp and EQ. I seem to get on perfectly OK with a Precision Lyte's preamp from the same period, though.
 
#19
I am tempted to get the cheap-and-cheerful Artec SE-2A to test. I can basically set that up with a spare mini-toggle 2-way switch with blend-tone-vol-switch and then switch to either go to the preamp (as two bands - I can just about understand two bands) or to the jack. That's a bit like the Westone but with EQ on two knobs rather than one. The bass currently has bass and treble on a single shaft, so it would end up looking the same. It means basically I am just resoldering pickup connections and jack and battery connections only and not touching anything else.

The other option would seem to be blend-vol-switch->jack and blend-vol-switch-preamp-jack and retain the current 3 bands of EQ but replace the existing mid pot with a dual shaft one with whatever it currently is (100k? 50k?) and a 250k one for the passive tone. I suppose in theory I could replace that mid with dual concentric but then I am into replacing knobs too...
 

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