Treble knob doubling as passive tone control

C

coolmaster310

Aug 2, 2019
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#1
Did some searching, can’t find any solutions to this.

Just bought a new bass with an active/passive switch. (‘96 Ibanez TR500. Freakin rules!) I have a newer Soundgear bass like it where the treble knob acts as a tone knob when in passive mode. The ‘96 bass doesn’t have that.

I’d like to make that happen without installing a new preamp if possible. I have no idea where to start. Anybody have any insight? Where should I look for a wiring diagram I could send to my luthier?

Thanks!
 
#3
JKos said:
I'm guessing you would need to replace the treble pot with a dual pot with one pot having the correct value for the preamp and the other pot having a typical passive tone pot value. You could either go with a concentric pot if you want independent control or a dual-gang pot for only a single knob.
Click to expand...

Thanks for the quick reply! Dual-gang pot is the word I was looking for.

Judging by your comment, my understanding is that a potentiometer is basically a remote that feeds some value into some other circuit? Meaning that I can replace the current treble pot with any other pot with the same “range”? And do the same with the twin pot for the tone circuit?

Here’s what I got so far: After the installation of the dual gang pot, each featuring the proper range of values for their particular function, I’d need to connect the treble pot to the preamp & the tone pot to a tone circuit (which would also need to be installed). What I’m still not getting is how to hook them up to be toggled by the active/passive switch. My best guess is that the switch & each pot would be wired to a switcher module of some kind before their respective functions? And this module would only allow one value to pass depending on the position of the switch?

Sorry if my ignorance makes this a tough read All insight & educational resources are greatly appreciated. Thanks!
 
#4
JKos said:
I'm guessing you would need to replace the treble pot with a dual pot with one pot having the correct value for the preamp and the other pot having a typical passive tone pot value. You could either go with a concentric pot if you want independent control or a dual-gang pot for only a single knob.
Click to expand...

Yep. Noll sells a dual gang one with a 50K linear section and a 250K log taper one. The 250K part only cuts from noon down, so that control at noon is "flat" in either mode, and just leaving it in-circuit in both modes works fine, you just get a double dip effect in active cut mode
 
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#6
JKos said:
Plus, given the (usually) low output impedance of a preamp, it wouldn't be doing much to the signal in active mode. I.e., the preamp's high cut would dominate anything done by the passive tone control.
Click to expand...

Good point. I've only tried wiring it in front of the preamp, which still worked really well. But that was with a preamp that barely cuts treble. ;)
 
#7
Passinwind said:
Yep. Noll sells a dual gang one with a 50K linear section and a 250K log taper one. The 250K part only cuts from noon down, so that control at noon is "flat" in either mode, and just leaving it in-circuit in both modes works fine, you just get a double dip effect in active cut mode
Click to expand...

Thanks for the help! That pot is pretty much exactly what i’m looking for!
 
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#9
JKos said:
The only things you likely need are the new pot and a good ol' passive tone capacitor.
Click to expand...

Yep. Your point about how there’s no need to bypass that tone pot (which only cuts tone at halfway point or less) when in active mode is much appreciated! I think I now have a good understanding.... Now to figure out how to buy this damn Noll pot lol. Gonna call a Noll dealer tomorrow and see if I can order one.

Thanks again for the help y’all!
 
#10
JKos said:
The only things you likely need are the new pot and a good ol' passive tone capacitor.
Click to expand...

The Noll one comes with a slick little breakout board and a cap already installed. I have a few without the little daughtercard kicking around too though (I roll my own), which I think my luthier friend bought straight from Noll in Germany.
 
#12
coolmaster310 said:
Yep. Your point about how there’s no need to bypass that tone pot (which only cuts tone at halfway point or less) when in active mode is much appreciated! I think I now have a good understanding.... Now to figure out how to buy this damn Noll pot lol. Gonna call a Noll dealer tomorrow and see if I can order one.

Thanks again for the help y’all!
Click to expand...

Best Bass Gear can probably hook you up, but Klaus Noll does sell direct if need be. You need to confirm that 50K is going to work with your existing preamp's treble control though.
 
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#13
It’s possible, but complicated. You might want to make active treble control and passive treble controls separate knobs, so you can use both in active mode.

Some folks prefer this way (I think of Marcus Miller, but not only him) as passive tone control and active sound differently.
 
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#15
I'd definitely go for a dual concentric style... two controls with independent settings (outer ring and inner knob). one for active, one for passive, and the passive one stays effective ALWAYS, whether or not the active one is running. I've done similar setups before an find the tone much more interesting with the passive tone control turned down some and the active treble control boosted some. I guarantee that depends on the active preamp and the tone capacitor, but for me it was magical. It's a little OCD though, I prefer lots of control, and I also am an audio engineer so I like to calculate what is going on behind the scenes and predict how each control will interact.... and that definitely isn't for everyone. I can never have enough controls on my bass LoL
 
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#17
Passinwind said:
Best Bass Gear can probably hook you up, but Klaus Noll does sell direct if need be. You need to confirm that 50K is going to work with your existing preamp's treble control though.
Click to expand...
Yep, already did Gotta check the size next i guess, this '96 preamp sits on a wide ass circuit board, we'll see if the Noll can fit.
Also considering skipping all this and upgrading my SR655 pre & moving that one to the bass in question
 
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#19
dkelley said:
I'd definitely go for a dual concentric style... two controls with independent settings (outer ring and inner knob). one for active, one for passive, and the passive one stays effective ALWAYS, whether or not the active one is running. I've done similar setups before an find the tone much more interesting with the passive tone control turned down some and the active treble control boosted some. I guarantee that depends on the active preamp and the tone capacitor, but for me it was magical. It's a little OCD though, I prefer lots of control, and I also am an audio engineer so I like to calculate what is going on behind the scenes and predict how each control will interact.... and that definitely isn't for everyone. I can never have enough controls on my bass LoL
Click to expand...

I did one like that last year for a customer who absolutely loves it. I used separates for the two controls though, as there were already two $$$ concentric pots in that install and a third one would've made for kind of a confusing control layout IMO. I'm not a big fan of concentric pots on the instrument, but they can be great for set and forget types for sure.
 
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#20
Passinwind said:
I did one like that last year for a customer who absolutely loves it. I used separates for the two controls though, as there were already two $$$ concentric pots in that install and a third one would've made for kind of a confusing control layout IMO. I'm not a big fan of concentric pots on the instrument, but they can be great for set and forget types for sure.
Click to expand...
cool yea. I agree about concentric pots.... I prefer single controls and more of them. But also cutting more holes and trying to lay it all out isn't always a preferable option, specially if you're not convinced this is the solution for you, and you want to undo it in the future (no empty holes left over). But yea, done right? more normal pots is nicer.
 
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