Metal Guitarist Forums banner

The 'Tight' control - simple passive bass cut

142K views 47 replies 25 participants last post by  Naama  
#1 · (Edited)
*This is a huge edit of the original post*

The typical guitar tone control doesn't get used a lot. A lot of players disconnect it in search of that extra touch of clarity. However, it is very simple to rewire the existing pot to give you something that most metal guitarists will benefit from - an extra touch of tightness :metal:

There are a couple of approaches to this one, one is slightly easier than the other, but the effect is less pronounced. BTW this is for passive pickups only at this stage.

First up we'll look look at a fairly typical humbucker pickup frequency response with a 500k volume pot at maximum. You'll see it's a flat response until the resonant peak, then it drops off.

Image


Next is the same theoretical pickup with a 1 Meg volume pot. You'll notice the peak is taller, which is why a 1 Meg pot sounds brighter and clearer than a 500k pot.

Image


Next up is the effect of using a 500k pot and cap as a bass cut, combined with a 500k volume pot. This is the easy mod. All you need is a different value of capacitor, and maybe some extra hookup wire. And a soldering iron, solder, and the appropriate skills.
The capacitor value that worked best for me was 0.0033uF (marked 332 on the cap itself). Smaller values will move the cutoff frequency up. The 0.0033uF works to kill the very low bass frequencies and make the low strings sound a little clearer. This is most noticable on the 8 string low F# and B strings. You might want to try 0.0022uF (222) and 0.001uF (102) as well, it depends what works best for you, but the cutoff point gets higher and starts effecting the mids. For reference, most humbucker equipped guitars use a 0.022uF (223) cap on their standard treble cut tone pots. This is the response with the 0.0033uF cap...

Image


Changing the bass pot from 500k to 1 Meg gives slightly more cut....

Image


So, how's it wired? I'll assume the guitar in question has a master volume control that runs straight to the output socket. The cap goes between lugs 1 and 3 on the pot. The wire that normally runs from the volume control to the socket now runs from the volume pot to lug 2 ('in') of the 'tight' pot. Another wire runs from the 'out' lug, as specified in the drawing, to the socket tip. You can wire it to cut bass when turned clockwise or anticlockwise, depending on your preference. Remember to bridge lug 2 to the outside lug that is not the output. And ensure the body of the pot is earthed. Here's a wiring diagram...

Image


OK, that's easy enough, but what if you want more bass cut? It can be done, but to retain the typical 500k volume resonant peak characteristics we actually need to change to a 1 Meg volume and add a 1 Meg resistor to the 1 Meg bass cut control. The choice of caps changes slightly too. The point of this is to cut more bass without screwing with the mids too much.

This is the response using the 0.0033uF cap, could be interesting on a pickup/guitar combo with excessive bass and low mids...

Image


Changing to a 0.0047uF (472) value gives us what I'm currently running in my own guitars...

Image


And a 0.0068uF cap takes us to a similar response to the first circuit...

Image


Here's the modifed wiring diagram...

Image


And here are the diagrams to wire it in permanently, or switched with a SPDT toggle...

Image


Adding a standard tone control

It's possible to add a standard tone control in the usual spot, again using a 1 Meg pot instead of 500k. Swapping the 1 Meg resistor to ground for a 4.7 Meg should give the same resonant peak characteristic as the graphs above.

As always, the only way to know if this kind of mod works for you is to try it :metal:
 
#8 ·
Yes, there is, but if it's an apparent boost you're after it has to be done as a treble and bass cut, which might give the effect of less gain. Then again, mids are what drive the amp input hardest, so the drop in gain might not be too drastic.

BTW, where does the bass "tight" knob start rolling off bass frequencies at? What frequency do most standard treble tone knobs start cutting treble at?
The bass cutoff frequency depends on the input impedance of the amp, I believe. I have to check calculations about 60 times before posting them so I'll look into that over the next day or so. For now let's say the 0.0033 is very subtle, it deals with 'thud' and 'woofy' bass. I'm not sure how much the pickup impedance effects this one. Same goes for treble cutoff. I can never remember the theoretical stuff :lol:
 
#13 ·
Updated once again with permanent and switched wiring diagram :shrug:

S7eve, you should keep the same tonal response you currently have by changing both your volume and standard tone pots to 1 Meg and adding the bass cut between those and the socket.
 
#17 ·
Bigger cap value. If you check out the last few graphs you'll see the effect of gradually increasing the cap value. The ideal way to incorporate this is by putting it in front of an onboard buffer preamp. That gives you a constant known impedance (load) on the pickups and ensures your cutoff frequency stays the same no matter what you've got the guitar plugged into.

BTW, I'm no longer using a low cut cap in my 8 as I've wound tighter sounding pickups for it.
 
#19 ·
There's also the fender tbx control, which has a center detent, then cuts treble when turned one way, and bass when turned the other way.

El caco, I remove the tone pots from my guitars...I even have a couple that were built without them. I basically can't stand having any roundness to my note attack, and removing the tone pot helps that.
 
#22 ·
Wirelessly posted (Hivemind: Mozilla/5.0 (iPhone; U; CPU iPhone OS 4_2_1 like Mac OS X; en-us) AppleWebKit/533.17.9 (KHTML, like Gecko) Version/5.0.2 Mobile/8C148a Safari/6533.18.5)

Works great man. Definately check it
 
#32 ·
Necrobump because I missed all this...



i thought it wasn't possible with actives? according to the OP.

More than anything im wanting to do it with my RGA as it had a stock active EQ with the stock actives.

So replacing that switch with something useful will be a good move.
It is possible with actives, absolutely. You'd need a 25k or 50k pot and probably different capacitor values. I haven't looked at cap values for low impedance circuits.

DPM,

Many thanks for the clear and concise post on the passive bass cut control.
I tried it recently and was very happy even with the simple passive form using the 0.0033 microF capacitor.

I have a couple of vintage guitars (single volume, single tone) that I would like to modify but I was wondering if it would be possible to introduce the simple passive low-cut mod on a 500 kohm pull-pot so that in the "down position" it would function as a normal tone control (i.e. high-cut, counter clock-wise - full signal at the full clock-wise position) and when pulled out bypass the high-cut and activate the low-cut circuit (preferably with the maximum cut in the full clock-wise position) - so that one can have the best of both worlds.

I'm not quite competent enough to know whether this can be done and if so how to do it, but I'm betting that you have the answers! Many thanks in advance for considering my question -

Thanks again for your post and expertise!

AABCEH
I just quickly tried drawing this and it doesn't look like a push/pull would do it. I might be wrong.