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Hi-pass Filter Trick


frank falbo
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Hi guys, I just posted this elsewhere, and I figured it would be good here, too. Here's the post:

I had a revelation today. I am a total idiot for not thinking of this sooner. It's so simple yet so usable. I don't like the HPF's because, although they're cool for using your volume knob like a gain knob, or a clean/crunch adjustment, I often play clean jazzy solo stuff with the tone control down. The problem I have is when you've got the tone knob down, and you're working the volume knob, you get a crappy sound because at the tone knob you're cutting the highs, while on the volume side you're letting the highs pass through while reducing the lows. You're sucking "tone" from both ends. If you have a neck single coil it's even worse. Here's my solution:

Instead of having the Hi-Pass cap jumping across the switch hot lug and the volume output lug, I run it through the tone pot. First, the wire that leads to the tone knob has to be coming from the switch hot (1st lug) not the output (center lug) and the tone knob has to be wired in the stock "modern factory guitar" fashion, with the wire from the pot going to the center lug of the tone pot, and the capacitor going from the right lug to ground. This leaves the left lug of the tone pot open. We will use that left lug. The little capacitor that jumps the two lugs on the volume pot needs to be removed from the switch hot lug only. Leave it connected to the center lug. Finally jump a wire from that open lug on the tone pot to the newly disconnected capacitor wire.

*Here's what it does:

When you have the tone knob all the way up, there's no change. The pickup hot is feeding 100% through the Hi-Pass cap to the center lug, and everything is as it was. But as you turn the tone pot down, the Hi-Pass cap becomes less and less "connected" to the pickup hot (due to the tone pot's resistance increasing) and therefore allows less and less "Hi-Pass" filtering to occur. Eventually, when the tone knob is all the way down, the Hi-Pass is disengaged. I did it today on a RG550 and it's awesome. It now makes the tone knob totally usable even when you're also playing with the volume knob! If anyone can tell me that there's a problem with this, I'm glad to listen, but I don't think there is. If it's been invented before, I appologize! Theoretically, I imagine that a 500k tone pot is ideal, since you want as little coloration as possible when the tone pot is at "10" but I don't think it really matters.

I am both a genious and an idiot. If only I could invent some sort of "Genious-Pass filter" :D

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No diagram. It's not that I can't make one but I never bothered to learn to post it or how to use yahoo's free pichosting.

If you have stock Ibanez-style wiring with the Hi-Pass filter cap across lugs 1 & 2, it is as simple as adding one wire. You just disconnect the cap from lug 1, attatch a jumper wire to it, and solder it to the open tone pot lug. That's it! If I ever get to learning pichosting I'll put it up.

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Well, I personally don't actually "do" anything, since I never found them usable until yesterday :D

The RG I did it on was the typical Ibanez volume pot with the single capacitor across the two lugs. Ibanez says its 330pf. But it's also common to couple that cap with a resistor to limit the flow through the cap by providing a parallel flow through the resistor. I don't know if it smooths out the taper of the treble passing or not, but perhaps that's also a byproduct of using the resistor. A resistor placed in series would simply reduce the Hi-Pass effect overall.

In my case, the RG's Hi-Pass (as well as any other Ibanez guitar I've had with it) is noticeable pretty early on in the travel. That's fine with me, since then it behaves as you'd want, for going from pseudo-clean to fat crunch. But it's that interplay between the volume and tone that was so repulsive to me. I thought about putting a push/pull to disengage it like the Satriani. Or you could wire it to disengage in positions 1 & 5 of the 5-way toggle, for use in the "in-between" positions only. But all that seemed too clumsy.

If you're into the Hi-Pass thing, perhaps experimenting with different cap values or resistors in series or parallel would be fun. I for one think the "Ibanez" one is fine like it is, because now I can have my cake and eat it too.

Remember, as you turn the tone control down it adds its own resistance between the cap and the signal, just like putting a resisitor in series. So it minimizes it's effect. That's the beauty of this design. But if you just wanted to see what it would be like to have a resistor in series, you could disconnect the tone capacitor. Then the tone knob would act as a variable resistor in series with the Hi-Pass capacitor. Once you got it where you liked it, you could measure the resistance across the pot and hardwire that particular value resistor for that effect. Then you can still use my interactive tone control mod on top of that, to further displace the Hi-Pass circuit as you turn the tone knob down.

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Thanks. The more I play around with the guitar the more confident I get in its mass appeal. On a lot of my guitars I actually prefer the darker sound you get when turning the volume down. I like that better for playing volume swells. So I personally won't be rushing install this circuit on all my guitars, but definitely a few.

I have no idea if this will work as a link or copy/paste, or if it will work at all! But here's a little diagram:

http://pg.photos.yahoo.com/ph/frank.falbo@...aef.jpg&.src=ph

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It might work now, there was a default setting for "sharing" photos set to "private" and I switched it to share with everybody. I won't claim to understand pichosting. :D

You got the diagram correct. Mine is a hacked-up diagram with drawings of the pots and switches, etc.

Let me know if any of you try it and how you like it!

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