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andrewthouston

Splitting piezo string outputs

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Wondering if this can be / has been done?

 

I'd like to be able to tap the piezo outputs from the 5 and 6 strings, and send them over to a second preamp (not sure what the options out there are, so let's say, a Graphtec acousti-phonic), to be output independently from the Variax output.

 

So for ex, if I play 3x0003 or x32010, all those notes would go to the Variax as usual. But the root note G or C would also be sent to the second output. This would then be sent to an octave divider (plus eq, etc). The result is a simple bass tone from that output, in addition to the full guitar chord (electric or acoustic tone) coming from the Variax output. Both outputs are then processed and amplified.

 

Is this workable? How is the string separation anyway? Will the #4 D string be leaking into my bass output? (Or, #5 when I only want #6, since octave dividers of course don't take kindly to chords.)

 

Originally, my idea was to build a custom 8-string, tuned to EAEADGBE, where the top six strings would be handled by a Variax, and the 2 low bass strings by "something else(?)". 2 short-scale bass strings on individual bridge saddles and pickups? A messy concept, even if you don't mind barring all those low notes. So I figured, if you're just going to duplicate the root of the chord for the bass, why not see if the electronics can do the heavy lifting?

 

TIA!!!

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No there is no feature in Variax that allows you to separate the string outputs.

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The string outputs are separate after the piezos so if you know what you are doing you can separate them.  Don't expect any help from Line6 though.

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But is it as simple as connecting a piezo's output to the two systems in parallel? How will that affect the signal electrically?

 

I believe it's often the case that when splitting an analog signal, each input is buffered so that the inputs can't see each other (as it sometimes causes feelings of jealously, insecurity, and general incongeniality).

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Well, for one thing if you split the individual piezo signals after they pass through the piezos and immediately route them separately, the ones you want isolated will have to pass to an output without any Variax Model processing. You'll just get the raw piezo signal. Once the individual signals are re-joined and fed back into the processing DSP there is no separating them again.

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Piezos require a charge amplifier to generate a signal so no you can't take a signal right from the Piezo.  You would have to take it after the amplifier that is on the board.  There is one for each piezo.

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Thx for replies!

Well, for one thing if you split the individual piezo signals after they pass through the piezos and immediately route them separately, the ones you want isolated will have to pass to an output without any Variax Model processing. You'll just get the raw piezo signal. Once the individual signals are re-joined and fed back into the processing DSP there is no separating them again.

They'd be sent to a 2nd preamp (such as the ghost acousti phonic), ouput from the guitar (separately from the Variax output), and sent to separate mfx and/or amp.

 

Like in my example, I want to play x32010, all 5 notes go to the Variax as usual. But the bass C also goes to the 2nd output, into an octave divider, and bass amp.

 

Piezos require a charge amplifier to generate a signal so no you can't take a signal right from the Piezo.  You would have to take it after the amplifier that is on the board.  There is one for each piezo.

Maybe not unlike how a condensor needs a charge to function? If the piezo is being split to the Variax, and another preamp (like acousti phonic), it should be getting the charge from both, no?

 

If there's a place on the Variax board to tap after the preamp, that may be handy. But also means I'd need to find a way to mix 5 and 6 together before output. (I'm guessing just shorting them together isn't the way to go.) Whereas with using the 2nd preamp like acousti phonic, for whatever strings I feed into it, all the output gets mixed. And you still have the separate gain controls, etc.

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You would have to tap the signal off before it gets to processor board,

and not mess up the input impedance in that signal line doing that mod.

 

-Not recommended, so don't do it.

 

-Trying to turn a 6-string guitar into an 8-string,... the other two strings

would have to be processed separately, and the processor isn't equipped

to do that.

 

-Running signal to an external processor is a dicey proposition. The insides

of these guitars are not able or designed to handle such modifications.

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You would have to tap the signal off before it gets to processor board,

and not mess up the input impedance in that signal line doing that mod.

 

-Not recommended, so don't do it.

 

-Trying to turn a 6-string guitar into an 8-string,... the other two strings

would have to be processed separately, and the processor isn't equipped

to do that.

 

-Running signal to an external processor is a dicey proposition. The insides

of these guitars are not able or designed to handle such modifications.

Well, I think more accurately that I'm simply hoping to tap into access to the piezo without going thru the Variax. Which I'm seeing is nothing new here. Only difference is that in this case I'm only looking for 2 strings, rather than all 6. Although having all of them available would certainly not be an issue, if there's separate level control on each string.

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Both.

And I'm someone who knows the insides of these guitars

really well. 

 

Hey Parkissian, do you think it would be possible to split the signal coming from the piezos before it goes to the motherboard processor?

I'm thinking if such mod is possible then one would be able to finally have the pure piezo signal and feed it to a separate output (preamped) or connected together on a stereo female jack in order to have both worlds combined. Just wondering if  that is possible? 

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Possible, difficult,... again, there are impedance issues, along with signal

and noise issues to overcome. And would have to be done in a way that doesn't

pull down supply voltages. It's touchy stuff, easy to make it all FUBAR.

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So... Is it Possible to have Graph Tech Acousti-phonic preamp on Variax, achieving separated raw piezo (without a DSP-delay) output? 

Graph Tech FAQ tells, that we can't use Hexpander Midi with Variax DSP at the same time from the only sets of saddles, due to impedance issues. How do you think, what about acousti-phonic? Same story? 

The main desire - achieve truly immediately response, little bit faster, then modelling sound. Magnetic pickups is nice solution, but i'm not sure about magnetic field influence on string sustain, and not ready to drill my Vax700. 

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More like a custom job, since you can't run these other devices off of a Variax supply line.

It also means that the Alt Tune would clash with standard tuned string signal.

Trying to tap the piezo signal off without pulling down the line,... you need someone with

intimate knowledge of Variax inside circuitry, otherwise the signal will be sucked away by the tap off circuit.

 

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