Is there a scientific way of doing this?

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fractalman

Member
Hello. I have a “one-off” guitar which has two humbuckers and piezos in the bridge/saddle. It has a push/pull knob to engage an onboard preamp which I’ve always used in the “on” position when using the humbuckers. It sounds great. I created all my FM9 Presets around it being “on.” Now the preamp is starting to fail, and the easiest thing would be to just stop using it – putting the push/pull in the “off” position” – permanently. I never use the piezos, anyway. It’s not that I don’t want to replace the preamp. It’s that the guitar maker is nowhere to be found and I have no way of finding out what this preamp is – assuming I could ever find the exact replacement.

While the preamp is still working (though intermittently), I’ve recorded my guitar with the preamp on and off and done an EQ match in both Logic Pro X and using Izotope. I spent 2 days trying to adjust presets to match the “preamp off” sound to the “preamp on” sound, by ear, and I can only get somewhat close. I’ve tried “boosts” in the amp block – just about everything. Is there a way to measure the “preamp on” signal compared to the “preamp off” signal in a more scientific way? If I could identify the exact value it would make changing all these presets so much easier!! Thanks.
 
I'm guessing that the preamp on position produces higher output. Did you try increasing the input trim in amp block? Not sure if this will help, but it's worth experimenting with, if you haven't already. The input trim is on the first page of the amp block in Axe Edit.
 
Yes, definitely. I can match the volume, but the preamp colors the tone in a way that I can only approximate. Of course, it all depends on how picky you are. I guess I'm pretty picky. I've spent so much time dialing in tones that I love with the preamp on, that I want to have the exact same thing again the preamp off :)
 
If you use an out block before your amp block and send it to your daw, you can record a reference track with the preamp on. Then use an eq matching plugin to analyze it and store the curve.
Then record a second track playing the same thing with the preamp off and analyze it against the reference curve. If it's just gain it will be simple, if the eq curves are different you can use an eq block in the fractal to get the preamp off tone to match the preamp on.

I use the free Gerriant spectrum match plugin for reaper to clone pedals and piezos.
 
fractalman said:
Yes, definitely. I can match the volume, but the preamp colors the tone in a way that I can only approximate. Of course, it all depends on how picky you are. I guess I'm pretty picky. I've spent so much time dialing in tones that I love with the preamp on, that I want to have the exact same thing again the preamp off :)
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+1 to @WKSmith's suggestions.

That said, it's not super likely it has always-on tone shaping built in.
Possible, but not typical.
You said the maker is gone, but who was that?

More likely, it has two main effects:
  • Level boost
  • Cable driver/impedance buffer

Level boost is easy in the Axe, in a million ways.
Isolating the guitar from a long cable run, which without a buffer cuts highs, is trickier, because it's an analog interaction with the pickups and controls, and isn't that easy to measure in isolation.

One easy thing you could try is setting the input block impedance to 1M.
That avoids loading of the guitar by anything inside the Axe, but not loading from your cable.

There are transparent buffers available that you or a decent tech could install to would have that effect.
 
Hi WKSmith. Yes, I've done the EQ matching in both Logic Pro X and with Izotope Ozone (please see my post). I then replicated the curve with a Parametric EQ. It helped but there's definitely something else that I can't seem to replicate.
 
@Dave Merrill is probably right on the money with that pre being a buffer. I use the L6 wireless plugs now ..as they have a buffer built in.

If you have a pic of that pre and some info on the builder we can dig a little bit.
 
Hi Dave. It's more like the guitar maker is not responsive to e-mails. I rather not post his name, as I'm not painting a flattering portrait, and he still makes great guitars. He's just not easy to work with.
 
If you have a tech you trust, ask them of they could recommend or install a transparent buffer, ideally with a gain trim pot, see how that goes. Keep the old one, to keep your options open.
 
A pezio transducer is basically a contact microphone attached to the saddles of your guitar. This is going to give a bright and immediate attack.

I would try taking a split from input one run this second line into a filter block with an aggressive low cut and high boost followed by a gate. With the gate you probably want it to clamp down pretty quickly. Loop that back into the signal chain before what would have been your first block on the fractal.

As for the pre amp, you could try reaching out to fishman about the preamp. There is a decent chance that they would have something that could replace your dying pre amp.
 
Onboard preamps can affect the sound many ways.

They can:
  • act as a buffer to remove the loading of the cables and effects.
  • boost the signal.
  • re-EQ the signal and boost or cut the frequencies to make the pickups sound like different single-coils or humbuckers; Fishman uses this to change the sound of their Fluence humbucker’s pickup’s basic sound from high gain to a slightly reduced output PAF with more highs. Fender uses one in the Clapton Strat because that’s how he gets his solo sound.
  • all of the above.
I used to put small op-amp buffers in my guitars years ago for the first reason and liked how the pickups retained their real sound in spite of the old pedal designs. On my Strats I also added the boost. Those two reasons would be enough to get me to consider replacing it, or at least digging in to figure out what its problem is. It might be a simple squirt of contact cleaner into a switch or DIP-switch or trim pot.

I’m sure you can find replacement preamps to replace whatever is in the guitar if you want. The current one is probably mounted on a PCB but a hacksaw, hammer and propane torch will quickly remove it. If you’re not familiar with using those tools on your guitar I’m sure a technician would be happy to do so. The result wouldn’t be stock, but might be more functional.
 
Thank you Greg. My guitar tech cleaned all the switches but I don't think he examined the preamp circuit board. The preamp appears to be a circuit board wrapped in a shielding material. I just got this photo from the guitar tech :) He took this while it was on the bench.
 

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fractalman said:
Thank you Greg. My guitar tech cleaned all the switches but I don't think he examined the preamp circuit board. The preamp appears to be a circuit board wrapped in a shielding material. I just got this photo from the guitar tech :) He took this while it was on the bench.
Click to expand...
Copper foil is good. Hopefully they can figure out what is happening. The foil and board might have an intermittent short or a solder joint failed, or a connector worked loose.

Or it used all its mojo. That’d be bad because mojo is in such short supply these days.
 
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