Ghost Acousti-phonic+Hexpander RF noise?

Started by kknyc, January 05, 2024, 06:04:12 AM

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HI, Im new to the forum—and to the hex pickup world in general. SO the 'obvious answers' are still hard to see....

I have an Emerald Balor5 with OEM GT GHOST saddles and Acousti-phonic installed.
The bass plays great thru the system, no issues / no noise.

I installed the Hexpander upgrade (piggy backed) to use with GR-55 but now I get noise (RFI) thru the 1/4" stereo jack if I plug in the 13pin cable at the same time.

NOTE: Both signals are silent (noise free) if I just use the 1/4"out OR just the 13pin out. Any RF/hum/noise is only present thru the bass 1/4" out if I try using both outputs at the same time.. Feels/sounds like a ground loop?

SO my question is... Can I use both the bass' 1/4" AND 13-pin outputs at the same time? Or is the system setup to use either/or?

Im aware that using the GR-55, I don't NEED to use the 1/4" out on the bass, I just want to ensure that my installation is correct, what my overall options would be.

thanks for your insights!


Both 1/4" and GK-13 outputs are low impedance on your Bass , but may experience a Ground Loop when both are used at same time

Insert a Passive DI on the 1/4" Output should tame the Hiss


Thanks Elantric much appreciated (link too)!

The hiss is minimal, but it picks up alot of radio freqs.
I'll def grab a passive DI.

Hmmm, I wonder if a balanced TRS—TS or XLR—TS cable aid this as well? ...heading off to the link now
balanced cables didnt help with the RFI


update... I guess in the haze of 'problem solving' I missed that the GR-55 has output L/R AND gtr out. (warned ya I was new to this ;D )

the RFI is coming from bass' 1/4" output jack AND the GR-55's Gtr Out signals only. The RFI also dips and clears out as I move around my apt. —Ive had similar issue with a few basses in the past but once shielded theyre dead silent, seems that I need to do the same here? (but where? the Ac+Hex piggybacked boards? the piezo leads?)

  • 13pin to GR-55 L/R outputs are silent/noise-free
  • Bass 1/4" w/out the PIN13 is silent/noise-free
  • RFI happens both thru an Amp or DAW—with both GR-55+AMP or GR-55+DAW on same grounded power source or different powers sources.

Theres an extra ground wire on the bass' 1/4" stereo switched output, would building a copper shielded 'cage'/box over the piggybacked boards tied into that ground wire help?

PS> Also tested my 13pin cable— all pin connections and outer shell ring have continuity to themselves alone, and the cable is in good working order (as read about here on VGF)


Review and read the prior posted link to solve your ground loop/RFI Noise

Solve Noise problems


I just tested a DI in-between the GR-55 Gtr out> and my amp (and again in-between the Bass 1/4" out and the amp) it didn't help, still got RFI. This is definitely feels related to the Ghost 13pin Module acting like an antenna. (touching the 13pin module doesnt help, but moving it or the bass around does)

And thanks again for the link Ive read thru. I'll look again maybe I missed something

(just ordered a PylePHE300 to further test... should arrive tomorrow, but ultimately would like to find an internal fix if possible over having 'another box' to add to my gear schlep)

As feared the source of the RFI is at the boards—the PHE300 had no affect on the RFI.

CH1 (bass 1/4" jack)
CH2 (GR-55 GtrOut)

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I am not sure the RFI is being picked up outside the guitar but inside. I suspect that snce the strings are not grounded (correct me if I am wrong) they may be acting as the antenas and the Hexpander might be indirecttly picking that too.

It would be good if you post detailed picutures of your installation.

I would try to test running a wire that touches all the strings down to a ground point, possibly the jack plate. Does it improve?

Failing that definetelly try shielding the Ghost modules.


Hi thanks guys. This bass/setup is basically like a big "Nylon string guitar" (ie classical guitar w/ piezo acoustiphonic+hexpander installed). So the standard 'string contact' grounding wont be the same here with Nylon/Silver wrapped string set.

Ive tried running a 'ground jumper' to strings (fashioned with a strip of copper tape woven across the saddles screws), and also contacted both the hex and 13pin modules in various places, etc. Nothing stops the RFI when the 13pin is plugged in. The bass runs silent otherwise and sounds great otherwise. (Having worked on my electric basses for decades, Im confident with proper shield techniques but this is a conundrum for me. I feel the Hexpander, or 13pin board, or both are the source of the RFI.)

I even tried taking my big roll of copper shield tape and try to clumsily 'cover' over the 13pin module... nada

Here are some images... not much to see, just the standard Ghost system in piggy-back setup mounted to the side wall inside my acoustic. and the 13pin module is going in a recessed the back plate im 3d printing. (currently taped to the inside of the bass)

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I'll try 3d printing a 'shield' cover this weekend for the boards and 13pin module and line it with coppershielding to see if that helps.

Thanks agin for insights!


further testing tonight...

I thought "let me unplug items from the signal chain one by one";

Balor/GT Ghost> Acousti+Hexpander> 13pin module> 13Pcable> GR-55. = RFI

Balor/GT Ghost> Acousti+Hexpander> 13pin module> 13Pcable.        = RFI

Balor/GT Ghost> Acousti+Hexpander> 13pin module.                  = minimal RFI

Balor/GT Ghost> Acousti+Hexpander.                                = silent

Well I didn't hear it initially, but boosting the gain the RFI is there even (just lightly) with the GK13 cable unplugged. So I imagine I'll need to find an internal shielding solution for this.
But once I insert the GK13 cable the RFI is significantly louder (like an antenna). Maybe a poorly shielded cable?

heres the cable that came with my GR-55 looks similar to images I see on the forum but no imprint on the cabling or jacks...
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Well, maybe a Primova cable order is in my future


There is a reason RMC Piezo are the recommended setup for Nylon Instruments. Particularly when used with a Modelled Guitar System vs a Guitar to MIDI system, which is what the  GraphTech electronics were designed for. Graphtech assumed the Hexpander user will always be connecting to a 13 pin  Guitar/Bass to MIDI interface or Guitar/Bass to PCM  system, ( like early GR-20), so they tolerate higher noise/hiss- as they figure none of that noise will be output from the MIDI SYNTH.

All that goes out the window when a Graphtech 13 pin system is connected to a Roland VBass, VB-99, GR-55 (COSM Mode) , SY-1000  which all rely on the Strings being the direct Oscillator pitch source - and any noise in the preamp signal path will become a portion of the output to Amplifier.

Enabling the Noise Suppressor on the Roland/Boss GK Processor is the method used to tame the noise generated from the  Graphtech Hexpander - but that restricts dynamic range vs the much lower noise RMC Polydrive 13 pin Preamp.


thanks Elantric, I'm quickly becoming aware of the RMC popularity here. I love the system too, merely took the path of (what I thought would be) least resistance since my instrument already had the Ghost saddles and pre installed.

Im trying to imagine how I could 'enclose' the boards and wiring in copper shielding to calm things down.


Ohhhh thanks Elantric! I was trying come at this from an EB/coppershield tape/cavity mindset, but how to section off the big interior of the acoustic corpus?

That amazon EM/RF blocking fabric looks great! (and some of those images of blocking wrap)

Tahnsk again, sometimes the hardest part is finding where to look first ;) I'll post some images when I come up with a solution—Thinking I'll probably move the whole thing to the back plate area and 3d print a cover with mounts and angled 13pin port printed into it.

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yeah I had also thought about something in a circular can to fit into the back plate access hole glued to the plate with all three board mounted inside.

I'll do some reading, do you know if the tin blocks as well as copper or nickel coated copper? (I'd like to avoid multiple testing and go right up to the most robust blocking potential— kinda "one and done" approach, as my schedule is kicking back in and time is getting tight. That military grade stuff looks great but I bet it cost prohibitive  ;D )


definitely an RF issue with the ribbon cable and 13pin module. I tried to do a "test wrap" and it worked for a minute, but the RFI came back. —but if that initial drop in RF works, I think remounting the boards and module in a 'cage' should help *fingers crossed*

wrapped the module in tape then covered in some tinfoil for a quick test. I did notice the ribbon cable acts like a mild antenna and when attaching the 13pin module, RFI increases significantly. So maybe keeping the boards and the module all the same shielded  container is best bet.

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Yes - shorten the ribbon cables,( they act as antennas for RFI/EMI Noise )  and verify the piezo saddle wires are shielded too ( Graphtech just provides 2 unshielded wires to each Piezo saddle -sad)

Earth ground reference all shielding too.
.remember the only available Ground on GK-13 plug is the large round chrome shell - reference your grounds to the shell  connection on the female GK13 jack.

Graphtech does a very poor job on the stock configuration , they definitely have very little knowledge about GK-13 interface on real time  Modelling Systems - like SY-1000. 

They assume the instruments electronic control cavity already has a complete EMI/RF Shield conductive paint and ground referenced

I will attempt a dialog with Graphtech  in 2 weeks at Winter NAMM- but last time I talked with the CEO, he was still believing that everyone was still connecting to a GR-20 PCM Synth - so why spend money on shielding?


I hope your contact helps! Please pass my woes to them ;D
I wanted to go this year to see my friends at Aquilastrings but I can't get away. (wish they did NAMM in NYC  ;) )

I emailed GT yesterday about offering any help/info (is there a grounding spot on the 13pin module? Hoping I could tie that to ground)

I have a milli-grid set of connectors coming this week so I'll replace the ribbon cables (or at least try) with a shielded custom harness between the the 13pin module and the Hexpander, AND the pickup extension ribbon, as well as try to move everything into a cage mounted on the back plate.

so much for the path of 'least resistance' LOL



The two large metal mounting tabs on each side of the GRAPHTECH HEXPANDER GK13 DIN Jack are Ground


I'll try building a cage tied into those screws then tied into the extra ground lead at the output jack.

Curious does anyone know or have experience with cutting RFI using CAT 6 grounded network cabling?

the ribbon cables included in the GT kit are a problematic source of picking up RFI. My thought is to replace that cable and thought about using CAT6 cable.

Since the pickup leads are 'sensitive' has anyone lightly twisting them in pairs to reduce noise? (they are very microphonic already wondering if splitting the leads and twisting/bundling them/wrapping in a grounded copper shield would help)


Id rewire the Graptech saddles to resemble RMC method, with individual coax shield per saddle = lowest crosstalk