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9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

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9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sat Sep 06, 2014 5:42 pm

I'm in supergeek mode again - and have made a 9V DC 'phantom' power supply box (pic below) for my electro acoustic guitar which has an LR Baggs Anthem dual source system.

Image

Via the ring of a TRS cable, it delivers 9V DC to the on-board preamp.

It works beautifully if I connect a 9V PP3 battery to my external power supply box. However if I connect a regulated 240V AC to 9V DC power supply adapter - it creates an awful noise.

The Anthem preamp does switch on, evidenced by the power LEDs lighting up, but there is no signal output at all. I'm getting a high-pitched whine and no guitar sound...

I'm fascinated as to why this might be… what do you think?

TRS Socket (on the left) - receives TRS cable from guitar
Tip- signal
Sleeve - ground and 9V DC negative
Ring - 9V DC positive

TS socket (on the right) sends TS cable onward to mixer / amp

9V DC sockets (in and thru) at the top.
+ve is linked to the TRS Ring
-ve is linked to the TRS sleeve / ground

The info below may (or may not) be relevant:

On the guitar I've used a TRRS end-pin socket.

The RING terminal of the default TRS output jack was not connected to the battery, but to a voltage-activated transistor that engages when that terminal is connected to ground. That circuit is between the terminal and the battery. This moves the power switching lead on the existing RING connection to the second RING of the TRRS and opens the standard RING for carrying the power back to the guitar.

I'd be most grateful for your expert opinions...
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Hugh Robjohns » Sat Sep 06, 2014 5:47 pm

Are you sure the mains PSU has the correct DC polarity, and can provide the required amount of current?

I suspect the external PSU isn't beefy enough and the power regulator is struggling to cope.

H
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sat Sep 06, 2014 5:53 pm

Thanks Hugh. The guitar works off a single PP3 9V battery.

The AC/DC adapter I used is a switching power supply (110-240V AC) rated at 1.5A at 9 volts DC.

Paul White wondered about the possible need for a capacitor, but recommended that I ask you :)
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby ef37a » Sat Sep 06, 2014 6:06 pm

Does the power supply have a metal earth pin?
If so I would put 5bob on the the sleeve of the power plug being tied to it. I take it the guitar rig feeds an (earthed) amp, so you have a hum loop. Or more precisely, a SMPSU tone loop!

Just about a year ago I waded through about 30 9V supplies from various sources and they all put out varying amounts of HF crap. The amplitude and frequency of said crap was also load dependent.

You might however try a 10mfd 22volt capacitor across the power socket and, noting Hugh's point, a 1N4008 or sim' diode as polarity protection. Wrong polarity will of course do a battery no good at all and might fork the PSU but better that than the guitar pre amp?

Dave.
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Hugh Robjohns » Sat Sep 06, 2014 6:09 pm

I can't imagine its a restricted current problem then.

So another possibility is that the power supply is producing very noisy DC and/or picking up RF, and that noise is being passed through the guitar preamp (this is where PW's suggestion of some smoothing/RF decoupling capacitors between the positive and ground would come in).

Or perhaps there's some odd grounding issues going on between the mains power supply and the rest of your audio system.

Without being able to poke around it with a scope it's a hard one to remote diagnose, I'm afraid.

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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Fri Sep 12, 2014 5:58 pm

Dear Hugh and Dave

I tried my set-up with a Voodoo Labs power supply. Worked like a charm...

Obviously my other switching mode supply is not very good :-(

Thanks for the advice...!

Kind regards
Jay
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby ef37a » Fri Sep 12, 2014 6:38 pm

JM-1 wrote:Dear Hugh and Dave

I tried my set-up with a Voodoo Labs power supply. Worked like a charm...

Obviously my other switching mode supply is not very good :-(

Thanks for the advice...!

Kind regards
Jay

STILL think you ought to fit a cap and a diode...***t'appen!

Dave.
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sat Sep 13, 2014 1:51 pm

ef37a wrote:STILL think you ought to fit a cap and a diode...***t'appen!

Dave.

Exactly what do I do please Dave? (I'm fine with a soldering iron...)
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby ef37a » Sat Sep 13, 2014 2:44 pm

JM-1 wrote:
ef37a wrote:STILL think you ought to fit a cap and a diode...***t'appen!

Dave.

Exactly what do I do please Dave? (I'm fine with a soldering iron...)

Simply connect a 10mfd* capacitor from the + to - pins on the power connectors and in parallel with the cap' a diode, 1N4007 or any 1 amp diode. Cathode of diode to the +ve pin.

PM me if you want a drawing, can't post attachments here.

*Could be bigger than 10mfds. Needs to be 16volts minimum but a higher voltage won't hurt. Pretty much whatever's in the remains bin!

Dave.
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sat Sep 20, 2014 12:30 pm

Thanks Dave

I'm going to solder the diode and capacitor today.

as you have instructed, the cathode of the diode goes to the positive terminal of the 9v dc socket.

The negative terminal of the electrolytic capacitor - does that connect to the positive terminal of the 9v DC socket too?

Kind regards
Jay
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby DGL. » Sat Sep 20, 2014 2:36 pm

JM-1 wrote:Thanks Dave

I'm going to solder the diode and capacitor today.

as you have instructed, the cathode of the diode goes to the positive terminal of the 9v dc socket.

The negative terminal of the electrolytic capacitor - does that connect to the positive terminal of the 9v DC socket too?

Kind regards
Jay

If I remember correctly, the capacitor goes across the positive and negative terminals, pos to pos neg to neg.
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sat Sep 20, 2014 6:07 pm

DGL. wrote:
If I remember correctly, the capacitor goes across the positive and negative terminals, pos to pos neg to neg.

I dearly hope you're wrong - because I've soldered the negative terminal of the capacitor (and the negative terminal of the diode) both to the positive terminal of the DC connector... :blush:

The box is enclosed - so if there's an explosion hopefully I'll be safe... :headbang:
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby DGL. » Sat Sep 20, 2014 7:57 pm

JM-1 wrote:
DGL. wrote:
If I remember correctly, the capacitor goes across the positive and negative terminals, pos to pos neg to neg.

I dearly hope you're wrong - because I've soldered the negative terminal of the capacitor (and the negative terminal of the diode) both to the positive terminal of the DC connector... :blush:

The box is enclosed - so if there's an explosion hopefully I'll be safe... :headbang:

Probably won't work esp. if the capacitor is in series with positive terminal and the diode.

What you are essentially trying to recreate is the output side of a voltage regulator. The capacitor is there is to smooth the output and to hopefully route any AC noise to ground (a capacitor blocks DC but allows AC to pass in this case to ground) and the diode as protection from polarity reversal (on the negative side and the positive side naturally won't care about 0v being applied to it, the negative side WILL care about 9V being applied to it).
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Jay Menon » Sun Sep 21, 2014 6:32 am

DGL. wrote:Probably won't work esp. if the capacitor is in series with positive terminal and the diode.

What you are essentially trying to recreate is the output side of a voltage regulator. The capacitor is there is to smooth the output and to hopefully route any AC noise to ground (a capacitor blocks DC but allows AC to pass in this case to ground) and the diode as protection from polarity reversal (on the negative side and the positive side naturally won't care about 0v being applied to it, the negative side WILL care about 9V being applied to it).

The capacitor and diode are both in parallel with each other and the terminals.

The cathode of the diode is connected to the positive terminal of the DC 9V input socket as instructed by Dave.

My doubt pertained to the capacitor, with of course has a + and a - wire...

This pic would indicate that you are right and that:

The + connection goes to the point with the highest potential (VCC or +V)
The - connection goes to the lower potential (-V)
Image

Fortunately it hasn't exploded (yet)
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Re: 9 Volt DC Phantom Power Supply for Electro-Acoustic Guitar

Postby Dheran » Sun Nov 15, 2020 5:56 pm

Jay Menon wrote:I'm in supergeek mode again - and have made a 9V DC 'phantom' power supply box (pic below) for my electro acoustic guitar which has an LR Baggs Anthem dual source system.

Image

Via the ring of a TRS cable, it delivers 9V DC to the on-board preamp.

It works beautifully if I connect a 9V PP3 battery to my external power supply box. However if I connect a regulated 240V AC to 9V DC power supply adapter - it creates an awful noise.

The Anthem preamp does switch on, evidenced by the power LEDs lighting up, but there is no signal output at all. I'm getting a high-pitched whine and no guitar sound...

I'm fascinated as to why this might be… what do you think?

TRS Socket (on the left) - receives TRS cable from guitar
Tip- signal
Sleeve - ground and 9V DC negative
Ring - 9V DC positive

TS socket (on the right) sends TS cable onward to mixer / amp

9V DC sockets (in and thru) at the top.
+ve is linked to the TRS Ring
-ve is linked to the TRS sleeve / ground

The info below may (or may not) be relevant:

On the guitar I've used a TRRS end-pin socket.

The RING terminal of the default TRS output jack was not connected to the battery, but to a voltage-activated transistor that engages when that terminal is connected to ground. That circuit is between the terminal and the battery. This moves the power switching lead on the existing RING connection to the second RING of the TRRS and opens the standard RING for carrying the power back to the guitar.

I'd be most grateful for your expert opinions...

Hello! This is a really old thread... But I'm desperately searching for a way to power my Baggs Element VTC from the outside. My battery bag adhesive failed once and i don't want to deal with it anymore... And also don't like to loosen strings to change the battery.

I made the same system as you, but there's no power in the guitar. I than realised what you wrote about a TRRS socket. Not sure I completely understand it, but do you think that could solve my problem? Thanks!
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