"remote powering" my guitar?

[eleanor296]

so... I've previously voiced that I love the idea of the Tillman guitar cable preamp... but I got to thinking... couldn't I use the same principle to power a circuit WITHIN a guitar?  See... I hate batteries.  I really do.  But having a preamp/buffer/booster on a guitar is such an AWESOME idea.  Would there be any problems I am not thinking of right now?  I mean, it'd be as easy as just using TSR jacks and plugs, wouldn't it?

Oh, and many thanks for you guys' creative insights everywhere!  Best/nicest/most knowledgeable people on any forum I've been on!

Andy

[ianmgull]

I've thought about this before. If you have an onboard buffer/booster why you should be able to power it via TRS. You're signal one one lead, +9v on another, and ground on the third. The only question is if there would be a problem with your guitar ground sharing ground with the power supply.

[earthtonesaudio]

No problem.  You can do the Tillman inside the guitar (and use a regular mono cable) with no changes to the circuit, just put it inside the guitar!  Of course you still need the external phantom power box, and a true-bypass switch if you ever need to go passive again (like if you forget to bring the phantom power box to a gig).

You could also do the stereo/TRS setup, but if you put +V on the ring and ground on the sleeve, you would have to be careful to never ever plug in a standard mono cable, as it would short the power supply.

[jalien21]

my understanding is that phantom power is like, when you superimpose a dc voltage on your audio signal, rather than have an extra wire. so you'd use a mono cable. condenser mics do it, anyway. why not just power your onboard situation with something adapted from that?

[Gus]

Been done before

look around this site
http://www.ebs.bass.se/2007/neodrome12.htm

[sean k]

I'm just thinking that, while a capacitor is used on a normal output to remove the DC and leave only the AC signal, in this case the opposite needs to occur at the preamp output to take the AC off the line and leave only the DC so only the DC sits on the power supply for the preamp in which case this could be done using a choke.

But the problem is that I would have no idea about how to figure what particlur mixture of inductance, DC resistance and AC impedace would be required in the choke. So the mono cable off the end of the preamp would have a capacitor in series from the AC output and an inductor in series to the power supply. The other end would be like most phantom supplies.

This though, (not having the inductor) is only because the preamp supply rails would have the output signal on it and that, to my mind, would be almost the same as the bootstrapping we had the contest about recently. If its a transistor out then the AC signal is on both ends of the collector resistor and if it's an opamp out then the same AC signal is on the supply and bias points while also being on the output but with an inductor, in series, that AC signal will be converted to DC... depending on the impedance... I think... possibly 

[earthtonesaudio]

Use a spare pickup as a power filtering choke.   











...just kidding.

[Gus]

IMO three wire powering is better for guitar bass etc tip signal, ring +9, and sleeve ground.  The ring connected supply needs to be short circuit proof for when the jack is inserted and the ring and sleeve might be touching the the sleeve contact surface in the jack.

   Phantom power for microphones is from a balanced XLR pins 2 and 3 and the return is pin 1 and the shield.  48 VDC is the voltage that is connected via matched 6.8K resistors.  The voltage advailable at pins 2 and 3 in the microphone is determined by the current draw of the microphone.

Other things to look up T power like used in older Gefell, Neumann and Schoeps circuits IIRC and other phantom power specs.

[chi_boy]

so... I've previously voiced that I love the idea of the Tillman guitar cable preamp... but I got to thinking... couldn't I use the same principle to power a circuit WITHIN a guitar?  See... I hate batteries.  I really do.  But having a preamp/buffer/booster on a guitar is such an AWESOME idea.  Would there be any problems I am not thinking of right now?  I mean, it'd be as easy as just using TSR jacks and plugs, wouldn't it?

Oh, and many thanks for you guys' creative insights everywhere!  Best/nicest/most knowledgeable people on any forum I've been on!

Andy

Are you talking about something like this:

http://www.guitarelectronics.com/product/PMTXBAT9/9_Volt_External_Battery_System_for_Active_Electronics.html





One of these days I want to figure out this thing too.  I thinks its's built into the one above, but haven't look into it in a while.

http://www.guitarelectronics.com/product/PMTLBAT/9_Volt_Low_Battery_Indicator_for_Active_Pickups_Electronics.html

[Zben3129]

I know I am missing something (never recorded in a studio etc.), but what is the point of an onboard effect if you need to use an external box to power it? Why not just put it in the external box. Only reason I can think of is phantom, but I didn't think that is what you were referring to.

Zach

[Gus]

http://www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=active_jazz_bass

What I think the X bat thing is doing.  Look at the circuit in the above link.  The battery is removed and the battery connector in the bass/guitar is jumper together.  The tip is the signal, ring is now supplied with +9 and sleeve is still ground.  Note you need to use a stereo cable from the box to the bass/guitar.  And it uses the tip ring sleeve jack that normally turn the installed active circuit on when a tip ring plug is inserted completing the neg leg.

 I think the EBS does the same but power is supply from a +9 power supply circuit in the amp.  

As I posted before a short circuit proof supply would be a good idea because the ring(+9) and sleeve(ground) can short when inserting a plug into the jack

So if you want to do this you will need to install a TRS jack.  Look up current limiting for voltage regulated supplies.  What you can do is build a regulated supply and set the current limit just above what the active circuit needs also the power pass transistor will need to survive the power rise if the output has an extended short.

[FiveseveN]

Zach, the way I figure it is the less cable between a pickup and a buffer/preamp, the better. That's obvious, but with (other) onboard effects you have the bonus of its controls at your fingertips.
You're gonna plug your guitar into a big heavy box anyway, you might as well move your power supply from hanging on your shoulders to that big box. I power my guitar through stereo cable/TRS jack from a multi-effect on my pedalboard because I always use them together. But I suppose I should make one of these "phantom power" boxes in case I'd ever want to use the guitar on its own. As yet another bonus, the box can either contain a battery or just be an interface between the guitar cable and pedalboard PSU (or standalone PSU if you go straight to amp).

[eleanor296]

chi boy, that's exactly what I mean!
Thanks for the help Gus, I'll have to figure this out some time... The next couple days I think I'll have my hands full modifying 2 preamps for Rusty Milner (Marshall Tucker Band).

[xshredx]

One of these days I want to figure out this thing too.  I thinks its's built into the one above, but haven't look into it in a while.

http://www.guitarelectronics.com/product/PMTLBAT/9_Volt_Low_Battery_Indicator_for_Active_Pickups_Electronics.html

You just want to be able to light a led when your battery voltage is below a certain limit...?
Isn't that done with a voltage comparator?   Basic op-amp function...  see for instance: http://web.telia.com/~u85920178/begin/opamp00.htm , which has a battery under/over voltage indicator schematic on that page...

[eleanor296]

no... not it at all.  I want to power a circuit built into a guitar from a guitar cable.  No batteries involved.

[Gus]

http://cache.national.com/ds/LM/LM317.pdf

look at page 20 for a current limiting voltage regulator

[chi_boy]

One of these days I want to figure out this thing too.  I thinks its's built into the one above, but haven't look into it in a while.

http://www.guitarelectronics.com/product/PMTLBAT/9_Volt_Low_Battery_Indicator_for_Active_Pickups_Electronics.html

You just want to be able to light a led when your battery voltage is below a certain limit...?
Isn't that done with a voltage comparator?   Basic op-amp function...  see for instance: http://web.telia.com/~u85920178/begin/opamp00.htm , which has a battery under/over voltage indicator schematic on that page...

eleanor296:  Didn't mean to highjack your thread, but I thnk xshredx was replying to my question about the Lo-Bat.

xshredx: Yes, that looks like it might be right.  I'll have to breadboard that and play a little.  Will be interesting to see the current draw.  Thanks for the tip!

[eleanor296]

Gus, thanks for the link.  Will check it out.

xshredx and chi boy, cool deal!  Sorry for the confusion.  Maybe I should read my own threads more thoroughly

[tempus]

I too have been thinking of doing something like this. In my case I have my pedals in a switching pedalboard anyway, so it wouldn't be that big of a deal to add phantom power so I could use a buffer (one of my electrics has a piezo bridge for acoustic sound, but the output Z is way high).

I think some of the responses here are making it seem more difficult than it actually is. I don't see any reason why the AC would need to be filtered out of the signal with a choke - a series capacitor will keep the DC off the pedal inputs and the guitar output. The short circuit issue may be a problem though, but the LM78xx series of regulators have internal short circuit protection. Would that be robust enough to protect against the inevitable short circuiting that would occur when the cable was plugged into the guitar?

[tempus]

I was reading the LM78xx datasheet a little closer. Check this out:

The LM78XX series of three terminal positive regulators
are available in the TO-220 package and with several
fixed output voltages, making them useful in a wide
range of applications. Each type employs internal current
limiting, thermal shut down and safe operating area protection,
making it essentially indestructible.

That's quite a claim...

It would appear that using a regulator of this type would solve our short circuit problem then. Any other thoughts on this?