Hi. My TE AH350X has both the usual jack input and an xlr input. No, I'm not confusing it with the D.I. out - that's a separate connector. I like to switch the amp eq out and go through my Sansamp pedal into the xlr socket and set my eq on the pedal. It would be so convenient if the head could supply 48V phantom power via the xlr cable. I have a small 48Vdc supply and there's plenty of space inside the amp case. I've seen an excellent web page showing how to wire the resistors - all pretty straightforward. I'm just wondering if any fellow TB'ers have done anything like this before. Any tips? Thanks in advance.
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Phantom power
- Thread starter Sneakypete
- Start date
billfitzmaurice
Commercial User
- Sep 15, 2004
- 16,860
- 278
- 76
- Disclosures
- Owner, Bill Fitzmaurice Loudspeaker Design
Phantom power is easy to implement, but it uses capacitors to isolate the DC, not resistors, so I question the web page you referenced.
I think he is referring to the close tolerance resistors used to apply the +48V to the balanced lines. The amps input capacitors from the XLR will need to be able to handle that 48V also.
Phantom Power Explained
I'm not very good at pasting links so this may not work. What it shows though is the positive side of a 48Vdc supply going to the junction of two closely matched 6810 ohm resistors. The 'free' ends of those resistors then go to pin 2 and to pin 3. The negative side of the supply is connected to pin 1 ground. There's a 68uF capacitor between the resistor junction and ground. The theory is that if the resistors are low tolerance (1% minimum, 0.1% recommended) then there will be no measureable voltage across pins 2 and 3. There will be 48V between 1 and 2 or between 1 and 3. This sounds to me like it should work. I know can get a dedicated unit with xlr in and out and an external, wallwart type power supply but I'd prefer to have it all neatly inside the head. Any thoughts?
I'm not very good at pasting links so this may not work. What it shows though is the positive side of a 48Vdc supply going to the junction of two closely matched 6810 ohm resistors. The 'free' ends of those resistors then go to pin 2 and to pin 3. The negative side of the supply is connected to pin 1 ground. There's a 68uF capacitor between the resistor junction and ground. The theory is that if the resistors are low tolerance (1% minimum, 0.1% recommended) then there will be no measureable voltage across pins 2 and 3. There will be 48V between 1 and 2 or between 1 and 3. This sounds to me like it should work. I know can get a dedicated unit with xlr in and out and an external, wallwart type power supply but I'd prefer to have it all neatly inside the head. Any thoughts?
It IS a very simple project and you have all the information that you need already contained in this thread.
Back in the day I added a seven transistor pre-amp to my '63 P bass. Bass, a preset pot, set flat and the normal tone control replaced by the treble pot. The pre-amp was built on a small PCB shaped to fit into the existing control cavity. Having no space for a battery I designed and built into my main pre-amp a +48V current limited supply feeding the ring on a TRS jack. The onboard pre received its power via the ring on the output jack. Using a two core plus shield cable terminated with TRS plugs completed the circuit. Worked beautifully for all the time I used it.
Back in the day I added a seven transistor pre-amp to my '63 P bass. Bass, a preset pot, set flat and the normal tone control replaced by the treble pot. The pre-amp was built on a small PCB shaped to fit into the existing control cavity. Having no space for a battery I designed and built into my main pre-amp a +48V current limited supply feeding the ring on a TRS jack. The onboard pre received its power via the ring on the output jack. Using a two core plus shield cable terminated with TRS plugs completed the circuit. Worked beautifully for all the time I used it.
Hmmm...interesting idea, Paul. The Sansamp also runs on 9V of course so I could do this by changing to trs plugs and sockets all round. I could also run my Pitchblack tuner on the same 9V. I believe I read something recently about EBS amplifiers having 9V phantom by the same method. It would be easier to transfer if I change heads too - xlr inputs aren't exactly common are they? Right - something to fill a lunch-hour or two at the dayjob!!
I really don't know why things like active basses aren't wired to accept phantom power
As you noticed wiring in the resistors means you have a voltage source with high internal resistance. and so it doesn't supply a lot of current, there's a lower voltage 10v standard that does supply up to 250ma. How much power does the Sansamp need?
When I need to run power and signal I tend to just tie wrap low voltage power cable onto the signal cable. If the signal cable is shielded well, or balanced it will be fine. And there's no worries about power with the signal and accidentally plugging into something that might have problems with it.
As you noticed wiring in the resistors means you have a voltage source with high internal resistance. and so it doesn't supply a lot of current, there's a lower voltage 10v standard that does supply up to 250ma. How much power does the Sansamp need?
When I need to run power and signal I tend to just tie wrap low voltage power cable onto the signal cable. If the signal cable is shielded well, or balanced it will be fine. And there's no worries about power with the signal and accidentally plugging into something that might have problems with it.
I tried to ask a question like this in the pickups and electronics forum a few weeks ago, and it got ugly
I was exploring the idea of taking the active DI out of the box on the floor and putting it in the control cavity. You'd then run your bass on phantom which would also replace the battery... I think I offended some folks over there, was really quite entertaining. Not very productive, but definitely entertaining.
If you short circuit the terminals of the battery connector and apply a 9V supply to the ring using a TRS cable just about any active bass can be phantom powered. The supply will need to be current limited to avoid damage when disconnecting the bass while the supply is hot.
I tried to ask a question like this in the pickups and electronics forum a few weeks ago, and it got ugly
I was exploring the idea of taking the active DI out of the box on the floor and putting it in the control cavity. You'd then run your bass on phantom which would also replace the battery... I think I offended some folks over there, was really quite entertaining. Not very productive, but definitely entertaining.
That's too bad. It looks to be too late anyhow.
Digital wireless is so handy, cables aren't needed. Wireless looks to have a strong future.
Even Fishman now has wireless digital converters for guitars.
Rechargeable batteries and better than they ever have been. Maybe bass guitar stands need induction coils to charge the batteries when you put then in their stands. Like electric toothbrushes.
