Power To Operate An Onboard Active From Outside Source?

SurferJoe46 · #1 06-09-2010, 07:58 PM

Would it be possible to carry a solid 9VDC power supply on the RING (+) and the SHANK (-) and the ACTIVE Output on the TIP (+) and the SHANK (-) of a TRS 3-wire cord to externally power the EQ inside the bass itself?

This would eliminate the dead battery problem when one could afford it least, I think.

The normal BASS-OUT (-) could share the GROUND (-) side of the jack with the 9VDC (-) of the external power supply, that is both of them on the SHANK. (#1 BELOW)

As normal the BASS-OUT (+) would be on the TIP, (#3 BELOW) while the 9VDC (+) would be on the RING (#2 BELOW)

I don't see the AMP-END being a problem with a TSR female that has a separate 9VDC power supply riding on the same line. It would have to be a very clean DC though.

Just a thought.
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**line6man** · #2 06-09-2010, 08:50 PM

This is exactly the way Line6 does their Variax guitars and (discontinued) bass.

The power is applied to the ring terminal, and there is a DI box that supplies it.

FWIW, I've been kind curious about phantom powering a bass for a while now. Apply the battery power directly to the tip terminal at the amp, and use an electrolytic capacitor in series with the signal path to remove the DC offset at the output.
Might be worth looking into.

Rick Auricchio · #3 06-09-2010, 08:53 PM

Yes, in theory, this would work well. You've got a variation of phantom power. But in practice, there are drawbacks:

1. You need a stereo cable (two conductors plus shield). These are not readily available in long lengths for instrument use. If your cable fails, where will you find a spare? If you make your own, they must be robust enough to endure the rigors of gigging.

2. There's a chance of noise pickup on the DC line along the cable length, which would add noise to the preamp.

3. Many amps use PC-mounted jacks for the instrument input. Modifications are difficult and risky. If you change amplifiers, you'd need to mod the new one.

3a. Nobody's backline amps will be configured to provide power via the input jack. Similarly, you can't grab another amp as a backup unless it was one of your modded ones.

4. If you plug in with the amp unmuted, there might be a huge pop as the preamp powers up.

5. If you plug into the amp first, each time you plug/unplug at the bass, there's a momentary short as the ring passes into the jack. You'd have to current-limit the 9v supply to protect it.

6. If you plug into the bass first, then the amp, you momentarily send 9v through the tip as it passes the ring contact. This could potentially damage the onboard preamp's output stage.

Betcha Paul, Bongo, and others will think of a few more...

But I applaud your inventiveness!

**line6man** · #4 06-09-2010, 08:57 PM

Quote:

Originally Posted by Rick Auricchio

2. There's a chance of noise pickup on the DC line along the cable length, which would add noise to the preamp.

If you are not using a battery to power it, you damn well better be filtering the crap out of your power supply to ensure the least amount of ripple possible. That should be a given!

Quote:

Originally Posted by Rick Auricchio

3. Many amps use PC-mounted jacks for the instrument input. Modifications are difficult and risky. If you change amplifiers, you'd need to mod the new one.

I don't think it's a good idea to be modding all your amps. It's much easier to build a small stompbox sized box with a regular output to go to your amp.

Rick Auricchio · #5 06-09-2010, 08:58 PM

Quote:

Originally Posted by line6man

FWIW, I've been kind curious about phantom powering a bass for a while now. Apply the battery power directly to the tip terminal at the amp, and use an electrolytic capacitor in series with the signal path to remove the DC offset at the output.

This is a much better idea, and it removes almost all of the drawbacks I listed.

You build a little "power box" with a capacitor so its output to the amp is DC-free. You add a cap inside the bass to block DC. Power on the tip/sleeve as you suggest.

For those who have pedalboards, the power-box is the first pedal in the chain. And they often have clean 9v handy.

**line6man** · #6 06-09-2010, 09:12 PM

Quote:

Originally Posted by Rick Auricchio

For those who have pedalboards, the power-box is the first pedal in the chain. And they often have clean 9v handy.

No, I would rather go higher than 9V actually, and put a resistor from the "blended" (Signal+DC power) output to the preamp's V⁺. That would provide some extra isolation between the signal and any loading from the preamp.

Since the output is of a low impedance, it would be desirable to place a high resistance between the preamp's V⁺ and ground. That would avoid "loading down" the signal, incase there was a low ESR/ high leakage/ whatever else between the preamp's V⁺ and ground.

Also, why not give the preamp 18V if it can take it?

Perhaps a standard 48V phantom would be a good idea?

I've actually got some 45V and 50V transformers on hand that I should try making a phantom power supply from.

It just bothers me to waste nice 1.5A or 2A transformers on a 1mA or 2mA power supply!

SurferJoe46 · #7 06-09-2010, 09:24 PM

Quote:

Originally Posted by Rick Auricchio

Yes, in theory, this would work well. You've got a variation of phantom power. But in practice, there are drawbacks:

3. Many amps use PC-mounted jacks for the instrument input. Modifications are difficult and risky. If you change amplifiers, you'd need to mod the new one.

3a. Nobody's backline amps will be configured to provide power via the input jack. Similarly, you can't grab another amp as a backup unless it was one of your modded ones.

But I applaud your inventiveness!

About section(s) 3 & 3a::: I bet that you could built an AUX box at the amp, not a part of it, but an accessory that has the TRS female and coming out would be a MONO 1/4" common male to go into the padded amp input or your preamp or whatever you first go into.

This same AUX box would then have a 9VDC power supply inside it (it could even carry several 9VDC batteries in parallel for those times when you don't have a lot of 117VAC outlets) and then this could get jacked into and out or from amp-to-amp, even any backline units as it isn't really a mod to the amp at all.

Just one more piece of gear - that's all.

tehbassist · #8 06-09-2010, 09:26 PM

Do I finally hear onboard 12ax7? because thats what I'm choosing to hear...

**line6man** · #9 06-09-2010, 09:28 PM

Quote:

Originally Posted by tehbassist

Do I finally hear onboard 12ax7? because thats what I'm choosing to hear...

At what voltage?

I don't want 200VDC+ in my bass, and at a low voltage like 9V, you're pretty much only good for a distortion/overdrive circuit of some sort.

SurferJoe46 · #10 06-09-2010, 09:28 PM

Quote:

Originally Posted by tehbassist

Do I finally hear onboard 12ax7? because thats what I'm choosing to hear...

Nasty boy - you like rubbing salt into wounds - do you?

SurferJoe46 · #11 06-09-2010, 09:29 PM

Quote:

Originally Posted by line6man

At what voltage?

I don't want 200VDC+ in my bass, and at a low voltage like 9V, you're pretty much only good for a distortion/overdrive circuit of some sort.

Let's use the words: "cold cathode" and see if that brings the engineers out of the woods.

tehbassist · #12 06-09-2010, 09:30 PM

Quote:

Originally Posted by line6man

At what voltage?

I don't want 200VDC+ in my bass, and at a low voltage like 9V, you're pretty much only good for a distortion/overdrive circuit of some sort.

You wouldn't have to pump too much into it if you just used it to buffer a passive tone stack would you?

**line6man** · #13 06-09-2010, 10:03 PM

Quote:

Originally Posted by tehbassist

You wouldn't have to pump too much into it if you just used it to buffer a passive tone stack would you?

You can run them at a pretty low voltage, but don't they sound terrible?

**line6man** · #14 06-09-2010, 10:15 PM

What do you guys make of something like this?

Of course, I would definitely be sure to filter the DC really well, maybe even regulate the voltage, but that's a given.
A simple Pi filter works for demonstrational purposes.

walterw · #15 06-09-2010, 10:29 PM

they're already doing it.

**line6man** · #16 06-09-2010, 10:42 PM

Quote:

Originally Posted by walterw

they're already doing it.

I would rather spend a few bucks doing this myself than to pay big bucks for their system, but that's just me.

FunkMetalBass · #17 06-09-2010, 11:06 PM

There are a few companies that do this to pedals and will do it for your bass as well.

I use a wireless too often to have it done, but it's a cool idea.