Outboard power supply for active bass guitar pickups and LED's

[oatmeal769]

When I built my last pre-amp, I put XLR-TRS combo jacks on the input. My idea was that since I only use active pickups and never wireless, I could run an DC power supply to the pickups on the third connection at some point. It could still work with passives as well, because the power line wouldn't be connected.

I have never fully understood Ohms law. I just can't get my head around how voltage drops, current rises, etc. Anyway, here's what I want to do. I would like to supply a solid 18-20 volt DC power supply to the pickups. AND also be able to drive 6-8 LED lights in a clear Lexan bass I have. The pickups draw micro-amps I believe, while the LED's would draw several mili-amps each.

EMG makes this,
http://www.emgpickups.com/es-18.html
which I'm sure could be reverse engineered pretty easily. I doubt highly it supplies enough current to drive LED's though. I just wonder if I could manage two different power draws with a power supply. The LED's will consume vastly more current than the pickups will. Is it as simple as adding a resistor to the pickup power in the bass?

Any comments/ideas/refinements? Ideally, I will put the power supply inside the pre-amp, almost like Phantom power.

 

[rayma]

I would like to supply a solid 18-20 volt DC power supply to the pickups. AND also be able to drive
6-8 LED lights in a clear Lexan bass I have. The pickups draw micro-amps I believe, while the LED's
would draw several mili-amps each.

Just run the raw DC to the bass, and split it into two branches inside. One branch is for the pickup,
and the other is for the series LED string (including a series resistor of 390 Ohms for 10mA current).

 

[Enzo]

What rayma said. The LEDs might like 10ma each, but current is current, steady through a series circuit, so you can use the same 10ma for ALL the LEDs by running them in series.

 

[rayma]

What rayma said. The LEDs might like 10ma each, but current is current, steady through
a series circuit, so you can use the same 10ma for ALL the LEDs by running them in series.

Yes, there should be just enough voltage available to pull this off. If not, either
lower the current to 5mA by using a larger resistor, or else remove an LED to gain 2V.

 

[benb]

Yes, there should be just enough voltage available to pull this off. If not, either
lower the current to 5mA by using a larger resistor, or else remove an LED to gain 2V.

Or you could wire the LEDs in two strings of 3 to 4 LEDs each, with an appropriate resistor in series with each string. The value of these resistors would be higher than in the other case, to drop the extra voltage and give the desired current.

 

[Enzo]

Yes, that would certainly work, at the expense of half as much current savings. But we don't really know the current available.

 

[oatmeal769]

Can anyone suggest a small, inexpensive transformer which will output 24 volts or so? I would build a power supply with regulator, rectifier bridge and caps to really smooth out the power - lest it make noise in the pickups.
I'm assuming I will suffer some voltage drop with this, so I think a 110 Volt AC to ~24VDC transformer would be fine, with the resultant clean power hopefully around 18-20 Volts. Obviously, the Amperage doesn't need to be a lot at all.
I like torroidals, but I'm open to others.