Determining current draw of active pickups?
 

I have a peavey cirrus that has a high current draw ~11mA. I was looking to upgrade to millennium preamp to hopefully fix this.

However I remembered that the pickups are active and if its the pickups drawing most of the power, then the upgrade wont help.

Is there an easy way to determine current draw of pickups?

I have another cirrus that only draws 1mA so I can swap with that to see if its just the preamp, just hoping there's an easier way.

With the bass unplugged, place your multimeter between the ring and sleeve terminals of the jack.

Wouldn't that give him total current draw, including the preamp, which he seems to already know?

Yeah, it sounds like you already know the total current draw. What you may want to try is measuring total resistance of the two. I would try removing the battery, set the controls to max, then to minimum. Record your measurements at both settings and compare.

Connect your multimeter between the battery and the circuit. Then set your meter for the appropriate current range.

http://www.electronics-radio.com/art...re-current.php

So the easiest way would be to connect the battery clip on just the (-) of the battery, and then connect the meter between the (=) on the battery and the battery clip. Then plug in your cable to switch the power on.

If your bass has a battery box you will have to splice into the power inside the bass. But the meter has to be connected in series with the battery.

Ok, then put it between the battery's positive terminal and the pickups' supply leads. Or check them individually by measuring one at a time that way.

Using two 9v battery connectors, you can rig up a tester that plugs in where your battery goes... One connector gets the battery, the multimeter goes in a loop to the other connector, which you plug into your bass...

So I just swapped preamps between my Cirrus' and it still draws a lot of current (11mA). I guess this means that the pickups on this particular bass are to blame and swapping to a Millennium preamp won't help?

I've read of a few other people getting similar current draw on the Cirrus, wondering if anyone got this resolved with a Millennium preamp or something else?

11 mA is very, very high for a preamp.
Are pickups themselves active?

Yea active pickups

Ok I just think I confirmed it's a pickup issue. The resistance between the V+ and GND of the pickups on the low current Cirrus is 100k ohm while the resistance on the high current Cirrus is only 10k ohm. That explains why the bass with the lower resistance pickups has exactly 10x the current draw of the other.

If your pickup is buffered via an active circuit, it has a much much higher impedance to ground...

No it doesn't. The output impedance of an active pickup is preferably around 10k-ish. (Or at least that is what companies like EMG seem to prefer with their opamp-based pickups.) You can't really measure that impedance accurately, however. What you do with a multimeter is DCR, which is at 0Hz. In any case, the OP is referring to the DCR between the supply lead and ground, rather than the DCR at the output stage. That's a different measure.

Just a technical point: note that the current consumption is not simply based on the DCR. 18V at 10k, for example, is 1.8mA, not 11mA. The load changes when the circuit is in operation. A 10k versus 100k comparison clearly indicates that something is not right with the pickup, however.

Hold on a second. Was that with the pickups still connected to the preamp, or out of circuit?

You didn't have to swap the preamps, all you needed to do was to disconnect the power feed to either the preamp or the pickups and see how much the current changed. But if changing out the preamp did not reduce the current then the pickups are indeed the main power hogs in this bass. Your only solution then would be to replace them with passive pickups or with new active pickups that draw less current, if you can find any.

Ken

Bought a set of pickups that have acceptable resistance measurements, and current draw is down to 1.4 mA. But now I have a different problem posted here: http://www.talkbass.com/forum/f38/hi...ntered-948893/