Active Pickups Anyone?...

[David Schwab]

I said I was.

[Mike Sulzer]

umm... Guys?


remember me?


...so... is anyone interested in a micro pre for active pickups?

What is it? I think the thing to use these days is a 5 volt rail-to-rail op amp that draws about 100 micro amps with a low current low dropout voltage regulator operating from three 1.5 volt alkaline cells.

[dpm]

I'm interested too. The variable input z is something I've played with myself, it's a great feature.

[David Schwab]

What is it? I think the thing to use these days is a 5 volt rail-to-rail op amp that draws about 100 micro amps with a low current low dropout voltage regulator operating from three 1.5 volt alkaline cells.

But who's doing that? Many instruments are, or can be set up for 9V batteries in the form of battery boxes and such. This is especially if they are also using a tone shaping preamp that runs on 9/18v.

[Wired]

Mine will be a 9V setup. I want them easily compatible with other circuits that are around. I haven't come across the rail to rail opamps that are quiescent at 100 microamps, but I haven't really been looking either... I can't imagine that they'd have a real quick slew rate, or much current drive (although this is not really critical in this application). Mostly I design discrete circuits, but the opamps I've been using for a little while are more like 180microamps. For a footprint as small as I'm hoping plus the differential input architecture, I will probably need to find an SMT IC opamp. If the pre draws less than 0.5 milliamps, I'll be happy. No point designing somthing super-efficient that sounds average...

I used to work for a guitar manufacturer here in Aus who uses a 3v preamp in their acoustics. I'm guessing that 2 AA batts have more energy density than a single 9v, and are cheaper too. Their pre had a discrete charge pump and a negative voltage converting circuit, so its actually +/- 6V (IOW, 12V).

Anyway, 9V is the standard, and really you don't need a voltage swing of anything like 5v, so there's heaps of opamps out there. Although batt boxes for 2 AA's that could be routed into a guitar aren't that hard to find, plus there's some pretty good charge pump ICs these days too.

[Mike Sulzer]

But who's doing that? Many instruments are, or can be set up for 9V batteries in the form of battery boxes and such. This is especially if they are also using a tone shaping preamp that runs on 9/18v.

You can use the regulator to drop the nine down to five. You are still ahead on power consumption over most traditional op amp. The energy these days in audio chips is in low voltage, low current stuff. Some of the higher voltage stuff is already going extinct.

[Mike Sulzer]

Mine will be a 9V setup. I want them easily compatible with other circuits that are around. I haven't come across the rail to rail opamps that are quiescent at 100 microamps, but I haven't really been looking either... I can't imagine that they'd have a real quick slew rate, or much current drive (although this is not really critical in this application). Mostly I design discrete circuits, but the opamps I've been using for a little while are more like 180microamps. For a footprint as small as I'm hoping plus the differential input architecture, I will probably need to find an SMT IC opamp. If the pre draws less than 0.5 milliamps, I'll be happy. No point designing somthing super-efficient that sounds average...

I used to work for a guitar manufacturer here in Aus who uses a 3v preamp in their acoustics. I'm guessing that 2 AA batts have more energy density than a single 9v, and are cheaper too. Their pre had a discrete charge pump and a negative voltage converting circuit, so its actually +/- 6V (IOW, 12V).

Anyway, 9V is the standard, and really you don't need a voltage swing of anything like 5v, so there's heaps of opamps out there. Although batt boxes for 2 AA's that could be routed into a guitar aren't that hard to find, plus there's some pretty good charge pump ICs these days too.

LMV651, 2, 4. 3 volts/microsecond slew, 12 MHz open loop BW, 120 micro amps power supply, 18 ma output. Surface mount only, of course.

[David Schwab]

You can use the regulator to drop the nine down to five. You are still ahead on power consumption over most traditional op amp. The energy these days in audio chips is in low voltage, low current stuff. Some of the higher voltage stuff is already going extinct.

Well that's a good thing. I'm making Music Man preamps, which used an LM4250 op amp. The original Music Man bass didn't even switch off the battery when you pulled the plug because the op am draws so little current.

Meanwhile some of the high end op amps like from Burr Brown don't work well on batteries.