Active Pickups Anyone?...

[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.

[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.

[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.

[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.

[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.

[dpm]

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

[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.

[David Schwab]

I said I was.

[Wired]

umm... Guys?


remember me?


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

[MrCandy]

Well, I am familiar with that discussion, and I did go back through it all again. It does not answer all my questions, especially about the huge claimed capacitive differences. I find only small differences in RP discussed there.

You can get large differences in capacitance with some types of coils. With larger, stiffer wire, you can carefully control the techniques, and the difference between layer winding (high capacitance) and bank winding (low capacitance) might be something like the order of magnitude we are talking about here. But I do not see how you do it with #43 wire. And I see no explanation in that other discussion.

Machine vs handmade winding, some tests with interesting results please take a look. - Page 2 - link 1 spectrograms attached.
Machine vs handmade winding, some tests with interesting results please take a look. - Page 2 - link 2.

We can do this experiment with 43 AWG 44AWG 45AWG and so and so......
If you cant see such results from well-known manufacturers, it does not mean we can not use our "free sound modeling" method.
You reminds me how Americans tried to invent a pen to write in space, Russians insted just took a pencil.

Thanks for interesting discussion
MrCandy

[Mike Sulzer]

Nevertheless it is a fact. If you check this thread in detail http://music-electronics-forum.com/t25556/ then you will find answers to all your questions.
How can not you notice the log in your eye?

Well, I am familiar with that discussion, and I did go back through it all again. It does not answer all my questions, especially about the huge claimed capacitive differences. I find only small differences in RP discussed there.

You can get large differences in capacitance with some types of coils. With larger, stiffer wire, you can carefully control the techniques, and the difference between layer winding (high capacitance) and bank winding (low capacitance) might be something like the order of magnitude we are talking about here. But I do not see how you do it with #43 wire. And I see no explanation in that other discussion.

[MrCandy]

All the coils seem to use the same bobbin with the same number of turns of #43 wire. If memory serves, the measured 1 KHz inductances are within 10% of one another. Twelve to one is hard to explain by winding pattern alone. Is the wire insulation thickness the same for all the test coils?

Every caliber of wire we use is made by its personal production machine, so that we can insure the isolation stability and other characteristics. All video experiments here on this forum are made with 43AWG and 42AWG wire from machine 1 and 2.
The isolation is the same from experiment to experiment and there is no trick. Also the isolation is very thin, but it was posted earlier.(1st video).

[Joe Gwinn]

So you are claiming that you can vary the coil capacitance nearly a factor of twelve depending on how you wind the coil. I find that very hard to believe.

All the coils seem to use the same bobbin with the same number of turns of #43 wire. If memory serves, the measured 1 KHz inductances are within 10% of one another. Twelve to one is hard to explain by winding pattern alone. Is the wire insulation thickness the same for all the test coils?

[MrCandy]

If I understand you last sentence, you are claiming that a 5,000 turn coil can have a resonance at 25.85 KHz or 8.3 KHz depending on how you wind it. These appear to be standard bobibns, and so the inductances would not be very different, and therefore it must be the capacitances that are different. Since the resonant frequency varies with the square root of cpacitance, the capacitances are in the ratio (25.85/8.3)^2 = 11.79. So you are claiming that you can vary the coil capacitance nearly a factor of twelve depending on how you wind the coil. I find that very hard to believe.

Nevertheless it is a fact. If you check this thread in detail http://music-electronics-forum.com/t25556/ then you will find answers to all your questions.
How can not you notice the log in your eye?

[big_teee]

If I understand you last sentence, you are claiming that a 5,000 turn coil can have a resonance at 25.85 KHz or 8.3 KHz depending on how you wind it. These appear to be standard bobibns, and so the inductances would not be very different, and therefore it must be the capacitances that are different. Since the resonant frequency varies with the square root of cpacitance, the capacitances are in the ratio (25.85/8.3)^2 = 11.79. So you are claiming that you can vary the coil capacitance nearly a factor of twelve depending on how you wind the coil. I find that very hard to believe.

+1