Charge Pump DC-DC Converter : too noisy for audio?

Hello everyone,

This is my first post, though I've lurked these boards for a few months now.

I'm designing a portable mic+pre powered off a 9V battery for field recording. I'm considering using a DC-DC charge pump converter in conjunction with a 9V battery to give me a full -9V to +9V voltage swing.

Here is the datasheet for the part I'm looking at:

http://ww1.microchip.com/downloads/en/DeviceDoc/21465b.pdf

National has a similar part, as perhaps others.

Has anybody had any experiences with parts like these? They use an internal oscillator that operates at 10 kHz, though they can be set up to run at a different frequency.

I'm hoping the a cap on the negative supply will absorb enough that the ripple is negligible.

Has anybody ever used a part like this or something similar it a power supply for audio equipment and had good (or bad) luck?

I have used a wide variety of charge pump converters in both audio and battery powered data acquisition devices.

Compared to the converters that use inductors, charge pumps are relatively easy to tame as far as noise issues are concerned.
I have used a simple inductor/capacitor filter to reduce any residual noise.

Charge pumps are also very efficient if your current draw requirements are modest (<100 ma typical).

The LT1026 is a good one for audio. +9 volts in, +-18 volts out.

I have used 3 of the National LM2665 charge pumps in my "FrankenTube"
phantom powered vacuum tube microphone.
No noise problems.

Inductive converters are another story.
You need careful layout and a good ground plane to tame the considerable trash that these converters can create.
I have been able to tame the noise but, it took extra parts and shielding to get a quiet supply.

That's my experience anyhow.

Others may have had better luck with the inductive variety of converters.

I used one to flip + to - for an opamp and it works good enough for non critical applications. Not to say my implementation was'nt high end, I just never measured it. I'm using a MAXIM device with an ne5532. It has a clock doubler to put the clock up above the audio range. We can't hear it. Just nice audio. We use it in an active splitter that runs on phantom power before the house mixer for sermon recordings at church. Into an audigy (yech..).

Hear it here:
www.rmbc.org

:Ron

Thanks for the suggestions, I'll post some photos and schematics as this project comes along!

I have used charge pumps in guitar fx. Even though guitar has a limited range, the circuits I have used are full range.

I have used the MAXIM 1044 which works well. Also the NJU7660 with an external clock.

http://www.geofex.com/circuits/voltpmp2.gif

They do work well. The MAXIM, even though more expensive, is worth it. Very easy to push the clock out of the audio range. Otherwise it can be difficult to get the noise out.

With the 7660, it took a 555 timer which is another DIP chip. Anyway, they work. But you also have to watch the power draw. As said earlier, about 100mA tops.