Charge pump -9v power quality? e.g. Road Rage

[baaron]

Hi all,

I haven't experimented with charge pumps in the past but I'm designing a circuit that needs a little extra headroom and good noise-free power.  I'm considering using a Road Rage to provide either +/-9v (and run it as a bipolar supply) or +15v regulated (and set the bias with the classic voltage divider method).

My question is: the -9v tap on a Road Rage board has a simple 10uF capacitor on it for filtering, which... doesn't seem like a lot.  Is the +/-9v bipolar supply going to be noisier than the 15v coming off the 78L15 regulator?

[madbean]

I would not expect any of the outputs on the Road Rage to be noisier than the other. So long as a decent pedal oriented (well regulated and isolated) power supply is used all the outputs should be equal in performance.

As far as the 10uF, keep in mind that's not the only supply filtering cap. C1 and C2 provide the important filtering on the front end of the circuit. 10uF should be sufficient enough for a lot of applications, but you could increase it to 22uF or 47uF.

There is an advantage to going split rail over +15v or +18v when using a charge pump. One is that it requires less parts because you do not have to create a virtual ground like you do with single supply circuits. The other is that with split rail, the current output restriction from the charge pump applies only to the negative rail (because the positive rail is using DC directly from your power supply). With a single supply design the current restriction applies entirely to the positive side.

[baaron]

Thanks Brian!  That's a good point on the current-restriction-benefit on the +9v supply.  I wouldn't have thought of that.

I was mostly worried about clock noise from the IC because of the ol' 1044's reputation, but a little more reading has laid that concern to rest.  I'll probably use an LT1054 - it's the same price as a 1044 from my supplier anyway.