Bipolar power supply problem

[salwa]

Hi to all.
I've decided to build Maestro FSH1, which probably will be bottomless source of other build-related problems for me, but here's first one - I've decided to use GGG bipolar charge pump http://www.generalguitargadgets.com/pdf/ggg_ps_cpbp_pcb.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a with 7660 chip onboard. After connecting charge pump to circuit and adding power, I have +8,92 volts on positive output (which, I suppose, is enough), but only -7,36 volts on negative output (which, I suppose, is not enough). What may be the source of this: bad chip or something else?

[R.G.]

What may be the source of this: bad chip or something else?

Likely a problem with capacitors or soldering. Just a guess. A really bad chip would not generate a negative supply at all.

Could be loading. check to see how much current is going out the negative supply. A 7660 looks like an 80-100 ohm resistor in terms of voltage drop. Too much current load sags the DC.

[amptramp]

Check the application section here:

http://www.intersil.com/data/fn/fn3072.pdf

The ICL7660 connects a capacitor across the input voltage terminals then breaks this connection and connects this capacitor across the output terminals where it shares charge with any other capacitor that is connected to the negative supply.  Therefore, you can expect the negative output to be somewhat lower magnitude than the positive voltage due to current drawn from the output capacitor and resistance of the FET switches.  The ICL7660 oscillates at about 10 KHz, so you may want to make sure the circuit you are using it with has planty of power supply rejection or you will not be able to get rid of 10 KHz noise in your circuit.  A lot of stages on the Maestro FSH-1 are referenced to the negative supply:

http://www.freeinfosociety.com/electronics/schemview.php?id=1125

So you may want to add capacitance.  There does not appear to be anything in the FSH-1 that requires exact balance between the supplies, so I doubt it is a problem.  If you suspect a bad chip, use a socket and try another chip in its place, but I suspect you will get the same voltages.

[jammybstard]

I think thats typical; I've just used the 7660 but as a doubler and I had about the same shortfall

[salwa]

Thanks for all answers. If it's common with 7660's then I think there is not much I can do. I'll try to run FSH1 with this voltages and see what's happening.