Question about charge pump

[musifalsk]

Hi everbody. Im brand new here so please go easy on me. I started making pedals this summer and so far ive made a couple distorion boxes, buffers and boosters etc. Simple stuff. I also made a tube pedal and loved it. So then I started out making my "Grand Oracle", a twin tube pedal (12au7) with 40V plate voltage powered by a 9v Power Supply. I bought some 7660S ICs cheap from ebay from a semi thrustable source. The thing is that wen i connect the power i can sometimes hear a whistling sound around 5 KHz. Sometimes its there and sometimes not. Sometimes it even modulates up or down. The charge pump is configured with a shortcut between pin 1 and 8 and as far as i understand this is supposed to boost the switching frequency.

So my question is this: what could this whistling come from? could it be that the charge pump is fake branded?
Sorry for my long letter

[anotherjim]

Could be heterodyne noise -  if some high frequency interference is present your 5Khz is the difference frequency between that and the pump freq'. Might go away when it's all boxed up.
Is 9v supply from a switched mode PSU?

[R.G.]

Yes, it could come from the charge pumps being counterfeit. Or it could come from a bad connection to the frequency boosting pins.

Or it could come from the circuit itself oscillating sometimes and the whistle being the difference frequency between the charge pump and the oscillation. Or it could be from several thousand other things. It's going to be difficult to fix this if it's not one of the first two I mentioned. It may need an oscilloscope to see what is happening.

[musifalsk]

thanks for the suggestion guys. i dont know about the supply.It was extremely cheap from ebay, but its supprisingly quiet on all guitar pedals i tried it on. I got a handful of the 7660s chips, so i will try to change that to night. Its attached with a socket so its easy to replace. I have suspected that it might be a 7660 ic without the s behind that has been rebranded or something. Its not the first time ive bought fake ics from ebay. Bought some tl071 once that was actually rebranded tl072. hehe....

[musifalsk]

Also one more thing worth mentioning is that when i touch/wiggle the connector on the psu cable it tends to affect the modulation in some way.

[musifalsk]

Oh and one more thing. Maybe this can tell something, i dont know, but when i put my tubescreamer in front of it, the whistling becomes more pronounced, even when the tubescreamer is in bypass mode... sharing the same power supply

[anotherjim]

If that power supply is lightweight, if it boasts a wide supply input voltage range like 100-230Vac, it's almost certainly a switcher. With 2 pedals, its noise also is in a ground loop between them. A normal stepdown transformer supply will always sport a bit of weight due to the transformer and a much more limited supply voltage range.

A switch supply can be quite with most pedals. It's switching frequency will be too high to be noticed. It's when you have something else in the signal path that runs at a similar high frequency, like your charge pump, then the two mix and produce a new frequency that often is audible.

[Keppy]

I have pedals that whine with switching power supplies, but not with simple transformer wall warts. I'm with the other posters, try a different power supply before trying anything else. A regulated transformer supply if you can find one. That's both the likeliest culprit (IMO) and simplest fix.

The datasheet for that chip describes how to use a capacitor on the OSC pin to change the oscillation frequency. You might be able to move the whine to an inaudible frequency.

Also, do you have a DMM that measures frequency? That would help confirm or rule out charge pump malfunction.

[vigilante397]

7660s charge pumps are notorious for whistling, and I've definitely noticed the problem to be significantly worse for tube pedals.

The datasheet for that chip describes how to use a capacitor on the OSC pin to change the oscillation frequency. You might be able to move the whine to an inaudible frequency.

This is probably your best bet, and is a fairly common fix.

[MrStab]

where does ground from the 7660S meet the ground of the rest of the circuit?