Power Supply whistle from NJU7660 (charge pump)

[nirvanas silence]

The NJU7660 is like a Max1044 and I am using it for a Maestro sample/hold filter that needs +/- 9V.  I am getting a loud whistling, even in bypass, when I use it and was wondering if there is anything I can do.  I tried a few caps in different spots but nothing quite did it for me.  Any tips for me?

[mikeb]

Yeah, read the info that is already available on RG's page.

Mike

[nirvanas silence]

Yeah, this is all I see:

"These chips all work in exactly the same circuit, except that pin 1 should not connect to +9v, and even if you connect it, it will not change the oscillator frequency, so you will have to wire carefully to keep whine out of your audio circuits. This can be done, it's just easier if you don't have to think about it."

[cd]

Re-wire/re-do the whole thing carefully so your power section is away from the audio section.  The 7660 is not quite like the 1044, with the 1044 you can boost the oscillator frequency past the audible range so you don't have to worry about whining or careful wiring at all.  

My advice, get some MAX1044s

[nirvanas silence]

Ok thanks.  So where can I get a MAX1044 shipped rather quickly for me?

[mikeb]

Apologies for my shortness - no coffee yet this morning.

Yes, just go with the 1044s - the slightly greater price is more than worth it when trying to get rid if the whine, especially if you are in the USA. I think most electronics stores online would have the 1044 - Mouser etc etc. Besides that you can work out of a frequency boost circuit for the 7660, but I spent ages 'redoing' wiring for the 7660 with no luck on one of my circuits.

Mike

[cd]

Mouser doesn't carry it, but Digikey does.  It's around $2 a piece, but naturally shipping is more than the part itself.

[nirvanas silence]

Digikey says minimum order is 100 of those.  Small bear has been slow lately too.  I just need 1 darn chip!  

[Torchy]

I got some samples from the maxim site (need to register). Took 4 days to ship to UK  

[cd]

Digikey says minimum order is 100 of those.  Small bear has been slow lately too.  I just need 1 darn chip!  

You can order one:

http://www.digikey.com/scripts/DkSearch/dksus.dll?Criteria?Ref=77727&Site=US&Cat=31588879

[R.G.]

Let me be more clear:

If you use the stereo jack switching trick, you run all of the battery (-) lead current down the input jack ground lead. If there's a 7660 over on the circuit board sucking down pulses of current at an audio frequency, the input to your effect sees the current times the resistance of that ground lead as an input voltage, so you get whine in  your output.

The way around that is to have the input stereo jack provide a signal to the battery voltage on the board to turn on and off, and never let the 7660 ground and signal ground share a common wire. That keeps the pulses I*R off the signal ground and you don't have a whine, except for any capacitor-coupled whine you may get by unlucky layout.

The Neutron filter from GEO is set up to work on these principles.

[yano]

I'd say thats the main difference between the 7660 and the max1044, the 1044 can operate above audible frequencies.