1044scpa vs 7662CP vs 7660

[rossbalch]

Sorry, didn't see this message until now. Honestly never tried. According to datasheet you can bring it up to 35k. That's the same as 7660S with pins 1 and 8 shorted. And you can get these to whine, too.

We won't hear the 25k nor the 35k. What we hear is heterodyning, when two of these overlap and the result is a lower freq. So the best thing to do is shield the rest of the circuit from the ripple.

The thread you linked earlier was pretty long. For a non engineer like me, what's the TLDR, are filter caps sufficient or is the ferrite bead and inductor worth an include too?

 

[micmac]

I just posted that link because I found it interesting in general, also as a showcase of how far some people are willing to go And I guess it's not easy to find with an internet search.

For guitar pedals the MLCC caps I had mentioned one post earlier seem sufficient.

 

[szukalski]

Thanks for the contribution @micmac , I didn't know that approach. Seems a great way to keep build costs low

Another option is to choose a 7660 model which runs at 10kHz and can be boosted with an external clock.
If you already had a MCU in play with a spare pin (controlling a relay for example), then that could be the external clock and you can run it at 40kHz or whatever. Efficiency will suffer at higher frequencies per the datasheet but I don't think that's an issue for pedal design. Another potentially cheap approach.

You can get a 7660 and STM8 for about 30c each at LCSC/JLC, that's cheaper than what most people pay for a 7660. Then you can do smart relay stuff. The STM8 is only 8-bit, but it's enough for turning on I/O ports and supplying a clock. Shrink it to SMD, add jacks and OVP, and you've got a handy IO board.

 

[Robert]

Have you tried adding a small capacitor (between 5pF and 20pF) between pins 2 and 7? According to the data sheet, that will increase the oscillator frequency.

Catalinbread does this on some of their new designs.

If you do include the cap you'll need to omit it if you use a 1044 or 7660, I had oscillation issues leaving the cap installed with anything other than an LT1054.

 

[jwin615]

I really think the best way to handle heterodyne is to use charge pumpd that set the f_osc via OSC pin and a capacitor. Use sh*tty +/-20% caps, maybe over a couple of values, and no pedal will be at the same f_osc. As long as you spec the cap+tolerance to result in a frequency outside of the audio band, you're good.