Biploar to single rail conversion question

[lars-musik]

Good news! I put the pcb together yesterday night and it works! Quite well. I don't think the world needs another Overdrive, but this one is nice. The clipping options (LED and 1N4148) are handy.

One point, though. I got a squeal from the 7660S charge pump (although the boos function was activated). The LT1054 works without that noise. But the SMD version of the LT1054 went up to 25 € at the moment, so this might stay a one off. I still have to test and compare the difference to a simple 9V Vcc.

Thanks all fpr your help!

[amptramp]

^^^

At that price, you can probably get a boost inverter using an inductor or flyback circuitry from the usual Chinese sources.

The charge pump circuit charges electrolytic capacitors in parallel then switches them in series to provide a boosted output.  You get noise from the inrush current of charging the capacitor and noise from the transfer of charge from the main supply and switching noise and charge pump current capacity is small.  The next step up is the flyback converter and you have some things in your favour there.  When the inductor is switched on, the current ramps up instead of switching suddenly, so one source of noise is reduced and the best way to reduce noise is to not generate it in the first place.  There is still noise when the inductor is switched off, but current capacity can be larger and efficiency is higher since switching on occurs at zero current.  Feedback is used to stabilize the output whereas a charge pump really doesn't do that.  You can get the switching frequency to be above the audible level with a number of designs.  There are only a few charge pumps with inaudible switching and as you say, 25 euros is a lot of money for an inefficient design.

[lars-musik]

Finished!

Here's my "Pathfinder 15 Pedal"

[ElectricDruid]

Finished!

Here's my "Pathfinder 15 Pedal"

The slightly-battered look of that etch is perfect for an old amp! Love it!

[Axldeziak]

I drew up a layout using the schematic in this thread and the suggestions given.
The charge pump is from the the Aion Tesseract (TC Electronic Integrated Preamp) since the Fortin 33 was the basis for the original on the schematic and lars said he had used the LT1054 instead. I did however add the original output buffer (with suggestions).