King of tone Power Section

[dfx_pedalpcbs]

Should this capacitor be more than 10uf as its on the 18V rail and its for audio filtering isn't it?

[GGBB]

It's a decoupling cap. The audio signal never passes through or past it. It's functions are to smooth out ripple, filter out noise from the power supply, and stabilize the DC supply by providing an on-demand "reservoir." Size of cap is not determined by the voltage it sees. We normally see 100uF decoupling caps in simple 9VDC pedals - largely for filtering reasons more than supply stabilization. this one has it on the Vref supply instead of Vin - which could be more important with op-amp designs - Vref touches the audio signal. Should C10 be more than 10uF? The circuit designer didn't think so. Can it be? Certainly.

[ElectricDruid]

+1 what Gord said.

It's not for audio filtering. It's part of the power-doubling circuit that creates the 18V supply. If 10uF is enough, then it's enough. That would depend on the power draw of the rest of the circuit, I would guess.

As Gord pointed out, the Vref supply is a more sensitive spot, and you'll see they've used 100uF there (C11). Sensible choice.

[PRR]

It also powers the opamps.

Peak-catching AC/DC supply design is based on supply frequency. For 50/60Hz system supplying 10mA, 10uFd or 100uFd may be ample. But the TC1044 runs near 40,000Hz, 666 times faster, so we could naively assume say 100uFd/666 or 0.15uFd. That's not really cheaper than 10uFd. The datasheet seems to use 10uFd as the default almost everywhere.

The fact that we may suck chunks of current at 82Hz or 41Hz not important. If we need *DC* power we do not have to have an "infinite" capacitor. We just need enough capacitance to transfer enough energy each cycle to keep the pipes filled.