Charge Pump Whine in Bypass Only

[idy]

I have two mxr microamps on a stripboard and used a 4pdt stomp so I can use them in stereo, or with "switching" jacks sum inputs and/or outputs. I used a millenium bypass also.
I noticed some whining and tried swapping out the charge pump, finally 1044SCPA I could hear no whine... until I bypass the circuit. Then I hear a whine that appears around the middle of the sweep of the gain control (double gang), clockwise bringing it down into audible range. It then does a pitch leap at the full travel of the pot.

[diffeq]

Could we see a schematic? I've tried looking up MXR microamp but could only find the single suppy (9V) version schematic.

I would try a bigger filter cap (470uF) on charge pump output, also putting a small resistor (47-150 Ohm) between output of the charge pump and mentioned cap.
It also could be a layout issue. Hard to tell without actually seeing it though.

[idy]

Thanks, will try. I did notice that moving the charge pump away from the gain control helps. Have to experiment with repacking this mess.

[pinkjimiphoton]

simplest solution maybe to just run a jumper from the input of the board to ground on bypass? its worked for me before

[idy]

I tried the 100ohm from the charge pump to a 470uf cap... no change... but moving the three circuits around does help. Still a bit of whine in bypass, and one strange thing that I did not mention before, the LED (millenium bypass) lights up in bypass when the gain control goes over 3/4.

[pinkjimiphoton]

i'd think that would indicate some signal leakage. how are your grounds?

[Scruffie]

Did you buy the charge pump from Tayda? If so I've had terrible issues with them bleeding.

[pinkjimiphoton]

me too. terrible pieces of kit.
their 1044's work better than their 660's.

some builds are pretty much unuseable. lotta hash gets dumped to ground, and polutes everything. not sure if its the chips or the cheap caps or both. tayda's quality seems a little off of late.

[idy]

Probably Tayda.
I also worry about this because as a "golden ager" I know that I can't even hear all the freqs that others can...
...I was using a little Marshall practice amp in a teaching studio and the repair guys outside (hammering on brass instruments) complained about the noise, the high pitched whistle that was driving them crazy but that I could not even hear...

I realize the grounds are daisy chained, jacks together, to charge pump, to board, to millenium, will try fixing that. And ordering better charge pumps.

[jonny.reckless]

The correct star grounding topology will usually fix this problem. You have to think about where the currents are flowing. Switched capacitor voltage converters have a very sharp peak current when the switches change over. There is a high dv/dt and di/dt at the switching frequency in the input and output. Try to think about the current pulses in and out of the chip when this happens. The whine is probably due to the fact that the switching current pulses are sharing copper with signal ground somewhere (and thus modulating the ground reference), or the fast dv/dt edges are capacitively coupling into a nearby high impedance signal.

Keep the switched cap supply grounds short and thick, connect them all together at the output cap, and then run a single ground to the rest of the circuit.
Use high quality 10uF ceramic X5R or X7R caps for the input bypass, pump and reservoir caps. Keep lead lengths to an absolute minimum. If doing a PCB, create a local copper pour area.
I usually add 470uF electrolytic bulk decoupling to both input and output. They go "outside" of the ceramics.
If you use a TC1044S, connect boost to V+ to move the switching frequency from 8kHz (annoying whine) to 40kHz (only your dog will hear it).
You can add a low pass filter to further remove noise.