7660 squeels even in BYPASS

[pqt_bach]

I use a 7660 in a circuit. I know that the switching frequency produce noise we can hear - but the thing is - it makes noise even when the pedal is in bypass mode... I checked the traces and there aren't any short-circuits...

So, what could it be? would the 7660 need different coupling or even to be separately tied to ground?
Could the noise in bypass mode be the result of a high gain current path "leaking" into the bypass path?


Any help appreciated
Thanks

[R.G.]

Here's what's happening.

The 7660 is a POWER switching chip. It opeates by repeatedly closing two switches to connect a discharged 10uF cap to the +9V line. This sucks in a current that is limited only by the resistance of the cap and the switched and the resistance of the copper leading to the chip and capcitor. It can under some circumstances be multiple amperes.

Those pulses happen FAST. The pulse pulls ground up and +9V down.

Whine method 1: If you have your signal circuits connected to the power supply and they can't somehow ignore the wiggling on the power supply, you hear whine.
Whine method 2: If you have high gain, high impedance circuits like JFETs, MOSFETs, or bootstrapped bipolars - including opamps - they can pick up those transients just by being too physically close to the wires that are switching by capacitance.
Whine method 3: If your power supply path from the battery to the 7660 + pin, through the chip to the - pin and back to the battery is a loop that includes a loop of the signal circuits, you will put the pulses into your signal by transformer action.

What can you do?
1. Decouple, decouple, decouple. Put a 100uF 16V cap and a 0.1uF MONOLITHIC CERAMIC cap as close to the pins of the 7660 as you can physically put them. An extra inch of wire may mean that the effort was for nothing.
2. Separate the power wires for the 7660 from the wires for the rest of the circuit. Ideally, it gets its own wires to/from the battery. If that is not possible, use a low value (10-100 ohm) resistor from the battery to both 7660 and your circuit, then decoupling caps like the 100uF/0.1uF at both circuit and 7660 to split the current pulse loop away from the signal circuit.
3. Get twisted: make sure that the loop that includes the 7660 power is as small a cross sectional area as possible to elminate as much mutual inductance as possible.
4. Do NOT use the stereo jack trick to switch power. If you do that, 100% of the pulsed power travels down the same wire as your input signal ground. Instead, use the second signal lug to pull a 10K resistor to ground. The 10K resistor is tied to the base of a PNP which turns on battery power to the circuit and converter. That keeps the ground current pulses off the signal ground line at the input.

Other that all that, you're fine as you are. 

[pqt_bach]

Well, seems I was in the ball park

Thank you very much, R.G.

I thought of "star grounding" the circuit: have the PUMP, power filtering+Vref divider, the OAs' ground pins, and signal and jack - each group tied to it self and sending one wire to a mutual GND point on the chassis.


And one more thing - I have a tube screamer that I want to squeeze a charge pump into - but when I do it sucks all of the power out of batteries in a few minutes, now - I know it shouldn't be THIS quick. With an adapter though, it work as expected. The spec sheet indicated that it needs only a few mA for the supply current.
So... what is going on, really?

[Phorhas]

One more thing - when "star grounding" a pedal, rather than an amp - will the "node groups" be differant?

[R.G.]

Yes.

The whole point of start grounding is to get sewer ground and reference ground on different wires. This includes sewer and reference for other sections of the circuit.

You have to think about what is reference and what is sewer ground and split into ground wires based on that.

[pqt_bach]

Thank you for the reply, R.G.

Though - I expressed my idea inaccurately, I meant to ask "what groups should I make?"
I was thinking of grouping to node by function: power, OA power, signal and AUX (meters and stuff)... am I in the ball park?