WBO2 speaker noise

I installed a 14point7 SLC Free 2 wideband last year and it has always had an annoying whine coming through the speakers when the radio is on.

It's independent of RPM and I've tried multiple power sources and grounds. The noise goes away when I power it from an external source. I also tried adding a capacitor to the power circuit and heater circuit to no avail.

The least noisy method has been powering it from the in-tank pump fuse and grounding the controller to the chassis near the parking brake.

Anyone recommendations on how to fix this? I've also emailed 14point7 to see what they think, waiting to hear back. Getting ready to replace the original speakers but I don't want to hear the whine in high fidelity

Edit: wasn't sure if this should be in performance or not, mods please move the thread if it belongs in non-performance

Radio only, or Radio+Amp?
Does it occur with aux/cd/tape or just FM?

You could try wrapping the radio switched +12V wire around a ferrite core (you can find clip-on cores that are easier to install on existing wiring), or you could try a 3-wire audio noise suppressor. Try an amazon search for "audio noise suppressor".

The noise is from the WBO2 PWM pulse width modulating (on-off-on-off-etc.) the heater circuit in the O2 sensor to maintain a fixed temperature, which may be switching 10amps [guess].

bobxyz said:

Radio only, or Radio+Amp?
Does it occur with aux/cd/tape or just FM?

You could try wrapping the radio switched +12V wire around a ferrite core (you can find clip-on cores that are easier to install on existing wiring), or you could try a 3-wire audio noise suppressor. Try an amazon search for "audio noise suppressor".

The noise is from the WBO2 PWM pulse width modulating (on-off-on-off-etc.) the heater circuit in the O2 sensor to maintain a fixed temperature, which may be switching 10amps [guess].

Click to expand...

Yes, the sound starts the moment the stereo powers on and is the same on radio or cassette.

I believe the heater circuit draws about 3 amps.

I also read on a Miata forum about making an inductor with a 1/4 bolt and 100-200 wraps of 20 ga wire, maybe I'll attempt that first since it's cheap and easy.