From Oakley Sound via analogue Sent Thu, Mar 7th 2019, 14:27
Nothing to do with impedance and probably not output level either. You can turn down the volume on the 303 to see if the problem goes away at lower levels but it probably won't. The problem is more likely due to the MXR D+ being a simple device that has no gain after the clipping circuitry. That is, the output is clipped to around 0.6V peak. Other distortion pedals may be better in this regard. The TS-9 is probably a better bet. Tony www.oakleysound.com