Based on what little I’ve picked up from my two very similar Audio Synthesis stepped attenuator pres I’d say you may want to balance out the Z-foil a little so I’d personally be inclined to go for ‘both’ or ‘neither’. My standard AS Passion has been upgraded with a Z-Foil shunt, the dual mono ProPassion hasn’t, and to be honest I prefer the latter by quite some distance. I totally get what people like about the Z-Foil, it is astonishingly clear and clean, it lets so much info through you couod hear someone drop a pin in an orchestral setting, but to my ears it sounds rather dry and lacking in body compared to the standard (Vshay) ProPassion.
Obviously one can argue I’m not comparing exact like for like as whilst the stepped attenuators are the same type of switch, the one in the Passion is stereo, the ProPassion has dual mono. When comparing I’ve used the Passion via its ‘direct’ input, so no input selector in circuit on either pre, so they should be exceptionally close, the shunt resistor really being the only difference. I have to admit I’m quite surprised by how different they sound! The Z-Foil Passion hyper-detailed and informative, the ProPassion fuller and more organic.
