ZP80 ground loop issue and solutions

The industry is very sloppy with its use of terms. A “preamp” could be a full function device with a full complement of controls (input selection, Volume, Tone, etc.) without a built-in power amplifier. A “preamp” could be a low level input device (no controls) for use with certain microphones (flat frequency response) or turntables (RIAA equalization). There are two variations of phono preamps, depending on type of phono cartridge. Microphone “preamps” may have RCA connectors or XLR connectors. The full function “preamp” first described above does not typically include capability for low level microphones, Therefore you’ll need a “preamp” for the microphone. An “amp” (“amplifier”) (“integrated amplifier”) (“power amplifier”) connecting to speakers may have no controls, basic controls, or full controls and inputs.

Here, each new poster lives in a particular context and a “preamplifier” or “amplifier” is a specific device in that context. Our job as general purpose commentators is to figure out which context the poster is referring to. Some posters become testy as we attempt to nail down the context that seems very obvious to the poster. 

Quick update. I bought two used ZP100s off ebay, reset them, tested them including the amp section and they are just fine. £50 each. I realise longevity is not guaranteed but an inexpensive, simple though imperfect solution for now. Appreciate all the feedback. My career was around testing ADCs integrated on complex microcontrollers and grounding was always a major consideration in design, integration & test. It reminded me!

You should have been on the ZP80 test team.

Marketers won’t want to hear it because their purpose is to force users up their own value chain of products and they don’t really want users to buy their cheapest ‘digital delivery’ units to integrate in their already high end DACs and amplification. However, designers could easily allow a grounding point just as has been catered for turntable users since time began.