using steel chassis as ground

[franjy]

Interested in a transformer based passive preamp from Elecro-print that uses the steel case as ground (negative) for all input, output and potentiometer connections. The female chassis output RCA's have only a positive interconnect cable and use the chassis connection as ground. How does this compare to 2 wire connections, aluminum case, isolated components and no chassis ground. This is how my present non-transformer passive is constructed and I have no hum problems. Using a case instead of wire concerns me.

[AndrewT]

Hi,
You must connect the mains safety earth to the steel chassis, no other option is permissible. Some manufacturers connect each removable metal panel with a flexible cord (wire) back to safety earth or adjacent fixed panel for added safety.
Many manufacturers and DIY isolate the chassis from signal and power ground. It helps stop hum and buzzing contaminating the signal ground and therefore your output should be cleaner.
A few do make direct connection from chassis to ground, but I have tried a few versions of this and none have been successful.
I recommend separate power ground, signal ground and final single wire between. A separate safety ground with 10R connection to power ground.

[richie00boy]

Your current isolated socket version with alu case is far superior as far as a connection scheme goes. Using the case as ground creates huge potential for local ground loops and this is exacerbated by the steel case which will support eddy currents. Quite poor design IMO.

[Sch3mat1c]

Originally posted by franjy
passive preamp

Huh?

Tim

[franjy]

This is a PASSIVE preamp. There is no real current here. except for the 2 volts the transformers see from a CD player. I don't think the same grounding concerns apply.