Pictures of your diy Pass amplifier

Aleph P 1.7
 

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Here's a little jfet boz I quickly slapped up together. I think I should use a shielded cable on the input. I'm going to use an external battery pack (2x 9v).

I think if you can avoid shielded cable do. I very rarely use it. You should not need it as all signal voltages entering the preamp should be better than a volt or two. Earth the case if you get hum. I power some of my BoZi on batteries but I have a very simple external supply made from a 24VAC wall wart. I rectify and lightly filter the power external to my BoZ (in this case my BoZSE). It does require that you have at least 20,000uf of storage cap on your BoZ cct.brd. as I do (BoZSE - 30,000uf). This is part Hiraga and Pass design to have this much storage directly on board.

Using the external DC PS means only DC (though only lightly filtered) enters the BoZ. In the PS I use a 10uf poly after the rec. bridge then a 680ohm resistor (can vary) then 1000uf low ESR cap.
 

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Thanks for the suggestions.

How do I go about earth grounding the case? I use a 24v dc walwart (currently) and there is some hum.

Remember there is DC going into the case. Take the negative of the PS and attach to the case. Usually the the negative (non-hot) wire of RCAs attaches to the case too unless you used isolating RCAs. I often use isolating RCAs because they look better then ground the negative of the RCA to the case.

Some like to use a 100ohm resistor to ground the negative of the PS to the case and some also by-pass this with a small cap.