Hi Ian,

A quick question. Is there any reason in particular that a TL072 is specified ? Power consumption perhaps ? I was thinking that if one used a 5532 then the box would have a bit more drive capabilty ?

It's cheap, does the job and does not consume much power. The output consists of a TL072 feeding a 150R resistor in series with a 15K resistor and a nother 150R resistor to ground. The 0dBu output comes after the first 150R so the source impedance is about 150R. This is designed to drive a line input so the load will be about 10K - well within the capability of the TL072. The -40dBu output comes from across the bottom 150R resistor so again the source impedance looks close to 150R which is probably what you want if feeding a typical mic pre with 1500 ohms or more input impedance.

Bottom line, unless you want the 0dBu output to drive a 600 ohm load then you do not really need a 5532. I am sure it would work fine instead of a TL072 but I am not sure how long the battery would last driving 600 ohms.

Cheers

Ian