I think selectable frequencies for the high and low bands would be a better addition than the mic pre. And would make the eq much more versatile.
I also think Baltimore's suggestion is much better than the preamp addition.. selectable frequencies are always good, if it's easy to do..
Earlier today I had time to think about the frequency selection option. There is actually space enough for two on-off-on miniature toggle switches in the front panel. Not the prettiest solution but could be worse too. Picture attached (you must be logged in to see it).
Only a little manual wiring and you get 3 selectable frequencies which should be enough most purposes. When I designed the board I included some extra pads to make the wiring easier. I will publish some documentation about it when I have time.
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I e-mailed the Gerber files to Gustav 5 days ago. No answer so far... Someone (jsteiger?) could also talk to him about gold finger plating. I have ordered boards with hard gold long time ago and things have probably changed a lot from those days.