Summing the Channels in a SD-2000 M/L

[Woody.au]

The good old SD2000 is a very good detector and can be made even better if one sums the two channels into one. The SD2000 is setup so that the dominate channel only outputs to the audio stage while the other is supressed. What I found is that running both at the same time i get a far better signal response and it also eliminates the warble that you get from a equal decay amplitude in each channel.
I left the gated switching as to allow for separate channel ground balance, I fed each channel in a dual gate mosfet BF966 I think it was for memory. Its a good mod and should help to ping those mid sized and mid depth Nuggets a lot better.
I estimate a 10 or 15 percent gain on certain size and depth targets.

[porkluvr]

Thanks Woody, for the insight. Can you please clarify what you meant by "I fed each channel in a dual gate mosfet...".

I have a multi-channel project in work but the receiver is flagging for lack of a clever combination strategy.

My rx topology will probably imitate either Eric Foster's GS4, or the SD2000 - as I don't want to be 're-inventing the wheel'.

[Woody.au]

The Dual gate fet is being used as a el cheapo audio mixer, i added it dead bug style to the circuit board just as an experiment. Better results would be obtained by using an opamp mixer approach as it will give some gain.