I want to mix up to four AC signals, that may or may not be DC biased, but will always be between -5.6 and +5.6.  For that I was going to use a summing amp. (If anyone wants to talk me out of that in a comment, feel free, but that's not the main focus of the question.)

I also want to be able to connect/disconnect the signals to the mixer via a microcontroller.  I'm not THAT concerned with a little distortion or delay, since the signals are monotone and mostly for testing purposes.  I have read that a relay is probably my best bet, but I don't have any around at the moment.  Therefore, I tried to design one using the discrete components I have, which are BJTs, MOSFETs, and the normal passives. I read [this post][1], but I'm not really sure how to apply SCRs or TRIACs. The TRIAC's wiki page lost me when it started talking about quadrants, haha.  I just want to pass the signal, or block it.

For instance, I drew up and simulated the following BJT schematic.  Since it's my own creation, I of course don't trust it, but it seems to work, with only 10nA pulled from the control pin.  Could anyone give me a reason why a relay is preferable? 

[![enter image description here][2]][2]

[![Output is OFF when VCON=5. Current leakage also shown.][3]][3]
Output is OFF when VCONT=5. Current leakage also shown.
[![Output is ON when VCON=0][4]][4]
Output is ON when Vcon=0

In reference to Russell's comment, I tried to simulate this circuit:

[![enter image description here][5]][5]

But the control (shown here as voltage source) cannot be grounded.  In this pic it works, because the control is isolated.  I tried adding a resistor between ground and sources, but that does not allow for full cutoff.

At Russell's behest, I built the NMOS version and it worked even though the simulations show only a dampening for the positive swing:

This was the circuit that was simulated and built/tested:
[![enter image description here][6]][6] 



Simulation result:
[![enter image description here][7]][7]

Oscilloscope measurement (when forgetting to ground the Source, or having very high R to ground):
[![enter image description here][8]][8]

Oscilloscope measurement with the 6.8k resistor from S to GND:
[![enter image description here][9]][9]

**Voltmeter measurements:**

When Vcon=HIGH: **0** uA from Vcon, **12** uA from signal into input, **9** uA from Source to GND.

When Vcon=LOW:**0** uA from Vcon, **0** uA from signal to input, **0** uA from Source to GND.


  [1]: http://electronics.stackexchange.com/questions/2010/using-a-transistor-with-ac
  [2]: https://i.sstatic.net/kgtq0.png
  [3]: https://i.sstatic.net/9b5o4.png
  [4]: https://i.sstatic.net/KGDYm.png
  [5]: https://i.sstatic.net/x1nrc.png
  [6]: https://i.sstatic.net/Ti8OR.png
  [7]: https://i.sstatic.net/P72xR.png
  [8]: https://i.sstatic.net/uaAPB.png
  [9]: https://i.sstatic.net/uSydD.png