AA/BB switch with monitoring output (3PDT must do)

[Thomeeque]

 Hey guys,

I am bulding this box for my friend, he want's to switch between electric guitar plugged into electric combo and acoustic guitar plugged into acoustic combo, he also needs monitoring output of selected guitar (mainly for his Harmony Singer, also for tuner etc.), input of non-selected amp must be mutted, switch state must be indicated somehow. All this of course with influencing signal coming through as less as possible.

I'd like to manage with 3PDT switch, I have came up with this (Variant 1):



What I don't know is if it is 100% OK to simply ground output of active electronics of the acoustic guitar (I am pretty sure preamp in the guitar will survive, but won't it cause some interferences etc.?).

Other option is e.g. Variant 2, but mixing buffer is little more complicated, also there is one switch in the signal path.

Thoughts, ideas?

Cheers, T.

[PRR]

> OK to simply ground output

IMHO, any electronics which won't survive a short is not stage-worthy. Shorts happen.

I agree that I would not try this on someone else's gear.

> Thoughts, ideas?

You could put your own short-proof buffer at each input. I bet you are reluctant to touch the precious signal.

If you have power for a buffer, you have power for a relay. The switch reduces to SPST. The LED needs no extra contact. 4P2T relays are fairly common. 6P2T relays are rare, but two 4P2T relays gives 8 poles which is way more than ample. Problem then is to define power source, monitor buffer, and relay to all agree on a voltage, and reasonable current. Buffer can eat 12V or 24V; relays in these values are common parts.

I agree that a relay will thunk; but as I understand the setup there will be thumps as the acoustic is put on a stand and the electric is slung over the neck; this isn't a mid-song between-notes sound change. The relay should take the raw power direct, and the buffer be fed through a 100r+100uFd power filter to smooth the supply voltage change as the relay takes power or not.

[Thomeeque]

 Hey Paul, Merry Christmas, thank you very much for your answer! You are right, relay makes another usable option. Recently I have bought Joyo JT-305 Pedal Tuner (looks like the Korg Pitchblack clone), it uses relay inside for true-bypass, would be maybe worthy to find what exact type it is (reliable at 9V battery power), even there is DPDT only iirc.

Anyway I am still considering Variant 1 for it's simplicity, maybe I'd just put small resistor (100R?) into acoustic guitar path (passive short-proof buffer, haha ), it should not make any noticeable impact on the signal as it is already preamped (and it is for stage use only), hmm..

Cheers, T.

[Thomeeque]

 Hello, so I have built Variant 1 with "passive short-proof buffer" on acoustic path, seems to work well here in my home setup (let's hope it will work well even for my friend):



(build gallery)

Cheers, T.