вот как у паркера, например
http://parkerguitars.com/media/pdfs/nitefly_manual.pdfцитата оттуда
"STEREO / MONO SWITCH
The NiteFly features a special Fishman® active circuit allowing you to blend the magnetic and
piezo pickup signals right on the guitar. The pickguard mounted Stereo / Mono Switch makes it
possible to mix (sum) the piezo and magnetic pickup signals and play both sounds through a single
amp, or split them to two separate amps or mixers.
1. MONO With the stereo / mono switch in the IN position, the guitar's two signals are mixed. In
this mode, simply use a standard guitar cable and a standard guitar amplifier. Thanks to the
NiteFly's active circuit, in the mono mode, the "Both" position offers some unique sounds!
2. STEREO With the stereo / mono switch in the OUT position, the guitar's output is stereo.
The special cable (stereo "Y") provided with the guitar allows you to send the two signals to two
separate amplifiers. The full sonic potential of the piezo pickup can be achieved by a high fideli-
ty, full-range amplification system such as a PA, an acoustic guitar amp, or keyboard amp.
• If a mono cable is used and the stereo / mono switch is in the OUT / STEREO position,
only the magnetic pickup sound will be heard.
• If the stereo to "Y" mono cable is used with the Stereo / Mono switch set in the IN / MONO
position, both the magnetic and piezo outputs will be heard through one amp and only the
piezos through the other."