QUESTION: I am trying to build a cigar box guitar with piezo microphone. Is it possible to amplify it with a HIFI tube amplifier with a wire with jack adapter / RDA without risk for the amplifier and microphone? Thank you in advance
The signal itself has no inherent load, so it is only after the amp that any damage could be done. For instance, going from a pre amp into the front end of another amp. The main restrictor will be the speakers that you use for finally delivery. HiFi speakers will distort very quickly.
Solid State amps are much more forgiving all round though should you have a small one lying around - even cheap to acquire and be battery powered! This is what I would plumb for.
As well as; a USB Pre amp device like a Focusrite Starfire, that will take your signal from your device by either XLR or 1/4" jack which can be run into a PC or other for recording or editing in a DAW (Cubase or Ablteon, Pro Tools etc) or an AMP SIM app such as Guitar Rig or Amplitude etc.
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QUESTION: My amp is an Audio Innovation intergrated lamp amp...does it change something to your answer ??
No, the amp is responsible for taking the signal and amplifying it... there is no load in the signal from the piezo pickup signal. If you are using a mic that already has gone through a preamp and as such is then an amplified output signal, then this may distort or damage the amp... If the mic is passive then no problem.