It is not uncommon to amplify quiet (solo-) instruments in connection with loud orchestras.
I always experience that when I do recordings in large concert halls. This is especially often the case when soft solo instruments play along with symphonic wind orchestras for example.
But the amplification often does not need to be very "strong". Usually a kind of support is enough. Nevertheless, you should have a good amplifier system (quality). Attention must be paid to the correct miking of the certain instrument as well.
If you want to keep the position of the amplified instrument, I recommend the amplification over only one speaker close to the instrument itself (
example). This preserves the character of a "playing instrument from the orchestra" just so as the listener it can see it as well. Often the mistake is made that the amplified instruments are transmitted over an entire hall speaker system. Of course... most listeners do not care about such details.
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