I am attempting, after many years of not working in electronics, to design a preamp + amp system for an audio product. The product is simply amplifying voice from a dynamic microphone and driving a 4 ohm custom speaker, using portable battery power ( 24V with 20 AA Ni-mH cells). We need as much power output to the speaker as possible without causing feedback. Our microphone outputs 300mV peak-peak max. under normal speech. We have tested a prototype, put together by another engineer, that worked acceptable using a preamp with a gain Vo/Vi = 40 (+32db), fed into a TPA3123D2 eval board, using only the left channel (not bridge tied), with it's gain set to +32db. As the TPA3123 spec sheet shows an absolute max. rating for Vin = 7V, and the preamp output had peak -peak voltages greater than 7V, we were getting clipped output to the speaker.
I would like to design another preamp/amp setup, and would like any suggestions for the power amp (would like to use an eval board if possible). Also, our preamp uses two OP07 op-amps with a common ground input and output, and I'd like any suggestions on a better circuit to consider for that.
I was considering the TPA3106D1, as it is a mono amp, or the TPA3123 in a bridge tied I/O.
Any other suggestions or direction is appreciated.
K2
