Preamp circuit including a loopback mode for data storage devices

A read channel of a storage device, the read channel comprising:

• a data generator configured to generate a test symbol;
• an encoding circuit in a write path of the read channel, the encoding circuit configured to (i) encode the test symbol as a write signal, and (ii) provide the write signal to a preamplifier circuit to be amplified by the preamplifier circuit;
• a decoding circuit in a read path of the read channel, the decoding circuit configured to (i) receive the write signal as amplified by the preamplifier circuit, and (ii) decode the write signal as amplified by the preamplifier circuit to determine a received symbol corresponding to the encoded test symbol;
• and
• a comparator configured to (i) compare the received symbol to the test symbol, and (ii) output, based on the comparison of the received symbol and the test symbol, an indication of whether the preamplifier circuit is operational.