Solid State Audio

2011

This page contains semiconductor audio projects S1 was the first listed, S3 the last. New additions will be made from time to time.

S1 Very simple one transistor microphone preamplifier.

This circuit was used in large quantities in the 1970's due to its simplicity and performance. Often feeding directly into a 100k pot.

S1_one_transistor_mic_preamp.asc This is the LTSpice file, don't forget to adjust the font size.

Red is Vin Green is Vout, sorry cut the y axis scale off!

S3 Simple two transistor preamplifier or line amplifier using one NPN and one PNP transistor.

Another old design with a good bandwidth and reasonably low z output. The only reason to use this these days might be the bandwidth, using the correct parts, values, and layout it can be made flat to about 10 MHz. Video output transistors can be a good choice for these applications.

The voltage at the base of Q1 is approximately 600 mV above the voltage at the collector of Q2 so calculating the bias resistor value is easy, if this circuit was to be modified for split rail use a bias resistor from the base of Q1 to ground would be acceptable leaving R8, R1, R2 and C4 out. The node formed by R2 and R5 would go to the neg supply, C1 would still connect to gnd.

This simple circuit when constructed using small SMD components is still a viable option in the 21st century.

S3_npm_pnp_mic_or_line_amp.png

S3_npn_pnp_mic_or_line_amp.asc

S4 50 watt FET audio amplifier

I have not actually built this amplifier the design is fairly typical of a simple amplifier, spice model only. Spice model built from scratch as exercise, needs refinement.

Test with spice and improve.

S4_50W_FET_amp.asc