- Simple two transistor stage pre-amplifier circuit, with a high impedance input stage suitable for musical instruments with passive pick-ups and an output stage with enough signal level to feed AV equipment.
- A brief description of the processes I used to fabricate the clear acrylic case I made.
Step 1: Make the Circuit
The input stage of this amplifier circuit is a Common Collector amplifier which has high input impedance, low output impedance, and high current gain. The output stage is a Common Emitter amplifier which has medium input and output impedance, and high power gain. The input and output is decoupled from the 3V DC supply power by C1, C2 & C3, R1 & R3 control the base current of Q1 & Q2, and R2 & R4 control the output current of each transistor stage respectively.
I used point-to-point construction for this circuit, however it could be built on a PC board if desired. I used aluminum duct tape to form power rails on the inside of the acrylic case. Since the tape can't be soldered I used small pieces of tape to fasten the connection points to the components. It was challenging to make reliable connections with this method. Alternatively copper tape, or wire could be used.
- Q1, Q2 = 2N3904 (most general purpose transistors could be substituted)
- R1, R2, R3 = 10K
- R4 = 22ohm
- C1, C2, C3 = 35v 10uf
- 1/4" Mono Input Jack
- 2 RCA Phono Plugs (I cut the thread on back shell to form nuts for panel mounting)
- 2 AAA Battery Holder
- Project Box (this is an alternative to the custom case I made)
I used male RCA plugs as the output termination because I wanted a compact inline connection, alternatively female RCA jacks could be used with patch cables. I connected the RCA output plugs in parallel to feed both the left and right channels of the AV receiver.
AV RCA phono plug on center spacing on my receiver is 13mm with a 10mm panel mount hole.