Direct Injection Box Amplifier How to Design? - Project

Thread Starter


Joined Apr 23, 2019
Hello everybody,

I am required to design an amplifier with the following specification, yet I do not have enough capability to design it so I need some help, anything would be appreciated.
The project is the following:

In recording studios and public address work the ‘Direct Injection’ (DI) box is a useful piece of equipment. It is simply a buffer amplifier suitable for coupling a high impedance output, such as that from some guitar pick-ups and microphones, into a medium impedance input such as a mixing desk or power amplifier line input.
Design an active DI amplifier which meets the following specifications:

 Input resistance of at least 1 M Ohm
 Voltage gain of between 1 and 1.5
 Maximum input signal 1 V peak to peak
 Flat frequency response from 20 Hz to 20 kHz under full load conditions
 Capable of driving a 600 Ω load
 Capable of battery operation using a PP3 9 V battery

Your design may be a mix of MOSFET and BJT types but cannot use more than three transistors. When simulating, use 2N3904 NPN transistors, 2N3906 PNP bipolar transistors, M2N7000 MOSFET transistors with their default models in Multisim. You must only use E24 value resistors and should attempt to minimise the total number of components required by your design. Design for maximum battery life.

(a) Build your design in Multisim and test the transient response with no load connected across the output. Use a 1 kHz 1 V peak to peak input test signal and run a transient simulation plotting the output voltage. The output sinusoid must show minimal distortion.
(b) Plot the frequency and phase response from 20 Hz to 20 kHz and show that this is within specification with a flat response ±0.5 dB.
(c) Over the same frequency range as (b), plot the amplifier’s input impedance show that this is within specification.
(d) Repeat (a) – (c) with a 600 Ω load connected across the output. Does your design meet the specification?
(e) Determine the quiescent battery power used with no input signal how long the amplifier would operate from a typical PP3 9 V battery.