Personal in-ear monitoring system:

This project was made on the request of a local band, "The Led" for using on stage instead of the usual monitor speakers. This project was finished in less than a week.

The system consists of a main distribution unit and 5 personal units. The main distrubition unit has 5 audio inputs with level controls and peak level indicators consisting of a signal and clipping indicators. The unit has 5 outputs for personal units. Each output has a selector knob which is used to select any of the five input channels to be sent to that output.  Power is also supplied to the personal units by the main distribution system. Each personal unit has a volume control knob, a power indicator, a signal indicator and a clipping indicator.


The HDM501 is a five channel personal in-ear monitoring system. It consists of a main distribution unit and a personal unit for each channel. The personal unit is connected to the main unit via a balanced jack lead. This lead sends both audio and power from the main unit to the personal units.

The distribution unit houses the power supply and the signal distribution electronics. Each of the five audio inputs has a level control and two indicator LEDs. The green LED is a signal present indicator while the red LED is a clipping indicator. Each headphone channel has a selecter knob which assigns one of the input channels to that channel. Each headphone power output is individualy short-circuit protected.

Front panel of main distribution unit

The power switch is to the left. The small knobs on the left side are to level control knobs for the five input channel. Above each of these knobs are two LEDs. The bottom LED is a signal indicator, while the top LED is a clipping indciator. The large knobs to the right selects which input channel is used as the source for that output. Below each of these knobs is the connector where a personal unit plugs in.

Back panel of main distribution unit

The personal unit is a small box with a belt clip. The bottom side contains two 1/4" jack sockets. The left socket is for audio and power input from the main distribution unit, while the right jack socket is for 1/4" headphones. The top of the unit contains three indicator LEDs, a volume control and a 3.5mm jack socket for 3.5mm headphone plugs. Note that although this is a mono system, it is designed to be used with stereo headphones, plugging mono jacks into the headphone sockets may damage the unit. The three indicator LEDs consists of a orange power indicator, a green signal present indicator and a reg clipping indicator.

Top panel of personal unit

The top-side of the personal unit has a 3.5mm jack for the headphones, a volume control and three LEDs. The LEDs are for Power, Signal and Clip.

Botton side of personal unit

The leads from the main distribution unit is plugged into the POWER jack socket above. The PHONES jack makes provision for headphones with a 1/4" jack plug.

Side view of personal unit


Main distribution unit:

Number of inputs: 5
Number of outputs: 5
Audio input:
    Type: 1/4" jack, balanced
    Sensitivity: -20dBV - +20dBV
    Impedance: 10k
Output to units:
    Type: 1/4" jack
    Connection: Tip Audio signal
    Ring +15V power
    Screen Common
    Signal level: 2V amplitude

Personal unit:

Headphone output: 1/4" or 3.5mm stereo
Power output: 100mW rms
Impedance: 8ohm-40ohm
Power supply: 15V
Signal input level: 2V