Retro 10W Hifi Amp Kit (1972 Design)

10W RETRO Low Frequency Amplifier

The kit is a module of an audio amplifier, based on an article in (Czech Magazine) Amateur Radio AR September 1972. Any preamplifier with an output voltage of ~300mV / 10 kΩ will give full power.

The amplifier features a large range of 12 to 40 V supply voltage and good frequency stability.

The Kit is supplied without the aluminium heatsink

Assembly Instructions :
The components needed to assemble the amplifier should be soldered into place in the following order: Resistors, Capacitors, Diodes, Small Transistors, Power transistors, mica washers, bushings and heatsink.

All solder into the printed circuit board. The exception is the transistor T2, which is sensing the temperature of the heatsink. This is connected to the PCB via 3 wires, soldered to the legs (insulated with heatshrink), the wires should be passed under the capacitor C6.

Power transistor mounting is shown in Figure 4. T2 is glued to the heat sink with the superglue.

That's it, the amplifier ready and ready for use.

Commissioning :
For startup, a 12-40V supply and multimeter are required.

1. Check it out:- correct connection of all components. If everything is OK, clean the board from soldering residues with Alcohol or IPA.

2. Connect the power

3. Set the the voltage at the + terminal of C6 to half voltage of the total power supply, with the trimpot P1 (About midway position)..

4. Connect the load - speaker: 8 or 4 ohm

5. The other set the quench current to 30mA.

6. Connect the input to a music source with an output level control (CD player, VHF tuner, tape deck, mobile phone, MP3 / 4 player).

7. Check the audio quality by playing a speech program.

Note the Input ground and the speaker ground should not be connected together (e.g. to a metal case)

Specifications :

Supply voltage: 12 to 40 V
Current consumption from the source: 800mA
Input sensitivity: 300mV / 10 kΩ (-8 dB)
Frequency range: 20 Hz - 20 kHz ± 0.5 dB
Max. Distortion in full range: max. 0.5% at P = 10 W
Signal-to-noise ratio: min.86 dB (input 10 kΩ)