HiFi power amplifier
I have made speakers earlier so I decided to develop a power amplifier now. This is not my first made power amplifier, so I put all my experience to this device. I decided the front panel not to overload by various knobs. The amplifier has only power switch and ALPS (Japan manufacturer) volume control knob. So power apmlifier is dedicated only for amplification without any signal processing. Every channel is drived by 4 MOSFET transistors: 2 x 2SK1058 + 2 x 2SJ162. Maximum output power 150W per channel.
There is a special commutator for comparing sound quality from 2 amplifiers on the same speakers.
Output transistors are fixed directly to a heatsink under the PCB. Additional wires are not used, so it saves sound quality.
Also electronic short circuit protection is not used in this amplifier. It also helps to save sound quality. . Fuses are used instead in a power supply circuit.
Toroidal power transformer (400W) is used for power supply.
There are photos how were output power measured and stress tests performed. Amplifier is supplied by +-55V voltage, so the load was made from six 12V halogen lamps connected in parallel and in serial to make 36V voltage. Load for single channel is: 3x50W + 3x35W = 255W. The tests were performed with sinusoidal and square waveform signals at frequences from 20Hz to 20kHz. Also I have tried to connect "cold" lamps to power amplifier at it's maximum power output (at this case lamps' internal resistance is very low). All the tests were succesfull!
At maximum output power load's (lamps') resistance is 4 Ohm. Multimeter shows 23,7V, so the power is 140W.
This is 1kHz signal on the oscilloscope screen (divider by 10 switched on). Amplitude is 36,4V, power - 165W.
Here is shown how much power amplifier consumes from the mains. Amplifier is switch off on the first photo and switched on at the maximum output power on the second one. Difference if 600W! It means efficiency is ~50%. After 30 minutes lasted test heatsinks were very hot but still not burned the hands!
