By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Tuesday, July 24, 2018
Beomaster 4400 (2419): Amplifier 50W Output Check
As a burn-in test I left the Beomaster playing the FM tuner for 24 hours. I varied the volume level every now and then but always kept it at normal listening levels (soft to loud). The output transistor heat sinks remained cool to the touch all during the burn-in testing and of course the sound was good.
Now it is time to see how the Beomaster does when full output power is requested.
First the test setup. My source input voltage is a 1KHz sine wave at 2Vp-p into the Beomaster 4400 Tape 2 DIN plug.
The output of the Beomaster will be measured using the speaker 2 output connected to my 8Ω dummy speaker loads. These are power resistors with heat sinks mounting on an even larger heat sink as the resistor loads will get pretty hot when full power is applied.
Here is the Beomaster with speaker 2 selected, Tape 2 selected and the volume level set to output 50W (the rated power output into 8Ω as listed in the Beomaster 4400 manual). I used my DMM to monitor the speaker load to check when 50W was reached. The QA400 analyzer connects to the dummy load as well via a differential probe.
The power test worked nicely. I ran the volume up until I got to 20 V on the DMM. A little bit higher and the Beomaster overload lamp came on as I would expect. I backed the volume down a bit to measure the distortion of the 1KHz signal across the dummy loads.
Both channels measured quite good. Just below 0.02% THD for a 1KHz signal at maximum power.
As with previous amplifier measurements using this setup... I can't really do a direct comparison with the B&O published specifications as their test equipment and methods are different from mine. The best I can do is repeat my own test setup with the amplifiers I restore and collect that data for my reference. In comparison to my recent Beomaster 8000 output tests the THD on this Beomaster 4400 also measures very good. Well below what human ears can hear.