Beomaster 4400 Type 2419: Checking the amplifier right and left channels

Before I finish reassembling this Beomaster 4400 receiver I made a few amplifier measurements to make sure the left and right channels are close to each other in their audio performance.

My testing methods cannot be the same as what Bang & Olufsen used back in the seventies so I am not looking to hit those same performance measurement values. The goal of my performance tests are to make sure the left and right channels perform the same...or at least very close to each other and that they are similar to other Beomaster 4400 units that have come across my workbench.. If one channel is way off the mark from the other on the same test then I have to figure there is something wrong.

The tests I like to use in comparing the channels are a Total Harmonic Distortion (THD) test on the output amplifier sections and the preamplifier sections. For that I use a QuantAsylum A401 Audio Analyzer to generate a 1Vrms sine wave test signal at 1KHz. That signal goes into the Beomaster 4400 Tape 1 source input. I measure the output at the preamplifier outputs then again at the output amplifier outputs (across an 8Ω dummy speaker load). It is actually an 8.08Ω load as I use a 0.08Ω series resistor as a sense load to make the measurements with the QA401 analyzer.

Here is the Beomaster 4400 connected up for testing.

The distortion measurements through the preamplifier were very good as expected.

So were the power amplifier outputs.

The frequency response measurements were also good. These tests are made using a frequency response plugin that is part of the QA401 Audio Analyzer. It executes a series of pulses at different frequencies and measures the output. The stimulus is still Tape 1 and the output is measured across the 0.08Ω dummy speaker load. When the test is complete the QA401 plots the output.

The end points (20Hz and 20KHz) are in the 1.0dB to 1.8dB range of the flat line which is pretty typical with this test setup. Both channels measure the same.

Satisfied with the electrical work so far, I will continue on with reassembling the Beomaster 4400 now and then some functional testing with all of the source inputs and listening tests of course.  Those are the most enjoyable tests to perform :-).