This week seems to be testing session after testing session. First up the Sansui 881 that was finished having its amp board, and power supply serviced. Testing done before service showed uneven output and a weak channel. This receiver’s factory spec was 60w on an 8 ohm load with both channels driven.
First test I always like to start with is 1kHz with both channels driven then each individually. Then a 400hz, 10kHz, and finally a 20kHz run which always seems to separate the men from the boys. I challenge any modern home theater receiver from a box store to a 20kHz output test; it will no where near put out half of factory spec power. Below are my results which were all performed on an 8 ohm load:
66.7w/68.4w @1khz both driven
80.6w/80.6w @1kHz driven separately
As expected the 20kHz was the killer though still very respectable. The big surprise to me was the individual channels at 1kHz were both a powerful 80.6 watts. Now the best part doing some listening.
The audible hum in the left channel is still present which in doing some research sounds like a common 881 presence. One theory that I feel may hold very true is the close proximity of the huge transformer to the speaker terminals. It is not a 60hz hum which was my original thought. It does not increase with volume and if not right up near the speaker you would not even hear it. Once listening, at least to my ears it is not audible. On the scope the left waveform would slowly move up and down and once volume increased from idle the bouncing stopped. Very odd; I will try several remedies to stop the noise although from many original 881 owners this was occurring to their 881s right out of the box in the early 70′s. Once a source is put through this amp you do not hear it anyway.
The stereo separation and staging on this receiver is excellent. Lead vocals are dead center with percussion just behind. Presence is very pronounced on songs that take advantage. Last listened to China Grove by the Doobie’s; lead guitar rips in the right channel then slowly moves to left of center in chorus. Will do more complete listening test when I can test all sources as well. Looking forward to vinyl on this receiver.
It is kind of late so will have to wait until tomorrow to give the 881 a run for its money. Tomorrow will be final bench test of the Pioneer SX-1010 from my last few posts which will be going home to its happy owner this weekend. Also, my personal McIntosh MAC 1900 that I would like to refurbish I will be testing before service. Coming soon will be another Pioneer SX-636 restoration, and hopefully my long overdue Harman Kardon TA-230 Stereo Festival valve receiver will get its new caps.