4 Ohm Loads
I have an old Boston Audio Society (BAS) report on 8 low-priced (less than $300) receivers from 1976 and one of the tests was the testing of the amplifier section into 8, 4, 3, 2, 1.3 ohms loads and the report stated that an ideal amplifier will double in power output when the resistance is halved (i.e 8 ohms then 4). This will occur with heavy-duty power supply design. The lower speaker impedance could cause the amplifier section to chatter or ring when trying to drive the low impedance loads.
The BEST amplifier in the test was the 20 watt rated H/K 330c ($220) which put out 24.5 watts at 8 ohms, 42 at 4 ohms, 48 watts at 3 ohms, 44 watts at 2 ohms, and STILL put out 40 watts at 1.3 ohms. None of the others (Pioneer SX-550, Marantz 2220B, Toshiba SA-420, Technics SA-5060, Nikko 3035, and Advent 300) came close including the Marantz 2275 ($650) which was also tested as a reference unit. The report ranked the H/K 330c as a best buy and that the relative amplifier performance outclassed the Marantz 2275 which put out 78 watts at 8 ohms, 127 watts at 4 ohms, 41 watts at 2 ohms, and only 21 watts at 1.3 ohms.
It noted that the GAS Son of Ampzilla ($450) amplifier chattered when driven into a 2 ohm load due to the protection circuitry cut in and out and this is not uncommon in amplifiers.
ps. Yes, I am partial to H/K products.
