![they can source 35mA. While you can achieve the](/images/new-backgrounds/17081/170813x1.webp)
looking for the UL label anymore. The Occupational Safety & Health Administration now certifies multiple companies to test consumer equipment for safety. These are called Nationally Recognized Testing Laboratories (NRTL). In most cases the testing standard used is the one developed by UL in the past. If the NRTL is not UL it will use its own Registered Certification Mark. The web site http:/ /www.osha.gov/dts/otpca/nrtl/nrtlmrk.html shows marks for each NRTL that would be placed on equipment for each NRTL that could test the unit. One wishes that OSHA would have established a single mark to indicate that an NTRL had certified a product was safe to OSHA standards, but instead we have to deal with many different marks that indicated a product has been tested to OSHA standards of safety.)
Class AB amplifiers running full out are approximately 70% efficient at full power so the power coming out of the wall is 13 amps, which is just under the rating
for a standard wall outlet (leaving 2 amps to supply everything else on the same AC
loop). Amplifier manufacturers selling
these amplifiers. I looked high and low at CES and not one of the manufacturers sporting an amplifier rated at 300 watts times 7 had an NSTL label on the back. In reality, you would need to hang a
Why has no 300 watt
I do not know about you, but I would worry about a power amp sitting in my living room that was not tested to UL standards by an OSHA- certified laboratory. Apparently, products without NTRL labels are available for sale in all states but Oregon. Go Beavers!
OK, back to the Sherwood
Both Sherwood units share a nicely designed circuit topology and some high quality parts. Attached to the big heat sinks are expensive Sanken 2SA1216/2SC2922
they can source 35mA. While you can achieve the
same thing more economically by putting multiple transistors in parallel, you would have a hard time achieving as low of junction capacitance. The devices have a unity current gain frequency (the frequency that a piece of
wire would do as well) of 40MHz. That’s twice as fast as most power transistors in this class, which is why the 2SA1216/2SC 2922 are more than twice the normal price. Faster is better, because the amplifier can be made more stable when driving complex loads at audio frequencies. The
To generate enough current at the base of the 2SA1216/2SC 2922, a