Despite my rush of enthusiasm for the BHK monos, I am reminded just how good the stereo version is by what we heard at the Munich show. For those unable to attend I used the BHK Stereo 250 to play a pair of power hungry Magneplanar 20.7 and the amplifier hardly broke a sweat doing so. To be honest I missed the monos not. The Signature 250 really showed off its colors and, I must say, coming back to roots playing the 250 was helpful - it brought the magnificence of the Signature 250 back into focus.
But I still want to examine how a great stereo power amplifier can be improved, further still, when made into a mono.
So, just what is a mono amplifier? A single channel power amplifier with its own power supply and chassis. Add another channel and you have a stereo power amplifier. And what of 'dual mono' power amplifiers? A stereo power amplifier in a single chassis with two separate power supplies, one feeding each channel.
Prior to Alan Blumlein's 1930 invention of stereophonic sound all power amplifiers were monaural - there was no need for two when the sound systems had only one speaker. Use of two mono amplifiers, even for the adventurous few adopting stereo, was always accomplished using twin amplifiers and preamplifiers. Stereo sound was rare into the 1970s when it became more accepted. It's hard to imagine today that manufacturers of audio equipment questioned whether stereo sound would ever be fully embraced by the public and if so, when. The breakthroughs began to happen in the early 1970s when brave manufacturers of media and hifi equipment took the risk to continue promoting the new stereo sound. LPs were released in increasing numbers recorded in stereo, and amps and receivers began to offer one-box solutions to the problem of multiple chassis.
By the mid 1970s stereo was fully accepted as valid enough to become the standard and mono began to fade from view, though there remains many mono fanatics to this day. Their claim is that when the shift to stereo began, we lost something mono recordings and systems had. And they may be right. Few innovations come with a free lunch.
For amplifier manufacturers it became obvious the most economical means of building a twin-monaural amplifier in a single chassis was to use one power supply to feed both channels. Power supplies in amplifiers tend to be huge and expensive.
Thus the stereo amplifier, integrated and receiver came into popular use and it is what we have today. But as good as stereo amplifiers are, and make no mistake about it - there are great ones out there - none are as good as mono amplifiers in separate chassis, power supply and line cord.
Tomorrow, the ways we think of amps.