450 Pound Monobloc Amplifier

New 650W Rowland model 725 monoblocks are only 54lbs (including fancy heavy case milled of single billet of aluminum). The key is power supply. Rowland uses quiet switching power supply (SMPS) that provides line and load regulation while traditional supplies are not regulated at all, noisy and require huge amount of output capacitors to hold voltage steady, not to mention gigantic transformer. Transformers in Rowland SMPS are small because they operate at higher frequency. Transformer that operates at 100kHz can be 10x smaller than one operating at 60Hz. Rowland operates at 1MHz. In addition it provides power factor correction, meaning it presents itself as resistive load, while typical power supply takes current is narrow current spikes of big amplitude increasing requirements for cable gauge, wall socket quality etc not to mention radiated noise.

Some people argue that class D, as good as it is for the money, cannot really compete with best traditional SS amp. I can see that, especially with still limited bandwidth, but most of the weight is in the power supply that can be definitely class D (SMPS) since it is only holding steady voltage (much easier task than driving complex load with music signal). Rowland does it so why not the others? I think it is for three reasons:

1. Design itself is much more difficult than just
transformer+rectifier+capacitors
2. SMPS have bad rap from crude cheap computer applications
3. Audiophiles still believe that it has to be heavy to
sound good.

Third point is very important - why to design complicated light power supply when market believes that heavy=quality.

The bandwidth limit causes phase shift in audible range possibly affecting harmonics summing. My amp, for instance, has -3dB at 65kHz causing 20deg phase shift at 20kHz. Mentioned Rowland model 725 has bandwidth of 350kHz.

Mapman - this question should be addressed to more experienced Audiogoners who have chance to compare them at shows. I can only comment on technical merits.

Minorl1 - no tricks, just different technology. Transformer operating at high frequency can be 10x smaller. For the same reasons capacitors don't have to be large. Smaller caps work great for filtering of higher frequency while voltage stability is handled by regulation. In comparison traditional supply doesn't have any regulation (line or load) and operates at 60Hz. Both conditions require huge amount of capacitors to keep voltage steady under momentary load and to filter out low 120Hz.

One review of my class D amp praised it composure during music peaks (orchestra forte) - that's what load regulated supply brings. In addition so called linear supplies are in reality primitive switchers operating at 120Hz and polluting with high current spikes. Rowland switcher has power factor correction and presents resistive load with smooth current. Jeff Rowland perhaps explains it better:

http://jeffrowlandgroup.com/kb/questions.php?questionid=144

People believe that the main reason for switching power supplies is efficiency and size while they produce noise (tradeoff). In reality switching power supplies executed properly allow to reduce noise. For that reason Rowlands Capri preamp is powered by switching power supply (where efficiency is not important)

Yes, switching power supply is the same as class D. In fact class D was invented when engineers who designed highly responsive switching power supply showed responsiveness by making power supply to play music.