Tube vs. Solid State Rectifier


How much does the rectifier stage effect the character of an amplifier. So far, on nearly every SS/Tube decision that's come down, I've gone with tubes. Now, I'm looking at two 300b push-pull integrated amps, the main difference between the two is that one puts out 18W/ch and uses tube rectifiers while the other puts out 25W/ch and uses SS rectification. The SS unit has a much greater bandwidth and just specs out better in general. I'm leaning toward the SS rectifier as long as the amp will still have that tube magic. Your opinions will be appreciated.
phaelon

Showing 1 response by atmasphere

Tube rectification is nice if you can do it! Newer tube amps have bigger power supplies and so can easily damage a tube rectifier during warm-up. So a tube rectifier usually means that the capacitance in the power supply is limited to a small value that might have been considered adequate about 40 years ago, but likely not in a lot of modern designs, especially higher-powered amps.

Tube rectifiers are nice due to their inherent low noise while converting AC to DC. Silicon rectifiers have a commutation (switching) noise that can contribute to the background noise of the amplifier. Commutation noise can be substantially reduced by small networks bypassing the rectifier's junctions, but usually this is not 100% removal. But generally semiconductor rectifiers can survive the large current inrush that is common in a lot of high end amplifiers. That extra capacitance of bigger supplies translates almost directly to better sound, so you can see that there **can** be tradeoffs.

In an SET I think tube rectifiers would be nice- this is an application where they can work quite well.

In amps that have too much capacitance for a tube rectifier to survive, you can often get a lot of the 'tube rectifier sound' by using superior semiconductors. HEXFRED rectifiers are a good example- the ultra fast/ultra soft recovery characteristics of HEXFRED rectifiers approaches that of the tube rectifiers, although they do not have the variable voltage sag with current that is also part of that sound. You really don't want the voltage to sag as you draw more current from the power supply!

In a class A amplifier, the voltage sag issue is not a concern as the draw on the device is constant. In a class AB amp a good semiconductor can actually sound better!