2. amps-preamps
  3. 1220199838

Buzz about pure class A solid state amplifiers ?

Fellow Audiogoners:

I would greatly appreciate all your input/insight.

Lately both in and out of Audiogon, I have been aware of a "buzz" and numerous praises about the benefits of pure class A solid state amplifiers, as an alternative to the more common high bias AB designs, and an alternative to the transparency and coherence of tube designs.

I have recently auditioned a current production 60 watt Accuphase class A solid state design, a fine amplifier indeed. However, up against my similarly priced VAC Phi 300 class AB stereo tube amplifier (used in ultralinear), it sounded mildly anemic, less transparent, and less coherent/detailed. This is with due respect to Accuphase products, which I have owned and enjoyed greatly.

So....please help me to understand all the purported benefits of the lack of crossover notch distortion, etc with class A push pull soid state designs, when excellent AB tube amps, with crossover notches, are IMHO more cohesive, transparent and resolving in comparison. Have designers, both tube and solid state, basically succeeded in rejoining positive and negative waveforms seemlessly, without perceptable crossover notch distortion?

Yes I did, admittedly, have an interest in simplifying my system, and going back to solid state after 14 years (with tube preamp); However my tubes are gonna stay :)

To all my solid state friends, please know that I have owned many solid state amps which I have truly enjoyed and have the utmost respect, dating back to the Reference Levinson 32's...and I know there are great SS amps out there, and primarily class AB designs.

Just wanted to share my experience, and learn alittle more about class A solid state, specifically.

With thanks in advance for your thoughts

Brian
audiobrian

Showing 1 response by liguy

liguy
228 posts
 
The advantage of a Class "A" amplifier is not:

"The class A approach minimizes the thermal distortions by maintaining a more or less constant device temperature, and therby reducing the distortions caused by heating and cooling (consider a class B amp: junction temperatures and the gain non-linearities rise and fall much faster than the massive heat sinks they are strapped to, which are more an RMS type thing).

Other positives about class A involve less modulation based noise on the power rails (since the output devices are constantly "on" the rails are subject to a more fluid load)"

as Dpac886 suggests. It is that the amplifying devices are constantly operated in their linear region, above cutoff and below saturation. By using Class "A" topology we can set the bias of the device to it's most linear region. This negates large amounts of negative feedback needed to correct for the extremely nonlinear characteristics of the transistors at the collector cut-off region and the turn-on/turn-off times of the devices in class A/B topology. There is a good explaination at Passdiy.com, Nelson Pass's contribution to the DIY Community.

http://www.passdiy.com/pdf/classa_amp.pdf
More to discover