Looking at an Usher R1.5, it is 89 lbs, 150 watts per channel at 8 ohm, guessing the first 25 watts is in class A as the R2.5 is 250 wpc AB/50 wpc Class A. Idle current is at 250 watts for the R1.5. From what I read, the amp is based on Nelson Pass' Stasis design. My Rotel RB-1090 is around 85 lbs but delivers 380 wpc in AB, 0.0000001 wpc in class A 🙂 The question is,why build an amp that weighs a ton, idles at 250 watts, but only delivers 150 wpc in Class AB?
That is class A for you. At least 70% of the power is wasted and draws at least 70% of full power all of the time.
A bad design in todays world of conserving energy.
A bad design in todays world of conserving energy.
It realy is not class A amps that is the problem regarding energy. Lookat house heating, insulation on so on. Over here up to 80% of the electric bill is regarding heating.
If a amp draw 250W or 100W do not matter much. how many lightbulbs VS LED's is needed to get that difference? the number is 3. switch out 3 lightbulbs for LED's and you have saved those 150W. And the lights are on for a longer time then a amp is.
If a amp draw 250W or 100W do not matter much. how many lightbulbs VS LED's is needed to get that difference? the number is 3. switch out 3 lightbulbs for LED's and you have saved those 150W. And the lights are on for a longer time then a amp is.
I've no idea why people build heavy, grossly inefficient power amplifiers. I guess its a distrust of smart engineering decisions! The KISS principle has its benefits, but hot-running amps are generally less reliable than cool ones, so I'm not sure it applies here. But people seem to enjoy building them...
To me engineering a power amp is an exercise in simultaneously optimizing several variables, noise, distortion, quiescent power consumption, efficiency with real signals, cost, reliability, failure modes, ruggedness to load, longevity, servicability etc.
One of the interesting points in this multidimension design space is the opamp array amp - many of the variables above are directly inherited from opamp's performace directly, and little extra protection circuitry is needed.
Pure class A is to my mind one of the least interesting points in the design space, several of the variables are just ignored, it seems an admission of failure to not address them at all.
To me engineering a power amp is an exercise in simultaneously optimizing several variables, noise, distortion, quiescent power consumption, efficiency with real signals, cost, reliability, failure modes, ruggedness to load, longevity, servicability etc.
One of the interesting points in this multidimension design space is the opamp array amp - many of the variables above are directly inherited from opamp's performace directly, and little extra protection circuitry is needed.
Pure class A is to my mind one of the least interesting points in the design space, several of the variables are just ignored, it seems an admission of failure to not address them at all.
I might agree except for the fact that I repaired a Pathos T.T. a while back. 32 kilograms (70lbs) for 35wpc.
Listening to music powered by the T.T. was an out-of-body experience. I was absolutely mesmerised and could not stop listening all night. I have wanted a 100 wpc version ever since and even toyed with making something myself based on the T.T. circuit.
My own amplifier is no slouch being a highly regarded Accuphase E-303X. I can't explain what might be making the T.T. so ethereal, but I would never poo-poo a class A amplifier again.
T.T.
One of the best sounding amps I ever built was the old prehistoric Nelson Pass 20 watt single ended class A using the paralleled bipolar outputs. I can understand why people like class A, but you just can’t go overboard on power. I’m not sure I’ll ever build one any bigger because of the heat - I’ve had the parts to do a 100 watt per channel version but never started it. Including the Signal 80-25’s that I picked up for a song - 20 years ago. That shows you how much of a hurry I’m in to build that space heater. Maybe one day, but for now If I’m building 90 pound amplifiers they get used to drive PA subs with 4” voice coils and can turn lesser speakers to charcoal - while putting out less heat.
My year-round shop amp is a Pass A40 I built years ago. It idles at 100W per channel and will drive any load you care to throw at. Currently powering Westlake BBSM-6s, less than 2 Ohms under 500Hz. I have the 20W article that wg-ski mentions but never got around to building it, circuit boards were available for the A40 so that's the route I took. Signal will still make the xfmrs but are not cheap anymore.
Craig
Craig
The transformers weren’t cheap back then either. When I had the opportunity to pick up a pallet of 80-25’s for $50 each, I jumped. Been using them in pairs as isolation trafos and battery backups (they have 20-40-60-80 taps). But *perfect* for a 100wpc class A if I ever get so inclined.
I think I paid close to $400 for mine, one time setup fee, winding and shipping. I was given a dead SUMO Andromeda II and using the heatsink article in the same issue of AA with the A40 in it I calculated the heatsinks were the perfect size. This chassis also had the correct amount of fuse holders for the A40 circuit. So my chassis was free and the circuit boards were given to me by Mr. Pass. I was able to track down a bunch of the original Lambda Darlingtons. I think I have about $600 in the amp.
Craig
Craig