SE Class A 200W PURE Heat
200 Watt idle
- 128 Watt across 8 Ohm Collector load
- 064 Watt 4 x MJL3281A
- 008 Watt 2 x 1 Ohm Emitter resistors
sum 200 Watt
It is possible to squeeze out more than 10 Watt RMS
at >0.1% pure Class A type Distortion, ear friendly 2nd dominant
1 Watt RMS into 8 Ohm shows only 0.014% Dist,
mainly 2nd and some 3rd but hiigher are VERY very low
Total system dissipation is 200 watt, but you will only get 50 watt rms from the load.
Each transistor dissipates only 30 watt. Problem with SE designs is that the sound falls apart totally when the four amps is exceeded.
I used a CCS instead of the 8 ohm source resistance. It is possible to wind a non-inductive resistor from wire but it may be quite large. I have in the past achieved this from using about 400 mm length of element wire from a broken toaster.
The THD figures looks good at around 0.2% at 100kHz. Harmonics increases evenly with frequency and the sound should be warm/friendly for lack of a better description.
Phase response is a 2 degrees over the audio band, but there is oscillation at about 7.5MHz. This can be overcome using a 220pF miller cap between collector/base of U1.
Otherwise, nice simple design. Build it and see what it sounds like.
In my opinion I would use a dual power supply, adjust the offset to close to zero and save on two caps, but this is not that important I guess.
For even more efficiency, graft in Pass' active current source. It changes the sound character a bit, but it may be to your liking.
It is possible to get 2 x 30W / 8 ohm in pure class A from push-pull, at 200W input iddle power. Distortion much lower, than shown by lineup. Low order harmonics.
you should be able to achieve +-22Vpk from a 50Vdc supply.
You can adjust the quiescent set point to achieve symmetric clipping.
This is about the 30W that the other respondents are predicting.
The 4Apk will allow the speaker impedance to fall to 5.5ohms.
This may suit a moderately reactive 8ohm speaker but probably not a severe reactance speaker.
I am not only predicting, it is my main amplifier and my design ;)
SE Class A 200W Fourier
I have trimmed the performance further.
Below is the FFT at 1 Watt and 8 Watt.
Especially 1 Watt looks just great. But also 8 Watt shows not much above -100 dB.
Even in reality, with real & good supply and real load, I think such an amplifier would sound very, very good :)
After all, we have no global negative feedback here and only one stage
using one Super Darlington Transistor.
Of course this amplifier need a very good, clean power supply.
Because PSU will effect the performance quite a bit.
I will try to make another 'light' version with 'only' 100 Watt idle.
As can be seen, besides the nice Harmonics,
the THD is 0.026% at 8 Watt RMS into 8 Ohm.
When I use Multisim analysis, having any other instruments connected to the circuit ruins the reading. I see a lot of stuff in yours above, but I'm not sure if these were there when you ran the Fourier.
You are looking for the "tube" sound maybe?
My saying is, once you show anything to anyone, nothing remains sacred.
Anyway, whomever was the designer, the THD at 100kHz at 30 watt is only 0.2%, not too shabby at all and bandwidth extends past 1 MHz.
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