Dear all,
I have been thinking too much about building a class A amplifier. Transformers and Heat Sinks and boxes are the biggest costs for all amplifiers, and suitable transformers and capacitors are nearly twice the cost for Class A amplifiers.
In general, do members of this group think that most 100 W class AB stereo amplifiers could be converted to Class A mono blocks with the same output power? This way we could avoid the costs of buying or building boxes and buying expensive transformers and capacitors.
I doubt this will be quiet possible, as has theoretical efficiency of 78.5% and class A a theoretical efficiency of 50%.
Having looked at my 3 Quad 303's I notice they have a Center tapped transformer. Even though the Quad 303 is a single rail powered amplifier.
They have approximately 70 V supply, and deliver officially 30 W RMS and 3 Amps into 16 Ohms hence the name.
If I put a single rail powered JLH class A amplifier inside, do you think I would over load (so the transformer starts to Buzz or some thing worse) the amplifier as a 15W into 16 Ohm mono block amplifier.
The idea would be to use the center tapped transformer and two diodes to halve the voltage, and half the time the current is used, and then since its a mono block I halve the power demand to make up for the approximate halving in efficiency over a class AB amplifier.
I don't think I am going to do this crime (at least permanently) as the Quad 303 is a lovely beast but if they remain so cheap broken on ebay in the UK I could be tempted, this said I will probably just spend the money some time a build a 25 W JLH Class A into 6 Ohms as I preferred the sound of no coupling capacitor when I played with the 1969 and 1996 JLH topologies, ( though I did feel that the need for some DC offset protection was a must with direct coupled amplifiers) but maybe some other less classic amplifier with higher power and and more current drive could suffer the fate of becoming a single railed JLH 1969 Class A amplifier using the same approach.
So please, if this could work, suggestions on good amplifiers to perform this butchery upon and suggestions of good value suppliers of transformers and suggestions for how much headroom I should need in transformers
Regards
Owen
I have been thinking too much about building a class A amplifier. Transformers and Heat Sinks and boxes are the biggest costs for all amplifiers, and suitable transformers and capacitors are nearly twice the cost for Class A amplifiers.
In general, do members of this group think that most 100 W class AB stereo amplifiers could be converted to Class A mono blocks with the same output power? This way we could avoid the costs of buying or building boxes and buying expensive transformers and capacitors.
I doubt this will be quiet possible, as has theoretical efficiency of 78.5% and class A a theoretical efficiency of 50%.
Having looked at my 3 Quad 303's I notice they have a Center tapped transformer. Even though the Quad 303 is a single rail powered amplifier.
They have approximately 70 V supply, and deliver officially 30 W RMS and 3 Amps into 16 Ohms hence the name.
If I put a single rail powered JLH class A amplifier inside, do you think I would over load (so the transformer starts to Buzz or some thing worse) the amplifier as a 15W into 16 Ohm mono block amplifier.
The idea would be to use the center tapped transformer and two diodes to halve the voltage, and half the time the current is used, and then since its a mono block I halve the power demand to make up for the approximate halving in efficiency over a class AB amplifier.
I don't think I am going to do this crime (at least permanently) as the Quad 303 is a lovely beast but if they remain so cheap broken on ebay in the UK I could be tempted, this said I will probably just spend the money some time a build a 25 W JLH Class A into 6 Ohms as I preferred the sound of no coupling capacitor when I played with the 1969 and 1996 JLH topologies, ( though I did feel that the need for some DC offset protection was a must with direct coupled amplifiers) but maybe some other less classic amplifier with higher power and and more current drive could suffer the fate of becoming a single railed JLH 1969 Class A amplifier using the same approach.
So please, if this could work, suggestions on good amplifiers to perform this butchery upon and suggestions of good value suppliers of transformers and suggestions for how much headroom I should need in transformers
Regards
Owen