And what did you think of the Technics SE-A1 Class A, which was modulated according to the input signal, which allowed you to always be in Class A by dissipating less heat
SE-A1 | Technics Chronicle
SE-A1 | Technics Chronicle
You may recall that with the 1975 release of the Threshold 800A, the product
category became hot, with many companies launching "efficient class A" amplifiers.
I think that the original design by Sano et al (patent #4,115,739) was the cleverest
of the bunch, although the bias was not modulated by input signal as you indicate.
Unfortunately it appears to have been quickly replaced by a cheaper product which
had a "non switching" circuit.
category became hot, with many companies launching "efficient class A" amplifiers.
I think that the original design by Sano et al (patent #4,115,739) was the cleverest
of the bunch, although the bias was not modulated by input signal as you indicate.
Unfortunately it appears to have been quickly replaced by a cheaper product which
had a "non switching" circuit.
I would like to educate myself and have some questions, so if there is someone who has a little time and the desire to help my understanding that effort would be very kind.
The context for the question is SMPS supplies for Class A:
My perception is:
When a Class A amplifier configured with a traditional linear supply & CRC bank and with voltage headroom beyond I(bias) x R(load), hits the `klunk' point the active device(s) pulls current beyond the bias level and it transitions to Class AB operation. For a single ended amplifier the gain device operates at a current that exceeds the bias. For a push-pull amplifier one device shuts down and the other continues to operate at a current higher than the bias.
A typical music waveform has a wide dynamic range with peaks well above the mean. So, assuming that some of these peaks would require current beyond the steady state capability of the power supply;
1. Is it accurate to state that these short-lived excessive appetites are fed by the capacitance of the CRC bank that is typically installed?
2. Is there a `best practice' calcuation for the voltage rail value(s) beyond the bias x load resistance to accommodate for `an acceptable majority' of these higher voltage excursions?
For a SMPS supply adding large capacitance introduces inrush current problems. And I am led to believe that specifying supplies with rated current capability well in excess of the load requirements can cause problems also. I also understand the high switching frequency results in relatively low ripple, but brings additional high frequency noise. Whereas
3. Is the correct solution to use a `slow start' or some other capMX type approach to enable the slow charging of a large capacitor bank of a similar size to that used in a comparable linear supply? Or is there a better solution for an SMPS?
your time is much appreciated,
BeardyWan
The context for the question is SMPS supplies for Class A:
My perception is:
When a Class A amplifier configured with a traditional linear supply & CRC bank and with voltage headroom beyond I(bias) x R(load), hits the `klunk' point the active device(s) pulls current beyond the bias level and it transitions to Class AB operation. For a single ended amplifier the gain device operates at a current that exceeds the bias. For a push-pull amplifier one device shuts down and the other continues to operate at a current higher than the bias.
A typical music waveform has a wide dynamic range with peaks well above the mean. So, assuming that some of these peaks would require current beyond the steady state capability of the power supply;
1. Is it accurate to state that these short-lived excessive appetites are fed by the capacitance of the CRC bank that is typically installed?
2. Is there a `best practice' calcuation for the voltage rail value(s) beyond the bias x load resistance to accommodate for `an acceptable majority' of these higher voltage excursions?
For a SMPS supply adding large capacitance introduces inrush current problems. And I am led to believe that specifying supplies with rated current capability well in excess of the load requirements can cause problems also. I also understand the high switching frequency results in relatively low ripple, but brings additional high frequency noise. Whereas
3. Is the correct solution to use a `slow start' or some other capMX type approach to enable the slow charging of a large capacitor bank of a similar size to that used in a comparable linear supply? Or is there a better solution for an SMPS?
your time is much appreciated,
BeardyWan
In the simplest analysis, the push-pull Class A amplifier's output peak klunk point is twice the bias current.
The single-ended amplifier biased by a constant current source hits the output peak klunk point at the bias current.
Ideally the switching supply should be able to deal with either of these values. If not, you would want some extra
filter capacitance as a reservoir.
Many switch-mode supplies have their own "soft start" which allows charging a fairly large capacitance if you
can keep the amp circuit itself from drawing much while this charging happens. A good example of this
situation is the ACA mini.
The single-ended amplifier biased by a constant current source hits the output peak klunk point at the bias current.
Ideally the switching supply should be able to deal with either of these values. If not, you would want some extra
filter capacitance as a reservoir.
Many switch-mode supplies have their own "soft start" which allows charging a fairly large capacitance if you
can keep the amp circuit itself from drawing much while this charging happens. A good example of this
situation is the ACA mini.
Many thanks Nelson.
I don't really have a feel for the dynamic range of `music'...
To take an example of the first watt. Assuming appropriate speakers and that `on average' a 1W power level encompasses much of what you listen to; then the question becomes how much greater are the occasional spikes and do you want to have 90% of the music within the class A envelope, or 75% or 50%. And then beyond that how much additional voltage headroom do you want to have to ensure that the capacitance on hand can accommodate excursions into class AB without clipping at these peaks?
Perhaps one listens at 1W average but to sound great the amplifier might be designed to stay class A to 10W and to be able to manage momentary peaks to 50W without clipping?
I appreciate that I could look at the many circuits that you have blessed us with and calculate rms W @8 ohms and then look at the voltage rails and project a theoretical momentary wattage for the spikes into the same load, but rather than try to `reverse engineer' the philosophy, I wondered if you might share some insights as to what makes an amplifier sound good
I don't really have a feel for the dynamic range of `music'...
To take an example of the first watt. Assuming appropriate speakers and that `on average' a 1W power level encompasses much of what you listen to; then the question becomes how much greater are the occasional spikes and do you want to have 90% of the music within the class A envelope, or 75% or 50%. And then beyond that how much additional voltage headroom do you want to have to ensure that the capacitance on hand can accommodate excursions into class AB without clipping at these peaks?
Perhaps one listens at 1W average but to sound great the amplifier might be designed to stay class A to 10W and to be able to manage momentary peaks to 50W without clipping?
I appreciate that I could look at the many circuits that you have blessed us with and calculate rms W @8 ohms and then look at the voltage rails and project a theoretical momentary wattage for the spikes into the same load, but rather than try to `reverse engineer' the philosophy, I wondered if you might share some insights as to what makes an amplifier sound good
