Lights dim because of a large current surge and for a SS amp, the power on current is much higher because of the large capacitor banks. It does not have much to do with energy consumption or class A: a lot of capacitance, especially when there is no soft start is guaranteed to dim the lights or even blow the fuses. A large toroidal power transformer can do the same.
If you were truly comparing conventional SS and tube amps with an honest 50 watt output it seems like the tube amp would loose on efficiency simply due to the filament power. It takes Large or paralleled tubes to do a true 50w classA. Most 50w tube amps are class AB. One other wrinkle is that tube amps usually have an output transformer which means you can use a lower power supply voltage to get the same push pull output power. I’m not sure how this would impact overall efficiency. If you want a simple solid state example, the MOFO amplifier uses a choke to provide a similar benefit.
A tube amp with the same energy storage in it’s power supplies as a solid state amp would draw the same power from the line at startup and could cause the same amount of flickering or dimming. The key is how quickly does it draw the power to charge up the capacitors.
Tube amps would have much lower capacitance in the PS but charge it to a higher voltage and the energy stored goes up with the square of the voltage.
It’s not that straightforward in the real world with circuit techniques like the Pass Aleph and variable voltage rails that can be used to raise the efficiency of class A solid state amplifiers.
There are many ways to build amplifiers and get good sound. That’s what makes this such an interesting industry.
A tube amp with the same energy storage in it’s power supplies as a solid state amp would draw the same power from the line at startup and could cause the same amount of flickering or dimming. The key is how quickly does it draw the power to charge up the capacitors.
Tube amps would have much lower capacitance in the PS but charge it to a higher voltage and the energy stored goes up with the square of the voltage.
It’s not that straightforward in the real world with circuit techniques like the Pass Aleph and variable voltage rails that can be used to raise the efficiency of class A solid state amplifiers.
There are many ways to build amplifiers and get good sound. That’s what makes this such an interesting industry.
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If you accept the premise that dimming is dependent on surge current, the above will no be true. The energy storage being equal while the voltage is much higher guarantees the charging current is much lower. Not only that, the caps get charged through a transformer with a much higher winding resistance, which additionally slows the rate of charge.
I believe what I’ve written to be true. Think of it in terms of watts drawn from the primary side of the transformer. The current on the tube amp secondary hv winding will be lower, but the primary side current of the transformer will be higher where in a SS amp the opposite is true.
I think it is much more common to see management of the power up sequence in tube amps due to the need to sequence the filament, bias and HV supplies to preserve output tube life.
It is not the watts drawn that cause the dimming. If this were indeed true, there would be a permanently reduced AC voltage for as long as you draw power. Yet, this is not the case.
There is a big current surge on power-on but with a very short duration determined by the capacitors charging and this causes the dimming. It has nothing to do with the steady state power drawn, especially in a tube amp where some time is needed before the anode current starts flowing and serious power being drawn.
There is a big current surge on power-on but with a very short duration determined by the capacitors charging and this causes the dimming. It has nothing to do with the steady state power drawn, especially in a tube amp where some time is needed before the anode current starts flowing and serious power being drawn.
You don´t understand it.
You are talking about the secondary current, but it´s irrelevant, what mains sees is current on the primary of the transformer, which will be exact same on both cases if, as bfpca correctly states:
Same thing, you forget that same power properly designed power transformers will have exact same primary resistance and inductance ... because they will have exact same cores and primary wire and windings.
If anything, the Tube amp PT will be the worst offender, because for same output power (50W RMS) it will need to be larger, both because of reduced efficiency and filament heating, so it´s actually opposite of what you say.
I was referring to the power on time period where a lot of current is drawn from the line to charge the power supply. The dimming you are seeing is the result of voltage drop from the large surge current flowing through the impedance of the AC voltage source. And there will always be a small voltage drop when the amplifier is running caused by the continuous current draw, unless you have a 0 impedance power source.
I agree with everything above. Perhaps we should put some real figures in order to do a meaningful comparison.
The solid state amp.
For 50W pp class A into 8ohms a 1.8amp bias current is required. This is probably arguable but i went for a 100mF capacitor for each polarity which will provide about 20mV of ripple. Unless i am wrong the surge current through the primary of the transformer will be about 11.4A. This is based on a 44A max current through each capacitor, 0.6ohm impedance seen at the secondary of the transformer and 12mOhm esr of the caps.
Any glaring errors?
For 50W pp class A into 8ohms a 1.8amp bias current is required. This is probably arguable but i went for a 100mF capacitor for each polarity which will provide about 20mV of ripple. Unless i am wrong the surge current through the primary of the transformer will be about 11.4A. This is based on a 44A max current through each capacitor, 0.6ohm impedance seen at the secondary of the transformer and 12mOhm esr of the caps.
Any glaring errors?
Surely the opposite is true? The OPT means you can have a higher supply rail voltage and still match the speaker impedance.Bfpca said:
Same energy, not same power.
Equal energy storage charged up in the same time means equal starting power.analog_sa said:
There is a lot of confusion and misinformation in this thread. As often is the case, JMFahey comes to spread some sense and reliable information.
I’m not sure how you came up with the figures above but it doesn’t matter what the load is. Consider that you have 2 transformers, presumably of equal volt amps and a rectifier/capacitor bank to charge with the same amount of energy stored in it. It’s really just transformer theory we are talking about here and understanding the formula for energy stored in a capacitor that was given above.
In the real world there are many variables that will determine the surge current in an amplifier design other than the type of active devices used.
In the real world there are many variables that will determine the surge current in an amplifier design other than the type of active devices used.