Hi guys ,
Is it a better idea to drive the input LTP , VAS and drivers stage with higher voltage than the output stage , what is the generally accepted Vsat for the output stage ? I am getting roughly 26V RMS output on a DC supply of 43V on 4ohms just before clipping load and 30V RMS output on a DC supply of 46.5V just before clipping
Is it a better idea to drive the input LTP , VAS and drivers stage with higher voltage than the output stage , what is the generally accepted Vsat for the output stage ? I am getting roughly 26V RMS output on a DC supply of 43V on 4ohms just before clipping load and 30V RMS output on a DC supply of 46.5V just before clipping
No. on high voltage for the input stage & vas. The voltage swing out of input and VAS is low enough, excess voltage to the collectors just turns to heat. More expensive transistors are required at higher voltages, also. Best to lose the rail voltage with a cheap resistor or regulator before the input & vas stage, if there is no low voltage winding of the transformer for the input stages.
If your 26 & 30 Vrms are signal to the speaker, that's okay. If it is hum with input shorted, it is not okay. Check the watts rating of your amp to see if the voltages measured before clipping are correct. P=(V^2)/Z where z is rating speaker impedance.
Vsat rating of transistors has to do with switching, which class AB audio amps do not do. A useless rating for class A or AB audio equipment. Switching class D amps use fet transistors, which don't have a Vsat rating.
If your 26 & 30 Vrms are signal to the speaker, that's okay. If it is hum with input shorted, it is not okay. Check the watts rating of your amp to see if the voltages measured before clipping are correct. P=(V^2)/Z where z is rating speaker impedance.
Vsat rating of transistors has to do with switching, which class AB audio amps do not do. A useless rating for class A or AB audio equipment. Switching class D amps use fet transistors, which don't have a Vsat rating.
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There is the classic diode+capacitor trick to prevent the IS/VAS rails from drooping with the OS rails - this gives extra headroom automatically when under heavy load as the IS/VAS rail is made to sag much slower than the main filter caps.
I'm a firm believer in higher supply voltage for the input and VAS stages. I like to cascode the VAS, so I like having a little more headroom. Don't go crazy. 5V extra is enough.
Of course, you need diodes to protect the first stage of your output stage if you have elevated VAS rails.
Of course, you need diodes to protect the first stage of your output stage if you have elevated VAS rails.