Hi,
multichannel systems or multiple way active speakers give big heat dissipation problems when using classA amps.
So my intention is to develop a classA circuit that increases the idle current with the output power, so that idle heat dissipation can be held very low at room levels.
One first, -ok- second aproach is the following circuit:
Idle current per output Fet is 200mA, which means, normally when the output current exceeds 200mA, the circuit goes to classB, because two fets run out of current.
Now when you look at output Fet N1, you see that the gate voltage goes higher if the op amps draw current.
On the positive halfwave one op amp draws current and on the negative the other one.
Normally if the output of op amp X1 goes negative, Fet N1 will not conduct current anymore because its gate voltage will go negative too.
But because op amp X2 draws current, Fet P1 conducts more current and the negative output voltage of op amp X1 can not pull down the gate of the output Fet N1.
Another is to regulate the idle with relais, depending on the position of a relais volume pot.
If the pot switches from 0 to -60dB, there could be 6 idle levels every 10dB.
Are there any known circuits ? Technics ClassAA ?
Greetings, Bernhard
multichannel systems or multiple way active speakers give big heat dissipation problems when using classA amps.
So my intention is to develop a classA circuit that increases the idle current with the output power, so that idle heat dissipation can be held very low at room levels.
One first, -ok- second aproach is the following circuit:
Idle current per output Fet is 200mA, which means, normally when the output current exceeds 200mA, the circuit goes to classB, because two fets run out of current.
Now when you look at output Fet N1, you see that the gate voltage goes higher if the op amps draw current.
On the positive halfwave one op amp draws current and on the negative the other one.
Normally if the output of op amp X1 goes negative, Fet N1 will not conduct current anymore because its gate voltage will go negative too.
But because op amp X2 draws current, Fet P1 conducts more current and the negative output voltage of op amp X1 can not pull down the gate of the output Fet N1.
Another is to regulate the idle with relais, depending on the position of a relais volume pot.
If the pot switches from 0 to -60dB, there could be 6 idle levels every 10dB.
Are there any known circuits ? Technics ClassAA ?
Greetings, Bernhard
Another version ClassA pushpull:
The connections can be made between the 5.6k resistors and rails to get 2 A idle current per Fet, 200W total dissipation and 60Vpp output.
or between 22k resistors and rails to get 25W total dissipation and 5Vpp without leaving classA.
So it is possible to regulate the idle with relais, depending on the position of a relais volume pot.
If the pot switches from 0 to -60dB, there could be 6 idle levels every 10dB.
The connections can be made between the 5.6k resistors and rails to get 2 A idle current per Fet, 200W total dissipation and 60Vpp output.
or between 22k resistors and rails to get 25W total dissipation and 5Vpp without leaving classA.
So it is possible to regulate the idle with relais, depending on the position of a relais volume pot.
If the pot switches from 0 to -60dB, there could be 6 idle levels every 10dB.
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