The fets always heat up.
The amp pulls the least amount of current with the bias potentiometer fully CCW.
Turning the bias potentiometers slightly more CW increases the current draw.
The amp pulls the least amount of current with the bias potentiometer fully CCW.
Turning the bias potentiometers slightly more CW increases the current draw.
What is the 'least amount of current'?
What is the DC voltage across the 0.1 ohm source resistors with the pots fully CCW?
What is the DC voltage across the 0.1 ohm source resistors with the pots fully CCW?
Least amount of current is 1.62A idle on 12.3V PS voltage with cold fets.
Due tue the fets heating up, the current draw increases. I shut it off before it overheats.
I have about 8-10 seconds to measure safely.
The fets I have installed with voltage across resistor value:
Q1026 (0.001V across resistor) fet does not heat up quickly
Q1022 (0.001V across resistor) fet does not heat up quickly
Q2023 (0.006V across resistor and increasing slowly) fet heat up
Q2025 (0.006V across resistor and increasingslowly) fet heat up
So seems like channel 2 is having a higher current draw than channel 1.
Due tue the fets heating up, the current draw increases. I shut it off before it overheats.
I have about 8-10 seconds to measure safely.
The fets I have installed with voltage across resistor value:
Q1026 (0.001V across resistor) fet does not heat up quickly
Q1022 (0.001V across resistor) fet does not heat up quickly
Q2023 (0.006V across resistor and increasing slowly) fet heat up
Q2025 (0.006V across resistor and increasingslowly) fet heat up
So seems like channel 2 is having a higher current draw than channel 1.
I understand, there is a seperate heatsink mounted on every fet and the voltage regulator card. This is just for testing and having the possibility to acces the PCB if needed.
When the fets are mounted onto the amplifier heat sink I am sure it keeps the idle current at 1.62-1.70A and this amplifier would test fine with audio.
But this does not change the fact that channel 2 has a higher current draw then channel 1. Since the schematics describes that 0.002V across the resistors is the correct value.
Is it normal/OK for amplifiers to have their BIAS pots fully CCW?
When the fets are mounted onto the amplifier heat sink I am sure it keeps the idle current at 1.62-1.70A and this amplifier would test fine with audio.
But this does not change the fact that channel 2 has a higher current draw then channel 1. Since the schematics describes that 0.002V across the resistors is the correct value.
Is it normal/OK for amplifiers to have their BIAS pots fully CCW?
What's important is that there is no distortion (from insufficient biasing) and that the idle current remains essentially the same through the entire thermal operating range.
The bias requirements can be dictated by the individual parts. The manufacturer tries to give sufficient bias range but there's no guarantee that it can compensate for all possible variations in the installed parts.
You need to clamp everything down and heat the amp up (from driving it hard into speakers/load) and check the bias current and for distortion at various points as it heats up.
The bias requirements can be dictated by the individual parts. The manufacturer tries to give sufficient bias range but there's no guarantee that it can compensate for all possible variations in the installed parts.
You need to clamp everything down and heat the amp up (from driving it hard into speakers/load) and check the bias current and for distortion at various points as it heats up.
Idle current is 1.62A at 14.4V PS voltage.
When the amplifier heats up it has an idle current from 1.7A at 14.4V PS voltage.
I got the feeling this amp is working very inefficient at the moment.
I have given this amplifier maximum 150 watts of power supply power.
This amp gives about 32 watts RMS into an 4ohm load (bridged channels)...
When the amplifier heats up it has an idle current from 1.7A at 14.4V PS voltage.
I got the feeling this amp is working very inefficient at the moment.
I have given this amplifier maximum 150 watts of power supply power.
This amp gives about 32 watts RMS into an 4ohm load (bridged channels)...
Class AB amps are very inefficient, especially at low power.
Are you saying that you are using 150W with only 11v across the 4 ohm load?
Are you saying that you are using 150W with only 11v across the 4 ohm load?
The amp used 150watt from the power supply, so let's say, 150 watt IN.
The amp produced 32 watt RMS bridged on a 4 ohm load, so 32 watt OUT
Means that it's 20-25% efficient....
I always use a 12inch subwoofer to test the audio sound. Mostly, every amplifier, no matter if it's class AB or class D, can move this subwoofer to it's mechanical limits with 150watt worth of power supply input, since this subwoofer is unloaded.
This amplifier could not drive the subwoofer to it's mechanical limit at the moment. Really tells me there is something wrong with the power output. That's why I calculated it.
The amp produced 32 watt RMS bridged on a 4 ohm load, so 32 watt OUT
Means that it's 20-25% efficient....
I always use a 12inch subwoofer to test the audio sound. Mostly, every amplifier, no matter if it's class AB or class D, can move this subwoofer to it's mechanical limits with 150watt worth of power supply input, since this subwoofer is unloaded.
This amplifier could not drive the subwoofer to it's mechanical limit at the moment. Really tells me there is something wrong with the power output. That's why I calculated it.