Banned
Joined 2002
Banned
Joined 2002
Preferably But maybe closely matched ? my blue amp died some how and now i'm getting rail voltage on the speaker out put. I have to re-bias it and change the out puts witch are 2 devices..
Come to think of it when biasing a amp you have to bias it with a meter on the positive rail in series Right ?
Come to think of it when biasing a amp you have to bias it with a meter on the positive rail in series Right ?
Biasing amplifiers
Most class A/B amplifiers would have fuses in series with the output stage. When setting the bias the fuses must be removed and replaced with suitable resistors. This will protect the output stage in case of a fault. Remember that the fault that blew your FETS could reside anywhere in the cct. If the fault is still there after you replaced the FETS one or both resistors will probably go up in smoke but this is better than smoking FETS.
Using just the multimeter in line with the positive rail will not provide any protection, except maybe the fuse in the meter.
Measuring the voltage across the resistors is an easy way to determine the bias curent (I=V/R).
Typical resistor values would be 50 to 200 ohms @ 1 - 5 watts.
Cheers
Most class A/B amplifiers would have fuses in series with the output stage. When setting the bias the fuses must be removed and replaced with suitable resistors. This will protect the output stage in case of a fault. Remember that the fault that blew your FETS could reside anywhere in the cct. If the fault is still there after you replaced the FETS one or both resistors will probably go up in smoke but this is better than smoking FETS.
Using just the multimeter in line with the positive rail will not provide any protection, except maybe the fuse in the meter.
Measuring the voltage across the resistors is an easy way to determine the bias curent (I=V/R).
Typical resistor values would be 50 to 200 ohms @ 1 - 5 watts.
Cheers
Banned
Joined 2002
I just asked about the biasing it is on the positive rail and in series It should have fuses in these amps * my bad * they do now but also the reason this went up was because i was adjusting the bias pot to make the one fet cooler because one was running hotter than the other for some strange reason.
Banned
Joined 2002
Banned
Joined 2002
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