What's the Idle Current of the F5 Power Amp

[umut1001]

I am using FQA now and it is reliable.I am not using thermistors and ztx.I will replace fairchilds with toshibas 2sk1530/j201. What do you think about feedback resistors? Should i increase/decrease them ?thanks

 

[umut1001]

It was the last question Mr Pass 🙂

 

[galop]

where to measure that bias,precisely? 🙂

 

[Jozef]

I use F5 without termistors with BUZ900/905 for few weeks now.
At 2A each with 23.5VDC from CLC supply.
No problemski amps played all day with 4 ohm speakers.
But my heatsinks are big and hot 48-49*C with 22*C room temp.
I try 100R feedback resistors but is not a my taste at all so
I comeback to 50R.Trafos 225VA for each monoblock.Looks like
I limited now by 2.5A chokes in PS :>(

 

[umut1001]

It is not suitable to use lateral tramsistor for F5 i think

 

[Nelson Pass]

It worked for the ProFet amplifier. The lower open loop gain does result in a different performance.

😎

 

[umut1001]

what kind of performance difference seems by feedback resistor in F5?only gain ?what about bandwidth and other things?

 

[bobodioulasso]

where to measure that bias,precisely? 🙂

One measures the voltage across the mosfet's sources resistors.
Look at the PDF...

 

[umut1001]

You can decrease the voltage a bit, but remember that the
capacitance of the devices is a function of the Vds, the voltage
from Drain to Source, and below 5 volts Vgs or so the
capacitance gets excessive.

😎

I did not understand this sentence.Which device ? when the voltage drops,how capacitance change ?

 

[umut1001]

Do you mean input capacitance ?

 

[a.wayne]

It would appear the capacitance of the devices will increase .


Is the improvement coming from the voltage or from the increased Bias ? Did you try increasing the bias with the higher voltage .

 

[galop]

Ok i measure voltage across the mosfet's sources resistors.How much voltage on source resistor is safe to amplifier?

 

[bobodioulasso]

...about 0.6v corresponding to 1.3A bias which is the value for 25w class A into 8ohms...
...The F5 PDF is very informative about every detail...

 

[a.wayne]

Does the f5 bias has to be different for different loads ?

 

[bobodioulasso]

See: "Leaving class A"
Pass DIY: Articles/Projects

 

[a.wayne]

Ahh OK....

I just don't want to hear it go klunk when it comes out of class A @ 2 ohms ...🙂

 

[AndrewT]

Ahh OK....

I just don't want to hear it go klunk when it comes out of class A @ 2 ohms ...🙂

it's not ohms that defines the ClassA limit.
The bias current determines the ClassA limit.
Set bias to 1.3A and the ClassA limit is 2.6Apk.

If you need to know how that translates for 2r0 then the output voltage would be 5.2Vpk and the delivered power would be 13.5Wpk.
If the signal were a sinewave then the average power would be 6.7W