That was my first thought, but OTOH we've seen here (almost) everything...
Diyaudio P-F5-2V20e boards and Caddock resistors
Hi,
I bought parts and Caddock resistors from tech-diy for my diyaudio P-F5-2V20e based F5.
I intend to use a small heat sink for the R1, R2 resistors but am unsure what I should do with the others. The layout of the board does not allow placing them on the main heatsink, unless the leads to R5, R8, R11 and R12 are extended using wires. Can extending cause problems?
Thanks,
Albert
Hi,
I bought parts and Caddock resistors from tech-diy for my diyaudio P-F5-2V20e based F5.
I intend to use a small heat sink for the R1, R2 resistors but am unsure what I should do with the others. The layout of the board does not allow placing them on the main heatsink, unless the leads to R5, R8, R11 and R12 are extended using wires. Can extending cause problems?
Thanks,
Albert
The JFET source resistors probably DO NOT have to be heat-sinked. They should mount OK on CVILLER's boards. The source resistors on the MOSFET's can be mounted pretty much adjacent to the transistors and tie off the IRFP240/9240 sources directly to the resistors. MP930's will only handle 2.25W in free air. The feedback resistors will, I believe, handle 1.25W in free air and should be heatsinked as they dissipate ~5W when the amplifier is running at full power into an 8 ohm load.
Thanks for that, Jack.
I will study the schematic, circuit board and your comments and should be able to work out a good solution.
The F5 is an ~25W into 8r0 ClassA amplifier. That requires an output of ~20Vpk and possibly as much as 10Apk into an 8ohm reactive speaker.
If the output load is an 8r0 resistor then Ipk for a sinewave signal is 2.5Apk.
The peak power across the 50r NFB upper resistor is {20Vpk*[50r/60r]}^2 / 8r = 5.56Wpk.
The average power dissipated in the 50r resistor when the amplifier is delivering a maximum sinewave power of 25W into 8r0 is ~2.8W. What is the thermal Time Constant of the pair of 100r resistors? What is the time period of an expected maximum signal of 20Vpk at the output?
If the output load is an 8r0 resistor then Ipk for a sinewave signal is 2.5Apk.
The peak power across the 50r NFB upper resistor is {20Vpk*[50r/60r]}^2 / 8r = 5.56Wpk.
The average power dissipated in the 50r resistor when the amplifier is delivering a maximum sinewave power of 25W into 8r0 is ~2.8W. What is the thermal Time Constant of the pair of 100r resistors? What is the time period of an expected maximum signal of 20Vpk at the output?
May I perhaps add to that excellent analysis.
For the F5X (balanced), the rails are +/-16V.
But the design is to allow 4V min for the MOSFETs.
So the designed output per phase (i.e. ref Gnd) is 12V max., of which 10V is seen by the feedback resistor.
The design calls for 4x 220R 1W resistors in parallel to make up Rfb of 55R.
Therefore power dissipation into each of the 220R resistors = 10x10/220/2 = 0.22W (assuming sine wave).
Thus a factor of 4 safety factor even at full load.
Similarly the shunt resistor is made up of 3x 33R 0.25W in parallel, and sees 2V max.
That corresponds to rms power of 0.06W for each of the 33R.
Again a safety factor of 4.
QED.
Patrick
For the F5X (balanced), the rails are +/-16V.
But the design is to allow 4V min for the MOSFETs.
So the designed output per phase (i.e. ref Gnd) is 12V max., of which 10V is seen by the feedback resistor.
The design calls for 4x 220R 1W resistors in parallel to make up Rfb of 55R.
Therefore power dissipation into each of the 220R resistors = 10x10/220/2 = 0.22W (assuming sine wave).
Thus a factor of 4 safety factor even at full load.
Similarly the shunt resistor is made up of 3x 33R 0.25W in parallel, and sees 2V max.
That corresponds to rms power of 0.06W for each of the 33R.
Again a safety factor of 4.
QED.
Patrick
Hi Guys
Please let's give the schematics and makes the final PCB of audio amplifiers F5.
Because here on the forum has over a thousand pages, and I do not have much time to read it all.
Give the schematic and the PCB and to making this amp a bit and I to enjoy its sound!
Thanks and cheers!
Please let's give the schematics and makes the final PCB of audio amplifiers F5.
Because here on the forum has over a thousand pages, and I do not have much time to read it all.
Give the schematic and the PCB and to making this amp a bit and I to enjoy its sound!
Thanks and cheers!
Yes, like NP says, the IRF's have been made in TO-3.
Alternatively, look at old stock Toshiba's. Easier. See my build description.
But be aware of new Toshiba Fakes.
Or you can go new production of the old design with the Exicon 10N20 10P20. At least this is not restamped, and the price is right.
albert
This has been done 2 or three times in the thread. You can buy boards from cviller and peter daniel and the schematic and BOM is in Nelson's pdf which can be found on his website FIRST WATT HOME or here http://www.firstwatt.com/pdf/prod_f5_man.pdf