F4 power amplifier

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#3,021
It might be too much effort to make exactly the circuit in post 3019, since this is based on the old version of F4. The boards I have made are based on papa's revised F4. But basic concept is still the same - pull out 2/3 of your mosfets and you'll basically have the same as in 3019.

EDIT: However if you are going to make a "headphone only" F4, then perhaps you should look into some nicer output fets. If you go way back in this thread, you'll see papa saying that the "mosfets are the elephants on the dancefloor".
 
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#3,023
Well I haven't researched the possibilities, but since you don't need as much current, you can use other parts - could be irf510/9510 or their fairchild counterpart. But don't obsess over this, the irfp240/9240 is great. 😉

You don't need the B1 unless you have a very weak source, long cables or want to avoid creating a low-pass with your attenuator. If you place your pot close to the F4 on the signal path, you should be just fine without the B1.
 
#3,024
Hi Liliya,

the new circuit is better as cviller says, Nelson P. comments it has a little bit less distortion and the chance to damage the Input FET´s is reduced. I wanted to show you the possibility to take less MOSFETs. But you know, you have no gain!
Some people even reduce the value of the source resistor, when they reduce the number of mosfets.
Maybe 0,33 Ohm are more suitable (I don´t know if it matters really).
 
#3,026
ZenMod is an alien lightyears before us.........
 

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#3,028
There is one issue to consider when downscaling NP designs such as this. If you look at the capacitance curves of most of the output MOSFETs we use, they really go crazy high at low D-S voltage. That is to say, they are non linear and much greater, below about 20Volts. This is likely true for the smaller FETs we might consider also. If you lower the rail voltages to downscale, you are entering into that difficult non-linear area at lower signal levels also. Keeping the 23V rails and only reducing current, or the number of FETs will avoid this phenomina.
Just :Pawprint: 2 cents 😀
 
#3,029
Buying FETs to F4

When I built my first F4 I went to US an ordered Fets from Tech-diy. Few days after I emailed my order, the stuff arrived on my adress in Norway.
Excellent.

The 29. of March I ordered again. So far, no answer. I mailed again 08. of April and asked if my first mail had failed. No answer.

Does anyone else on this forum have any information about Tech-diy that can explain this problems or had simular problems with this firm??

Or should I contact Pay Pal about my problems??

Eivind Stillingen
 
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