F5 power amplifier

[triode_al]

Originally Posted by Floric

I think the only difference is 0,5R (Source Resistor) and the voltage drop across it which does not matter that much. The V2 has the advantage that it is easier to find a layout with the ntc closely mounted to the mosfet.

Regards

Flo

the difference is the AC amps.
Compare it with a tube follower, with a very small cap (10 nF) and a 1 meg to the kathode resistor for bias, the virtual impedance is magnified greatly (yes there is a formula that also goes for the FET), and the input by consequence needs only that little cap for a 1 Hz bandwidth.

[bobodioulasso]

a 1 Hz bandwidth

Very little.

[triode_al]

Originally Posted by bobodioulasso

Very little.

well, the bottom side at least.

[Floric]

Originally Posted by triode_al

the difference is the AC amps.
Compare it with a tube follower, with a very small cap (10 nF) and a 1 meg to the kathode resistor for bias, the virtual impedance is magnified greatly (yes there is a formula that also goes for the FET), and the input by consequence needs only that little cap for a 1 Hz bandwidth.

Thanks,

n ow I got it - we often think on rails and sometimes we get the wrong ones.

regards

Flo

[wengtech]

hi i am interesting to build F5 PA
there are 2 diff schematics :
2008 version


and 2012 version


both are original from F5 manual.

which one will provide a better sound?

and also, at the manual said:
"You can simply raise the supply rails to +/-32 Volts and get 50
watts into 8 ohms right away without other modification. 24 V AC secondaries
on the power transformer will do it. Don't forget to use higher voltage power
supply capacitors. Probably you should also upgrade R9 through R12 to 5
watt resistors. Depending on your heat sinking, you will probably want to
adjust the bias so that the power transistors don't run too hot."

so, this means i can simply use 2x24vac transformer without any problems?

are there anything i have to adjust? (for +/-32volts rails)

please some advice. thanks a lot.

[Bksabath]

No no need to change much realy but is question of personal choice
I have been running on 24 volts trafos since last August

As I have 4 homs (nominal speakers) I have used twin outputs from start and did not use the current limiters (got speaker protection to keep woofer safe)

Just bear in mind the reccomendations for the resistors that you already posted and
Enjoy

On the other hand
Few things came up like P3 mod
And lateley Papa Pass mentioned that tweaking feed back resistors values gives more gain.
All this and many more Mods have been made.

Just go for the vanilla version to start and you will not be disapointed.

Till the mod bug bites that is, so my 2 cents get 68 V rated capacitors they came handy for when you will decide to take the rails up.

[wengtech]

Bksabath:
thanks for the response,
so you mean i take the 2008 version to start with,
i have unused nichicon 10000uF/50v 8pcs and two 24VCT/10A transformer.
i hope this will be enough power to handle the 32v rails.

[Bksabath]

Prety good Caps and transformer is right.

Go for it

Are you cooking your own boards?

If that is the case include the traks for P3 You won't need to use it straight away but once bug bites...

Have a good look at what is being said about Heath sinks once that is sorted you are almost done.

[AudioSan]

Originally Posted by wengtech

Bksabath:
thanks for the response,
so you mean i take the 2008 version to start with,
i have unused nichicon 10000uF/50v 8pcs and two 24VCT/10A transformer.
i hope this will be enough power to handle the 32v rails.

24VCT will not even get you close to +/-32V rails.
24VCT is a 2x12V that is centertaped.

[jameshillj]

Two 24V 240VA Txrs (sec in series) will be okay for single Txr supply and seperate bridges , etc after that - 8 x 10mF Nichicon are okay, particularly if KG - suggest you start with discrete diodes rather than cheap block bridges - can use one of those 12volt taps to drive a dc protect/delay cct.

Suggest get the pcbs from 'the Store' here, and can easily mod them later.