F5 power amplifier

[Neutrality]

And about the mosfets - the max Vgs of +/- 20V is not a problem at all. When you are running the amp, Vgs is adjusted to be around 4.3V no matter how high voltages you are running on the rails.

Thanks alot, thats an answer thats short and to the point.

 

[Neutrality]

I think you can use the 22VAC trafos without any problems, but I have not heard any reports about what is the highest possible voltage with cascodes and I haven't tried it myself. You need a large heatsink to run this beast though...
A tiny correction: the standard current is 1.3A through each device, but you might want to go for a lower current per device.

The standard F5 current is 1.3A pr device, 2.6A total pr channel, to keep the same total bias pr channel in a cascoded, dual output pair configuration you would need to reduce the bias for each FET to 0.65A( 4 x 0.65A = 2.6A pr channel)

As for supply voltage I am going for either 2 x 22 VAC or 2 x 25 VAC, havent decided yet. The 2 x 25 VAC would be nice, giving mere a decent power reserve of about 55 W Class AB in 8 Ohm.

(You might be getting an order tommorow, just have to sleep on it before I decide whether to pull the trigger or not)

 

[AndrewT]

The standard F5 current is 1.3A pr device, 2.6A total pr channel, to keep the same total bias pr channel

The standard F5 is a one pair mosfet output stage.
Both mosfets are biased to 1.3A.
The total bias is 1.3A

 

[Neutrality]

The standard F5 is a one pair mosfet output stage.
Both mosfets are biased to 1.3A.
The total bias is 1.3A

You are absolutely right.

 

[fingerx]

Some Pic of my FFive

Now just fine tuning the sound,
sweet point 0.6V with no doubt
gate stopper set to 47ohms which I cannot hear the different to 150ohms
Thanks all, Thanks Nelson Papa

 

[jacco vermeulen]

Rectifier diodes look much smarter with heatsinks attached.

 

[fingerx]

Don't worry mate, those diodes heat up to 40C only with no heat sink, agree they will look smarter when mount on some handsome heat sink

 

[umut1001]

Hi.It looks good.Minimum value of gate stopper(gate stopper is a resistance to eliminate oscillations) is 47ohms and 150 ohms will not make a sensible difference.Do you know that you need a preamp to get full power with this player?Is there a preamp in the amplifier?Regards

 

[Renron]

Do you know that you need a preamp to get full power with this player?Is there a preamp in the amplifier?Regards

Could you explain this statement please?

I thought it was at full power all the time without a preamp / attenuator. ?

Unless you were thinking of an active preamp which adds to the gain.


Ron

 

[labjr]

I forget what the sensitivity of the F5 is but it's only at full power if the source has enough output voltage to drive it to full power. Since it has 15db of gain some sources may not have enough output.

 

[umut1001]

F5 amplifier has a gain of 5.5 so 2volts rms source signal multiplies with 5.5 and it makes about 11volts rms.F5 gives about 15volts rms max.So you can not get F5's max power with many sources without preamp(voltage gain)

 

[tinitus]

Just turn it up at full blast and you have all the power that would make any sense anyway, like maybe 20watt out of the possible 25watt (just a guess)

 

[Renron]

Voltage gain, not needed, but preferred,
that's what I thought you were talking about.
Thanks,
Ron

 

[umut1001]

It is needed if you do not have about 4volt rms source(to get full power from F5 amp)
Of course it is not needed if you preffer only 25watts to 8ohms

 

[tinitus]

It is needed if you do not have about 4volt rms source(to get full power from F5 amp)

And then you may be able to drive it to just above half attenuation, or overdrive it, with increased distortion

 

[Neutrality]

(You might be getting an order tommorow, just have to sleep on it before I decide whether to pull the trigger or not)

Trigger is pulled, now the waiting begins.

Hate waiting, lol,

 

[Blues]

With a true rms voltmeter, set to measure instantaneous max voltage, connected on my speaker outputs -loud music/movie in a 25'x14'x9' room registered at 4.8Vrms and that is about 7Vpk (14Vpk-pk) or about 35% of what's available on a +/-24V or a +48V supplied amp. Lots of headroom using an LDR vol control...system is as posted on Pass projects thread.

 

[fingerx]

Do you know that you need a preamp to get full power with this player?Is there a preamp in the amplifier?Regards

hi, my source 1212M with LDR+DCB1, they sings too loud to me

 

[umut1001]

Singing too loud does not mean you get full power If you use 100dB speaker it will sing much louder If you think you get enough power there is no problem then.1212M's output is enough to get full power from F5 amp though.Some sources does not have such a high output swing.

 

[Renron]

The specs. of my Oppo BDP 83 say 2.4V -2.5V output. Still plenty loud enough with 89dB speakers. Sounds even better with a tube preamp in front.

Ron