F5 power amplifier

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AudioSan

Member
Joined 2009
JeffYoung said:
83dB is moderately loud (a bit louder than a garbage disposal). That figure is presumably @ 1w @ 1m.

Sound falls off by the square of the distance. So if you're sitting 10' (3m) away from the speaker, you'll need 9w to generate the same volume.

Every 3dB louder takes twice the power. Humans experience "twice as loud" as roughly 10dB. So you need roughly 10 times the wattage to go twice as loud. Since your F5 won't push 90w, you're only going to get to about half-again as loud (around 90dB at 10').

Only you can answer if that's loud enough. It's certainly not live rock concert levels (100+dB); on the other hand it would be loud enough for some.

Cheers,
Jeff.

(PS: this is how I understand it, but I'm no expert. Corrections welcome.)

(PPS: that's a pretty inefficient speaker. I think the majority of speakers would be in the mid- to upper-80's, while high-efficiency designs would be in the upper-90s into the 100s.)
Click to expand...

it is 83db (2.83V/1M) and 4ohms. 2.83V @4ohm=2W
 
2 picoDumbs

2 picoDumbs

Member
Joined 2013
A quick test is just hook a cd player with 2Vrms output directly to the amp, and decide whether that sounds:
1) Bloody loud
2) Aaah just in the ball park
3) Aaah bastard that would put a bloody baby to sleep.

At 2.8V peak output of the cd player you'll be seeing 2.8V x 6 dynamic peaks out of the amp which will be under clipping of the amp.

My family starts complaining at anything over 15W rms (that's dynamic peaks not average) on 87dB speakers.

If you have 4 Ohm speakers, the F5 sounds better with less source resistance on the Fets anything under 0.2 Ohms is a decent improvement, or just remove all together. You'll need to go through the biasing procedure again (back it off first)
 
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phil0702

Member
Joined 2011
ok, fine! thanks to all. So I will just give it a try and see if I get happy with the volume ;)

Just in case, two more questions:

- how do i actually notice if I am in the clipping area of the F5? I really don't want to blow up the amp...

- the louder I listen to music, the more power I need, thus more heat is produced? so even if I am not in the area of clipping, it might not be a cosy area for the amp with respect to the heat? (It a really really warm summer here in Austria...). Or is the main heat produced due to the bias current which is constant?

thanks, philip
 
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Kosst Amojan

Kosst Amojan

Member
Joined 2017
That's a bit lower in efficiency than would probably be ideal for the F5 in stock form. The 25 wpc RMS is what it will do in class A and that doesn't change based on impedance. The original design will push 10 amp according to the owner's manual, which is well over 50 watts, but it won't do it for long, and that's well outside of class A. The F5 Turbo would be better suited to the demands of your speakers, but that's not to say a standard F5 won't sound great, just not loud.
 
Kosst Amojan

Kosst Amojan

Member
Joined 2017
The best way to tell if you're overdriving the amp is by temperature. Once the outputs start pushing current outside the class A envelope they'll heat up. You're going to end up getting some heating because there's always going to be peak transients that push the amp outside class A, but if it's operating there consistently you're going to find that it gets too hot to touch. I'd say heatsink temps over 60 would be cause for concern. My build sees heat sink temps a bit over 57C and that usually means the outputs themselves are running in the low 80's which is about as hot as I really ever want to get them.
 
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AudioSan

Member
Joined 2009
Kosst Amojan said:
That's a bit lower in efficiency than would probably be ideal for the F5 in stock form. The 25 wpc RMS is what it will do in class A and that doesn't change based on impedance. The original design will push 10 amp according to the owner's manual, which is well over 50 watts, but it won't do it for long, and that's well outside of class A. The F5 Turbo would be better suited to the demands of your speakers, but that's not to say a standard F5 won't sound great, just not loud.
Click to expand...

Class A power doesn't change based on impedance??? yes it do. a 25W@8ohm device only do 12.5W@4ohm.

But F5 is a push pull class A/B it will swich to class A/B when pushed beound it's class A current range.
 
Kosst Amojan

Kosst Amojan

Member
Joined 2017
Wait... I misread your reply to me. The F5 isn't a current source amp. It's voltage source. It doesn't reduce it's power into lower impedance. Amps like the F4 and J2 do that. The F5 much different than them. The actual class A envelope on an F5 is 50 watts peak. It's explained in the F5 and F5 Turbo articles as well as Burning Amp 2016.
 
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