F5 Turbo Builders Thread

[Juuso]

Thanks for the comments.

Originally Posted by MASantos

There is nothing wrong with replacing the transformer, and the required parts, but if you do that and don't want new boards, you could wire another pair of output mosfets to share the heat dissipation.

Would you be kind enough to walk thru a newbie on what's actually needed, in very practical terms? I do need to study this much more by myself, but all advice is welcome to push me not to make things too difficult.

Originally Posted by jacco vermeulen

No, and you quoted the reason why yourself.

It's much easier just to quote than to really understand the contents of the quote.

Should I need to replace the resistors on PS board as well; to something more than 3W?

[jacco vermeulen]

From 25W to 50W is +3dB.
50W in 8 Ohm is 20V.
22 dB gain is about 12.6 times. (18dB+4dB = 8 times ~1.58)
20V divided by 12.6 is ~1.6v input

100 ohm divided by 2 is 50 Ohm.
50 + 10 = 60.
60/10 = 6
20 log (6) = 15.6 dB

220 divided by 2 is 110.
110 + 10 = 120.
120/10 = 12
20 log (12) = 21.6 dB

Difference is 6 dB [220/100=2.2 20log(2.2) = 20log(2) +20log(1.1) = ~7dB]
6dB minus the 3dB extra to reach 50W is extra 3dB gain left.
The gain margin is for stability, read Bode plot papers (the name Bode is Dutchie lingo for messenger )
You may not need the extra 3dB gain with single outputs, but if you leave gain as is, you need close to 5V in to reach 100W peak in 8.

(for dB estimates, it's handy to have the gain factors for +1dB to +5dB in head)

[Juuso]

Thanks Jacco Vermeulen. Highly appreciated your explanation.

This seems now rather straightforward, referring to F5 schematic:
R9, R10, R11, R12: 100ohm 3W -> 220ohm 5W (altho in V1 they are 3W?)
Transformer: 2x18V -> 2x24V (should 500VA do?)
Right? That's it? Well...
In the text Mr Pass states that it may be beneficial for bias stability to increase R7 and R8 to .68ohm (from .47ohm) "without significant penalty". It also seems V1 has 2 x 1ohm 3W here for increased dissipation. If I should change R7&8 anyway to 5W, I could go for .68ohm at same time. What is this "not significant penalty" Mr Pass is referring to?
Yes, I can see there are other differences in turboV1 to F5, but I'm trying to follow Mr Pass's "simply" path, having F5 boards etc available, still without risking of making a good thing less good.

Having studied adding extra output devices per MASantos highlighted...
That would apparently require dropping R13 and R14 values to half and paralleling them for another pair of mosfets, and paralleling R7 and R8 as well, if I get it right (the other differences from F5 to TurboV1 not related to double output devices?). Two resistors and a mosfet added on each side of each board sounds doable by hardwire even for me, but I'm still wondering about if I'd just get into more trouble by doing this than by leaving it undone.

The speakers in use are 4ohm and they do dip below the nominal.

[Bksabath]

Originally Posted by Juuso

Thanks Jacco Vermeulen. Highly appreciated your explanation.



The speakers in use are 4ohm and they do dip below the nominal.

Jeah me think that when Jacco is in a good mood he is getting really good at explaning things.

Maybe he could write a book like the Idiot guide to Power Amplifiers
I could suply same of the stupid ( but not for me )questions...

For now I have started to collate same of thos most precious post and one day maybe put them on a blog...

Tanks Jacco


Any way Juuso I have started like you with 4 Homs nominal speakers
Like you I am asking amplifier to do duble duty so
I have built my first F5 making duble Mosfets duble Bias asumption.
And I am pretty happy with it
BUT now I want more


500 VA total 2 rails 48V 500/48 = 10 A (aproximate) with 2 mosfets bias total 2.6 A
and suply 2 channels call it 5 A so you got duble current capacity.
consider that Toroids can stand shorth burst of power you may be ok.
But Papa said on F5 to use triple that as probably he was considering a large group of user with many different set ups.

You may ask yourself

What is the real impedence of your speakers?
How loud do you need to go?
This depends on your room, your speakers Kind of music you listen to and how loud you like to listen to.
How often are you going to as your traffo to suply load of current?

A Test. How much Voltage (power) do your speakers need?
May be easy way to answer most of abowe questions

My 2 cents: Do not skimp on traffo you going to be stuck with it.
The other parts like Capacitors and the rest can all be recicled.

I got trafos with 20 and 24 V taps now I wish I had 30V taps as well.

About gain
The low gain of Vanilla F5 was decided as a compromise with sound quality
F5 was posted on the First Watt site as First Watt product where the sound of the first watt is all that mater.

By increasing gain one compromise with sound quality no way out of this.
Or one can get Preamplifier with enoug output to give the F5 (is it 5 V?)
what it needs.

Sems to me that there are quite a few things on the Turbo left for us to decide (I like this wery much) Papa shown us the way to do things properly with the F5 now is your time to go walk about.

For one no single bridge rectifier in mine that is as far as I go for now.

[BigE]

I have a 2000 VA transformer with 60/0/60 volt outputs.

Can the F5 turbo V3 run with 112 volt rails?

I'm trying to drive a load that dips to about 2 ohms... maybe less.

[AudioSan]

60-0-60V is more like +/-75-80V where did you get 112V from?

[Zen Mod]

why not with 224V rails .......

do you really need both V's and A's , in same time ?

[AudioSan]

Originally Posted by Zen Mod

why not with 224V rails .......

do you really need both V's and A's , in same time ?

+-224V rails and bias 12A

[CanAm Man]

Originally Posted by Zen Mod

why not with 224V rails .......

do you really need both V's and A's , in same time ?

Well, heck, yeah!!!! Since we to "direct couple" the stages of our audio systems, why not "direct couple" our power rail requirements directly to our (local) power mains. Just think--eliminate the cost and weight of the toroid....

Hhhhmmmm--wondering about the safety considerations.....

[Zen Mod]

next step - direct connection between my inner self and Audio Source .....

taaa daaa !

I don't need amplification and speakers anymore