Can I do this with my F5?

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#21
Hikari1 said:
kj123:

Why don't you try increasing bias on your F5 as it is now? If you have the 5U chassis it can take more bias than the stock 1.3A because the big heatsinks can deal with the increase in temp. It depends on your ambient temp but since you are in Canada I don't think it will be a problem. I have the f5 w/the 5U chassis biased at 1.7A and it seems to have more power and drive and just plain sounds better. I can still hold my hand on the heatsinks forever except in the summer when it's hot. Which is almost never. I have no AC here in Seattle (which is almost Canada) so I tend not to use the F5 too much in the summer anyways.

This may not be the solution but it's free to try.
Click to expand...

Thanks Hikari, that's an excellent advice. I guess 0.2v increase in bias won't hurt. When I had the boards in the case (I am using the Aleph j now), the heatsinks were warm at best. I wonder if I could do the same with the Aleph J 🙂 although this one runs "hotter"... And you're right, heat is not going to be an issue for few months...it's already reaches -10c outside up here 🙁

P.S. If I manage to bias at 1.7A does that mean that it could output a max power of 46w?
(Ibias*2)^2 * load /2 = (1.7*2)^2*8 /2 = 46.24
 
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#22
the heat can be a issue even if the sinks are however so big. internal temperature of the transistors will be alot hotter. this will shorten the lifespan of the transistors.

your calculation is correct. however, you will not get 46W class A @8ohm with +/-24V rails. the power @8ohm will still be voltage limited to 25W.
 
#23
kj123 said:
Hi there,

So I finished my F5 and then Aleph J as per Jim's build guides. I use the same chassis 5U and power supply (just swapped boards). I would like more power 🙂 and I was thinking: can I do just the first part (simplest) of F5 Turbo V1 in Mr. Pass' article.

If I understood that part correctly, what I would need to do to push the amp to around 50w in 8 ohms is :

Change the transformer to 2 x 24v (I have now 2 x 18v)
Change the caps on the power supply board (maybe 50v or 63v)
Replace R9, R10, R11 and R12 with 5w resistors on the amp boards.

Would it work with these simple adjustments? Will I risk burning out something 🙂? Am I missing anything? You advice is really appreciated. thanks

KJ
Click to expand...

What are you running for speakers and preamp? Only curious because I am considering a speaker change and right now with 90db Focal towers and a BA-3 preamp running about 20db gain I am pretty satisfied with the hot-biased F5. I usually listen around 85-90db at the listening position. I am usually using about 70% of the volume knob at this level.
 
#24
kj123 said:
Thanks Hikari, that's an excellent advice. I guess 0.2v increase in bias won't hurt. When I had the boards in the case (I am using the Aleph j now), the heatsinks were warm at best. I wonder if I could do the same with the Aleph J 🙂 although this one runs "hotter"... And you're right, heat is not going to be an issue for few months...it's already reaches -10c outside up here 🙁

P.S. If I manage to bias at 1.7A does that mean that it could output a max power of 46w?
(Ibias*2)^2 * load /2 = (1.7*2)^2*8 /2 = 46.24
Click to expand...
the maximum power remains at 25W for an F5 running on +-25Vdc.

If you increase the output bias current, you are in effect increasing the maximum ClassA current ability.

That means the load can draw more current than the normal 2.5Apk and still stay in ClassA.
All speakers draw a current that varies with the signal. Fast transient voltage make the reactive load DEMAND more current than a rurely resistive load would demand.

All our conventional power calculation use resistors as the nominal load.
That does not give a useful picture of how the amplifier interacts with speakers.

Increasing the bias so that more of the transient peaks stay in ClassA may give a "nicer" sound.
The only way to find out is to try it, if you have spare cooling capacity.
Even a temporary fan for a temporary increase in bias may be a useful experiment that gives you data to decide whether an "improved" version is worth starting.
 
#25
Hikari1 said:
What are you running for speakers and preamp? Only curious because I am considering a speaker change and right now with 90db Focal towers and a BA-3 preamp running about 20db gain I am pretty satisfied with the hot-biased F5. I usually listen around 85-90db at the listening position. I am usually using about 70% of the volume knob at this level.
Click to expand...

Hi Hikari,

I have the full range Statements (Statements) and use an ARCAM AVR300 as preamp. I too like to listen in the same range 85-90db ... but close to 90, I start to hear some slight distortion.
 
#26
AndrewT said:
the maximum power remains at 25W for an F5 running on +-25Vdc....

Increasing the bias so that more of the transient peaks stay in ClassA may give a "nicer" sound.
The only way to find out is to try it...
Click to expand...

Thank you Andrew for the explanation. I was a bit confused as why the power output would not increase.

I went ahead and put the F5 boards back in the case. I re-biased to 0.75v. All went well. The offset is less than 1mv for both channels. I tried some music with but could not push it hard it was getting late.. I will do some more listening later this evening.

thanks for your input everyone

KJ
 
#27
Hi there, a little update. I have been listening to the F5 for the last hour or so and I'd swear it plays way louder than before or at least louder then the Aleph J that was in the case up to yesterday. No distortion and no clipping that I can hear. I pushed it to 95db, still no clipping, but that's way too loud for my casual listening. The surprising thing is that the heatsinks are just warm, I can keep my hand on them forever. I think I have my solution and it was an easy/free one....thank you Hikari and to everyone else for your input

KJ
 
#29
Good night.
I apologize for being to use this topic but I think that is the place.
I am thinking of building another f5 std but now in mono block using transformers 240 / 20v + 20v 300VA with filtering clc 47000uf - 2.5mH - 47000uf, bias to 0.75V. It is thus possible to make psu?

I liked that they gave a help to choose which the best components for F5

thank you so much
 
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