F5 Turbo Circuit Boards

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For me I want to build a V3 100W class A exactly as per the published design- to understand what kind of case/heatsink is needed a good refernce would be the musical fidelity AMS 100 - though this is balanced and bridged design (class A 100W into 8 ohm and 200W into 4Ohm)- it weighs in at 100Kg I recall

so all these cases/heatsinks discussed so far I expect will be far to small for a stero amp.


The plan is to use the Fischer SK535 (500 long * 400mm high) 0.08 K/W

SK 530 ... <br>SK 531 ... <br>SK 533 ... <br>SK 535 ... <br>SK 536 ... <br>SK 537 ... <br>SK 538 ... <br>SK 539 ... <br>SK 540 ..., Standardstrangkhlkrper, Khlkrper f.cool, Fischer Elektronik

So with 240 watts of dissipation then I hope to get around 20 degrees of rise.

And use the type of construction as per the recent absolutly amazing (or Fugly as some say) F4 posted in the Amp secton of this forum (bolt the top, bottom front ad back panels to the heatsinks)

I live in switzerland and to get these things made here will be quite expensive so maybe it will be cheaper just to by the 16k Euro AMS than build a case for the F5T ? lets see.
 
Good joke;)

Dissipation is 260W per channel and I measure app. 45°C.
Don't know how you claculate but these mono chassis (4 of these heatsinks) have 0.07 K/W

From past experience they looked small for a 200 watt/ch Class-a amp ...

What's wrong with 150W of ClassA into 8r0?

That just 6.13Apk into the load.
And from a Push Pull amplifier like the F5, would require a bias of ~3.1Adc

The F5T would be equivalent to 75W into 4r0 from each half of the balanced amplifier.

Still a lot of heat and consumption .....
 
I had considered having an enclosure made in the U S. However, it is quite a project to take on and there wasn't much interest last year. Everyone seemed to want the cheapest thing that would work. Personally, I like elegant stuff and it would be in my living-room so I don't have a problem if it costs a bit more than the cheapo offerings.

Would be even more difficult to do something for the F5-T since there are so many variations of the amp with different heatsinking requirements. So there proably won't be a one-size-fits-all enclosure.

Reading some of these posts, I think some maybe taking on a rather difficult project with V3 versions etc. I know, as I read the manual, I started to wonder if I really need more power than the original F5's 25 watts.

For most home audio situations I suspect that you are correct about 25 watts being enough. I am a firm believer in the FirstWatt principles.
 
I still have a hard time understanding the operation that allows it to move from idle current over the source resistors to the diodes themselves. Is this determined by the diode behavior and characteristics?
Can someone spell this out for me using simple words, and easy math? :confused::D

I think the diodes don't conduct until a certain voltage is reached. .4 V I think, when they start conducting the output sees a lower resistance path and allows full current without the limitations of the resistor. The resistor is by passed by the diode only when the diode starts conducting. So you can set the idle current with the resistor, but don't go over the diode forward voltage limit (.4 V).

Someone please correct me if I am wrong!

Rush
 
The direct I/V function of the diode is used to simulate an Rs that diminushes as current increases.
At 20amps Vdrop is about 1V only, as if Rs were 0.05 ohms
The bias is set such as V (Rs) is nearly the threshold where the diode conducts..
Apearent Rs is about 0.47 ohms.
Then, as current increases, apearent Rs diminushes.

As for the maths, not me.

Edit: cross posting
 

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OR to put this another way given 10 V and 1 homs source resistor
and taking mosfet as dead shorth as they do same time and 0 load just for easy life

10 V / 1 = 10 A that is max current that can go troug the source resistor
decrease source resistor more current.

Or put a diode there
same electrons go trogh source resistor causing a V drop and diode start to conduct and open a gate so same electrons will say F... that and go that way (but actualy closes the gate just to make thing even more confusing)

You still got a few that go to the pub insted but...

Now clever thing about diode is that as soon as current demand drop that gate close (but it actualy opens) so electrons got to waith in bliping quee insted to go and melt your heath sinks
 
I think the diodes don't conduct until a certain voltage is reached. .4 V I think, when they start conducting the output sees a lower resistance path and allows full current without the limitations of the resistor. The resistor is by passed by the diode only when the diode starts conducting. So you can set the idle current with the resistor, but don't go over the diode forward voltage limit (.4 V).

Someone please correct me if I am wrong!

Rush

Another area I don't understand is why this stays in Class A. Doesn't the amp quickly shift to Class AB?

The sentence I'm stuck on is "In addition, with Fets you get an output stage that will deliver more Class A power at a given bias figure due to the square law character of the Fets."
 
The MF has CLC power supplies, the 2 toroidal transformers and 4 block chokes (EI look) account for most of the weight.


Yes I agree that the units has a number of parts that are heavy, the only thing i wont have is the chokes, so I expect the V3 properly done with 2 large toroids lots of caps , but no chokes is stll going to come in at 60 to 80 Kgs ( Just the heat sinks will be around 40Kg, 500mm x 400mm 0.8 d/w) ( I may look at CLC if I can find a source for chokes with a suitale currnet rating)

I think this only confirms what others have stated early on that a well done V3 is going to be quite a costly exercise - no chance to do this one on the cheap
 
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