F5 Turbo Circuit Boards

[beetle]

3A bias is coming very close to that. Serious heat sinks from fischer or so are really costly. Can buy only two for a modushop case.

 

[AndrewT]

are you allowing for 3A bias at +-24Vdc from each half of the balanced amplifier?
i.e. 288W dissipation per channel.

3A bias gives ~ 6Apk of ClassA and results in 36W of ClassA into 2r0. This when feeding a 4r0 load from the two halves of the balanced is roughly 72W of ClassA into 4r0. Double the power into double the load impedance.

Working back from your 200W into 4r0 balanced, needs 100W into 2r0 from each half.

That requires a ClassAB output of 20Vpk and 10Apk. Probably a sensible target from +-24Vdc rails biased to a total current of 6A.

 

[a.wayne]

beetle. (bias x2) x (bias x2) x impedance /2.
so say 2A bias. it is 4 x 4 x 2 / 2 = 16W class A at 2ohm

or 64 W @8ohm

So ~3A bias 24V rails then. I would assume that Modushop 5U 500 has not the right sinks for 576W per channel. Or does it?

1kva 18V toroid will be costly. Any good source in Europe?

I would expect a total power of up to 200W in 4 ohm Class B and 36W class A. Right?

32 watts ...

 

[AndrewT]

I understood he wanted to bridge the outputs as described in options of the F5t.
That's what I assumed in my response of post1782

 

[beetle]

are you allowing for 3A bias at +-24Vdc from each half of the balanced amplifier?
i.e. 288W dissipation per channel.

3A bias gives ~ 6Apk of ClassA and results in 36W of ClassA into 2r0. This when feeding a 4r0 load from the two halves of the balanced is roughly 72W of ClassA into 4r0. Double the power into double the load impedance.

Working back from your 200W into 4r0 balanced, needs 100W into 2r0 from each half.

That requires a ClassAB output of 20Vpk and 10Apk. Probably a sensible target from +-24Vdc rails biased to a total current of 6A.

Aren't the speakers seeing the double voltage when bridged?

 

[AudioSan]

or 64 W @8ohm

correct

 

[AndrewT]

Aren't the speakers seeing the double voltage when bridged?

.............correct

yes,
how does knowing that help you?

Do you understand how an amplifier works?
Do you know the difference between ClassA operation and that for ClassAB?
Do you know how a bridged and balanced amplifier operates?

 

[beetle]

Bridging means that one amp is inverted or the signal. Current will remain the same but voltage is double.

Besides this a little, still learning. In this case we have a push pull amp. In this particular F5 design the first stage is splitting the signal in two halves. One inverted. The F5 is class A up to the bias. Then it transitions to class B. I think this describes it well: Push pull amplifier, working and theory. Class A , Class B , Class AB circuit diagram

Still learning.

 

[AudioSan]

andrew. why do you quote my answer in there??
i answered wayne.

but to answer how it helps to know that.
it makes a huge differnce on the dissipation.

 

[AndrewT]

you told him "correct".
I agreed, "yes".

But does the questioner know what he is doing?
Now that Beetle has posted 1788, it is obvious he does not have a clue.

 

[beetle]

Me no clue, no.

 

[AudioSan]

andrew.
i told wayne correct.
that 16W class A at 2ohm = 64W class A at 8ohm.

 

[AndrewT]

post1776 asked a question.
It has been answered a few times. We are all in agreement. All except Beetle

It's Beetle that is lost.

 

[AudioSan]

Me no clue, no.

bottom line. i will not advice you to build a balanced version. for many reasons.
1. 4 ohm speakers is not a good load for it.
2. it is hard to build.
3. it demands a good match between the 2 amps.
4. it demands 4 times the output fets.
5. it is never been done. and a exact schematic do not exist yet.

 

[AndrewT]

F5t shows the balanced arrangement.
F5x is a balanced arrangement.
But I agree with Audio, on all 4 points 1 to 4 incl.
Building a balanced amplifier is not a beginner project.

 

[AudioSan]

andrew. F5X is been done but not the turbo.
the schematic that is releast is only a guide.
it will demand som trying

some will most likely do that soon

 

[buzzforb]

Should be no big deal if you stay with V2, getting each half working at similar parameters, then tying them together. Getting it working, and getting it sounding good are two VERY different things.

 

[AudioSan]

buzz. think of the outputs. and the J-fets but one set of J-fets can drive 4 pairs. so you might get away with it. but then again. whats the gain? exept ballanced inputs?
you can get the same power out of a V3 at half the price on ampboards and parts

 

[buzzforb]

All true. I believe you rea need to burn at least a couple of transistors before your having fun

 

[pchw]

All true. I believe you rea need to burn at least a couple of transistors before your having fun

I did try BBQ-ing the dead fets at the end of my last backyard BBQ to make sure they were really toasted. The smell certainly was not fun especially the significant half's look