F5 amp for three way active speakers

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#41
Nelson Pass said:
Anyway, the whole point of active crossovers is to find work for all the amplifiers we build.
😛
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Hello, Mr. Pass! Nice to meet you in this thread))
But seems, I'm coming from the opposit side to the problem since I haven't build them enough yet 😀

By the way I'd like to ask you if F5 can work normally at lower PSU voltage?
Say, 16V to reduce power dissipation if I don't need too much voltage for 4 Ohm drivers? Worth it in my case, how do you think?

My idea is based on the power calculation for my drives in post #26.

1) Woofer has 8 Ohm coil and needs 21W (limited by Xmax), so it needs 1.62A in class A.
So, I suppose I can stay pretty happy here with my regular F5 having 24VDC and Iq=1.2-1.3A.

2) Mid has 4 Ohm coil and needs 16W (to create same SPL as woofer), so amp has to output 2.0-2.2A at least (Iq=1.0-1.1) but voltage required is 8V only (11.3V peak) now.
If we can deal with 16-18VDC rails here for F5?
In this case dissipation will be 35-40W with 16-18VDC and Iq=1.1A.

Same is for twitter (even less power required normally).


Anton
 
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#42
As already mentioned above, there is no real argument (for me at least) for using Class A for Woofers.
For 4 ohm 16Wrms, you need 2.8A peak at ~11.2V, so at least 1.4A bias and 16V rails.
More bias and voltage headroom will reduce distortion.
But then you would not be using all 16W anyhow for listening.

The F5X has +/-16V rails and we have over 100 units in the field.
That is assuming you use 2SK1530 / 2SJ201 MOSFETs for the output.

The rest is already mentioned in post #19, and more or less repeated in post #32.
But do what you think is best for you.


Cheers,
Patrick
 
#43
Dear Patrick,
You are right about peak current - my mistake...
Please, don't get me wrong, I don't want to make everything on my way despite on any advice.
I just would like to cosider all other ways to go assuming the the hardware I already have.

I like the approach described by you and in post #32 (except that I will need passive crossover to build).
I have nothing against AB class for woofer also but my F5 is almost ready.
So it would be nice to decide if I can use it correctly in the system.

If using of F5X (instead of F5) is required now I will have to rebuild F5 and build some new AB amp...
This means a new trafo for F5X as well as soon mine gives 24VDC...
I just thought to leave the existing F5 somehow - for woofer for example (as soon it is ready and fits to woofer demands).

BTW, do you think 5U chasis (200x300 mm heatsink) is OK for F5X?
I need to study the thread about it.

Anton
 
#44
AntonTR said:
BTW, do you think 5U chasis (200x300 mm heatsink) is OK for F5X?
I need to study the thread about it.

Anton
Click to expand...

I don't know if it is adequate, but long (400mm) 4U should be better dissipation than 300mm 5U, because longer heat sink is much more efficient than higher heatsink if the area is the same, and long 4U heatsink seems to have slightly more area. 🙂
 
#45
I see,
Patrick! Thanks for your remark.
Here is my F5 assembly (on 5U chassis).
attachment.php

Ok, I need to study F5X and passive crossover details for mid and high.

Anton
 
#46
EUVL said:
As already mentioned above, there is no real argument (for me at least) for using Class A for Woofers.


The rest is already mentioned in post #19, and more or less repeated in post #32.
But do what you think is best for you.


Cheers,
Patrick
Click to expand...

What is an acceptable upper freq for the woofers in class AB?

600Hz is too high?

My mid-tweeter is compression driver could go down to 600Hz
 
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