F5 power amplifier

[jacco vermeulen]

Definition : 2.83V corresponds to the average voltage across a standard 8 Ohm speaker, driven at 1W.

Referenced to a 4 ohm speaker it would be 90db/2W/M, is 87dB/W/M. (2.83*2.83/4 = 2W )

[KatieandDad]

Originally Posted by AndrewT

No, they are not 90dB/W @ 1m
They state 90dB/2.83Vac @ 1m and they imply their usual tolerance on sensitivity.

If one accepts that these 683 are 8ohms speakers then one will find that many 8ohm capable amplifiers will not perform at their best trying to drive the 683s to highish peak levels on transients.

If one were to instead read the specification and decide they are probably 4ohms to 8ohms speakers and select 4ohms capable amplifiers then you are likely to find that the same peak currents into transients, as demanded by the 683, will not cause as much if any problem.


I would look at 100W and above into 8r0 amplifiers and only select those that are capable of at least 180% of that rated power output into 4r0 and are stated as 4ohms capable as being likely candidates for your 683s.

The Aleph probably, or almost certainly, meets all of those conditions.

[KatieandDad]

Nelson has been saying that the F5 Turbo might be better with the B&W's.

[jacco vermeulen]

He may be right.
=> B&W 683 Surround Speaker System Measurements | Home Theater

[KatieandDad]

Someone did post the F5 turbo schematics but I cant find them.

The one on the STORE page is misleading as it's in Black and White and there seem to be connections where there shouldn't be.

I'm dubious about this - it's just the DIY bug has bitten again and I wonder if the F5T is any better than my very much loved Aleph 4.

[jacco vermeulen]

Other option would be to compare the schematic of the Aleph 4 with the one of the Aleph 2, and transform it into an Aleph 4.2

(as in : same peak output current as the Aleph2, with the quiescent current setting of the Aleph 4)

[KatieandDad]

I was looking at the Aleph J-X as it shares a lot of the Aleph 4 components.

My Aleph 4 has pretty well matched quintets of IRFP244s but are they matched closely enough for an X build ? Who knows.

[jacco vermeulen]

Regular Aleph J-X has 1.8A bias, you'd lose another 2.5dB SP under 1KHz.

(a loudspeaker with high impedance in the mid/high frequencies and low impedance in mid/low bass region, is better off with reasonably high Class A power, and plenty peak current in the oomph zone)

[KatieandDad]

I think I am going around in circles here. I love my Aleph 4 and it suitsthe B&Ws. Maybe I should find another home for the DIY bug.

[pdhanwada]

Planning to build pass F5 with dual output mosfets.

I went thru the forum, Not many people implementing speaker protection circuits.

Let me know if anybody has implemented any. If so what are the ways of doing it and what are the repurcussions.

thanks
pandu