F4 power amplifier

I always thought AlephP v1.7 was incredibly versatile, can run bal/unbal on both inputs and outputs, has some input attenuators (to deal with hot inputs), a single pot for internal gain adjustment over a wide range, and a volume attenuator at output (a little unortodox but attenuates the pre noise as well; can be omitted in integrated amps). I have two kits of parts and will be making boards for one stereo pre next winter; (if you are interested in the other kit drop me a PM).

> as for your needs to have it both ways, passive and active, you may also want to go back in time and look at Papa's AlephL which was exactly that combo (if i recall correctly).
 
F4 balanced question

and since I am on F4 thread I might as well ask, and would appreciate some answers (of course will pay beer when we meet :D ):

I have always had in the back of my mind the idea of making an integrated AlephP/balancedF4 amp for higher power.

I am not quite clear on how much heat dissipation and distortion this amp would have? in the original article it says something like "100W into 8 ohms at 0.5%" (which sounds kind of borderline acceptable even for a desirable 2nd harmonic?). and how about such an amp playing into 4 ohms? (I am afraid if I go parallel SE route (which might make more sense for 4 ohm load) the voltage swing from AlephP may fall short of the required full range?

p.s. I wish Papa revisited the F4 concept and maybe improved on it a bit or pushed the boundary like he did for F5 with F5T and X. apparently he is busy with a whole bunch of new FW amps so I am hoping ... :spin: ).
 
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.......
p.s. I wish Papa revisited the F4 concept and maybe improved on it a bit or pushed the boundary like he did for F5 with F5T and X. apparently he is busy with a whole bunch of new FW amps so I am hoping ... :spin: ).

being able to judge that revisit is absolutely necessary (even possible) , makes you completely able to make that revisit , by your self ......

:devily:
 

6L6

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I am not quite clear on how much heat dissipation and distortion this amp would have?

That's 2 different questions, but both are answered in the F4 manual...

1W distortion .05%@1Khz. Please remember this is a zero (global) feedback amp, so that number is quite impressive.

Bias is .43A/device, x12 devices = 5.16A*23V rails = 118W of bias, and that's before any losses, the better number is the current draw from the wall, 180W, which is mainly going to be converted into heat.

p.s. I wish Papa revisited the F4 concept and maybe improved on it a bit or pushed the boundary like he did for F5 with F5T and X. apparently he is busy with a whole bunch of new FW amps so I am hoping ... :spin: ).
There is two was of looking at that - one, the BA-3 complimentary is taking this idea further. Or, two;

There honestly isn't much more that could be done to 'improve' this circuit. There aren't many other ways to connect a complimentary PP pair in source follower, and the bias arangement is really, really fantastically clever. It's about as simple as anybody could do it, and Papa has shown that simple sounds fantastic.
 
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6L6

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What is it in these preamps and buffers that I need to look for to judge that they can handle the 8v signal? Could, say, an Aleph J handle it? Why?

I'm not sure what you are asking - can you clarify?

The Aleph J will go to full output with about 2V in. More than that and all you are doing is overdriving the input clipping the output. 8V in will just **** it off and might be a signal it's completely unhappy with.

The F4 has no voltage gain, so if you want full output you will need a 45V signal pk-pk which is 15.9V RMS. Not many preamps that can do that, but that said, not many people actually need a F4 running at full output. It's a powerful amp. I used it with a preamp that could sting 7V and it was loud enough for 99% of my listening.
 
My active xover puts out 8v balanced. That's enough volts, so I want a current buffer... but I'm being fussy about noise/CMRR because >1000Hz i have 110dB/w/m and they'll be 3m away. Maybe I should develop some faith in the bal/stereo F4... and attempt to fix tge MiniDSP 2x8's noisy outputs :/

Re: the A-J, I want to know why 8v would make it angry. Is there just no swing available in the input? Is it just because the gain's too high for that already?

Noone ever discusses minimum gain in the circuits I find...
 
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6L6

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Just because your xover has the ability to output 8V doesn't mean that it will take any input you give it and output 8V. It has level controls somewhere. Or just place an attenuator or pot in between it and the F4 for volume, which is almost painless as the Jfet input buffer section of the F4 is more than happy having a pot in front of it.

The AJ has a gain of about 20db, which is a voltage gain of about 10x. Meaning that a 2V signal on it's input will be increased to 20V on it's output. The AJ has 23V rails, and any more input voltage will just drive it well past clipping... 8V will try to be increased to 80V, and there just isn't that kind of voltage in the amp for the output section to be able to follow, and as soon as the wave becomes higher than 23V, it can't do anything else, and chops off the higher voltage part of the waveform, I.E., 'clipping'

Now the F4 has no voltage gain, in fact it's ever so slightly negative. So if you were to put a 8V signal into the F4 you will get a 7.99V signal on the output, but with many, many times the current and therefore the ability to drive speakers.

The real question is what is your speaker efficiency? For example, if you are using drivers that are very efficient, like horns or Lowthers, 8V will make you deaf. Seriously into hearing damage range. I think you said you are running horns, so output is not going to be an issue.

I have a mid horn, 103dB and treble 110dB. I will be listening from less than 3m. Processing done by a MiniDSP with 2v SE, 4v SE or 8v BAL.
I've concluded that 8v will give me a satisfactory SPL when 'cranking' the DSP to 0dBFS, and I want to optimize my gain structure for the sake of the noise floor.
It will not be 'satisfactory output', it will be high enough output to cause permanent, irreversible hearing damage very quickly.

If you are currently using these speakers, and not totally angering all your neighbors and the police, you obviously are using less than your full output. :) :)

Did you mention that your miniDSP has noisy outputs? That is likely a separate issue, and that noise must be found before you can have a quiet system.
 
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6L6

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I just don't understand enough to work out whether I could simply reduce its gain, or whether there's some limiting factor in the topology, etc...

Turn the volume down.

Just because the miniDSP has the ability to output 8V doesn't mean that all signals get amplified to 8V. It has level control. And anyway, that's only in balanced mode, where SE can only make 4V

Also, if you are genuinely worried about noise floor, place a pot/attenuator after the miniDSP, and that will attenuate the noise of your system, as well as get your listening levels to an enjoyable level.


F4 it'll be, though, and I'll experiment with frontends.

F4 frontends? Or something else? The "crippled' F4 is (in my opinion) not worth the bother, as the Jfet buffer is a bigger benefit when installed than without.
 

6L6

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More is better, although diminishing returns kicks in quickly...

Max bias should be when your:

Heatsinks are a maximum of 55C and pin 2 of the Mosfets is no more than 65C

And/or when your bias current is 1/2 the current of the transformer. I.E., if you have a 300VA transformer, the entire amp can't be biased to more than 150W
 
More is better, although diminishing returns kicks in quickly...

Max bias should be when your:

Heatsinks are a maximum of 55C and pin 2 of the Mosfets is no more than 65C

And/or when your bias current is 1/2 the current of the transformer. I.E., if you have a 300VA transformer, the entire amp can't be biased to more than 150W

Thanks that means I cant go above 293mV over a 0.47ohm.
 
balanced F4

Thanks 6L6.

I appreciate your comments regarding the simplicity of the F4 topology and your putting its distortion into perspective given no g feedback.

still fuzzy though: Does a 4ohm load lend itself to being driven by a balanced F4 (with the same heat dissipation and distortion estimates as those for an 8ohm load)? I feel like driving the preamp (AlephP) in the balanced mode.

Or should I start thinking about an alternative SE preamp and paralleling F4s? or maybe start considering a BA-3 like amp? soundwise though I have not seen as much positive comments about BA-3 as I have about F4, thus the current preference ;).
 

6L6

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Balanced F4 can drive anything. You just need 2 - as the entire amp becomes a monoblock. If you have enough gain in the Aleph P, using it balanced is a great idea.

The BA-3 is fantastic, completely smashing, an amp anybody would like -- it's a F4 with gain. The output stage is identical, and the driver is quite similar to a F5 with no feedback. I'm very hard pressed to decide which is my favorite, BA-3 or Aleph J. They are both wonderful.
 
dwfish: not my discussion really but people gave you all the info you need. you have come a full circle from saying you considered miniDSP outputs noisy, to now not wanting to "spoil them with pots". to reiterate the input from others: you can either use your dsp to run an F4 to just add current to it (and 8V may do it given your high sensitivity setup), OR you can come up with less hot outputs at source (by making jumper selections in miniDSP or otherwise) and feed that to a high quality amp with fixed gain (like you entertained an AlephJ at the beginning).