F4 power amplifier

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#2,321
OK, I am preparing my PSU-shoot-out... i will hopefully get new transformer next week 800VA types, absolutely quiet. The rectifieres are already Schottky diodes, so next are the PSU-CAPS:

- Panasonic TSHA (currently in there in a CRC)4*22000uf per Monoblock vs
- Jensen 4pole, 4*47000uF, I am here still thinking if I should really insert the 0,1-R resistor or simply bridge it.
- BHC Slitfoils, 4*22000
- Normal Aerovox
- Normal Phililps 051
- Mundorf HC-lytics: Monster-Caps 4*47000uF
- I was not able to get any 10000uF BlackGates any more, maybe better for my bank account. Maybe if I am crazy enough, I will create a bank of parallel Panasonic FCs ore even Silmics...

I have still a few nice chokes with 30 mH / 6 A around, so maybe I experiment with those as well. I am as well thinking to put a 0.1uF-Mundorf Supreme in parallel to the lytics, what Do you think ?

Any bets which combination will be the winner or how big the sound difference will be ?
 
#2,325
Some unconventional finish

Hello mates, while my build is goin' on (waiting for the last components to start assembling), I was playing with my aluminium panels, and here are two pics of the front panel "First Watt F4" logo:

[img=http://img134.imageshack.us/img134/8397/foto178xv1.th.jpg] [img=http://img134.imageshack.us/img134/1627/foto176rd4.th.jpg]

To do that, I simply copied the logo by hand on a piece of paper, then sticked it on the panel surface with some tape, and finally used a hammer and a nail... Very long process, but the result is funny, I like it 😀

Giacomo

P.S.: Do I need to put a (C) as well?
 
#2,327
I got both my F4's running this week. I am running full balanced and driving them with a X-BOSOZ pre. I know there is no where near enough voltage swing to get all the power out of the F4's but my speakers are 96 db efficient, so they are ok for now. What I have found interesting is that previously, I was driving a single F4 in stereo with a J-BOZ pre running on 2 - 9V batteries. I think I liked it better. It added a nice touch of emotion to the mids that is lost with the X-BOSOZ. The BOSOZ has more detail and resolution, but without the gain, there is a bit of snap lost. I have been resisting doing a pumpkin and trying to hold out for SY's tube pre. Maybe I will just have to bite the bullet and do both. 🙂

All of my stuff is far to ugly to post pics right now. Functional does not mean finished by a long shot. I have found that using Clementine boxes for mounting electronics works quite well. The cost is right as they are included with a pound of clementines. They are really easy to work with. If you screw up, you just eat some more clementines. The end result is not exactly child friendly, but I feel much better knowing that the electronics work properly before sinking time into building nice boxes.:smash:
 
#2,329
I picked up a used Transcendent GG to use with my progressing F4 build as the gain is adjustable at either 12db or 30db. In every system I have used it in so far, the 12db setting is too much gain. I'm looking forward to using it with an amplifier that does not hve gain because the sound is quite good.

Chris
 
#2,330
Nelson Pass said:
www.passlabs.com/np/F4 Power Amplifier.pdf
Click to expand...


From the Texas TL431 datasheet
This device contains 12 active transistors.
Click to expand...

Which makes one original F4 amplifier have:
- 2 JFET, for input
- 12, mostly bipolar, transistors for Vbe multiplier control
- 6 HEXFET for output

My attachment is one of my testvariants of F4 setup. Simulation data are good! 😎

The TL550C, is my own working clone spice model of TL431.
Done with discrete BC550C + BC560C.
My clone uses 11 transistors. The 12th they mention, I do not know about ....
Anyway, my TL550C works. Regarding setting keeping precise voltage.

In reality it wouldn't. Because the bandgap is set up to fit IC chips transistors.
Not BC550C / BC560. There would be a temperature drift.

In this picture I used IRF640/9640, '
but of course we should use something more heavy:
The original IRFP240/9240 should be our first option!

🙂 My circuit uses 2 current sources, at 10 mA. (Could be raised a bit).
The upper CCS is adjustable for DC-offset trimming.

🙂 I also very much prefer separate voltage supply. for input / output.
This is an option many forget .. because commecial amplifiers reduce production cost (for maxmial profit)
by ONLY put in 1 Transformer.
A little transformer with, say 5-10, higher voltage, say 10 VA is a small cost.

This is to minimize un-wanted 'feedback' distrubance in power supply rails.
From output to input side ..
also of course we can use a very precise regulated input supply.
We also may have a better pwerformance before output does clipping.


Regards
lineup 🙂 just another of all doing clones from Master Nelson stuff 😀
 

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#2,331
Grounded Grid + F4

Hello Chris:
I took my F4 to a good friend's house that has a Transendent Audio Grounded Grid pre amp. We were both quite impressed with the combination. We were listening to a nice set of Fostex 126 Frugal horns he had built.
The combination was open and clear with great band width. A very good combination well worth having.
Another combination I have recently been listening to is the F4 with an Aikido 6sn7 pre amp. I think the gain is about 15 db ( not real sure though). My speakers are reasonably sensitive bipolar Fostex fe127's in a fonken style enclosure. I am really liking the sound. The gain is just about right for my room. It could be a bit more but I am not unhappy. It is loud enough to get my wife frustrated with me. The clarity and open-ness of the Aikido is really great. I really like the dead silence during quiet sections and lack of distortion and colouration. Sound stage and depth is great.

Anny way just another perspective on a great amplifier
 
#2,333
when i started my F4 for the first time i could only adjust the left channel to 250mv the right channel i could adjust to 300+-so i set both at 250mv and set the offset,when the amp warmed up i could get 300+ out of the left so i reset both to 300mv and reset the offset then ran it for 6 hours--when i went to shut it off and was by the speakers i noticed a hum from both channels--i put it back on the bench and the right channel was 450mv!(left had drifted up slightly but not like right) and the offset on both channels was off.i left it off for a couple days and started over today-could only get 250mv out of the left again-i let it warm up and they have drifted up to 275mv and the right offset had to be reset 2 turns-but what gets me is that there was no hum when cold and now that it has warmed up it hums again-would someone please give me some advice!!!-mark
 
#2,335
The FW version is set at a cold bias of 300 mV and over the course of
an hour or so it drifts up to about 400, at which time the bias and
offset are trimmed. Then it is checked again after a day or so.

Your results will vary depending on the effectiveness of your cooling.
 
#2,336
thanks nelson!! hum is slight but i was wrong it is there when cold-just couldn't hear it over the buzz of the fluorescent lights in shop. got the big conrad heatsinks-it takes several hours to come up to 105F. i assume the hotter the heatsinks run the more the bias will drift up?
 
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