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Old 12th April 2010, 09:47 PM   #7711
awc is offline awc  New Zealand
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I've been running F5 for close to 4 months every day, the sound has change several times over that period and only in last month has it good to where id called burnt in, during that period I've tried different types of speaker cable and interconnects, so if you want sibilance go to QED silver Anniversary's, once its burnt in I think you will find Ant-cables work best. You could put some 8 - 10 ohm resistors in place of speakers and let it run 24/7. But leave it 2 or 3 months before final adjustments.

and Thank you Nelson, and my neighbours thank you, Music Reference valve pre, 91db Tannoys, means plenty of volume. thanks to all contributors as well.
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Old 12th April 2010, 10:07 PM   #7712
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Listening to this approach of F5, I agree with Tee-bag's description:

Click the image to open in full size.

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Old 12th April 2010, 10:15 PM   #7713
a.wayne is offline a.wayne  United States
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Why would the burn in process take so many Hrs ? due to the type of outputs?
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Old 12th April 2010, 10:31 PM   #7714
tinitus is offline tinitus  Europe
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I havent yet heard the F5, but I doubt very much it would lack resolution

I trust it enough to blame the speakers
Well, I probably would in almost any case....speakers are mostly the problem

Anyway, I usually need some time to get accustomed to new gear
Goes for anything, a different car, new bike, etc
A new stove may take up to a year

Lets talk again in a year, and you might say the opposite
sometimes we know very little, and sometimes we know too much
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Old 12th April 2010, 10:49 PM   #7715
awc is offline awc  New Zealand
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This has all what you'd expect from a moderately high end amp, so its worth the rest of your system being up to that standard to hear it at its best, and other High Fi buffs that have listened agree.There's been nothing fancy added like extra mosfets etc, its just as the master designed it.
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Old 13th April 2010, 12:09 AM   #7716
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Location: New York State USA
The sound of the F5 can vary all over the map.

NP already said that the bias setting alone will change things.

The brand of resistors seems to change it.

I have heard the very same amp go from stunningly clean and clear to rather fat, recessed and somewhat dull... just some seemingly minor changes made that happen!

Break-in? Roll the dice.

http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- every once in a while I say something that makes sense... ]
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Old 13th April 2010, 12:14 AM   #7717
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Location: Westmont, IL
@prooptiki: Thank you! That is just what I have been looking for.

I am building my first F5 exactly to the masters original design (updated w/22K current limiters) with IRFP240/FQA12P20, but I have a set of Toshibas for a second set of monoblocks. I was not going to use them unless a saw some well-explained mods to the original circuit, or, a revised schematic. Prooptiki's schematic matches my notes for the most part. I plain to do direct A/B comparisons when finished.

Anyone else have experience/comments on prooptiki's Toshiba implementation?

From my notes:
I use Toshiba outputs, sound wonderful, and w/o tempco they are very DC stable.
I think they are a bit more detailed than Nationals, while not sounding peaky or rough.
They are smooth and refined. I use .47r, but lowered R3 and R4 to 1K to get a little more
'action' out of the 5K pot. They otherwise bias up very quickly.

As posted here ages ago, my preferred configuration is Toshiba 2SK1530 / 2SJ201, balanced,
2A bias, 0R22 source resistors. I like Toshibas better than Fairchilds, but I am known to be biased.

> Am I right in thinking that we'd need to see ~2.7V across R3/R4 (instead of the 4.2V for
the IR or Fairchild parts) in order to bias the Toshibas to 1.3A?

Yes, so you need to adapt the circuit (e.g. lower bias for the JFETs).
I used 6mA Idss, which are unfortunately not easy to get. You can of course also lower the resistor value
at the drain of the JFETs.

i only reduced the trimmer value and got 2,7 volts for 2sk1530/j201..and everything is allright..
i didnt change anything other..
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Old 13th April 2010, 01:02 AM   #7718
tinitus is offline tinitus  Europe
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I got these Wild Burro 8" fullrange and my plan is to mate them with a 35mm TB, in a floor based omni design
In my experimental setup the small TB sounds pretty good, with lots of resolution, when carefully adjusted
When I get around to build my F5 I will know if its a good match
Maybe next year
sometimes we know very little, and sometimes we know too much
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Old 13th April 2010, 01:22 AM   #7719
kp93300 is offline kp93300  Malaysia
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Originally Posted by markofka View Post
I thought this is the key too... Now the last cap is small siemens sikorel,but i think good MKP should have positive influence,as i know allready, with these a-class transistor amps ANY mod in PSU are noticable.
I really hope that F5 can give suzuki superbike like performance with my titan dioxide tweeters,more "being there" felling.Now it's just amp that dont involve me much in the music.With harsh cd,speakers,maybe it would be very good.
I would also like to share that in my set up , the addition of a pre transforms the sound for lethargic, lacking drive to' being there " with the musician experience . The treble in my ribbon tweeter is very detail and precise . The varying force of the drummer on the hat could be appreciated.

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Old 13th April 2010, 02:26 AM   #7720
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Originally Posted by bear View Post
The sound of the F5 can vary all over the map. NP already said that the bias setting alone will change things.
Bias is important, but also the F5 depends on a specific "sweet
spot" or nulling effect where the positive and negative halves
are just right. It takes a distortion analyzer to find it quickly
or a very good ear to find it slowly. Go off the balance and it
fattens right up, and some like that.

Personally I find it to be partly a function of the loudspeaker
driver. With something like the Feastrex D9nf, a little fat
doesn't hurt, or you can switch to an F3, or perhaps a nice
glass of cabernet.

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