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Old 24th November 2009, 04:02 PM   #1
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Default F5 Listening Impressions & Discussion

Hi F5'ers...

My friend Rick decided some time ago to try his hand at building an F5. Since he is somewhat a newbie when it comes to ground up construction, the F5 appealed to him due to the almost complete lack of parts!

So, he brought his first version, on plywood, over for an audition.

It wasn't bad, but it sounded a bit "funny" - somewhat thinish and somehow a bit "uncorrelated".

We were listening on my horn system which consists of a relatively rare Japanese compression driver from 300Hz up and a 15" midbass "filler" down to my Quadripole subs... the main amp, in this case w/F5 substituting runs the horn + woofer. Horn is 109db (padded down to meet) the 15" at ~99dB (real 99dB, not wanna be). We also ran it direct to the horn.

The beauty of this arrangement for me is that there is ~10dB sensitivity difference between the horn at 109 and the woofer at 99, which corresponds almost exactly to the gain diff between my main amp (Symphony No.1) and the F5... voila magique! Auto level matching!

Long story short, it sounded good, but a bit lackluster.

Rick stopped back several times, each time with an upgrade:
- resistors
- power supply
- wires
- layout

The details of it aren't totally important.

What is important to me is that we recently auditioned it vs. a homebrew all Tango 300B amp, a Welborne Labs 300B amp, a Cary 811-3 amp, and of course my Symphony No.1 amp.

We used WE300B and others... fyi.

Very very easy to hear what is going on with this system...

Bottom line subjective result for me is that the F5 seems rather sensitive to details of implementation but is silky smooth on the top end, beating out the SE toobes that were here by some degree, seems to not create much if any sibilance (that HF grain on the top of voices)... now I do have to find out why this is so - but even if it is a flaw it is a really really nice flaw!

Still not sure about the sense of dynamics, or if the darn thing is just super clean sounding, so that is what is going on or not...

Quite an exciting amp so far!

PS. not sure that this is really a good amp for most folks unless you have very high efficiency horns like I do, or a very very small room... bridged seems interesting though...

_-_-bear
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Old 24th November 2009, 08:59 PM   #2
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I find that the most important details relate to the bandwidth.
The typical - 3dB point is out around 1 MHz, so without
compensation you can see all manner of effects.

Any time there is a question about this possibility, it's helpful
to throw a small capacitor across the feedback resistors and
see if it changes anything.

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Old 24th November 2009, 11:26 PM   #3
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Hi Nelson!

I'll suggest to Rick that he try that. It is his amp.

We can see if that effects the resulting sound or not.

Most of the positive improvements came from better wiring, layout and some PS "upgrades". The overall sound remained the same, but continued to refine for the better.

I seem to recall looking at the amp with a scope and saw nothing but a very very clean square wave without any "fuzzies" or other anomaly.

Imho, if anything it seems to be subjectively ever so slightly compressed sounding, and as I said the highs are seductively smooth. Of course the square wave says that they are not rolled off, as does your spec, so if there is HF "droop" on peaks it is some sort of dynamic phenomenon.

I speculated that it might have to do with the jfets not being able to supply enough current to overcome the input capacitance of the Mosfetters. These are the IRFs, I think... Otoh (as you know) I had a SE Mosfet (DC coupled amp) out a few years back (yikes! more than a decade!) and it used the same jfets to drive 3 Hitachi Mosfets, and that set up had an essentially neutral presentation in terms of subjective dynamics, and did not exhibit this slightly extraordinary presentation of the highs as does Rick's F5.

I suppose that somehow someone local will have to build up another one and see if we get the same subjective presentation (the circuit doing it) or if not then perhaps it has something more to do with his specific implementation detail...

_-_-


PS. I am curious what everyone else has felt about the F5 sound vs. everything else - of course GIGO means that a perfect amp will reproduce grunge of any sort perfectly, so one might think the amp is NG as a result...
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Old 25th November 2009, 12:59 AM   #4
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The P channel IRF's have some issues which can create
those effects, which are often pleasant. The F5 uses Fairchild
parts, and you can also use Toshibas to get past that.
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Old 25th November 2009, 03:36 AM   #5
AR2 is offline AR2  United States
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Quote:
Originally Posted by Nelson Pass View Post
I find that the most important details relate to the bandwidth.
The typical - 3dB point is out around 1 MHz, so without
compensation you can see all manner of effects.
I completely agree that it is all about the bandwidth. It is hard to explain this, and it is against all the teachings that we canno't hear anything that is above 20KHz or at our ages pass 15 KHz. And yet, we hear the difference between wide bandwidth amp and the one that is not so wide. Any time I listened amp or preamp that is really wide in bandwidth I liked the details at the top of the range. I guess that makes me bat, but I am not the only one to hear that. Obviously I am talking just about the details in the top end. Mids and bottom are different story, but if you listen to the horns or ribbons detail in the top is something that you would pay a lots of attention to. These speakers are very sensitive to the amp and they uncover everything about the amp that are driven with.

In addition to this, and to answer Bear's question on someone else's opinion on F5. If you followed the thread on the visit to Mr. Pass, where a small group of fortunate DIYers, including myself, had an opportunity to listen to several First Watt amps, than you know what the verdict is. We listened several amps and out of them all in our mind J2 was the best one, and very close to it was F5. I mean very, very close to it. That is particularly when we talk about the detail in the top end. I could quite understand your excitment, we felt the same. It is very good amp. I am just about to make the one and I have the same concern on the total output power for not as sensitive speakers. In the mega F5 builders tread it seems that they are getting close to making a X or balanced version. I am curious to compare F5 to Aleph J which I have slated to complete on my bench, together with F3.
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Old 25th November 2009, 04:12 AM   #6
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I'm very impressed with the F5. I've had a decent gainclone implementation, a pair of 500W icepowers, and the F5 in my system so far, and the F5 is by far and away the best.... despite the tranny hum. I need to put a DC blocker in my powersupply this weekend.

The dynamics are what really surprised me... its like someone doing very intricate chinese caligraphy and then the floor shakes. It goes beyond control.

On the scope we found that the "overshoot" occured at 1.04MHz on each channel, and I'm using the IRF parts. What are the corresponding Toshiba part numbers?

ps. need to thank Scott and Chuck, who've held my hand getting this thing built. It takes a lot more know-how than the audiosector, or even the miniA which somehow worked right away.
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Old 25th November 2009, 02:47 PM   #7
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I have sets of the 2SK1530 AND 2SJ201, and I expect that
they will work well, but I haven't gotten around to trying
them yet.

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Old 25th November 2009, 03:45 PM   #8
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Originally Posted by Nelson Pass View Post
I have sets ...
If I just put these in my digikey cart does that imply that I have some sort of disease?
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Old 25th November 2009, 04:57 PM   #9
Bigun is offline Bigun  Canada
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Quote:
Originally Posted by AR2 View Post
I completely agree that it is all about the bandwidth. It is hard to explain this, and it is against all the teachings that we canno't hear anything that is above 20KHz or at our ages pass 15 KHz. And yet, we hear the difference between wide bandwidth amp and the one that is not so wide.
I've heard this comment before and also wondered at the reason. The only reason I came up with relates to amps with negative feedback - where the supersonic bandwidth improves the phase accuracy of the feedback at the high end of the audible range.

Somebody knows the answer...?
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Last edited by Bigun; 25th November 2009 at 05:05 PM.
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Old 25th November 2009, 05:39 PM   #10
EUVL is offline EUVL  Europe
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You just need to play 10kHz sine wave, triangular wave and square wave, and hear the differences. Then you know why you want 300kHz+ power amps.

Nelson,

Please give the Toshiba's a try. I love them.


Patrick
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