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
 
The one and only
Joined 2001
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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.

:cool:
 
Hi Nelson! :D

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... :D:D

_-_-


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...
 
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.
:cool:

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.
:spin:
 
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.
 
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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Not sure about the Tosh's but the Hitachi N & P ch are not exact matches when you look at the complement's curves(!). So, to some extent the feetback is going to be responsible for "correcting" the curves in practice...

I've listened to slow, fastish and Mhz bandwidth amps and I can not draw any correlation to listening fatigue or pleasure on that basis alone. Others may have had different experiences.

So, wondering if the Tosh's are better compliments or??

_-_-bear
 
> So, wondering if the Tosh's are better compliments or??

I have already published curves of the TOS MOSFETs at the F5 thread ages ago. They are perfect. The JFETs are not, so you need to fiddle a bit to get open loop gain to match by mismatching degen resistors, etc..

(The grey coloured crosses belongs to the 2SK1530, the red line 2SJ201. If I use red & blue lines, you cannot tell them apart.)


Patrick
 

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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.

Well, this is to be expected if you feed high bandwidth signals into an amp. I could as simply say, try a 100kHz square wave on a 300kHz+ power amp and you will need a MHz-amp for your pleasure.

In music, frequency content above 1 kHz goes down at 6dB per octave, so at least technically no need for such radio receivers.

Your mileage may vary though.

Have fun, Hannes

PS: the 10kHz sine wave should be ok on any amp with a frequency response of above 10kHz.
 
The technical relationships regarding bandwidth and N & Pch curves are of course interesting. But what I am interested in is more what the listening experience becomes when a comparison is made between them/it!

Obviously something needs to be said to provide context to those comments since a "dark" sounding amp connected to a "bright" speaker will "sound better" than a truly "neutral" amp connected to the same speaker, etc... But I am still interested in hearing what others have heard from this F5 amplifier.

One of the interesting aspects is that since there are so few parts involved one might expect that it could be possible to correlate some sort of actual empirical measurement back to the resulting sound - whereas with a complex "modern" amplifier design the number of variables is extremely high.

So for now I am curious if others (especially those with other high performance amps and supporting gear) are hearing the same thing or something different than i do here.

_-_-

PS. An interesting note which speaks to the subjectivity and sensitivity of all of this stuff to the specific and particular system & implementation is that in the main F5 thread a poster said that his implementation of Borbely's DC100 amplifier was "darker" than his F5. My own experience with the DC100 is the opposite, the F5 seemed to have less sibilance than the DC100 - which BTW is a rather nice , clean, and somewhat warmish sounding design (properly implemented).
 
it's the hook-up wire :D. seriously, i hope to have a functional F5 planked out on plywood within the next week to compare with my Krell.

You'll sell the Krell. If you do the implementation well.

(not so simple)

But there is a huge diff in the power available so that may prove to be a real issue for you.

But maybe ur joking about the Krell?

And, yes the wire made a difference - he started out with some rather thin stuff for things that carry some current...

_-_-bear
 
i'm using Peter Daniel's boards with Toshiba JFETs and IRF MOSFETs. i have a 500 VA SumR TX with standard recovery rectifier bridges - i'll have plenty of room to try some boutique diodes down the road. my PS will have 132,00uF of caps - i'm building it P2P with turrets and G-10 fiberglass. the PS will be in a "proper" chassis with 2 towers of heatsinks mounted on top, housing/sandwiching the amp PCBs. Cardas wire, jacks, and binding posts. i've spent nearly a month just drawing and planning the chassis and layout.

the Krell is an integrated KAV-400xi 200W/8ohms, driving a piggish load ATC SCM12 83-85dB. my room is only 10x13'. i'm not sure that the F5 will be up to the task, but after living with a friend's uFonkens with Fostex FF85K for a week, i don't care if the ATCs go. i have an extra set set of drivers and CNCed BB for a pair of uFonkens to build for myself with intent on pairing them with a small sub. these little suckers are sublime, especially in my small room.


You'll sell the Krell. If you do the implementation well.

(not so simple)

But there is a huge diff in the power available so that may prove to be a real issue for you.

But maybe ur joking about the Krell?

And, yes the wire made a difference - he started out with some rather thin stuff for things that carry some current...

_-_-bear