User reviews of our new Fet Valve 600R & 400R amplifiers

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tonyptony

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #40 on: 23 Dec 2011, 02:12 am »
Over the years, as we have significantly improved the high frequency linearity of our amplifiers, their dislike has significantly reduced.  Now the Salks are appreciated by all here.  We still get the high frequency detail, air, and transparency as before, but the last trace of grain and brightness has been removed.

Frank, what engineering parameters are factors in the reduction of grain and brightness? How is "brightness" differentiated from high frequency extension? Fellow engineers would appreciate the elaboration.

I.Greyhound Fan

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #41 on: 23 Dec 2011, 04:22 am »
Clearly the sound of the amp is system dependent.  I did an intial review of the 600R when Frank loaned me the amp. I paired it with a modded Ultra preamp and modded Ultra DAC along with my Magnepan 1.6's.  The amp had tremendous air and transparency with the best treble and high frequency resolution and detail that I have heard.  However, the sound leaned slightly on the bright side until I rolled some warmer sounding tubes in my preamp and DAC.  In Franks studio with the HTR3's I did not notice any brightness.  I found the speed and attack of this amp to be phenomenal.  If any if you guys want to sell your 400 or 600R give me a PM.  I would be more than happy to take it off your hands :D

avahifi

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #42 on: 23 Dec 2011, 05:45 pm »
Tony asks what engineering parameters are factors in the reduction of grain and brightness?

Good question, there is no simply answer we are aware of other than doing our best to design circuits that improve linearity, even if we cannot measure the changes with our test equipment.

In our big hybrid power amplifiers, I can kind of give you a time line of the things that have been improved over the years.  Each made easily audible improvements in musicality and reduction of grain and listening fatigue, but almost none can be observed with our test equipment.

Probably the first important improvement was going from the original Hitachi power mos-fet output devices to Exicon devices.  This change was forced upon us as the Hitachi devices went out of production.  The only circuit changes necessary were an increase in the value of the gate resistors from 100 ohm to 220 ohm to insure high frequency stability.  The musical differences were obvious, not only in our hybrid amplifiers, but in our solid state amplifiers too.  The most notable audible effect was a sense of "sparkle" and life to the high end previously missing.  That and a feeling of overall clarity too, with no negative effects at all.  The necessary changes in gate resistor values told us the Exicons were faster devices, but nothing at all different about them we could see up to the three meg limit of my generator and scope.

Another fairly early change was done to eliminate a hump in the ultrasonic frequency response around 200K Hz.  Way up there beyond the hearing of bats, the square waves were not perfect.  We finally traced the issue down to the outputs being slightly loaded by the protect zeners installed to make sure that the allowable gate voltages were never exceeded.  Changing one set of 1000 ohm resistors to 100 ohms fixed this issue.  It also made another useful reduction in grain and brightness in the hybrid amplifiers, of course with no measurable effect other than that now ultrasonic square wave performance was perfect.

Much later, Dean Kayser, our resident EE expert, suggested that the same active regulated power supplies that we had installed in the hybrid and tube preamplifiers would also be useful in the hybrid amplifiers.  This required a new multi-stage power supply board, with active regulators for the tube and for the mos-fet in the small signal transimpedance loop.  We did regulated power supplies for each tube heater at the same time.  This provided a major improvement in overall clarity and musical involvement. Again, we could hear it and knew that it was better engineering, but could not measure it within the capabilities of our test equipment.

That next step was finding a replacement for the Hitachi J79 mos-fet being used in the audio circuits.  This was a tough one because there seemed to be no suitable replacements out there.  We finally decided to give the Exicon 10P20 plastic case mos-fet a try as it had the voltage and current requirements, but somewhat higher gate capacitance.  In spite of this, it made a major improvement musically.  Evidently the Hitachi had some unpublished characteristics that was limiting its value in a music amplification application, again something we cannot verify on the test bench but certainly can hear.

More recently, we had the entire audio circuit reanalyzed by an outside EE and he came up with only one useful new suggestion, that the capacitor across the bias pot was limiting internal bandwidth, the effect being masked by the feedback.  That part went from one micro-farad to 10,000 micro-farads, with another improvement in overall musicality and purity.

Finally, in the release before the current new production Fet Valve 400R and 600R amplifiers, we redesigned the audio boards to allow one more active regulated power supply per channel, so that the tubes no longer had to share one supply per channel, now each tube plate and the accompanying mos-fet each had their own independent active regulated power supply.  Again an engineering improvement we knew would be worthwhile, but as usual, not one we can measure, except with our ears.

The final breakthrough has been providing active regulated power supplies for the output transistors themselves.  This is a tough one, as since all the current supplied to the loudspeakers has to first pass through the power supplies, each active regulated power supply must have at least the same current and thermal capacity as the output mos-fets do themselves.  We were able to meet this goal with a clever use of the new Exicon double die mos-fets.  Two in parallel per channel with a zener reference, provides the amazingly stable active regulated power supply we were looking for.  An added benefit is that the amp runs cooler as the output devices no longer see the whole hear 200V raw power supply rails, just the appropriate lower regulated rails.  The regulator devices run very safely too.  At idle, they see high voltage but no current draw.  At clipping, they must provide very high current, but as the raw supply pulls down from demand, the voltage across the regulators substantially decrease, keeping them always in a secure safe operating area.

As usual, nothing new to see on the test bench.  The bandwidth (3 dB down at 350KHz and 4Hz) remains the same and square wave performance is still perfect and the slew factor remains infinite. However, as all of you have reported, the overall musically of the new Fet Valve 400R and 600R is quite amazing.

So, what engineering affects grain and brightness?  All of the above.  Just lots over very hard work applying improvements that we know are good engineering efforts even though the test bench does not give us much help.  I think the Fet Valve amplifiers are a done deal now, unless, of course, the future reveals new concepts to try.  Right now I am just enjoying the music.

Best regards,  and Merry Christmas,

tonyptony

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #43 on: 23 Dec 2011, 06:50 pm »
So, what engineering affects grain and brightness?  All of the above.  Just lots over very hard work applying improvements that we know are good engineering efforts even though the test bench does not give us much help.  I think the Fet Valve amplifiers are a done deal now, unless, of course, the future reveals new concepts to try.  Right now I am just enjoying the music.

Best regards,  and Merry Christmas,

Frank, I can't tell you what a big smile is on my face after reading your comprehensive and willingly offered summary of design improvements for the FetValve. It makes my engineer's heart proud to hear how you worked through to the result we have now - even if some of it can't be measured! :beer:

Merry Christmas to you and the whole AVA family. :xmas:

dlparker

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #44 on: 23 Dec 2011, 07:09 pm »
Quote

from: avahifi on Today at 05:45 PM

     So, what engineering affects grain and brightness?  All of the above.  Just lots over very hard work    applying improvements that we know are good engineering efforts even though the test bench does not    give us much help.  I think the Fet Valve amplifiers are a done deal now, unless, of course, the future reveals new concepts to try.  Right now I am just enjoying the music.

    Best regards,  and Merry Christmas,

Frank, I can't tell you what a big smile is on my face after reading your comprehensive and willingly offered summary of design improvements for the FetValve. It makes my engineer's heart proud to hear how you worked through to the result we have now - even if some of it can't be measured! :beer:

Merry Christmas to you and the whole AVA family. :xmas:

See what I mean?  This is more evidence in support of my theory that Frank is in fact the real, genuine, dyed-in-the-wool Santa Claus!

AVnerdguy

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #45 on: 23 Dec 2011, 07:45 pm »
  An added benefit is that the amp runs cooler as the output devices no longer see the whole hear 200V raw power supply rails, just the appropriate lower regulated rails. 

So I wasn't imaging things! I thought the amp ran cooler than the previous version. Good to know.

Great amp with outstanding performance. I hate to say it but this will be the last thing I buy from AVA - it's so good I have no reason to and I'll be using this one for many years to come. Well, maybe many years down the road I'll replace the AvaStar with the new Fet Valve that is....... :D


rlee8394

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #46 on: 23 Dec 2011, 07:46 pm »
Frank,

That is a great explanation on the circuit enhancements for the amps. Many of us engineers and technical folk appreciate that kind of circuit description over the usual marketing speak. That's the kind of information that makes your equipment even more valuable in my estimation. I miss that kind of detail that I used to get from your Audio Basics newsletter. Wish you had more time to elaborate on all of your designs in that matter. As tonyptony said, we do appreciate the elaboration.

Congrats to you and your team for continually designing exceptional equipment. Looking forward to new AVA products in 2012.

Ron

mark funk

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #47 on: 23 Dec 2011, 08:07 pm »
Oh, I miss Audio Basics. This sounded just like it! Wish we had more. Keep it coming Frank. :thumb:



                                                                                         :smoke:

plaf26

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #48 on: 23 Dec 2011, 08:20 pm »
Quote
now ultrasonic square wave performance was perfect.

Aha, thought so!  Been wondering what that square wave response is like.  Bravo!  I'm one very happy 400R owner! :singing:

Merry Christmas, everybody!

trebejo

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #49 on: 23 Dec 2011, 09:26 pm »
In our big hybrid power amplifiers, I can kind of give you a time line of the things that have been improved over the years.

...

Best regards,  and Merry Christmas,

This is a lovely present to us and to the whole audio community. Thanks Frank and team AVA!  :thumb: :thumb: :thumb:

modular747

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #50 on: 24 Dec 2011, 05:10 am »
Frank, thanks for the excellent discussion of your circuit developments.  It also provided clear insight into how you and your team go about the quest for improvement. 

It's not surprising that standard measurements fail to show the sonic improvement (or just change for that matter), with the circuit changes mainly involving power supply and component updates.  I'm wondering if the new Fet-Valve preamp and DAC, which have a completely new voltage gain stage topology (as well as no global feedback), show any measurable changes?

Merry Christmas!

festuss

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #51 on: 24 Dec 2011, 01:46 pm »
What, no magic internal hookup wires?  From Shabango Shuntatatatatata, with anti electron strand hoping twists?  You mean it's all about electrical design and components!  Oy Vey, reality, what a concept!  AVA sonic bliss and perfection, still.

pelliott321

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #52 on: 24 Dec 2011, 02:17 pm »
I see I generated a lively debate
Ok after 100hrs I can report I am about 80% there.  The raindrops are now clearly audible with the 400R but at a slightly reduced volume over what I am use to. 
I know Frank said burn in would not make a difference, but it did.  I even burn in used equipment before I listen, you just do not know how long the caps have been idle.
I think I can beef up the ribbon a bit at the xover. 

pelliott321

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #53 on: 24 Dec 2011, 02:29 pm »
I do need the input impedance of the 400R Please

festuss

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #54 on: 24 Dec 2011, 02:34 pm »
 :scratch: Only 80% ? Are you saying if my AVA stuff is off for a week, I need to play it 100 hours before I listen to it?   :scratch: :scratch: :scratch: :scratch: :scratch:

avahifi

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #55 on: 24 Dec 2011, 05:01 pm »
Festuss please!  This thread is for users to report on what they hear, not for arguing about what they hear.

If pelliot says the treble improved to his hearing after a 100 hour burn in, that is what he hears.  There is absolutely no point to debating about what he says he hears.

I want a kind and interesting discource here, free of flames and fireworks.  It is altogether possible for extended run time to improve vacuum tube based equipment such as the Fet Valve 400R and 600R amps.  The small signal tubes do indeed need run time to settle down.  What an owner hears as this happens is what he hears.  When it comes to tube equipment the user may very well hear the equipment evolve into even better than out of the box musicality.

Best regards, and a wonderul Christmas and great New Year to all.

Frank Van Alstine

P.S.  The input impedance is 1 meg ohm, its a triode imput.

trebejo

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #56 on: 26 Dec 2011, 08:35 am »
Oh yeah, tubes do take a bit of time to settle down. So, apparently, do the rest of us.  :wink:

Ok time for my daily "effing AVA" moment. The Dhol Foundation's debut album has some percussion work that is meaty beaty big and bouncy. It has never failed to sound anything less than excellent to me. They can put on a bit of a show live, apparently, e.g.

http://www.youtube.com/watch?v=uNDPRHH5BUc

But now, with the 600R...

:o 8) :lol: :icon_lol: :thumb: :angel: :rotflmao: :inlove: :dunno: :eyebrows: :drool: :singing: :xmas: :hyper: :dance: :bounce: :rock: :kiss: :birthday: :wtf: :deadhorse:

 :bowdown: :notworthy: :bowdown: :notworthy: :bowdown: :notworthy:

avahifi

Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #57 on: 26 Dec 2011, 03:27 pm »
Are yuu saying that you really like your Fet Valve 600R amp?

Frank

Ray Bronk

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #58 on: 1 Jan 2012, 07:57 am »
Are yuu saying that you really like your Fet Valve 600R amp?

Frank

Hi Frank,

I'm wondering if this is also a matter of toning down harmonic frequencies that would have ordinarily cause the perception of brightness? When Hugh Dean and his amps were on the circle, that was one thing he strived to deal with. And you know, his newer amps are right up there in sound quality with the best of them. Not to detract from this thread, I was just also thinking about the fact that even though we humans can't hear above 15K or 20K if we're lucky, the harmonics associated with the wide band amps do make a difference. So have you ever plotted the harmonic freqs? This stuff will be even more true as the devices get faster.

Ray Bronk

Ray Bronk

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Re: User reviews of our new Fet Valve 600R & 400R amplifiers
« Reply #59 on: 1 Jan 2012, 08:03 am »
Are yuu saying that you really like your Fet Valve 600R amp?

Frank
Almost forgot, now, is there anything more you can do to improve your SolidState stuff? I know this is not on topic, but i didn't see anywhere else to ask this?

Ray Bronk