VFET Absolute Audio Labs SIT-A15 power amp

[MattyW]

It's very much a warts and all system...... But the warts sound amazing too! 

 

Even the faults in a recording give greater insight into how it was recorded, produced etc. Even the most flawed recording is enjoyable. The system walks that fine line between incredible detail and transparency, and musicality. Everything is exposed yet it's enjoyable nonetheless. A bit mind blowing that there's still plenty of burn in to go and perhaps further improvement to be had via low mass binding posts and RCA sockets. Then there's the possibility of the Thor mains filter improving things still further 

Edited July 3, 2022 by MattyW

[MattyW]

It's funny, my icOn 4PRO preamp is away to have the gold plated brass RCA sockets changed for WBT-0310 Cu NextGen sockets. Yes, massive loss of sound stage, detail etc yet the SIT-A15 carries the system despite the handicap. It's still enjoyable and listenable with the cruddy passive pre I temporarily have in there. The musicality and solidity of sound ensures the amp can never actually sound bad unless there's a poor source up front. 

[MattyW]

Get my preamp back today. Can't wait to see what difference this has made. Then the weekend after next my amp will be away to have it's damaged side replaced. The last link in the chain will be changing the brass RCA sockets on my DAC for WBt-0210 Cu. Then I'm out of upgrades...... Maybe I can get a faux wood finish done on my speakers or something like that. Out of audible upgrades which can be done though.

Edited July 24, 2022 by MattyW

[MattyW]

Many thanks @muon* for changing the side panel on the amp for a new, undamaged panel and cleaning up my shoddy soldering on the RCA’s and binding posts and apologies for the near seizure moment exposure to my soldering brought about.

 

 

 

 

Looking as it should now:

 

 

Edited July 24, 2022 by MattyW

[muon*]

Where I indicated CCS is the regulator device for the constant current source I'm guessing, looks weird now looking at CCS there

[STlN]

How you liking it so far?

[MattyW]

Stunning yes. There’s no where for me to go from here

[Grizaudio]

The case you have there seems to be identical to the Firstwatt amps. Looks great.

I quickly went  through the thread pages.... How much did the amplifier end up costing all up, delivered?  

 

Do you get any small thumps when turning on or off? I didn't see any speaker relay delay circuits, same as FW. 

 

I wish I had of kept my F7 to driver my compression section. Something lovely about low gain class A. 

I personally wouldn't use a low power class A to driver large woofers, but for small drivers and compression = amazing match / very detailed/holographic, etc. 

 

 

Edited August 11, 2022 by Grizaudio

[muon*]

I had the opportunity to try it in my system here while I had it, It's a very impressive sounding amp, has a sense of a good valve amp but with a 'Ï gotcha by the...' sense of control, the bass I miss the most, it really took command when I decided to spin Led Zeppelin ll and does dynamics really well when called upon but was equally impressive with Suzanne Vega and Sarah Blasko, nicely defined separation of things too.

 

Edit: it had a very nice tonality also, and engaging.

The longer I'm around the more difficult is to articulate these descriptions of sound, at least for myself would be easier to state what the amp didn't do well, but I cant think of anything.

Impressive sounding amp all round.

Edited August 11, 2022 by muon*
Typos

[andyr]

On 11/08/2022 at 9:46 PM, Grizaudio said:

Something lovely about low gain class A. 

I personally wouldn't use a low power class A to driver large woofers, but for small drivers and compression = amazing match / very detailed/holographic, etc. 

 

Agreed, Griz!    As you say ... very detailed and holographic.

 

The combination of my 40w (AKSA-designed) Class A "Alpha Nirvana" amps and my 2-way active 'zero-baffle' spkrs - here:

 

 

 

... is a wonderful combination.  (They cross over to subs @ 110Hz.)

 

Andy

 

[MattyW]

@Grizaudio $3500 AUD landed. Pretty reasonable I think.
 

No thumps turning on or off either. Sound is there within a second of powering on but when powering off it fades away as tube amps tend to do. 

Edited August 21, 2022 by MattyW

[MattyW]

This past week I’ve literally had my mind blown with increased transparency, soundstage depth and tonal richness. I almost put it down to burn in but then it occurred to me that it’s been a few degrees warmer all week. I’ve even used my ceiling fan a bit.

 

I asked Watchara about it and it seems the explanation is in the amp design. It’s operating temperature determines bias point, which in turn determines its curve so yeah….. It sounds better when the temperature is warmer. Best from 26 to 30 degrees ambient room temps.

 

Very much like Digital Do Main apparently: https://6moons.com/audioreviews/roadtourdigitaldomain/visit.html

 

Any it’s nice to know it’s not all in my head. It actually is sounding better with warmer room temps.

Edited September 18, 2022 by MattyW

[Rottalpha]

On 27/04/2022 at 4:51 AM, Aspen said:

Matt,

Impressive, and your Thai guru knows his stuff and builds very nice gear.

I have been eyeing the Tokin devices for years, it seems the most linear of all the FETs, but unobtainium and VERY expensive.  I will await your thoughts on the sound......

Thanks for sharing this stuff.  It's cutting edge.

 

Hugh

hello Hugh,

why do you think the Tokin devices are most linear devices of all the FETs?

[Rottalpha]

On 18/09/2022 at 3:45 AM, MattyW said:

This past week I’ve literally had my mind blown with increased transparency, soundstage depth and tonal richness. I almost put it down to burn in but then it occurred to me that it’s been a few degrees warmer all week. I’ve even used my ceiling fan a bit.

 

I asked Watchara about it and it seems the explanation is in the amp design. It’s operating temperature determines bias point, which in turn determines its curve so yeah….. It sounds better when the temperature is warmer. Best from 26 to 30 degrees ambient room temps.

 

Very much like Digital Do Main apparently: https://6moons.com/audioreviews/roadtourdigitaldomain/visit.html

 

Any it’s nice to know it’s not all in my head. It actually is sounding better with warmer room temps.

So in colder weather you would need to pop the hood and adjust the bias to bring back the magic you experience in the summer?

It is interesting that the bias circuit does not have thermal compensation built in. You should be able to set the bias to what it best suits your listening experience, agnostic of ambient temperature (within the technical abilities of the amp).

Do you have a copy of the schematic he is using? It would be interesting to see if there is room for any improvement to the bias circuit. 

Edited November 4, 2022 by Rottalpha

[MattyW]

53 minutes ago, Rottalpha said:

So in colder weather you would need to pop the hood and adjust the bias to bring back the magic you experience in the summer?

It is interesting that the bias circuit does not have thermal compensation built in. You should be able to set the bias to what it best suits your listening experience, agnostic of ambient temperature (within the technical abilities of the amp).

Do you have a copy of the schematic he is using? It would be interesting to see if there is room for any improvement to the bias circuit. 

I think the answer is aircon.

[Hugh Dean]

Rottalpha,

I have read most of the stuff around the traps and did see a set of curves.

It seems very linear, more like a triode than a fet.

However, I will go looking for the datasheet - if it's around - and give you a more detailed response.

In closing that any single ended, low paper Class A is always very linear, and crossover of course is absent which prevents lots of high order harmonics.  I would think the most silicon state topology would be a bipolar in constant current driving a mosfet in CFP - that would be the most linear system of all and like you, I'm a bit concerned about the temperature dependent on the quiescent.  It should be rock solid and compensated;  however, Matt says this is a brilliant amp and I believe him.

 

Hugh

[Hugh Dean]

This gives you something to hang your hat!   Used as a source follower, this curve should give you an indication of how it behaves under use in Class A SE.  Ideally, as current increases, transconductance (volt change at gate for current flow at source) should be a straight line, and ideally (which never happens of course) it should be a horizontal load - gm constant for current from zero to 2.4A.

But a straight line at an angle will introduce only H2 in source follower.

This has a FET curve, a square law (parabola) curve.

You would set the device at about 1A (the 182 is 600V 2.5A 6.5ohm) which would put the gm at the start of the upper curve, around 1.8 Siemens.  But lower current would bring rapidly lower gm.

 

By comparisons with triodes, this is a very good curve.

 

HD

 

[MattyW]

Given how good this amp sounds, I see no need to change a thing. I’ve never experienced better. It’s a nice space heater in winter yet cooler running than tube for summer. No downsides really

 

My attention is now on selling off properties to get the perfect block of land in the right location….. Then a new home. I rather like the look of Metricons La Pyrenee. Get rid of the fireplace in the living area by the kitchen to ensure space for the stereo, and have wiring done for 5.1 audio in the downstairs sitting area. CAT8 cabling throughout and dedicated mains circuits for audio with a Thor DRM95/20. Nice floor layout that suits my wife and I and the aesthetic is gorgeous.

 

https://www.metricon.com.au/home-designs/queensland/la-pyrenee?fpv-fp-id=47817

Edited November 4, 2022 by MattyW

[Rottalpha]

15 hours ago, Aspen said:

This gives you something to hang your hat!   Used as a source follower, this curve should give you an indication of how it behaves under use in Class A SE.  Ideally, as current increases, transconductance (volt change at gate for current flow at source) should be a straight line, and ideally (which never happens of course) it should be a horizontal load - gm constant for current from zero to 2.4A.

But a straight line at an angle will introduce only H2 in source follower.

This has a FET curve, a square law (parabola) curve.

You would set the device at about 1A (the 182 is 600V 2.5A 6.5ohm) which would put the gm at the start of the upper curve, around 1.8 Siemens.  But lower current would bring rapidly lower gm.

 

By comparisons with triodes, this is a very good curve.

 

HD

 

Hi Hugh,

thanks for the data.

There is no doubt in my mind that the vfet is likely the most linear device / best device for audio. What I was actually asking for is why do you see Tokin as being the most linear devices and no the Yamaha or the Sony devices?

 

Pete

 

[Hugh Dean]

I'm sorry Pete,

I have never seen the Sony or Yamaha curves.  I'd have to go search for them........

I think the word 'linear' is problematic.  Do we mean voltage drive over current output, in which we are talking of transconductance?  In that situation you want a straight line, but you have to be careful to ensure that both axes are either linear or log.  The idea design would be constant transconductance over a limited working range, but nothing offers that performance.

I'll have a look.

Hugh

[MattyW]

Well I’ve nothing further to contribute to this thread so I guess anything further will be relating to the ASL-1Z preamp. It’s meant to be highly complementary to the SIT-A15 having been designed for it. Details over here.

 

I may have another thread regarding a Lii Song Platinum 10 PT-10 - (click here) based speaker though I think I’m nearing the end of my journey. Initial reports of those reviewing pre-production drivers indicate it’s up with the very best mega buck drivers on the market so I’m pretty keen on getting something based on them.

 

EDIT: Nix that..... Just gonna go with Klipsch Cornwall IV when the time comes. I've always wanted a pair of Cornwalls. Won't physically fit in my current listening space though.

Edited November 23, 2022 by MattyW

[MattyW]

Well, nix the Cornwall IV idea.... I've a pair of Lii Song Platinum-10 on pre-order. I snagged one of the first 3 pair produced. 

 

Nonetheless it will be years before I can have cabinets made and get use of them. They'll need cabinets made which make even Klipsch Cornwall look like small speakers. Those will not fit in my current home.

 

 

[ICUToo]

4 hours ago, MattyW said:

Well, nix the Cornwall IV idea.... I've a pair of Lii Song Platinum-10 on pre-order. I snagged one of the first 3 pair produced. 

 

Nonetheless it will be years before I can have cabinets made and get use of them. They'll need cabinets made which make even Klipsch Cornwall look like small speakers. Those will not fit in my current home.

 

 

Amazingly flat trace for FR, MattyW.

Where is the trace from ie manufacturer or someone who built up a working pair?

Is the subtext to your post that you are looking to sell them if you can't build a cabinet for years? 

Edited December 23, 2022 by ICUToo

[MattyW]

24 minutes ago, ICUToo said:

Amazingly flat trace for FR, MattyW.

Where is the trace from ie manufacturer or someone who built up a working pair?

Is the subtext to your post that you are looking to sell them if you can't build a cabinet for years? 

 

Haha, nice try..... You'll need to pry these out of my cold dead..... Ah, never mind I got a little carried away 

 

Lii Song get the trace done by an external lab as they lack the setup to do it themselves. I'll be retaining these drivers until such time as I've space for some big speakers then I'll get a local maker to design appropriate cabs to get the best from them. These should go extraordinarily deep for a fullrange in a humongous cabinet. There will never likely be that many of these made as the idea of Lii's Platinum range is to build the very best driver that they're capable off without paying attention how much they'll end up costing. To put it gently, these are not cheap and there are many very nice speakers can be purchased for the cost of the drivers alone. I do believe that these will produce the best sound I've ever experienced. My end game speaker, which is good as I suspect once in place I'll struggle to ever physically move them. I'll get the cabs built from hardwood 

 

I figured it makes sense to do this as the rest of my system is already at that end game level (for me) although the icOn 4PRO passive pre might be displaced by an Absolute Audio Labs ASL-1Z depending on which sound better to my ears. Either way I think I'll need to retain both pre's to try with this speakers when the time comes. See which sounds more spookily real to my ears 

 

That said the track is -120 to 120db..... Sort of artificially flattens the curve. Would be better if they showed 0 to 120db I think.

Edited December 23, 2022 by MattyW

[MattyW]

Interesting, Nelson Pass new SIT-4 will be using Tokin VFET’s just like my SIT-A15