Champions of Class "A"

[Mike]

Who are the champions of Class A solid state?

Accuphase
Pass
Vitus
.....who else?


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[mep]

I think the original Krell company deserves some credit. Back when David Manley was still running VTL, they actually had a pure Class A amp. You rarely ever see that amp come up for sale on the used market which tells you something.

[Mike]

Mark - I believe Brett D'Agostino is building class A amps too.

Luxman is another.

Still racking my brain...


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[mep]

We should get Bret over here. Bret is a good guy. He's the one that told me to buy the KRC-HR preamp which I appreciated.

[Mike]

We should get Bret over here. Bret is a good guy. He's the one that told me to buy the KRC-HR preamp which I appreciated.

Bret is here lurking somewhere.


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[Myles B. Astor]

We should get Bret over here. Bret is a good guy. He's the one that told me to buy the KRC-HR preamp which I appreciated.

+1

[annapolis Raider]

Boulder, Viola, Gryphon....

[blackdog]

Pathos, Grandinote out of Italy
The Grandinote are particularly nice

[the professor]

My vote is for Accuphase. I do think Krell deserves an honorable mention for their older stuff tho.

[rockitman]

Add the old classic Madrigal Labs (Mark Levinson) No. 20.6 monos. pure early 90's class A sex.

[Mark Jones]

The original Classe amps and Bedini. Maybe not the champions but worthy of mention.

[puroagave]

using the wayback machine...Levinson ML-2, Classe DR-2/DR-3, Pioneer M22, Threshold stasis 2, all the early fan-cooled krells (KSA-50 & 100, KMA-100 & 200) and the mack daddy KRS series (any of them).

[Mark Jones]

I loved the KSA-50

[JBLfan]

Given his history with Threshold & now Pass Labs - Nelson Pass get's my vote. Even offers a Class "A" integrated

[Mark Jones]

Agreed, Nelson is the champ.

[cmalak]

Class A SS:

Pass Labs
Accuphase
Gryphon
Lamm (M1.2...100wpc Class A with tube input driver)
Luxman
Monarchy Audio
Musical Fidelity
Plinius
Krell (old school)
Boulder
Threshhold (precursor to Pass)
Halcro

[Albert]

I have a Bedini 100/100 1 meg amp and a 25/25 1 meg amp. They have the most natural sounding midrange of all my amps and the 100/100 1 meg has very good bass with my Acoustat 2+2. It does consume a lot of power and gets quite hot. When first turned on, it would make the lights in the house flicker. She's a lovely beast.;)

My Threshold 400a is a nice amp as well. Does sliding bias class A count?

[MrAcoustat]

Class A SS:

Class A SS:

Pass Labs
Accuphase
Gryphon
Lamm (M1.2...100wpc Class A with tube input driver)
Luxman
Monarchy Audio
Musical Fidelity
Plinius
Krell (old school)
Boulder
Threshhold (precursor to Pass)
Halcro

Yes sir Krell KRS-100 ( old scholl ) the good old days.:)

7376 7377 7378 7379

[CharlesL]

Tube amps:
Jadis (JA-200)
CJ (Premier 8 XS)
7380

[wizard]

AM Audio
Venture
Audio Power Labs
David Berning

[sharkmouth]

Class A SS:

Class A SS:

Pass Labs
Accuphase
Gryphon
Lamm (M1.2...100wpc Class A with tube input driver)
Luxman
Monarchy Audio
Musical Fidelity
Plinius
Krell (old school)
Boulder
Threshhold (precursor to Pass)
Halcro


Cyril, I was wondering when someone would mention Plinius, they were a hell of an amp in the early days, still are for that matter.

[Bruce]

Yes Indeed any best of --

you cannot leave out the venerable Electro Research A75 Amp

I had two of them BiAmped into Snell AIII's--boy could they Boogie OOOOOh yeah!!

Bruce




7381

[CharlesL]

Class A amps can further be categorized as fixed bias (or pure class A) and adaptive bias. Boulder is adaptive bias. So were the Krell FPB and KAS series.

[BretDago]

A little bird told me there was a thread about Class A, which of course is so near and dear to my heart. How are the folks on the Shark today? My 2 cents is that: 1. This would have to be focused on solid state amps as correct me if I am wrong but most tube amps are closer to Class A by design than not? I have very little experience with tube circuits so forgive my ignorance. 2. Adaptive bias is not really Class A as there is a frequent transition state for the devices, and in my experience this negatively affects the sound. To that end the products that use/used adaptive bias may actually sound better if that circuit were eliminated. Even dear old dads monsters from the past using adaptive bias would have been better without it. He and I have discussed this many times... But from a marketing standpoint it sounds much better to have Class A in the description and save a huge amount of space using smaller heat sinks. So that being said, we can eliminate many from the list and add BSC because even though my company is only 4 years old I have had only Class A amps from the start and don't plan on going anywhere for the next 15-20 years or so. :) I still contend the biggest and baddest of all the Class A amps is the KRELL KRS-200. I don't think anyone has come close to surpassing this Fixed Class A monster. I do have plans for a 7 series amp that in concept will better the KRS-200, but it is time, budget, and market dependent. I also agree Nelson Pass designs to be #1 as he was one of the first and continues to deliver fine Class A products, but Krell shouldn't be #9 as the first 15 years of its existence were based on Class A designs. Definitely Gryphon and Accuphase are greats on this list, the 1st Levinson 25 watt class A ML2 should be an honorable mention, good amp!. Also some Class A efforts from Bedini and Belles which I believe had good sounding Class A SS amps.

[cmalak]

Hi Brett...I shouldn't have put numbers to suggest an order. I was simply enumerating and in no way suggesting that this was in descending order of any kind. That would be simply silly as there is no way to make an objective comparison of similar amp designs to begin with and even if there was it would only be one person's opinion in their particular test system. So again no order being suggested. I will go ahead and edit my post and take out the #s.

[BretDago]

Hi Brett...I shouldn't have put numbers to suggest an order. I was simply enumerating and in no way suggesting that this was in descending order of any kind. That would be simply silly as there is no way to make an objective comparison of similar amp designs to begin with and even if there was it would only be one person's opinion in their particular test system. So again no order being suggested. I will go ahead and edit my post and take out the #s.

+1

[Albert]

Thanks Brett for the insights on class A amps. In my limited experience I find the class A ss amps to sound faster than the sliding bias class A amps. I suppose having the transistors always on at full power might have something to do with this.

[Mike]

Hi Bret - tweet tweet.....good to see you back.

[joeinid]

Brett,

Looking forward to your S5 amp. One of my dealers is eager to get his for demo.

BSC (http://bscaudio.com/5series.html#S5)

http://bscaudio.com/images/DSC02378r.jpg

[BretDago]

Hi Bret - tweet tweet.....good to see you back.
Good to be back, just finished the last go around with the L5 Preamp and anxious to get these to my dealers in the next few weeks, details forthcoming. Now I can take a deep breath before I jump into the I3 and I5 integrated amps.

[BretDago]

[QUOTE=joeinid;90425]Brett,

Looking forward to your S5 amp. One of my dealers is eager to get his for demo.

Thanks for the kind words Joe, what dealer are you working with?

[joeinid]

Jaguar Audio in WA. Darin is a great guy.

[Kt77]

If we aren't referring to high dollar items?, I'd have to give a shout out to Sudgen in the UK, whom I think were one of the first companies to use class a in their designs during the 60s/70s:

J. E. Sugden Class A amplifiers - The 1960s and 1970s (http://www.audiomisc.co.uk/JES/)

Another nice sounding brand was Forte from the 80s, which was an outshoot of Threshold as I recall. I'm sorry to come across as a troubler, if I do?, it's on,y because I see/hear things/components at both ends of the cost range, as a means to assist friends along the ways, as I once worked as a buyer for a few audio shops here in Michigan, back in the day, I've always felt it important to know which stuff was musical regardless of cost!, we of course had ones with deeper pockets and serviced their needs, but we never forgot about the average joe sorts either, it's more universal then merely catering to the wealthy, and overlooking the needs of the few.


I'm used to associating with the rich, as well as the not so well off, but in the end, to me it has always been about finding something to fit a friends requirement regardless of which!, I've heard the extreme, but in the same listening sessions, have heard cheaper items that can hold their own as well, I'm not here to challenge anyone, yet I do think about the small guys as well.

[BretDago]

Jaguar Audio in WA. Darin is a great guy.Darin is a cool guy and his unit ships this week...

[Albert]

The Forte model 4a is said to be a very good amplifier at 50w/ch class A. I have a Forte model 5 (along with a model 2 preamp) which is class AB 200W/ch. A good amp but I don't think as good as the model 4a.

[KeithR]

Class A amps can further be categorized as fixed bias (or pure class A) and adaptive bias. Boulder is adaptive bias. So were the Krell FPB and KAS series.

Bingo- a lot of "class a" amps on this thread really aren't.

[KeithR]

The Valvet A3.5 monoblocks are very nice 50w Class A amplifiers using a single pair of transistors and with no negative feedback- $6k list, so a bargain.

[psjl]

.....2. Adaptive bias is not really Class A as there is a frequent transition state for the devices, and in my experience this negatively affects the sound......


Bingo- a lot of "class a" amps on this thread really aren't.

Hi All,

I thought I would chime in here.

I am glad that this topic regarding class A amps has been brought up, because I have often wondered why there seems to be a disconnect between fixed class A bias and variable class A bias. Companies like Gryphon, Plinius and BSC Audio, that produce fixed class A bias amps have a manual user selectable switch that allows you to go into high/low bias class A/B and, unlike variable class A bias amps, is a separate control that when bypassed does not effect the amp's full class A rating. With variable class A bias amps that claim class A, it is hard to tell how much class A bias (if any) is implemented and whether it is even truly near its rated power.

In response to Bret D'Agostino's earlier post, I agree that there seems to be an effect on the sonic performance of variable class A bias amps because of the transitioning bias which inevitably points to the transistors turning on and off frequently and therefore the transistors are not being allowed to "settle" into a steady state. In addition, when I look at fixed class A bias amps like Gryphon, Pass Labs, old Krell, BSC Audio, etc., they obviously have very large heatsinks which seems to me to be a basic requirement in an air-cooled design. I have to question the heatsink size on variable class A bias amps as to whether they have very much class A at all, compared to that of fixed class A bias amps. Of course I am not an engineer or technically inclined, so I hope that Bret will chime in about what I have said, just in case I am speaking out of turn.

[joeinid]

Welcome to the forum Philip!

Thank you for joining.

[Mike]

Welcome Philip!


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[psjl]

Welcome to the forum Philip!

Thank you for joining.

Thanks Joe! :hey:

Hadn't seen you around AA.org for quite a while, but really glad to see you over here in AudioShark.org!

[psjl]

Welcome Philip!


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Thanks Mike! :hey:

Great forum you have here! :coolyeah:

[psjl]

Brett,
Looking forward to your S5 amp. One of my dealers is eager to get his for demo.


I have also been closely following Bret D'Agostino's development of his 5 Series amps/preamp for quite sometime now, and it really is quite exciting stuff!

After CES 2014 in January, I visited BSC Audio in Milford, Connecticut. Bret was very kind to invite me to listen to his 5 Series M5 class A monoblock amps in his personal home setup. The amps were driving a pair of Wilson Audio Sasha W/P speakers (Series-1) and hooked up directly to a Bricasti M1 DAC with Transparent Audio Reference MM2 cabling throughout. Without going into a whole bunch of descriptives, I can say that I was pretty stunned with the sonic performance, and this is coming from an owner of his Dad's Momentum monoblock amps. The rest of my system consists of Wilson Audio Sasha W/P speakers (Series-1), Ayre KX-R preamp, Playback Designs MPS-5 player, and Transparent Audio Reference cabling throughout.

I also had listened extensively to his Classic Series BSC-100m class A monoblock amps when they first came out and was extremely impressed with their sonic performance. They were really fast/dynamic amps which is exceptional for class A amps. Expansive 3D soundstage, highly musical yet transparent, and in particular, very full-bodied/soulful. At USD 14,750 per pair it was a (relative) steal. Had I not already bought his Dad's Momentum monoblock amps, I would have given Bret's gear serious consideration and saved a bundle of cash as well.

But his 5 Series monoblock amps are something else altogether.......They were like his Classic Series BSC-100m class A monoblock amps on steroids, and then some! I do love my D.D. Momentum monoblock amps, but Bret's amps were sonically so very tube like, and yet had tremendous speed, super rich timbre/tone, great layering of instrumentation, ultra-wide soundstaging, as well as having the good ol' Krell "slam" in spades, the difference being that it was very well proportioned top-to-bottom with great musicality. In addition, there was also a startling sense of palpability and realism to percussive instruments. The "twang" of the guitar intro. on Gotye's "Somebody That I Used To Know" gave me serious goose bumps and has stuck in my audio memory to this day. I hate to say this, but when I listen to this same track on my D.D. Momentum monoblock amps back home, I unfortunately don't get the same type of goose bumps.

Bret's new 5 Series amp design aesthetics are inspired by performance cars, as can be seen by his 2-tier top panel with the grills dominating the top panel. In fact, Bret has actually enlarged the grills in order to add more of the muscle performance car look & feel, as well as increasing the more rapid & efficient flow of heat up and away from the amp chassis - and it does look a lot more "meaner" (in a very good way). In addition, the front panel is sculpted to reflect the strong curves and elevation changes much like a performance car, and the 2 bulges on the front panel flanking his center column (housing the power button & bias control) convey a sense of serious power from within, very much like the bulge that one sees protruding up from the bonnet of a muscle car.

Bret's 5 Series M5 monoblocks and S5 stereo amps are full class A amps which will double all the way down to 1 ohm (with room to spare), and I believe they are rated around 150 watts & 75 watts respectively. Class A bias can be reduced from 100% down to 50% or down to almost 0% which is in effect a low power Eco mode via the triangular knob on the front panel. Also, the S/N ratio is around 110dB (unweighted) which is equal to or better than his Dad's Momentum monoblocks amps, thus making for a very low noise floor. I also really like the fact that his heat-sinks are all internal, and that his output devices are nestled right in-between his massive heat-sinks thereby creating a "chimney effect" for the heat to shoot straight up instead of radiating heat laterally when the heat-sinks are bolted externally to the sides of an amp which will likely heat up a listening room considerably.

I was about to pull the trigger on his Dad's Momentum preamp, but have now decided to wait to audition Bret's L5 preamp with 3-Band Tone Controls WHICH can be controlled remotely (whereas his father's tone controls cannot be controlled remotely), plus I believe that Bret's preamp will be about HALF the price of his father's Momentum preamp (USD 32,000). If Bret's preamp matches up nicely with his Dad's Momentum monoblock amps (which I currently have), then I'ed just have saved a ton of cash!!

[joeinid]

Great info on Bret's creations. It all sounds very exciting and I can't wait to get my dealers report. I love the tiered bias scheme. It is often I listen to music in the background and having the ability to tailor power consumption to listening mode seems extremely smart.

This is my new home now, lots of great members here.

[psjl]

Great info on Bret's creations. It all sounds very exciting and I can't wait to get my dealers report. I love the tiered bias scheme. It is often I listen to music in the background and having the ability to tailor power consumption to listening mode seems extremely smart.

This is my new home now, lots of great members here.

Joe,

I have been lurking around this forum for quite sometime now, and have to agree that this is indeed a great forum with great members!

Glad to see that you are a Super Moderator in this forum.

Thanks for having me in this forum!

[joeinid]

The pleasure is ours. Thank you for the kind words.


Joe,

I have been lurking around this forum for quite sometime now, and have to agree that this is indeed a great forum with great members!

Glad to see that you are a Super Moderator in this forum.

Thanks for having me in this forum!

[Mike]

Has anyone heard the new Krell Solo 375/575 amps?

http://www.krellonline.com/images/Solo375_lg.jpg

http://www.krellonline.com/images/Mono_Back_lg.jpg

[joeinid]

If that thing needs 4 fans, it must get pretty hot :(

[CPP]

Has anyone heard the new Krell Solo 375/575 amps?

No, but I wonder what is this iBias.

The Krell site notes:

How iBias Works
Class A amplifiers eliminate crossover distortion (the distortion that occurs when the audio signal shifts from positive to negative polarity) by operating the output transistors at full power all the time so they never shut off. Any energy not required to drive the speaker is dissipated through the amplifier's heat sinks.
In an iBias amplifier, a circuit continuously measures current flow through the amplifier's output transistors, and instantly adjusts the power (or bias) going to the transistors to suit the demands. The output transistors never shut off, yet very little power is wasted as heat. Not only does the amplifier consume less power, it runs cooler and can be built into a more compact chassis.
"The iBias amplifier is like a high-efficiency 12-cylinder automotive engine in which some of the cylinders shut down when you don't need all that power," McKiegan explained. "Just as that engine can run efficiently yet deliver 600 horsepower in an instant, the iBias amplifier can run efficiently yet in a matter or microseconds gives you hundreds of watts of full Class A bias for musical peaks."

Thats interesting, so I guess the amp will only put out what it needs to drive the speakers

[audio.bill]

Yet another name for what has previously been called adaptive bias, sliding bias, dynamic bias, etc. The difference with this implementation as I understand it is that it adjusts the bias by monitoring the current through the output transistors themselves and adjusts the bias as needed to maintain Class A operation. Most previous implementations would monitor the incoming signal and modulate the output device bias accordingly based upon predicted output power demand.

[Myles B. Astor]

I have also been closely following Bret D'Agostino's development of his 5 Series amps/preamp for quite sometime now, and it really is quite exciting stuff!

After CES 2014 in January, I visited BSC Audio in Milford, Connecticut. Bret was very kind to invite me to listen to his 5 Series M5 class A monoblock amps in his personal home setup. The amps were driving a pair of Wilson Audio Sasha W/P speakers (Series-1) and hooked up directly to a Bricasti M1 DAC with Transparent Audio Reference MM2 cabling throughout. Without going into a whole bunch of descriptives, I can say that I was pretty stunned with the sonic performance, and this is coming from an owner of his Dad's Momentum monoblock amps. The rest of my system consists of Wilson Audio Sasha W/P speakers (Series-1), Ayre KX-R preamp, Playback Designs MPS-5 player, and Transparent Audio Reference cabling throughout.

I also had listened extensively to his Classic Series BSC-100m class A monoblock amps when they first came out and was extremely impressed with their sonic performance. They were really fast/dynamic amps which is exceptional for class A amps. Expansive 3D soundstage, highly musical yet transparent, and in particular, very full-bodied/soulful. At USD 14,750 per pair it was a (relative) steal. Had I not already bought his Dad's Momentum monoblock amps, I would have given Bret's gear serious consideration and saved a bundle of cash as well.

But his 5 Series monoblock amps are something else altogether.......They were like his Classic Series BSC-100m class A monoblock amps on steroids, and then some! I do love my D.D. Momentum monoblock amps, but Bret's amps were sonically so very tube like, and yet had tremendous speed, super rich timbre/tone, great layering of instrumentation, ultra-wide soundstaging, as well as having the good ol' Krell "slam" in spades, the difference being that it was very well proportioned top-to-bottom with great musicality. In addition, there was also a startling sense of palpability and realism to percussive instruments. The "twang" of the guitar intro. on Gotye's "Somebody That I Used To Know" gave me serious goose bumps and has stuck in my audio memory to this day. I hate to say this, but when I listen to this same track on my D.D. Momentum monoblock amps back home, I unfortunately don't get the same type of goose bumps.

Bret's new 5 Series amp design aesthetics are inspired by performance cars, as can be seen by his 2-tier top panel with the grills dominating the top panel. In fact, Bret has actually enlarged the grills in order to add more of the muscle performance car look & feel, as well as increasing the more rapid & efficient flow of heat up and away from the amp chassis - and it does look a lot more "meaner" (in a very good way). In addition, the front panel is sculpted to reflect the strong curves and elevation changes much like a performance car, and the 2 bulges on the front panel flanking his center column (housing the power button & bias control) convey a sense of serious power from within, very much like the bulge that one sees protruding up from the bonnet of a muscle car.

Bret's 5 Series M5 monoblocks and S5 stereo amps are full class A amps which will double all the way down to 1 ohm (with room to spare), and I believe they are rated around 150 watts & 75 watts respectively. Class A bias can be reduced from 100% down to 50% or down to almost 0% which is in effect a low power Eco mode via the triangular knob on the front panel. Also, the S/N ratio is around 110dB (unweighted) which is equal to or better than his Dad's Momentum monoblocks amps, thus making for a very low noise floor. I also really like the fact that his heat-sinks are all internal, and that his output devices are nestled right in-between his massive heat-sinks thereby creating a "chimney effect" for the heat to shoot straight up instead of radiating heat laterally when the heat-sinks are bolted externally to the sides of an amp which will likely heat up a listening room considerably.

I was about to pull the trigger on his Dad's Momentum preamp, but have now decided to wait to audition Bret's L5 preamp with 3-Band Tone Controls WHICH can be controlled remotely (whereas his father's tone controls cannot be controlled remotely), plus I believe that Bret's preamp will be about HALF the price of his father's Momentum preamp (USD 32,000). If Bret's preamp matches up nicely with his Dad's Momentum monoblock amps (which I currently have), then I'ed just have saved a ton of cash!!

This was after his earliest effort. You heard his latest version. His amps are more based in the earlier KSA 250 than the later Krell products.

Bully Sound (http://www.positive-feedback.com/Issue59/bullysound.htm)

[blackdog]

Adaptive bias is not really Class A as there is a frequent transition state for the devices

I'm glad Bret mentioned this. I agree sliding bias is not Class A. A good example is the new CEC amps. They claim Class A, but doesn't come close.

One I forgot to mention is the Blue Circle BC2. I'm re-building a pair right now that somebody absolutely destroyed trying to mod (pics available if you want a good laugh). These amps are hybrid with a tube front end, and a single ended solid state output. When they work, they sound great.

[Myles B. Astor]

A little bird told me there was a thread about Class A, which of course is so near and dear to my heart. How are the folks on the Shark today? My 2 cents is that: 1. This would have to be focused on solid state amps as correct me if I am wrong but most tube amps are closer to Class A by design than not? I have very little experience with tube circuits so forgive my ignorance. 2. Adaptive bias is not really Class A as there is a frequent transition state for the devices, and in my experience this negatively affects the sound. To that end the products that use/used adaptive bias may actually sound better if that circuit were eliminated. Even dear old dads monsters from the past using adaptive bias would have been better without it. He and I have discussed this many times... But from a marketing standpoint it sounds much better to have Class A in the description and save a huge amount of space using smaller heat sinks. So that being said, we can eliminate many from the list and add BSC because even though my company is only 4 years old I have had only Class A amps from the start and don't plan on going anywhere for the next 15-20 years or so. :) I still contend the biggest and baddest of all the Class A amps is the KRELL KRS-200. I don't think anyone has come close to surpassing this Fixed Class A monster. I do have plans for a 7 series amp that in concept will better the KRS-200, but it is time, budget, and market dependent. I also agree Nelson Pass designs to be #1 as he was one of the first and continues to deliver fine Class A products, but Krell shouldn't be #9 as the first 15 years of its existence were based on Class A designs. Definitely Gryphon and Accuphase are greats on this list, the 1st Levinson 25 watt class A ML2 should be an honorable mention, good amp!. Also some Class A efforts from Bedini and Belles which I believe had good sounding Class A SS amps.

Hi Brett!

Welcome! How'd the move go?

[BretDago]

Hi Brett!

Welcome! How'd the move go?
Hey Myles,

Staying in CT for a while, son is going to school here and no need to jump ship just yet... Need to visit each other soon!

[BretDago]

I have also been closely following Bret D'Agostino's development of his 5 Series amps/preamp for quite sometime now, and it really is quite exciting stuff!

After CES 2014 in January, I visited BSC Audio in Milford, Connecticut. Bret was very kind to invite me to listen to his 5 Series M5 class A monoblock amps in his personal home setup. The amps were driving a pair of Wilson Audio Sasha W/P speakers (Series-1) and hooked up directly to a Bricasti M1 DAC with Transparent Audio Reference MM2 cabling throughout. Without going into a whole bunch of descriptives, I can say that I was pretty stunned with the sonic performance, and this is coming from an owner of his Dad's Momentum monoblock amps. The rest of my system consists of Wilson Audio Sasha W/P speakers (Series-1), Ayre KX-R preamp, Playback Designs MPS-5 player, and Transparent Audio Reference cabling throughout.

I also had listened extensively to his Classic Series BSC-100m class A monoblock amps when they first came out and was extremely impressed with their sonic performance. They were really fast/dynamic amps which is exceptional for class A amps. Expansive 3D soundstage, highly musical yet transparent, and in particular, very full-bodied/soulful. At USD 14,750 per pair it was a (relative) steal. Had I not already bought his Dad's Momentum monoblock amps, I would have given Bret's gear serious consideration and saved a bundle of cash as well.

But his 5 Series monoblock amps are something else altogether.......They were like his Classic Series BSC-100m class A monoblock amps on steroids, and then some! I do love my D.D. Momentum monoblock amps, but Bret's amps were sonically so very tube like, and yet had tremendous speed, super rich timbre/tone, great layering of instrumentation, ultra-wide soundstaging, as well as having the good ol' Krell "slam" in spades, the difference being that it was very well proportioned top-to-bottom with great musicality. In addition, there was also a startling sense of palpability and realism to percussive instruments. The "twang" of the guitar intro. on Gotye's "Somebody That I Used To Know" gave me serious goose bumps and has stuck in my audio memory to this day. I hate to say this, but when I listen to this same track on my D.D. Momentum monoblock amps back home, I unfortunately don't get the same type of goose bumps.

Bret's new 5 Series amp design aesthetics are inspired by performance cars, as can be seen by his 2-tier top panel with the grills dominating the top panel. In fact, Bret has actually enlarged the grills in order to add more of the muscle performance car look & feel, as well as increasing the more rapid & efficient flow of heat up and away from the amp chassis - and it does look a lot more "meaner" (in a very good way). In addition, the front panel is sculpted to reflect the strong curves and elevation changes much like a performance car, and the 2 bulges on the front panel flanking his center column (housing the power button & bias control) convey a sense of serious power from within, very much like the bulge that one sees protruding up from the bonnet of a muscle car.

Bret's 5 Series M5 monoblocks and S5 stereo amps are full class A amps which will double all the way down to 1 ohm (with room to spare), and I believe they are rated around 150 watts & 75 watts respectively. Class A bias can be reduced from 100% down to 50% or down to almost 0% which is in effect a low power Eco mode via the triangular knob on the front panel. Also, the S/N ratio is around 110dB (unweighted) which is equal to or better than his Dad's Momentum monoblocks amps, thus making for a very low noise floor. I also really like the fact that his heat-sinks are all internal, and that his output devices are nestled right in-between his massive heat-sinks thereby creating a "chimney effect" for the heat to shoot straight up instead of radiating heat laterally when the heat-sinks are bolted externally to the sides of an amp which will likely heat up a listening room considerably.

I was about to pull the trigger on his Dad's Momentum preamp, but have now decided to wait to audition Bret's L5 preamp with 3-Band Tone Controls WHICH can be controlled remotely (whereas his father's tone controls cannot be controlled remotely), plus I believe that Bret's preamp will be about HALF the price of his father's Momentum preamp (USD 32,000). If Bret's preamp matches up nicely with his Dad's Momentum monoblock amps (which I currently have), then I'ed just have saved a ton of cash!!

Good to see you on the Shark Philip... And thanks for all of the great comments, I did enjoy our time together immensely. I noticed elsewhere you were at the HK show? Did you manage to see the L5 Pre-production prototype in HK? Hoping you will attend 2015 CES? Let's chat soon.

[cmalak]

I have also been closely following Bret D'Agostino's development of his 5 Series amps/preamp for quite sometime now, and it really is quite exciting stuff!

After CES 2014 in January, I visited BSC Audio in Milford, Connecticut. Bret was very kind to invite me to listen to his 5 Series M5 class A monoblock amps in his personal home setup. The amps were driving a pair of Wilson Audio Sasha W/P speakers (Series-1) and hooked up directly to a Bricasti M1 DAC with Transparent Audio Reference MM2 cabling throughout. Without going into a whole bunch of descriptives, I can say that I was pretty stunned with the sonic performance, and this is coming from an owner of his Dad's Momentum monoblock amps. The rest of my system consists of Wilson Audio Sasha W/P speakers (Series-1), Ayre KX-R preamp, Playback Designs MPS-5 player, and Transparent Audio Reference cabling throughout.

I also had listened extensively to his Classic Series BSC-100m class A monoblock amps when they first came out and was extremely impressed with their sonic performance. They were really fast/dynamic amps which is exceptional for class A amps. Expansive 3D soundstage, highly musical yet transparent, and in particular, very full-bodied/soulful. At USD 14,750 per pair it was a (relative) steal. Had I not already bought his Dad's Momentum monoblock amps, I would have given Bret's gear serious consideration and saved a bundle of cash as well.

But his 5 Series monoblock amps are something else altogether.......They were like his Classic Series BSC-100m class A monoblock amps on steroids, and then some! I do love my D.D. Momentum monoblock amps, but Bret's amps were sonically so very tube like, and yet had tremendous speed, super rich timbre/tone, great layering of instrumentation, ultra-wide soundstaging, as well as having the good ol' Krell "slam" in spades, the difference being that it was very well proportioned top-to-bottom with great musicality. In addition, there was also a startling sense of palpability and realism to percussive instruments. The "twang" of the guitar intro. on Gotye's "Somebody That I Used To Know" gave me serious goose bumps and has stuck in my audio memory to this day. I hate to say this, but when I listen to this same track on my D.D. Momentum monoblock amps back home, I unfortunately don't get the same type of goose bumps.

Bret's new 5 Series amp design aesthetics are inspired by performance cars, as can be seen by his 2-tier top panel with the grills dominating the top panel. In fact, Bret has actually enlarged the grills in order to add more of the muscle performance car look & feel, as well as increasing the more rapid & efficient flow of heat up and away from the amp chassis - and it does look a lot more "meaner" (in a very good way). In addition, the front panel is sculpted to reflect the strong curves and elevation changes much like a performance car, and the 2 bulges on the front panel flanking his center column (housing the power button & bias control) convey a sense of serious power from within, very much like the bulge that one sees protruding up from the bonnet of a muscle car.

Bret's 5 Series M5 monoblocks and S5 stereo amps are full class A amps which will double all the way down to 1 ohm (with room to spare), and I believe they are rated around 150 watts & 75 watts respectively. Class A bias can be reduced from 100% down to 50% or down to almost 0% which is in effect a low power Eco mode via the triangular knob on the front panel. Also, the S/N ratio is around 110dB (unweighted) which is equal to or better than his Dad's Momentum monoblocks amps, thus making for a very low noise floor. I also really like the fact that his heat-sinks are all internal, and that his output devices are nestled right in-between his massive heat-sinks thereby creating a "chimney effect" for the heat to shoot straight up instead of radiating heat laterally when the heat-sinks are bolted externally to the sides of an amp which will likely heat up a listening room considerably.

I was about to pull the trigger on his Dad's Momentum preamp, but have now decided to wait to audition Bret's L5 preamp with 3-Band Tone Controls WHICH can be controlled remotely (whereas his father's tone controls cannot be controlled remotely), plus I believe that Bret's preamp will be about HALF the price of his father's Momentum preamp (USD 32,000). If Bret's preamp matches up nicely with his Dad's Momentum monoblock amps (which I currently have), then I'ed just have saved a ton of cash!!

Hey Philip...good to see you posting here :thumbsup: Great info on Brett's amps.

[Myles B. Astor]

Hey Myles,

Staying in CT for a while, son is going to school here and no need to jump ship just yet... Need to visit each other soon!

Yes let's figure something out after Labor Day!

[cmalak]

Has anyone heard the new Krell Solo 375/575 amps?

http://www.krellonline.com/images/Solo375_lg.jpg

http://www.krellonline.com/images/Mono_Back_lg.jpg

Ken Kessler recently reviewed the Krell Duo 300 and let's just say he wasn't impressed: http://www.absolutesounds.com/pdf/main/press/KR_Duo300_HFN_Octo14.pdf

[BretDago]

This was after his earliest effort. You heard his latest version. His amps are more based in the earlier KSA 250 than the later Krell products.


I have also been closely following Bret D'Agostino's development of his 5 Series amps/preamp for quite sometime now, and it really is quite exciting stuff!


I'm glad Bret mentioned this. I agree sliding bias is not Class A. A good example is the new CEC amps. They claim Class A, but doesn't come close.

I think this is a good discussion in regards to variable vs fixed class A bias. I remember way back in the day when Krell designed and patented the sustained plateau bias scheme which was a signal level triggered bias adjustment scheme. The cool thing about that technology was that it held its class A state until the signal level either increased, where it then ramped up to the next level and stayed, or decreased if it were fixed for a long period of time and eventually drop to a lower level when average signal level decreased, hence the “sustained” in the name. It is indeed a clever solution to the transition problem but invariably didn't solve the problem.

Dan and I have often discussed how good some of the earlier Krell designs would have been if the SPB scheme wasn’t implemented. There is a certain coldness and edge along with diminished depth and stage I associate with the sliding designs that are eliminated with a fixed A/B or A bias scheme. There are measureable distortion effects, but it is more than that in my opinion, in a really simple description it’s like the transistor isn’t ready to pass the signal and sounds agitated for lack of a better word. I associate this sound with the Class D or switching designs as well. Although some sound better than others for sure, I can’t shake that certain sound. FYI I get that feeling about A/D D/A conversions as well…
In my opinion anything you can do to turn the transistor, or any device for that matter, On and leave it on leads to better sound. Active devices work really well when they turn on, get some power flowing through them, and settle to a certain temperature and stay there. They are extremely predictable in this state. This is why audio equipment typically sounds better when it has been on for a while as opposed to a cold start. Even in my designs if you switch to one of the other Class A/B modes it takes a bit of time to get all of the romance back in the 100% class A mode.

To that end of course the big problem with fixed level class A bias is heat and power consumption. Really no way around it if you want that sound, and why some of us believe this is the only way to hear music. It's easy to claim you are a Class A amplifier with variable bias schemes because technically when the signal is passing through the output stage it is biased in Class A, but of course it doesn't take into account the negative effects of turning the transistor Off and then back on again etc. etc.. In my opinion it is way more musical to have a conventional A/B design than get involved with the variable bias schemes. At least with a fixed bias starting point whether that be high or low, a set bias point has been established, and much of the playback will have hints of the class A sound.

I am so glad Philip brought up heat sink size, I love when a product is advertised as Class A or some percentage of Class A and doesn't have enough cooling surface area to actually sustain class A rated power, or even half power for that matter, for any extended amount of time. Even a 30 Watt class A amp requires a fair amount of heat sink or fans to keep the output devices within a safe operating temperature range. You won’t believe how much heat a 300-400W amp with even a little class A bias will create let alone a 500W plus amp. The Krell amps with SPB had huge heat sinks because they actually did have a ton of class A bias at certain points. On the topic of fans and class A amplifiers, fans actually are great for cooling but they do make noise and wear out or clog. In the case of class A amplifiers the fans actually come on at the worst possible time. Class A amplifiers are at their absolute highest temperature when they are sitting idle, they actually get cooler as the power is transferred to the speaker. Because of this the fan will be at its loudest (highest speed) when the amp is at its quietest state (at idle or during low level passages) and slowing down when the most amount of power is being delivered to the speaker where you wouldn’t be able to hear the fan at high speed.


I am sure many may disagree with my observations, and that’s ok because everyone is certainly entitled to an opinion, but these are my experiences. It would be much easier for me to make a smaller, cooler running, cost effective, class A/B amplifier that sounds really good (just turn the bias dial on one of my amps to 50% mode), but when you really want to get in touch with your music, it’s fixed bias Class A Baby… As much as you can get.

[Heckler75]

what about the German Kraft 400 Mono's (discontinued) Wow these sound great, probably my favorite SS

[KeithR]

Nice fans, Krell.

[psjl]

I'm glad Bret mentioned this. I agree sliding bias is not Class A. A good example is the new CEC amps. They claim Class A, but doesn't come close......

+1 :snicker:

[psjl]

Hey Philip...good to see you posting here :thumbsup: Great info on Brett's amps.

Hey Cyril!

Great to see you in AS!

It's a great audio forum and I see quite a few familiar faces from AA over here as well.

[psjl]

This was after his earliest effort. You heard his latest version. His amps are more based in the earlier KSA 250 than the later Krell products.

Bully Sound (http://www.positive-feedback.com/Issue59/bullysound.htm)

Hey Myles.....Great to see you here in AS!

If I recall correctly, I think that both of BSC Audio's "Classic Series" & "5 Series" fixed class A bias amps are largely based on Bret's experiences with the fixed class A bias amps from the Krell KSA line (KSA 50/80/100/200) as well as the Krell KRS line (KRS 100/200), as opposed to the Krell KSA 250 fixed class A/B high biased amp or the Krell KSA 300 variable/sliding class A bias amp.

[psjl]

Good to see you on the Shark Philip... And thanks for all of the great comments, I did enjoy our time together immensely. I noticed elsewhere you were at the HK show? Did you manage to see the L5 Pre-production prototype in HK? Hoping you will attend 2015 CES? Let's chat soon.

Hey Bret,

Yep, I certainly had a blast when I last saw you in January 2014, and looking forward to spending time with you again come 2015 CES.

Actually, I did in fact get to see your pre-production prototype 5 Series L5 preamp at the 2014 Hong Kong High-End Audio Visual Show (8 to 10-Aug-2014), and it looked great.

Just like your amplifier, your L5 preamp was built like a tank and its aesthetics were bold, unique and positively eye catching. I have to say that there was certainly a great deal of entralled/enthused chatter amongst the show attendees regarding the amp & preamp aesthetics, and they sounded great despite the less than ideal sonic environment at the show. BTW, I also heard that your H.K./China distributor was receiving quite a lot of inquiries!

In addition to the L5 preamp aesthetics, a lot of attendees really liked the 3 chassis configuration all on 1 base, as well as the 3-band tone controls which many felt would be ideal given the sometimes small an odd-shaped listening environments over here in Asia, in addition to the fact that the tone controls could be entirely switched out of the audio circuit.

http://i1080.photobucket.com/albums/j331/psjl1/psjl%20-%20AudioAficionado/DSC02374_zpsc098392a.jpg

http://i1080.photobucket.com/albums/j331/psjl1/psjl%20-%20AudioAficionado/DSC02446_zps17aa3b8f.jpg

[BretDago]

Hey Bret,

Yep, I certainly had a blast when I last saw you in January 2014, and looking forward to spending time with you again come 2015 CES.

Actually, I did in fact get to see your pre-production prototype 5 Series L5 preamp at the 2014 Hong Kong High-End Audio Visual Show (8 to 10-Aug-2014), and it looked great.

Pics look great snoopster, many thanks for the kind words. We will talk soon. B

[Dave]

In order:

FM Acoustics
Accuphase
Luxman
Pass Labs

[MusicDirector]

I like threads like this. They serve to let me know what is out there in the sense of names to look at. (Not just me of course, many folks).
For me, it's nice to know whenever I need to replace my amp/receiver or something which with any luck at all is once every 10 years and with very good luck, once every 20 to 30 years.
What I really need is for someone to come out with a publication of some sort describing the different classes of amps and the differences pro and con between them in easy language because I would not know a class A from a class B, D or any other letter of the alphabet. Now there is the addition of SET amps which to me could stand for Search for Extraterrestrial amps for all I know.:)

[Mike]

For me, these are! :)

8131


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[joeinid]

Wow! Congratulations Mike. Beautiful.

[Paul]

For me, these are! :)

8131


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Excellent. Tell us more !!!!!

[Mike]

Excellent. Tell us more !!!!!

These amps have black black backgrounds while taking micro dynamics to a whole new level. Bass is detailed, tight and fast. Vocals are to die for. Heat, so far, knock on wood, has not been an issue. The four boxes do not get more than warm.

The synergy with the Strads is as good as I remember it when I had Strads and Pass XA160.5's.

And the XS preamp is also outstanding.

Everything is breaking in - so I will update as time goes on.

But these amps are freaking amazing!


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[Alpinist]

These amps have black black backgrounds while taking micro dynamics to a whole new level. Bass is detailed, tight and fast. Vocals are to die for. Heat, so far, knock on wood, has not been an issue. The four boxes do not get more than warm.

The synergy with the Strads is as good as I remember it when I had Strads and Pass XA160.5's.

And the XS preamp is also outstanding.

Everything is breaking in - so I will update as time goes on.

But these amps are freaking amazing!


Sent from my iPad using Tapatalk HD

Wow Mike, congratulations!!! I knew that XS Preamp would bowl you over. :)

Enjoy,
Ken

[Audioseduction]

Good job Mike! :D

[Mike]

Wow Mike, congratulations!!! I knew that XS Preamp would bowl you over. :)

Enjoy,
Ken

Thanks Ken.


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[Mike]

Good job Mike! :D

Thanks George. You coming down for a listen?


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[sharkmouth]

Mike, wow, you & & I are at opposite ends with where we are exploring at the moment, looks like a whole lot of fun, congrats.

[Mike]

Mike, wow, you & & I are at opposite ends with where we are exploring at the moment, looks like a whole lot of fun, congrats.

It's all about synergy Kev. If you recall, I experimented a lot with the Strads my first go around with them - and nothing could touch the Pass/Strad synergy. This included the infamous 2301's (which I still love and would like to own again one day....but after the XS150's, not sure why.) Those that heard it at my house, were amazed and some even sought out the combo for themselves.

The XS150's (and XS preamp) reduce background noise to inaudible levels, reduce any hint of grain, tighten up the bass, have wonderful PRAT and add a level of sweetness which is very nice indeed!

As I understand it, the a First Watt SIT-1's were used as the starting point for voicing the XS amps (a process which took Nelson and his team over 3 years). The SIT-1's are voiced very closely to world class SET amps.

At first listen, I can say the XS amps give me the magic of some of the best SET amps I've owned and heard, the power and control of solid state, with a dash of other magic not associated with anything else.

I'm hesitant to say, because no amp is perfect, but these appear to do it all.

[MDP]

Congrats Mike, they look beautiful :congrats:

[The Sandman]

Mike - which preamp were you using when you had Charles' 100.8s over for a visit?

[Mike]

Mike - which preamp were you using when you had Charles' 100.8s over for a visit?

The special VAC....it's a cross between the Master and the Statement.

[The Sandman]

Ah - that might account for some of the difference in sound as well compared to say the 100.8s and the XP-30 vs the XS champions.

[Mike]

Ah - that might account for some of the difference in sound as well compared to say the 100.8s and the XP-30 vs the XS champions.

The XA100.8 in my system was superb (as well as my previous XA160.5's and XA60.5's) and probably the reason why I went for Pass over anything else. When Charlie brought over his XA100.8's for my to hear and compare, they beat every other amp I had on hand. There is no denying the synergy.

Did I mention how big these amps are? Did I mention I carried all four pieces up the stairs by myself? Good thing we both know a good chiropractor. :)

[The Sandman]

Did I mention how big these amps are? Did I mention I carried all four pieces up the stairs by myself?

I'm not impressed unless you did it all in two trips.

[Mike]

I'm not impressed unless you did it all in two trips.

Two trips? I was referring to four at once. I had to make a second trip for the preamp pieces. Couldn't balance them on top. Gotta work on that.

[The Sandman]

Two trips? I was referring to four at once.

I totally believe you Mike but I'll need to see proof. Were you able to snap a selfie?

[CPP]

Two trips? I was referring to four at once. I had to make a second trip for the preamp pieces. Couldn't balance them on top. Gotta work on that.

I once carried my wife upstairs, BUT that was about 25 years ago when I was "in shape" and the valet was holding on to my waist and my wife's back. No further details are available.

[Mike]

I totally believe you Mike but I'll need to see proof. Were you able to snap a selfie?

No. Come by and I'll repeat the feat for you. :)

[KeithR]

I foresee a pair of SIT-1s for your Spatials now :)

[Mike]

I foresee a pair of SIT-1s for your Spatials now :)

Possibly. I'm loving the Luxman M600a Class A amp/preamp on the Spatials. Best combo so far. The LM has some added magic however.


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[still-one]

I saw Brett's new M5 amps at Paragon when I stopped by yesterday. They look great. I did not have a chance to listen to them but I will at one of Paragon's Fall events on the 20th of November. Brett will be there.

http://bullysound.com/images/DSC02378r.jpg

[sharkmouth]

I totally believe you Mike but I'll need to see proof. Were you able to snap a selfie?


HA! :D :D :D :fingers:

[The Sandman]

I totally believe you Mike but I'll need to see proof. Were you able to snap a selfie?


HA! :D :D :D :fingers:

You know what they say... trust but verify. :)