Champions of Class "A"

joeinid said:
Brett,
Looking forward to your S5 amp. One of my dealers is eager to get his for demo.
Click to expand...

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!!
 
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.
 
joeinid said:
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.
Click to expand...

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

psjl said:
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!
Click to expand...
 
Has anyone heard the new Krell Solo 375/575 amps?

Solo375_lg.jpg


Mono_Back_lg.jpg
 
Mike said:
Has anyone heard the new Krell Solo 375/575 amps?
Click to expand...

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
 
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.
 
psjl said:
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!!
Click to expand...

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

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.
 
BretDago said:
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.
Click to expand...

Hi Brett!

Welcome! How'd the move go?
 
psjl said:
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!!
Click to expand...

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.
 
psjl said:
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!!
Click to expand...

Hey Philip...good to see you posting here :thumbsup: Great info on Brett's amps.
 
Myles B. Astor said:
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.
Click to expand...

psjl said:
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!
Click to expand...

blackdog said:
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.
Click to expand...

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