300w Pure class A Monoblock search!

[fpitas]

Exactly. Some class AB amps are biased high enough to remain in class A up to several watts of output. So you get the benefits of class A beyond low and into moderate listening levels. Of course, whether that is necessary is debatable.

In any event it's still kind of a gimmick. If you care, you do something like Benchmark does, in their case a feed-forward to linearize the crossover region.

 

[Koeitje]

Now we are getting somewhere. If you are indeed looking to build a system "that tend not to colour the source with any magic", I suggest you take a big step backwards, as you are approaching it exactly wrong. To start with, the speakers you propose to use are highly colored. Briefly, the order in of what affects the sound of your system:

1) Room
2) Setup
3) Speakers
4) Equipment

If you seek as system that is true to the source, I would strongly encourage you to proceed as follows:

1) Establish your total system budget;
2) Start to look at active monitor speakers like Newman and Genelec, or passive speakers like Revel and Kef;
3) Start reading, and reading, and reading. What you should be reading is the Audio Newbie/Beginner Technical Forum and Room Acoustics and General Speaker Discussions.

Based on the speakers you listed, it appears that you are looking to spend about $6,000 - $7,500 U.S. total for your system. This can build you a very nice system. If it were me, I would be putting the vast majority $5,000-6,000 towards speakers/subs (yes 2 or more subwoofers), with the remainder towards a preamp/processor that can measure, perform equalization, time adjustments, and crossover in the digital domain. For an amp (if you use passive speakers), a Hypex NC252MP based amp (i.e. $500) will get you plenty of power and performance that far exceeds any human's hearing. Leave a couple hundred dollars for some GIK Panels in case you need to treat your first reflection points and enjoy audio nirvana.

I'd put speakers above setup and on the same level as the room. Better loudspeakers do better in bad rooms than worse loudspeakers. If your speakers are shit no amount of setup or changes to your room matter.

 

[BDWoody]

Class AB means it is in class A for small signals, where it matters, then moves into class B as the signal gets larger to save power.

Question from the peanut gallery...

Is there a way to determine from the standard specs given where that transition takes place?

 

[ahofer]

One thing about those Stereo Review tests. They used Magnepans. So you say? Well Maggies come very close to being a purely resistive load. Almost no other speaker does. So differences in FR and even variations in current vs voltage phase would not come into play with Maggies, but might with most speakers.

Yes. Some might say that's a feature, because its absolutely true that high amp output impedance and/or difficult speaker loads may alter frequency response and depart from fidelity. Of course, if altered FR is what you want, there are better ways to achieve it than plowing large sums into boutique amplifiers and difficult speakers.

 

[CDMC]

Question from the peanut gallery...

Is there a way to determine from the standard specs given where that transition takes place?

I may be incorrect, but the only place you are likely to find this would be in the service manual where it give the spec voltage the amplifier should be biased. I know that in the old days, some would increase this voltage over spec to push their amp further into Class A operation, at the expense of generating extra heat.

 

[TonyJZX]

thats a fair question as so many amps say 10w in class A or that sort of thing so one might assume that the vast majority of your typical usage is in Class A

 

[RayDunzl]

I have a pair of Krell FPB 350 mcx monoblocks, almost 20 years old now, if they were made in 2005.

With "Plateau Bias",

At standby each pulls 30W from the wall.

Ready to play, 100W.

And remain there for low level listening.

As you increase the signal volume, the power draw increases in steps so the rails remain above what is necessary to supply the requested voltage swings to the speakers.

I measured the first few steps once, but don't remember the exact values.

Something like 100, 150, 250, 400, 600 watts and I stopped.

The specification says they'll pull much more than that at full output.

They have large heatsinks (of course) and I've seen 140 degrees F on them after some "normal" Beer Saturday listening with Audio Buddy.

The spec says 1700W maximum draw.

There seem to be some minor copy/paste errors in that spec when compared to the stereo versions, but irrelevant for this discussion.

I see pairs come up on eBay occasionally:

There's a pair now.

They still seem to attract a bit of interest when they show.

 

[Astoneroad]

I have a pair of Krell FPB 350 mcx monoblocks, almost 20 years old now, if they were made in 2005.

With "Plateau Bias",

At standby each pulls 30W from the wall.

Ready to play, 100W.

And remain there for low level listening.

As you increase the signal volume, the power draw increases in steps so the rails remain above what is necessary to supply the requested voltage swings to the speakers.

I measured the first few steps once, but don't remember the exact values.

Something like 100, 150, 250, 400, 600 watts and I stopped.

The specification says they'll pull much more than that at full output.

They have large heatsinks (of course) and I've seen 140 degrees F on them after some "normal" Beer Saturday listening with Audio Buddy.

The spec says 1700W maximum draw.

View attachment 274073

There seem to be some minor copy/paste errors in that spec when compared to the stereo versions, but irrelevant for this discussion.

I see pairs come up on eBay occasionally:

There's a pair now.

View attachment 274074

They still seem to attract a bit of interest when they show.

Do all the lights in the neighborhood for a 3 miles radius dim as you crank that up? That strikes me as something that you need to harness a lightning storm to power in order to reanimate the dead. Wow.

 

[sergeauckland]

Question from the peanut gallery...

Is there a way to determine from the standard specs given where that transition takes place?

Not from standard specs, but as CDMC mentioned above, the service manual will state the standing current for the output transistors. The standing current is the amount of current one can extract before the output device cuts off, so to a first approximation, that's the maximum current where the output device stays in Class A.

The amount of power that provides is then calculated from P=i^2R where P is the peak power. Divide by 1.414 for mean power.

A typical SS amp with, say, 50mA standing current, mean Class A power into 8 ohms is 14milliwatts, so not a lot!

S.

 

[CDMC]

I have a pair of Krell FPB 350 mcx monoblocks, almost 20 years old now, if they were made in 2005.

With "Plateau Bias",

At standby each pulls 30W from the wall.

Ready to play, 100W.

And remain there for low level listening.

As you increase the signal volume, the power draw increases in steps so the rails remain above what is necessary to supply the requested voltage swings to the speakers.

I measured the first few steps once, but don't remember the exact values.

Something like 100, 150, 250, 400, 600 watts and I stopped.

The specification says they'll pull much more than that at full output.

They have large heatsinks (of course) and I've seen 140 degrees F on them after some "normal" Beer Saturday listening with Audio Buddy.

The spec says 1700W maximum draw.

View attachment 274073

There seem to be some minor copy/paste errors in that spec when compared to the stereo versions, but irrelevant for this discussion.

I see pairs come up on eBay occasionally:

There's a pair now.

View attachment 274074

They still seem to attract a bit of interest when they show.

The high bias Class A amps remind me of an audio dealer years ago saying when it got cold in the showroom in the winter, they would just turn on the Argon for a while (they were highly biased into Class A). For those that don't know, Argon amps were designed by Dan D'Agostino, who later went on to found Krell, so a similar design philosophy and bias (pun intended) towards high Class A biased amps.

 

[Blumlein 88]

Yes. Some might say that's a feature, because its absolutely true that high amp output impedance and/or difficult speaker loads may alter frequency response and depart from fidelity. Of course, if altered FR is what you want, there are better ways to achieve it than plowing large sums into boutique amplifiers and difficult speakers.

It is not about a back *sswards way to change FR. It is about the fact the test used a highly unusual speaker load not at all representative of 99% of speakers. Now simplifying first to move toward the truth makes sense. And one could say you've shown amps sound the same if FR isn't different with different amps. Some of those amps in the test with a good many speakers would in fact sound different enough it might be detectable by FR alone. And DSP wasn't available then.

 

[CDMC]

Do all the lights in the neighborhood for a 3 miles radius dim as you crank that up? That strikes me as something that you need to harness a lightning storm to power in order to reanimate the dead. Wow.

A true Class A amp (transistors fully powered all the time) draws the same power with not signal as at full output. A true Class A will run cooler the harder you drive it, as some energy is being dissipated through the speakers instead of the output devices.

 

[BDWoody]

Ready to play, 100W.

And remain there for low level listening.

I believe I remember that you also have a kav250a (can't remember if 2 or 3 channel), but that idles along at about 200w and stays warm to the touch. Leaving it on a few times helped give me the motivation to actually get off my ass and run a trigger cable.

 

[RayDunzl]

Heat and power:

For the daily drivers now, I have a pair of JBL LSR 308 which pull 5W.

They are satisfactory for use with the TV and casual "background" listening.

Special movies and spirited musical listening - I'll power up the Krells and the Martin Logans.

Listening with them now, for TV:

Beginning heat sink standby - 82 degrees F, room 79F.

After 30 minutes: 93 degrees, TV playing

After an hour: music with 85dB average, stabilized at 107 degrees F

 

[RayDunzl]

Leaving it on a few times helped give me the motivation to actually get off my ass and run a trigger cable.

I was motivated to investigate Solar at the time back when, which seemed expensive.

I took that money and instead bought stock in the local Electric Utility, where the dividends still pay most or all of the electric bill, not counting capital gains which would have paid for every piece of audio hardware I've ever bought..

The local Utility is building Solar Farms so I don't feel entirely out of the green loop.

 

[sejarzo]

This. It appears the OP is asking for something without knowing what he/she/they is asking for or why.

Regrettably, that is becoming rampant here in many threads from folks who seem to have missed that this is Audio Science Review, not Audio Subjective Opinions and Advice Review.

It's why I quit participating on head-fi years ago. 90% of the threads were simply trying to explain the same things over and over to new folks who didn't take the time to RTFF or other use other sources to learn before asking questions that could have been answered by spending 15 minutes with the search function or Google...even before objectivity became anathema to most of the users who were merely seeking justification for their subjective opinions.

 

[Martin]

Pass Labs XS300

XS300 - Pass Labs

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Just $85,000 per pair.

Martin

 

[Martin]

Bob Carver Black Magic 350

Black Magic 350 | BobCarverCorp.com

www.bobcarvercorp.com

Only $9,500 per pair.

Bob claims 350W so they may put out 35W if you're lucky.

Martin

 

[fpitas]

Bob Carver Black Magic 350

Black Magic 350 | BobCarverCorp.com

www.bobcarvercorp.com

Only $9,500 per pair.

Bob claims 350W so they may put out 35W if you're lucky.

Martin

He seems to chisel on the transformers. Maybe you get close to 350W at 1kHz.

 

[sejarzo]

In any event it's still kind of a gimmick. If you care, you do something like Benchmark does, in their case a feed-forward to linearize the crossover region.

I am unsure if it really qualifies as a "gimmick" as it was the only viable option to reduce power consumption for many years versus Class A while avoiding the obvious problems with a purely Class B design. While the best solution to date is Benchmark's, everything audio is a compromise given the limitations of fundamental components, isn't it?