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300w Pure class A Monoblock search!

Zapper

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Hi my sofa is 6.2m from where the speakers would stand.


Open to suggestions from those more versed than myself for sure!
For $2000 for a floor standing speaker, I would consider the Revel F206 or the KEF R5 Meta. Neither is as impressively big and loud as the RF-7. I haven't seen any measurements of the RF-7 but I expect that the Revel and KEF both offer much better sound quality.

Here are measurements of a bunch of Revel speakers, including the F206. The tonality number is an indication* of the overall sound quality based on the measurements. Excellent scores start around 6 with higher being better. Here are measurements for KEF speakers. You'll see a lot of 6's and 7's for Revel and KEF. Now here's Klipsch. Not bad (with a few exceptions), but not in the same league. But they are big and loud and look cool. And sometimes that is worth more than accuracy. Klipsch are great party speakers and will impress your friends. You might want to look at customer ratings though. I've seen a lot of complaints about early failures and poor customer support.

*No one number can adequately describe something as complex as speaker sound quality. Yet there is a good bit of science behind this metric and a high correlation to perceived quality.
 

dlaloum

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Thank you for the concise reply.

The reason i was aiming towards class A is that i have read a lot of information about them being the 'purest sounding' amps that tend not to colour the source with any magic. This would be the easy starting point as i want the amp to sound as natural to the recording as possible. I mean, that's the goal right?

So are we saying that the difference between classes in inaudible?

The reason for the 300 watts, is to drive some RF-7 floor standers I have my eye on.

So if the power requirements of the speaker exceed the capabilities of the budget or the power, or the seaker class vs heat production. Then i need to look at something else in terms of amp class to better suit my budget/speaker requirements.

Thanks again!

OK ... the Klipsch RF-7 have a sensitivity of 100db @ 2.83V / 1m - nominal impedance is 8ohm....( we can talk about real impedance later)

If you are listening to them in a large room (requiring more power) - you could be listening to them at say 4m

The base spec, tells you that for an input of 1W (2.83V into 8 ohm) you will get Sound Pressure Level of circa 100db at 1m from the speaker (in free air, away from walls)
Distance will affect this, as the SPL will drop by 6db for each doubling of distance

So at 4m your output at 1W will be 100db - 2x6db = 88db

Assuming you are running a stereo pair, having two speakers running will double the output taking it to 88db + 3db = 91db

Now to work out what your power requirements are (roughly)...

Reference level in homes (as opposed to theatres) for continuous output at the listening position is 75db, with a 20db peaking allowance (so max of 95db) - Pro/Theatre levels are normally set as 85db continuous and +20db / 105db peak

Your power output SPL table looks like this (@8ohm)

1W 91db
2W 94db
4W 97db
8W 100db
16W 103db
32W 106db
64W 109db
128W 112db
256W 115db

So with those speakers, in a relatively large room, listening to the speakers at a 4m distance, you need a total of 4W to achieve the peak reference "home" levels of loudness... and 32W will be ample if you aim for the theatrical reference of 85db/105db (continuous/peak)

Given the above, it is highly likely that you could get by more than adequately with a 35W amp. (!!!)

A 35W class A amp could be viable within your budget, although you might have to go used...

There are a couple of complexities to take into account - although "nominally" 8ohm, a number of measurments/tests have shown that the RF7's drop down to around 4ohm... to provide the same output at 4ohm as at 8ohm requires twice the current / twice the power...
So if you need a 35W amp rated at 8ohm, you need a 64W amp rated at 4ohm... - the two are almost the same, but the 4ohm rated amp would have a larger power supply, and larger heatsinks, and possibly more transistors etc... - even though when driving an 8ohm speaker it would sound no different to an amp rated only at 8ohm. (so worthwhile checking the 4 ohm rating for the amp, given the RF7's do drop down to that level at crossover point)

P.S. for a 6m distance, you would take the power requirements up one notch on the table, as you will lose around 3 to 4db of loudness... so you will need to double the power.... from 32W to 64W @ 8ohm (assuming a pro/theatre target) or 8W for the standard "home" target
 
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CDMC

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OK ... the Klipsch RF-7 have a sensitivity of 100db @ 2.83V / 1m - nominal impedance is 8ohm....( we can talk about real impedance later)

If you are listening to them in a large room (requiring more power) - you could be listening to them at say 4m

The base spec, tells you that for an input of 1W (2.83V into 8 ohm) you will get Sound Pressure Level of circa 100db at 1m from the speaker (in free air, away from walls)
Distance will affect this, as the SPL will drop by 6db for each doubling of distance

So at 4m your output at 1W will be 100db - 2x6db = 88db

Assuming you are running a stereo pair, having two speakers running will double the output taking it to 88db + 3db = 91db

Now to work out what your power requirements are (roughly)...

Reference level in homes (as opposed to theatres) for continuous output at the listening position is 75db, with a 20db peaking allowance (so max of 95db) - Pro/Theatre levels are normally set as 85db continuous and +20db / 105db peak

Your power output SPL table looks like this (@8ohm)

1W 91db
2W 94db
4W 97db
8W 100db
16W 103db
32W 106db
64W 109db
128W 112db
256W 115db

So with those speakers, in a relatively large room, listening to the speakers at a 4m distance, you need a total of 4W to achieve the peak reference "home" levels of loudness... and 32W will be ample if you aim for the theatrical reference of 85db/105db (continuous/peak)

Given the above, it is highly likely that you could get by more than adequately with a 35W amp. (!!!)

A 35W class A amp could be viable within your budget, although you might have to go used...

There are a couple of complexities to take into account - although "nominally" 8ohm, a number of measurments/tests have shown that the RF7's drop down to around 4ohm... to provide the same output at 4ohm as at 8ohm requires twice the current / twice the power...
So if you need a 35W amp rated at 8ohm, you need a 64W amp rated at 4ohm... - the two are almost the same, but the 4ohm rated amp would have a larger power supply, and larger heatsinks, and possibly more transistors etc... - even though when driving an 8ohm speaker it would sound no different to an amp rated only at 8ohm. (so worthwhile checking the 4 ohm rating for the amp, given the RF7's do drop down to that level at crossover point)

P.S. for a 6m distance, you would take the power requirements up one notch on the table, as you will lose around 3 to 4db of loudness... so you will need to double the power.... from 32W to 64W @ 8ohm (assuming a pro/theatre target) or 8W for the standard "home" target
Except Klipsch is widely optimistic in their sensitivity ratings. They have overstated them for decades. At best these are 92 db/w, so would require about 6 times your estimate. Even then 150w/ch would hit 105 db reference levels comfortably (which for those who don’t know, is extremely loud).
 

garbulky

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As you've probably found out by now, what you are asking is unrealistic. However, I currently use an Emotiva XPA-1 gen 2 monoblock setup. They are high-bias class A. It means as long as you play at below 60 watts you are at class A. When you get past 60 watts at any time, it switches to class A/B and it can produce 500 watts of power @ 8 ohms, and 1000 watts at 4 ohms. Now what's important for you to understand is that for the most part you won't be listening to more than a watt or two of power - even for modestly loud parts of music. Which means that for the vast majority of time you will be listening to class A.
Now it is not a TRUE class A amp because it does switch back to class A/B when it exceeds 60 watts. Its noise and distortion levels are far higher (though I can't hear it) than class leading class D amps. But it will let you listen in "class A" i.e. no crossover notch distortion for almost all your listening.

Having said that, I have listened to class D. I heard a modest ICE power amp class D that sounded AWESOME, almost as good as my XPA-1 gen 2 monoblocks. The class D Emotiva PA-1 it was $600. The XPA-1 gen 2 about $2500. I could fit about 5 PA-1's into each of my XPA-1 gen 2 amps. They weighed three pounds versus the 73 pounds of the XPA-1 amp. Don't get me wrong the XPA-1 gen 2 is my go to for my use and yes I do think it sounds just a hair bit better than the Emotiva PA-1. But seriously that class D amp just sounded so good.
Hope that helped. If you did want an XPA-1 gen 2 amp, you can buy them used on the Emporium section of the Emotiva Forum. Post a "WTB (Want to buy) ad" there and someone will sell it to you. Emotiva also has an old XPA-1-L amp which was 30 watts class A and 250 watts @8 ohms. That's on sale right now on the emporium.
 

dlaloum

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Except Klipsch is widely optimistic in their sensitivity ratings. They have overstated them for decades. At best these are 92 db/w, so would require about 6 times your estimate. Even then 150w/ch would hit 105 db reference levels comfortably (which for those who don’t know, is extremely loud).
The point is - in reality a heck of a lot less power is needed.

I use 86db/w speakers and listen at a distance of circa 3m - I almost never use more than 5W - I estimate that the loudest peak my system has ever experienced would have been just under 16W.

To take it to 6m.... would require multiplying my own power requirements by 4... so rather than 16W max peaks, around 64W max peaks...

With my inefficient and difficult to drive (1.6ohm impedance) speakers.... 64W would be ample in the OP's situation

The Klipsches run a lot louder than my Gallo's - so there is every likelihood that in his setup, he would never need more than 32W.

We all like to have more "margin" / " Headroom" - just to be sure!

But a high bias Class A / AB amp, which runs in Class A up to around 30W, then switches to Class AB, would probably be the perfect alternative for the preferences discussed...
Such an amp would almost always be running in class A... avoiding crossover distortion - and it would have substantial peak capabilities beyond that "just in case".
 

CDMC

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The point is - in reality a heck of a lot less power is needed.

I use 86db/w speakers and listen at a distance of circa 3m - I almost never use more than 5W - I estimate that the loudest peak my system has ever experienced would have been just under 16W.

To take it to 6m.... would require multiplying my own power requirements by 4... so rather than 16W max peaks, around 64W max peaks...

With my inefficient and difficult to drive (1.6ohm impedance) speakers.... 64W would be ample in the OP's situation

The Klipsches run a lot louder than my Gallo's - so there is every likelihood that in his setup, he would never need more than 32W.

We all like to have more "margin" / " Headroom" - just to be sure!

But a high bias Class A / AB amp, which runs in Class A up to around 30W, then switches to Class AB, would probably be the perfect alternative for the preferences discussed...
Such an amp would almost always be running in class A... avoiding crossover distortion - and it would have substantial peak capabilities beyond that "just in case".
Agree, except he doesn’t need a Class A amp. He needs a methodical approach, not being distracted by false distractions like Class A will transform your life.
 
D

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Thank you for the concise reply.

The reason i was aiming towards class A is that i have read a lot of information about them being the 'purest sounding' amps that tend not to colour the source with any magic. This would be the easy starting point as i want the amp to sound as natural to the recording as possible. I mean, that's the goal right?

So are we saying that the difference between classes in inaudible?

The reason for the 300 watts, is to drive some RF-7 floor standers I have my eye on.

So if the power requirements of the speaker exceed the capabilities of the budget or the power, or the seaker class vs heat production. Then i need to look at something else in terms of amp class to better suit my budget/speaker requirements.

Thanks again!
Forget about what you have read on class A and crossover distortion on A/B
Those Klipsch towers need a beefy A/B amp. You need more power than you think for transients. And I guess you like loud dynamic music when buying those speakers. You will not be satisfied with two digit watt amplifiers.
What is it you are looking for?

The audiotorium is a mess, as usual...

View attachment 274094

TV: someone getting into big trouble flying into cloud near a mountain ridge without proper instruments in New Zealand.
you are married good, not at all or it's a picture from a shed in the garden.
 
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D

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The point is - in reality a heck of a lot less power is needed.

I use 86db/w speakers and listen at a distance of circa 3m - I almost never use more than 5W - I estimate that the loudest peak my system has ever experienced would have been just under 16W.

To take it to 6m.... would require multiplying my own power requirements by 4... so rather than 16W max peaks, around 64W max peaks...

With my inefficient and difficult to drive (1.6ohm impedance) speakers.... 64W would be ample in the OP's situation

The Klipsches run a lot louder than my Gallo's - so there is every likelihood that in his setup, he would never need more than 32W.

We all like to have more "margin" / " Headroom" - just to be sure!

But a high bias Class A / AB amp, which runs in Class A up to around 30W, then switches to Class AB, would probably be the perfect alternative for the preferences discussed...
Such an amp would almost always be running in class A... avoiding crossover distortion - and it would have substantial peak capabilities beyond that "just in case".
No.
It depends on the music, dynamic range, transients. 32 Watts for these klipsch at anything other than near field? Forget it. Maybe for "girl & guitar" it's fine.

Also no crossover distortion is present in quality amps today.

Watts are cheap. Get plenty and don't worry!
 
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Thorsten Loesch

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Hi

Never posted before. But I am in the search for a set of pure class a Monoblocks with a wattage output of 300w into 8ohms…..

Yamaha MX-10000 comes close at 250W/8R but is not Monobloc:

https://audio-database.com/YAMAHA/amp/mx-10000.html

It actually is a clever mix of a Class A amplifier operating at very low power supply voltage with a powersupply that is modulated to provide extra voltage if needed. A modern Class D Amp would be good in this role.

The CAT Tube Monobloc's have less power, i once had a pair of monoblock 16 KT-88 versions in for rebuild/repair and rather liked them.

https://www.soundstagenetwork.com/revequip/cat_jl2_signature_mk2.htm

Most "Class A" amplifiers sold are actually "high bias class AB", meaning they are class A for the first few watts and then slide into AB.

In practice this a sensible design compromise, as "overbias" increases THD by raising low and even order harmonics (because P & N transistos are not well matched even today) which are inaudible at quite high levels while "underbias" raises high order and odd-order harmonics that tend to be more audible and objectionable.

Due to thermal issues output stage bias for AB amplifiers changes with temperature over time, imprinting a signal history in thermal distortion.

Cheaper AB amplifiers skimp on heatsinks and use "optimum bias" as this measures best in the lab. They are also designed to throttle the bias as the heatsink heats up, leading to underbias after loud passages, often for tens of seconds after the high power event.

So after an FFFF passage the following PPPP passage often is subjected to significant crossover distortion that leads to audible and objectionable distortion not present and measured in the Lab.

Using intentional overbias and heatsinking the Amplifier accordingly eliminates this problem at the cost of a lot of extra metal and higher measured distortion (THD/SINAD) compared the more common solutions.

Finally, in terms of subjective sound quality most Class D amplifiers, TO MY EARS, are still miles behind fairly basic Class AB Amplifiers.

This a direct consequence of "designers" treating them as "audio amplifier" with cursory nods to RF, instead of treating them as high power long wave AM transmitters.

My office has a small china made class AB amp, really simple, essentially a Rod Elliott PA3 near "clone" 30W/4R, with small modifications.

My living room has a 150W/Ch TPA3255 Amp with post filter feedback and some of the most serious design flaws corrected. For music at sane levels the class AB amp sounds way better to my ears.

Thor
 
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LTig

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OK ... the Klipsch RF-7 have a sensitivity of 100db @ 2.83V / 1m - nominal impedance is 8ohm....( we can talk about real impedance later)

If you are listening to them in a large room (requiring more power) - you could be listening to them at say 4m

The base spec, tells you that for an input of 1W (2.83V into 8 ohm) you will get Sound Pressure Level of circa 100db at 1m from the speaker (in free air, away from walls)
Distance will affect this, as the SPL will drop by 6db for each doubling of distance
These are not the conditions in the OPs room. In domestic rooms SPL drops much less with distance, AFAIK rather around 3 dB per doubling.
 

Zapper

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These are not the conditions in the OPs room. In domestic rooms SPL drops much less with distance, AFAIK rather around 3 dB per doubling.
I agree - the inverse square law 6db per doubling distance is for free space, not a reverberant field like an living room.
 

Zapper

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As an aside, this thread has commenters claiming an audible advantage of Class AB over Class D, and others claiming audible transparency for well implemented amps of all classes.

The published double blind ABX testing of amps I've seen pre-date Class D. Are there any recent properly conducted ABX listening trials for Class AB vs D?
 
D

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As an aside, this thread has commenters claiming an audible advantage of Class AB over Class D, and others claiming audible transparency for well implemented amps of all classes.

The published double blind ABX testing of amps I've seen pre-date Class D. Are there any recent properly conducted ABX listening trials for Class AB vs D?
Some reading which may or may not be interesting to you-->
 

antcollinet

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Some reading which may or may not be interesting to you-->
Which for most speakers are not that relevant. If you run electrostatics, then perhaps worry.
 

Zapper

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Some reading which may or may not be interesting to you-->
Interesting but I agree with tonycollinet - not relevent to most users. The NC252MP doesn't like a low-ESR 2.2uF cap on its output. Not something that most speakers would have. Although there isn't anything in the NC 252MP datasheet forbidding it.

A lot of old class AB amps used to have a low value inductor in series with the output to prevent external cap from destabilizing the amplifier. Improved transistor frequency and amp topologies made that unnecessary.
 

dlaloum

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These are not the conditions in the OPs room. In domestic rooms SPL drops much less with distance, AFAIK rather around 3 dB per doubling.

Which would indicate my estimates are more conservative than necessary (ie: less power is needed)
 

LTig

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Which would indicate my estimates are more conservative than necessary (ie: less power is needed)
Way less actually: 6 dB which is a quarter.

Edit: actually not, see posting #121 below.
 
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Blumlein 88

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These are not the conditions in the OPs room. In domestic rooms SPL drops much less with distance, AFAIK rather around 3 dB per doubling.
If you measure it you can find the critical distance which is where reflected sound energy equals direct sound. You'd find the first doubling from close is a 5-6 db drop. Cricitical distance is where a doubling causes a 3 db drop. Eventually the drop with doubling pretty much dissappears as you are in a reverberate field. I've found in most rooms people end up sitting about at the critical distance. In most rooms it is 3-5 meters from the speakers.
 
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