# Recommended Amp for driving a pair KEF R900



## sonixpc (Jan 26, 2012)

hello again everyone,

what amp would you wisely recommend for this setup?

-Stereo 2.0 with two KEF R900. Mostly for music listening (all genres)
-They are hooked meanwhile to an Onkyo TX-NR709. But I can use it as a pre-amp, this one have pre-out for 7ch.
- listening distance 12-15ft. Big living room 17x14x11 ft.

i contacted emotiva and they suggest me to buy two XPA-100 (rated 250Watt @8ohm THD<1%). I like them because I'll have channel separation, plenty of power I guess, and right now are 359USD each.

but of course I want to have a second opinion with you. the idea is they manage the full range since there'll be no bass for now. 

Appreciated any comment.


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## mikmaz (Jan 9, 2014)

You could also look into the rotel power amps. I use an rb1080 with 200wpc into 8ohm. It's a big upgrade from a receiver.


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## WLDock (Dec 19, 2009)

Nice speakers. Deserving of a nice 2 ch pre amp, amp, or integrated.


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## tcarcio (Jun 27, 2007)

Another option could be a pro amp. Lots of people use them including myself and you get more bang for your buck,IMO. B+H photo is having a sale on some nice Crown amps and these are the ones that have very quiet fans. http://www.bhphotovideo.com/c/product/674284-REG/Crown_Audio_XLS1500_XLS_1500_DriveCore_Stereo.html


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## NBPk402 (Feb 21, 2012)

tcarcio said:


> Another option could be a pro amp. Lots of people use them including myself and you get more bang for your buck,IMO. B+H photo is having a sale on some nice Crown amps and these are the ones that have very quiet fans. http://www.bhphotovideo.com/c/product/674284-REG/Crown_Audio_XLS1500_XLS_1500_DriveCore_Stereo.html


Yup Pro amps are a great way to get excellent sound and save some cash. :T :T


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## sonixpc (Jan 26, 2012)

tcarcio said:


> Another option could be a pro amp. Lots of people use them including myself and you get more bang for your buck,IMO. B+H photo is having a sale on some nice Crown amps and these are the ones that have very quiet fans. http://www.bhphotovideo.com/c/product/674284-REG/Crown_Audio_XLS1500_XLS_1500_DriveCore_Stereo.html


Thanks for your suggestion, I didnt know them, On paper they have great specs, and the price is really temptive. Do you have any link to a review?? 
What would be the drawbacks if any vs Emotiva xpa-100?... I assume the cost of two emotiva XPA-100 $700 or the rotel rb1080 $1000 must excel at someting or justify the higher cost.


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## sonixpc (Jan 26, 2012)

ellisr63 said:


> Yup Pro amps are a great way to get excellent sound and save some cash. :T :T


I see this one it's a class D amp. vs emotiva class A/B... sorry for my ignorance, but what are the pro and cons of each one?


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## sonixpc (Jan 26, 2012)

mikmaz said:


> You could also look into the rotel power amps. I use an rb1080 with 200wpc into 8ohm. It's a big upgrade from a receiver.


seems like a good amp, but doing a little search on google I found some people worried about it driving 4ohms loads.


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## tonyvdb (Sep 5, 2007)

Some people say that class D amps color the sound somewhat I think thats one reason many manufacturers stick to the tried and true class A/B amps. Emotiva makes a great amp for the money and no fan noise at all.


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## sonixpc (Jan 26, 2012)

tonyvdb said:


> Some people say that class D amps color the sound somewhat I think thats one reason many manufacturers stick to the tried and true class A/B amps. Emotiva makes a great amp for the money and no fan noise at all.


By color you mean it changes the freq. response. am i right?


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## tonyvdb (Sep 5, 2007)

Yes, some reports say that the High end sounds more "airy"


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## 86eldel68-deactivated (Nov 30, 2010)

sonixpc said:


> ... what amp would you wisely recommend for this setup?
> 
> -Stereo 2.0 with two KEF R900. Mostly for music listening (all genres)
> -They are hooked meanwhile to an Onkyo TX-NR709. ...
> ...


The speakers are 8-ohm and 90dB sensitivity. According to Audioholics, the AVR is _"rated 110 watts per channel at the traditional measurement of 8 ohms, 20 Hz-20 kHz, 0.08% THD, and 2 channels driven."_ The AVR should be more than enough to drive those speakers. But since you're looking for more, I'd go with the pair of XPA-100s.


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## ajinfla (May 10, 2009)

sonixpc said:


> By color you mean it changes the freq. response. am i right?


Hi sonixpc,
That may have been true for some older class D designs, but many of the most modern ones have HF output filters that are load invariant, that is, inaudible to human ears regardless of your speakers impedance. One benefit of class D amps (type, not brand) is that they are very efficient, thus consume less power in daily use, if you are so inclined. For your stated budget, one of these would power your KEFs without drama.
Monoblocks are cool looking, but the purported channel separation issue is audibly benign. What isn't benign is the increased possibility of ground loops over a single chassis.

cheers


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## ajinfla (May 10, 2009)

eljay said:


> The speakers are 8-ohm and 90dB sensitivity.


Hi eljay,
Yes, just like the Q900 are "8 ohm, 91 db sensitivity". Which is probably why Dr Floyd Toole remarks there is far better info of the side of car tires. 
As can be seen, it is anything but "8 ohms":









Amplifier "specs" being only slightly "less worse".

cheers


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## 86eldel68-deactivated (Nov 30, 2010)

ajinfla said:


> ... Dr Floyd Toole remarks there is far better info of the side of car tires.  ...


Yup, that's funny.


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## tcarcio (Jun 27, 2007)

sonixpc said:


> Thanks for your suggestion, I didnt know them, On paper they have great specs, and the price is really temptive. Do you have any link to a review??
> What would be the drawbacks if any vs Emotiva xpa-100?... I assume the cost of two emotiva XPA-100 $700 or the rotel rb1080 $1000 must excel at someting or justify the higher cost.


Here is some more info on the Crown XLS series. https://www.google.com/url?sa=t&rct...=O6qoIQ3AuUXhFkKeGrhONA&bvm=bv.97653015,d.aWw
And here...
https://www.google.com/url?sa=t&rct...7VFeA0VWLZxLcBCpQ&sig2=PfxS_MpGp7S9oASxFTd0mQ


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## sonixpc (Jan 26, 2012)

ajinfla said:


> Hi sonixpc,
> That may have been true for some older class D designs, but many of the most modern ones have HF output filters that are load invariant, that is, inaudible to human ears regardless of your speakers impedance. One benefit of class D amps (type, not brand) is that they are very efficient, thus consume less power in daily use, if you are so inclined. For your stated budget, one of these would power your KEFs without drama.
> Monoblocks are cool looking, but the purported channel separation issue is audibly benign. What isn't benign is the increased possibility of ground loops over a single chassis.
> 
> cheers


Thanks for the explanation, This class D you mentioned is really good looking, pretty small, plenty of power and one thing I appreciate is fanless. but its price equals two emotiva xpa-100 (without S&H), Wont you incline for the emotica anyway? I mean what consistently is better on Class AB than even class D dont have?


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## ajinfla (May 10, 2009)

sonixpc said:


> Thanks for the explanation, This class D you mentioned is really good looking, pretty small, plenty of power and one thing I appreciate is fanless. but its price equals two emotiva xpa-100 (without S&H)


You're welcome. Yes, the SDS-470C is around equal (slightly less without S/H) than the 2 Emotiva monoblocks. But??



sonixpc said:


> Wont you incline for the emotica anyway?


No. But I'm not the one buying either.



sonixpc said:


> I mean what consistently is better on Class AB than even class D dont have?


Nothing electrically or audibly.
Popularity? Weight? More heat? Guess it depends on how one defines "better" with this scenario.


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## TomFord (Jul 15, 2014)

sonixpc said:


> hello again everyone,
> 
> what amp would you wisely recommend for this setup?
> 
> ...


None. Use the surround channels on the Onkyo to power the terminal for the highs. At 6 ohms ( the KEF says 8 ohms but use a multimeter and put it on the terminals. It will read 5.9-6.0. I've purchased some additional R series speakers and none have measured above 6 ohms. 5.7-5.9 is the reading I always get)
the Onkyo is rated at 130 watts per channel. Of course those #'s are never accurate RMS values so I would say with 4 channels driven it would deliver 115-120. × 2 and your right near the highest wattage specs of 250 for the KEF 900 providing it with 230-240. 
Recommend purchasing 20 feet of canare 4S11. Got mine on bluejeanscable.com yet there are many other places. Believe 20 feet would be around 30$. It has 2 positive and 2 negative wires and you could connect to your Front L&R and Surround L&R with the same cable. Cut them both at the exact same length. 
Tried connecting to both terminals on the towers but noticed no difference in a number of configurations and products. 

Don't waste your money. If you feel the need, do what I did and demo one. Go that route to put your mind at ease. Have to admit I had the "more power bug for a few months" thankfully I did demos before learning of no difference. 
Be surprised if you noticed any difference other than slightly cleaner bass below 80 Hz. If music is the primary and you want to get what's best for your system, purchase a subwoofer. The 900's can't handle anything below 35-40 Hz. 40 Hz most likely. Buy what's designed to handle the first 3 octaves. You're actually hurting your speakers when you play anything that has a signal below 40 Hz. Outside of classical, pretty sure all genres hit below that frequently. They try, and the 8' woofer puts up a good fight yet they're simply unable to reproduce that frequency. 

Best bang for your buck subwoofer I've heard that gets the job done and exceedingly more is the NXG BAS 500 which is $240. 

Here's the test bench on my 838 which is rated at 135 to give you a better idea of what your Onkyo will do at 4 channels 

Test Bench
Two channels driven continuously into 8-ohm loads:
0.1% distortion at 134.9 watts
1% distortion at 173.4 watts

Five channels driven continuously into 8-ohm loads:
0.1% distortion at 110.5 watts
1% distortion at 129.3 watts

Seven channels driven continuously into 8-ohm loads:
0.1% distortion at 84.9 watts
1% distortion at 100.0 watts


Read more at http://www.soundandvision.com/content/onkyo-tx-nr838-av-receiver-test-bench#PyQ3HaYTkJelDBCJ.99


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## ajinfla (May 10, 2009)

Hi Tom,
Hard to tell if you're kidding and joking without any smilies, but...



TomFord said:


> At 6 ohms ( the KEF says 8 ohms but use a multimeter and put it on the terminals. It will read 5.9-6.0. I've purchased some additional R series speakers and none have measured above 6 ohms. 5.7-5.9 is the reading I always get)


No. That is measuring the DC resistance of the speaker, not the impedance. Different thing. Won't tell you a thing about the impedance over the audio bandwidth of the system, as I linked earlier for a Q900.



TomFord said:


> None. Use the surround channels on the Onkyo to power the terminal for the highs.
> the Onkyo is rated at 130 watts per channel. Of course those #'s are never accurate RMS values so I would say with 4 channels driven it would deliver 115-120. × 2 and your right near the highest wattage specs of 250 for the KEF 900 providing it with 230-240.


Unfortunately that is also incorrect. You don't double power by biamping. It stays roughly the same. The amp is a voltage source and the XO a voltage divider.

cheers


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## robsong (Apr 3, 2010)

I'm using a Denon 4311ci to drive my KEF Q900 with out any problems at -10. Just ask 
ellisr63 he was at my house this past Sunday checking out my set up.


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## sonixpc (Jan 26, 2012)

tcarcio said:


> Here is some more info on the Crown XLS series. https://www.google.com/url?sa=t&rct...=O6qoIQ3AuUXhFkKeGrhONA&bvm=bv.97653015,d.aWw
> And here...
> https://www.google.com/url?sa=t&rct...7VFeA0VWLZxLcBCpQ&sig2=PfxS_MpGp7S9oASxFTd0mQ


Thanks, it's interesting to know that not necessarily class AB amp are the only way to go in consumer-audiophile speakers right now. I see they talk about noise floor being higher on the XLS 1000, is the noise floor of the XLS 1500 still an issue?, given it'll be installed on a living room?


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## tcarcio (Jun 27, 2007)

sonixpc said:


> Thanks, it's interesting to know that not necessarily class AB amp are the only way to go in consumer-audiophile speakers right now. I see they talk about noise floor being higher on the XLS 1000, is the noise floor of the XLS 1500 still an issue?, given it'll be installed on a living room?


If your pre-amp outputs put out at least 1.4v, higher is better, you shouldn't need to run the amps gain wide open and then the noise floor shoud not be an issue. I run my amp at half gain for my mains and 1/4 gain for the amp for my sub and I reach reference spl's and more with no problem. If you can't find a pre-amp with that much output a Art cleanbox or a Rolls MB-15 is a great idea. I use the Rolls. http://www.google.com/aclk?sa=l&ai=...ls&Q=&sku=217366&is=REG&BI=225&kw=ROMB15B&m=Y


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## sonixpc (Jan 26, 2012)

tcarcio said:


> If your pre-amp outputs put out at least 1.4v, higher is better, you shouldn't need to run the amps gain wide open and then the noise floor shoud not be an issue. I run my amp at half gain for my mains and 1/4 gain for the amp for my sub and I reach reference spl's and more with no problem. If you can't find a pre-amp with that much output a Art cleanbox or a Rolls MB-15 is a great idea. I use the Rolls. http://www.google.com/aclk?sa=l&ai=...ls&Q=&sku=217366&is=REG&BI=225&kw=ROMB15B&m=Y


Great, my question is how can i measure this Vrms at pre-out? i have a true-rms multimeter. AC or DC voltage?


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## willis7469 (Jan 31, 2014)

TomFord said:


> You're actually hurting your speakers when you play anything that has a signal below 40 Hz. /QUOTE] not true. The frequency response and crossover will make sure they're safe.


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## tcarcio (Jun 27, 2007)

sonixpc said:


> Great, my question is how can i measure this Vrms at pre-out? i have a true-rms multimeter. AC or DC voltage?


Your manual should have that info. If you don't have the manual google it. Also I have never done it but I would think you can measure it with a multi meter.


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## Lumen (May 17, 2014)

sonixpc said:


> Great, my question is how can i measure this Vrms at pre-out? i have a true-rms multimeter. AC or DC voltage?


RCA pre-outs are single-ended signals, and so are referenced to ground. But ground may be floated from chassis. Either way, you should get an accurate reading measuring ACV across the RCA sleeve and the center pin.


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## TomFord (Jul 15, 2014)

willis7469 said:


> TomFord said:
> 
> 
> > You're actually hurting your speakers when you play anything that has a signal below 40 Hz. /QUOTE] not true. The frequency response and crossover will make sure they're safe.
> ...


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## tonyvdb (Sep 5, 2007)

I dont want to drag this off topic so lets put this in a new post here regarding running speakers full range causing damage.


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## sonixpc (Jan 26, 2012)

tcarcio said:


> Your manual should have that info. If you don't have the manual google it. Also I have never done it but I would think you can measure it with a multi meter.


You're right on the manual states:

Rated RCA Output Level and Impedance
200 mV/470 Ω (Pre out)
Maximum RCA Output Level and Impedance
4.6 V/470 Ω (Pre out)

Are those values Ok?...


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## tcarcio (Jun 27, 2007)

That should be fine...:T


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## sonixpc (Jan 26, 2012)

tcarcio said:


> That should be fine...:T


Thanks man, After your suggestions and reading a lot about this crown amp, I made my mind and ordered the XLS 1500. Thanks for all.


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## TomFord (Jul 15, 2014)

That's a low priced model I've never heard in home. Know some DJ's that use them on their racks. Intrigued to hear how it sounds? Notice much of a difference? 

When trying new gear I feel there's a placebo effect (for myself and the majority) although I could be wrong. Did you run REW before and after to see the difference in headroom, etc?


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## TomFord (Jul 15, 2014)

ajinfla said:


> Hi Tom,
> Hard to tell if you're kidding and joking without any smilies, but...
> 
> 
> ...



Not when I had the meter set on impedance. The drivers in the KEF R line (haven't measured the sub) all read 6 ohms. 
If we're talking about them being wired in series vs parallel that's a different discussion, but can you clarify on why you believe my readings are DC resistance?

Correct, the power will not double unless you're working with better gear e.g. Emotiva XPA 500. Was using the specs from the test bench to give him a rough idea. It would be near the numbers I stated, tye surrounds would probably deliver 20 watts less than the mains yet it seems the point is moot now


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## gdstupak (Jul 13, 2010)

@TomFord

Speaker resistance is a DC measurement which can be measured with a multi meter. It is a single measurement. (This is what you measured).

Speaker impedance is an AC measurement that is measured with a dedicated impedance meter that uses a sinewave generator. This measurement varies with frequency (see AJ's chart, post #14). This impedance cannot be measured with a simple multi meter.


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