Adding a power amp

[Naz.shr]

Looking to add a power amp to Cambridge Audio CXA60 which is 60 watts per channel, will be connected to B& W 706 S2. Never used one before and wanted to ask if there are any issues when adding a power amplifier. 

Thanks. 

[Irek]

It depends, sometimes there might be compatibility issues. 

Saying that, maybe/probably/very likely adding subwoofer will be more beneficial. 

[blakey72]

There shouldn't be any problems however why are you wanting to? What do you think is missing? What are you wanting to achieve? It could be a costly exercise without much benefit. Are you wanting 'louder'?

[Al.M]

A well matched subwoofer like a Rel would fill in the low frequency much better that many small bookshelf speakers can’t manage.

 

If really low frequency and quantity bass is less important to you then maybe sell the CA and get an overall better quality and more powerful amp that can really grip the speakers better. There is an amp shortlist on the amp forum.

[Naz.shr]

1 hour ago, blakey72 said:

There shouldn't be any problems however why are you wanting to? What do you think is missing? What are you wanting to achieve? It could be a costly exercise without much benefit. Are you wanting 'louder'?

Speakers sensitivity is 88db, was thinking adding a power amp around 100 wpc might be helpful in getting more out of the Speakers 

[Al.M]

36 minutes ago, Naz.shr said:

Speakers sensitivity is 88db, was thinking adding a power amp around 100 wpc might be helpful in getting more out of the Speakers 

In similar discussions about whether an amp can drive a speaker well enough, it’s often said that an amp should be able to drive the speaker at its lowest impedance measurement so the B&W speaker brochure says the lowest is 3.7 ohm so is the CA amp able to do that well and it’s own spec brochure says 4 ohm at 90w vs 60w at 8 ohm load, implying maybe not great. 3.7 ohm is getting low so you might find a better result with another amp that can really drive the speaker well at that low impedance load. It’s not only about increasing the watts to 100w as another better amp at say 50w at 8 ohm which doubles easily to 100w at 4 ohm can be better. It’s difficult to know until you try it but the difference in sound can be like hearing a lot clearer treble, midrange coherence and more bass, which might be equal or better than using another power amp. Also, I have never been satisfied using the preamp section of an integrated amp connected to a separate power amp as the matching can be very uncertain.

 

To demonstrate this further I have just discovered that my Kef Ls50 which have a difficult load and usually need powerful amps, works extremely well on my 20w into 8 ohm NAD 3120 amp, much better than other more powerful amps. The NAD 3120 is of course a vintage legend that can triple to 70w into 2 ohm loads. The difference in sound like hearing the speaker twice as loud, much clearer and bass punchy.

 

 

Edited February 24, 2021 by Al.M

[Guest Eggcup the Dafter]

Looking at the specs alone for the Cambridge, if the 706 is anything like the 705s I heard recently the amp is underpowered (90w into 4ohms on the company website). A lot of these B&W designs dip well below 4 ohms and make the case for makers having to quote minimum impedance as well as the usual spec. I’d want a bit more power into 4 ohms, or quoted power a bit closer to doubling to make me feel confident with a speaker that probably goes closer to 3ohm minimum impedance.

You don’t mention your source. What would worry me is if the 706 has that rising treble as well - the DAC may hold you back as much as the power. Especially if you are using the Bluetooth adaptor.

You may need a better integrated rather than a power amp. The Arcam SA30 would suit as a plug-in replacement that I’ve heard with the 705, but is possibly outside your budget?

[Naz.shr]

30 minutes ago, Al.M said:

In similar discussions about whether an amp can drive a speaker well enough, it’s often said that an amp should be able to drive the speaker at its lowest impedance measurement so the B&W speaker brochure says the lowest is 3.7 ohm so is the CA amp able to do that well and it’s own spec brochure says 4 ohm at 90w vs 60w at 8 ohm load, implying maybe not great. 3.7 ohm is getting low so you might find a better result with another amp that can really drive the speaker well at that low impedance load. It’s not only about increasing the watts to 100w as another better amp at say 50w at 8 ohm which doubles easily to 100w at 4 ohm can be better. It’s difficult to know until you try it but the difference in sound can be like hearing a lot clearer treble, midrange coherence and more bass, which might be equal or better than using another power amp. Also, I have never been satisfied using the preamp section of an integrated amp connected to a separate power amp as the matching can be very uncertain.

 

To demonstrate this further I have just discovered that my Kef Ls50 which have a difficult load and usually need powerful amps, works extremely well on my 20w into 8 ohm NAD 3120 amp, much better than other more powerful amps. The NAD 3120 is of course a vintage legend that can triple to 70w into 2 ohm loads. The difference in sound like hearing the speaker twice as loud, much clearer and bass punchy.

 

 

Thanks for the feedback, I think will keep looking for a used integrated in the forums.

[Naz.shr]

26 minutes ago, Eggcup the Dafter said:

Looking at the specs alone for the Cambridge, if the 706 is anything like the 705s I heard recently the amp is underpowered (90w into 4ohms on the company website). A lot of these B&W designs dip well below 4 ohms and make the case for makers having to quote minimum impedance as well as the usual spec. I’d want a bit more power into 4 ohms, or quoted power a bit closer to doubling to make me feel confident with a speaker that probably goes closer to 3ohm minimum impedance.

You don’t mention your source. What would worry me is if the 706 has that rising treble as well - the DAC may hold you back as much as the power. Especially if you are using the Bluetooth adaptor.

You may need a better integrated rather than a power amp. The Arcam SA30 would suit as a plug-in replacement that I’ve heard with the 705, but is possibly outside your budget?

Yes definitely out of my price range. I have spoken to ppl in the B&W Facebook group and Rega Elex-R has been mentioned to work well..  My source is Arcam Aplha 7 cd, Project Debut turntable and Sonos Connect. 

[Bunno77]

If you plan on keeping the speakers you have they will definitely benefit from a sub regardless of the amp you use. 

 

Agree with aim and egg above in every regard. 60w to 100w isn't really worth mentioning. It's the first watt that matters. 

 

I really like your Cambridge and would try a sub first. All pretty common components and would think it pretty easy to demo your setup with sub and or different amp. Think there's some good stores over there. Always best to demo

[Naz.shr]

6 hours ago, Bunno77 said:

If you plan on keeping the speakers you have they will definitely benefit from a sub regardless of the amp you use. 

 

Agree with aim and egg above in every regard. 60w to 100w isn't really worth mentioning. It's the first watt that matters. 

 

I really like your Cambridge and would try a sub first. All pretty common components and would think it pretty easy to demo your setup with sub and or different amp. Think there's some good stores over there. Always best to demo

Thanks for your feedback. What do you mean by the "first watt"? Still learning..

[DJGopal]

There's just no way that little 60 watt Cambridge amp is driving those 88db B&Ws properly.  No chance.

[Cloth Ears]

4 hours ago, Naz.shr said:

Thanks for your feedback. What do you mean by the "first watt"? Still learning..

One Watt per channel (or probably, more specifically, 2.83v/channel) will drive your speakers to 88dB - if you're sitting 1 metre away from them. If that doesn't sound good, then no amount of extra power will make them sound any better.

 

It depends on your listening room size and layout, and your music choice as to what you might need. The 706's don't go below 50Hz, so a subwoofer, taking the output from your 'pre-out' on the CXA60, would definitely benefit your overall sound. But a better amplifier section might also help. Is there a possibility of borrowing a couple of the power amps you are thinking of? Simply plugging them in to the pre-out will give you an indication as to whether you will perceive better sound or not. If it don't grab you in the first hour, then I wouldn't bother - try another amp.

 

1 hour ago, DJGopal said:

There's just no way that little 60 watt Cambridge amp is driving those 88db B&Ws properly.  No chance.

You think? There's amps and Watts and unless you've tried it you will not know. I used an AMC 50 Watt amp to drive a pair of Watt/Puppy (4, I think) pretty darn well - at least, the people who were listening were gob-smacked. Unfortunately, it didn't drive my speakers well enough for me to keep it.

 

Edited February 25, 2021 by Cloth Ears

[Guest Eggcup the Dafter]

4 hours ago, Naz.shr said:

Thanks for your feedback. What do you mean by the "first watt"? Still learning..

The theory is that most of the time music is not that loud, so the bulk of the time, the amplifier is idling and less than one watt of power is actually being sent to the speakers. As a result, the "sound" of the first watt of output of an amplifier is what determines its overall "sound".

The other side of this though is what happens when the louder sounds appear. Now the amplifier has to put out sufficient power at sufficient speed to produce the louder sound properly, and the amp and speaker have to work together to track the decay back to the quieter sound. In fact, even within that first watt, the sound is constantly still getting louder and quieter - the same challenge is there all the time, just to a different degree.

The problem we are identifying with your amplifier and speakers, is to do with those loud transients. At frequencies where your speakers' impedance drops below 4 ohms, you need over twice as much power (current, to be precise?) as for the frequencies where the impedance is actually 8 Ohms. if you are playing at a reasonably loud level, the amplifier may not be able to meet those transients for the frequencies with the lower impedances, resulting in distortion and clipping, despite the amplifier meeting the apparent requirements of the speakers from the headline figure. Indeed, this may not be a problem for you at all, since the actual performance of each item may differ from the specifications quoted (amplifier manufacturers often quote conservatively these days) but the drop in power quoted between 8 and 4 Ohms for your amplifier, and the reputation of B&W 700 and 800 series speakers in this regard, rings alarm bells.
 

If you are sat close to the speakers and listening at a lower volume, this may not be a problem, or only occur rarely.

[andyr]

15 hours ago, Eggcup the Dafter said:

At frequencies where your speakers' impedance drops below 4 ohms, you need over twice as much power (current, to be precise?) as for the frequencies where the impedance is actually 8 Ohms.

 

Not sure that your maths is correct EtD?

 

Say your amp is putting out 100w into 8 ohms.  The equation "power = I^2 * R (where R=8)" means power EDIT: current is the squ rt of 100/8 ... which means current = 3.5a

 

When the spkr impedance drops to 4 ohms, using the same equation we get power EDIT: current is the squ rt of 100/4 - which means current = 5a (not 7a).

 

Quote

if you are playing at a reasonably loud level, the amplifier may not be able to meet those transients for the frequencies with the lower impedances, resulting in distortion and clipping, despite the amplifier meeting the apparent requirements of the speakers from the headline figure.

 

Correct - the amp's PS may just not be able to supply that current.

 

Andy

 

Edited February 25, 2021 by andyr

[aussievintage]

 

All these people who are sure what size amplifier you need.  Try this.  Move your chair half the distance towards your speaker.  You know have 4 times the sound, roughly speaking all things considered etc etc  

 

I am sitting less than 2 metres from my speakers usually, but then I use a 2 watt amp into 91+ db speakers. 

[Guest Eggcup the Dafter]

2 hours ago, andyr said:

 

Not sure that your maths is correct EtD?

 

Say your amp is putting out 100w into 8 ohms.  The equation "power = I^2 * R (where R=8)" means power is the squ rt of 100/8 ... which means current = 3.5a

 

When the spkr impedance drops to 4 ohms, using the same equation we get power is the squ rt of 100/4 - which means current = 5a (not 7a).

 

 

Thanks

[Guest Eggcup the Dafter]

1 hour ago, aussievintage said:

 

All these people who are sure what size amplifier you need.  Try this.  Move your chair half the distance towards your speaker.  You know have 4 times the sound, roughly speaking all things considered etc etc  

 

I am sitting less than 2 metres from my speakers usually, but then I use a 2 watt amp into 91+ db speakers. 

That’s right. A common piece of advice you’ll see is that sound “improves” if you move your speakers further away from the walls., which is often really just making your amp’s life easier when they are nearer you.

(I think that there is a best compromise position with standmount speakers, in particular between bass reinforcement and midrange clarity, and your seating position follows that. My experience is limited though)

 

[Naz.shr]

7 hours ago, Eggcup the Dafter said:

The theory is that most of the time music is not that loud, so the bulk of the time, the amplifier is idling and less than one watt of power is actually being sent to the speakers. As a result, the "sound" of the first watt of output of an amplifier is what determines its overall "sound".

The other side of this though is what happens when the louder sounds appear. Now the amplifier has to put out sufficient power at sufficient speed to produce the louder sound properly, and the amp and speaker have to work together to track the decay back to the quieter sound. In fact, even within that first watt, the sound is constantly still getting louder and quieter - the same challenge is there all the time, just to a different degree.

The problem we are identifying with your amplifier and speakers, is to do with those loud transients. At frequencies where your speakers' impedance drops below 4 ohms, you need over twice as much power (current, to be precise?) as for the frequencies where the impedance is actually 8 Ohms. if you are playing at a reasonably loud level, the amplifier may not be able to meet those transients for the frequencies with the lower impedances, resulting in distortion and clipping, despite the amplifier meeting the apparent requirements of the speakers from the headline figure. Indeed, this may not be a problem for you at all, since the actual performance of each item may differ from the specifications quoted (amplifier manufacturers often quote conservatively these days) but the drop in power quoted between 8 and 4 Ohms for your amplifier, and the reputation of B&W 700 and 800 series speakers in this regard, rings alarm bells.
 

If you are sat close to the speakers and listening at a lower volume, this may not be a problem, or only occur rarely.

Thanks for your explanation, still lots to learn

[Al.M]

Also, as mentioned before while a subwoofer can make a big difference in the bass extension, depth and overall quantity, do you really need all that if your expectation of bass isnt there, music tastes don’t demand it or you feel no need. 50hz at +/-3 dB for your speakers on paper is quite sufficient as many bookshelf speakers only manage around 60-70hz bass extension and it’s about the same or close to what many medium size floorstanding speakers can do.

 

If the amp is only sounding average with the speakers with dull voices and treble, you could end up with that plus a big bass that is just a big blurry sound. In addition, subs need quite good matching with the speaker to sound coherent and not muck up the stereo imaging and bass punch and texture.

 

My general preference for a good stereo system is not to use a sub for those reasons, instead to try to achieve the best possible with the two front speakers first, and if not satisfied only then look for the extra bass  with a sub.

[DJGopal]

19 hours ago, Cloth Ears said:

You think? There's amps and Watts and unless you've tried it you will not know. I used an AMC 50 Watt amp to drive a pair of Watt/Puppy (4, I think) pretty darn well - at least, the people who were listening were gob-smacked. Unfortunately, it didn't drive my speakers well enough for me to keep it.

 

There's being able to drive a speaker well enough for it to work, then there's being able to drive a speaker well enough to control it properly. 

Those B&Ws are extremely power hungry.  I'd be willing to bet money that the bass drivers are barely moving and that when you turn the volume up, only the mids and highs get louder and then break up.

You need an amp with lots of Watts, Amps and Damping factor for speakers like those.

[Guest Eggcup the Dafter]

1 hour ago, DJGopal said:

There's being able to drive a speaker well enough for it to work, then there's being able to drive a speaker well enough to control it properly. 

Those B&Ws are extremely power hungry.  I'd be willing to bet money that the bass drivers are barely moving and that when you turn the volume up, only the mids and highs get louder and then break up.

You need an amp with lots of Watts, Amps and Damping factor for speakers like those.

It's 88dB/w at one metre into 8 Ohms, I doubt a lot of watts (by modern standards ) are really needed. Without opening a massive can of worms, I don't believe you need a massive damping factor with B&W bookshelves either, though this comes from anecdotal reports rather than any experience.

What you do need is the ability to drive the lowest impedences that they reach. You need sufficient amps. A reminder of what I got wrong...

 

18 hours ago, andyr said:

 

Not sure that your maths is correct EtD?

 

Say your amp is putting out 100w into 8 ohms.  The equation "power = I^2 * R (where R=8)" means power EDIT: current is the squ rt of 100/8 ... which means current = 3.5a

 

When the spkr impedance drops to 4 ohms, using the same equation we get power EDIT: current is the squ rt of 100/4 - which means current = 5a (not 7a).

 

We shouldn't forget sufficient heat dissipation, and that with valve amps distortion comes into the picture in a different way.

Even apparent powerhouse amps can have problems in this regard. Looking at the Marantz  amplifiers, the big (and class D) PM-10 is measured independently at 550w plus per channel at 8 ohms in different reviews, despite the spec saying 200W/channel. Because it's bridged, and they used "sensible" power supplies, it may not drive a difficult speaker as well as the smaller Model 30, which has a decent power supply into single modules and is rated 100W/channel. The headline figures rarely tell the whole story.

[GregWormald]

A lot of what's above is correct.

 

You want to get "more out of the speakers" isn't specific enough.

More what? Overall volume with same quality? More bass to fill the room? More quality?

 

Overall volume, same quality? 100 watts won't do it. Doubling the power only gives you another 3dB which would be barely noticeable. Tutorial here.

 

More bass? A powered sub-woofer would definitely help, as properly set up it would take some of the bass load off the speakers. Bass takes most of the power of an amp.

 

More quality? Better pre/power or integrated. The Cambridge has a fairly good quality reputation so more here could get expensive.

[Guest Eggcup the Dafter]

14 minutes ago, GregWormald said:

A lot of what's above is correct.

 

You want to get "more out of the speakers" isn't specific enough.

More what? Overall volume with same quality? More bass to fill the room? More quality?

 

Overall volume, same quality? 100 watts won't do it. Doubling the power only gives you another 3dB which would be barely noticeable. Tutorial here.

 

More bass? A powered sub-woofer would definitely help, as properly set up it would take some of the bass load off the speakers. Bass takes most of the power of an amp.

 

More quality? Better pre/power or integrated. The Cambridge has a fairly good quality reputation so more here could get expensive.

Good post. I think we've jumped onto a perceived mismatch between amp and speakers, and have dealt with the amp side in our posts.
Generally, this would be my preferred approach for two reasons - firstly people choose their preferred sound when buying a speaker, and secondly, if they are happy with the speakers and they're not a mismatch to the listening space, I think it's best to get the most out of those speakers before upgrading. Upgrading speakers is often more painful than the rest of the system.

Upgrading in terms of watts into 8 ohms, I agree. This looks to be about current and driving the minimum impedance.

But we should have asked about the  the room and the position of the speakers and listener as part of this... it may be that the speakers are completely unsuited to the task, or something about the room size or reflections are actually damaging the sound quality. We'll look stupid if a rug on the floor is all that's needed here, won't we?

@Naz.shr details please?

[DJGopal]

Meep

Edited February 28, 2021 by DJGopal
Meep