Amplifier power

Hi....Ive used a rotel ra1062 amp ,with quad 22l speakers ,and cambridge audio 740c cd player,for over a year now and the sound is great with music and vocals having a live in the room feel.However after reading many reviews about the cambridge audio 840a v2 amp ,i thought id try that ("upgrade") as it matches the cdplayer.This amp is rated at 120 watts per channel ,has a huge transformer and weighs about 3 times as much as the rotel which is rated at 60 watts.Apart from the sound not being as good as the rotel (possibly doesnt get on with the speakers?),i cant believe how much i have to turn up the cambridge to hit the same volume as the rotel.Listening in my living room id have the rotel volume at most set to 10 to (third of the way up).However to get similar volume out of the CA i have toturn that up to 10 past (2 thirds of the way).The display shows -29 decibels.Why does a 120 watt rated amplifier perform so badly compared to one half its rating?.Could the speakers not matching the amp really have such a performance hit?.
tia
ellison

 

Isn't this likely to be the result of differing input sensitivities on the two power amps?

 

There's a decent article in a hi-fi choice mag about power a few issues back. I found the article (and topic matter) more complicated than previously thought. I don't have an engineering degree and could hardly understand it. The article was fairly useful but still targeted at someone with at least some basic technical understanding (which was a little frustrating for me).

An amp supposedly supplies both voltage and current to the speakers. Volt (akin to pressure) x current (akin to size of a pipe) = power.

A speaker takes in the power. However, a speaker has a resistance rating (in Ohm) plus a decibel per watt rating. That is, I learned how much power it takes to drive a speaker depends on the speaker sensitivity, and how much current is required for a speaker depends on the speaker's resistance specification. For example, a large speaker with good sensitivity of say 90 decibels per watt (ie something like 1 watt will produce 90 decibels of sound pressure) and 4 O (versus bookshelves normally rated at 8 O), will require little power to generate the sound but a lot of current (since resistance is fairly low). Further, I suspect both the sensitivity and resistance are not constant during a track of music.

When you put these 2 together, what it seems to say is that an amp's power rating only gives you partial answer to how much "power" it really has. How much current it can supply is also important - I don't understand how to read that from an amp's spec (but it may be to do with linearity of power versus resistance, eg if power is 100w at 8O does it double at 4O, and even that is weird to me at this point of my beginning stages of understanding these specs since W = V x O, so why W doubles as O halves is strange since it should be V that doubles when O halves to keep W constant).

So a possible explanation is, if a piece of music suddenly drops to say 2 O at a point in time then your amp will require to produce much more current - which rotel might be able to do but cambridge might not.

Also, amp rating is quite trickly because of the logarithmic relationship power versus decibel. That is, it takes exponentially more power to produce additional decibel. Something like, if 80 watts is required to produce 100decibel, then 800 watts would be required to produce 110 decibels. Under this framework, certainly the first watt is the most important and any additinal watts is relatively "cheap". 60W versus 100w does may not be as different as the numbers suggest.

My reply is full of holes but hopefully a start for someone else with more knowledge to explain further...

 

Could it also be how the gain is set. Different think, bu I use a rega cursa + power amps and the gain has three settings, on one you have the volume dial ''off the clock'' before you reach unbearable , on another and just over halfway is unbearable. The power amps output has not changed,but with the first you can acheive much better control over the listening level. especially with the remote.

 

Thanks to all for replies...
@ynmoan
Im not that technical however manuals say
1.rotel RA 1062 impedance =160Mv/24Kohms
2.CA 840a v2 impedance = (just says)20 Kohms
I dont know how that translates in listening terms?

@KW13
Nice read ,though as I say im not technical either .I just expected a £750 amplifier with double the rated output and 3 times the weight due to the massive power supply to sound a little louder through my speakers than it is

@dudywoxer
That intigued me the CA allows you 2 gain controls
1.Input gain trim =Allows gain only to be CUT ,and is used so that all inputs like sky tv,cd,dvd etc can be set at similar levels.Th default is 0 and gain (volume?) can oly be adjusted quieter
2.Fixed level input adjustment.=Can set different inputs to a higher gain ,but then volume wont work and the level is set at that "fixed" volume,so i guess none of these options suit me.The volume control on the CA amp does have better incremental control than the rotel though ,but im worried having to turn the amp to 10 past (sometimes quarter past) or 3/4 of the way up to get similar volume out of my speakers that the rotel had.Could this harm the speakers or amp?The amp doesnt seem to get that hot and has circuit protection so i guess the amps ok but will it harm the speakers long term?.I have to turn the CA up to about quarter to , to get any volume out of the speakers at all.

Ive been reading a few more articles on the quad 22l speakers that i use and one article written by a guy who runs a hifi specialist shop says that the quads sound can change dramatically depending on the amp....more so than any other speakers he has demonstrated at the shop.So maybe it is just a case of speakers dont like the amp.One more thing regarding the actual sound ,which doesn't sound as good (it sounds constrained and held back ...especially vocals)to my ears.Could these specifications (taken from the amps manuals) have anything to do with it?
Rotel ra1062 frequency response =10Hz-100Hz , +1,-3db
CA840A V2 frequency response =10Hz-50Hz ,+/- 1db

Quad 22l speakers =nominal impedance 6ohms
Sensitivity (2.83v@1m)=89db
Frequency response=30Hz-24KH
Frequency Fb=35Hz

The frequency response of the rotel seems to go up to 100hz whereas the ca reaches 50hz.Is that the reason why i get a constrained ,held back feeling when listening to the CA?, or wouldnt i be able to distinguish frequency s in that range anyway?.I can use the CA for up to 30 days with full refund (minus shipping i guess) on return so ill listen to it a little longer,however im already missing the sound of the cheaper rotel.
ellison

 

it could be anything.

for example I changed a potentiometer (Volume control) from an alps to an equally-rated stepped attenuator - and the actual volume per setting was massively more.

 

These 2 amps do have very different volume controls.The rotel is "normal" potentiometer type control ,whereas the CA uses some sort of relay system.It rattles quite loudly turning the volume up or down ,though apparently this is normal for the CA.I tend to think though that this a real good example of how speakers dont like the amp
ellison

 

My strong suspicion is that the difference in volume is due to different gain between the two amps. At the end of the day, if both produce useable volume and sufficiently fine control over volume then it doesn't really matter

 

Thanks i guess i could live with volume ,but im still getting this constrained laid back sound especially with vocals (prominently female).Its almost as if the speaker grilles are put back on my speakers,.It sounds like the vocals are struggling to be set free if you know what i mean.Are the specs i gave indicative of this or shouldn't
i notice at these frequency levels anyway?
ellison

 

It could quite simply be that you prefer the sound of the Rotel
________
Ceramic bongs

 

Mmm that maybe true ,however im trying to analyse why.I dont think its just my taste.At present the CA doesnt seem to deliver the clarity and freeness of vocals through the quads.Im going to set the rotel back up next to it and compare them all day i think.I know some folks regard a "breaking" in period for amps but ,i think after an intergrated amp has warmed up for an hour or so thats about as good as it will get .......or your ears will just get accustomed to the different sound.With a fresh pair of ears this morning im going to compare the two again.
thanks everyone
ellison

 

There was a discussion on WigWam about the new CA preamp which sounds as if they have taken a similar/the same approach to the volume control.

The volume control issue is separate from the sound quality issue I think.

One of the guys who was involved with the design specifically stated that they had calibrated the volume so that there was a lot of fine control in the first half of volume control, (presumably with with very small differences in the level of attenuation with each step). In the second half of the volume control, the volume increases very much more rapidly. This is unlike most typical pot controls where all the action is usually between 8 and 10 o'clock. You will probably find that either preamp will, if the speakers are capable of it, go unbearably loud. In which case not to worry.

The shut in sound thing just sounds like a preference for one over the other. CA claim their amps need some considerable run in before they loosen up (if you believe such a thing of course).

http://www.hifiwigwam.com/view_topic.php?id=28754&forum_id=1

see post 11 for a brief description re the volume control

But the general answer to the question "Why does a 120 watt rated amplifier perform so badly compared to one half its rating?" is that there isn't any reason it should or shouldn't, power ratings having no direct connection to sound quality.

 

Thank you.That reference has helped a me a lot in understanding the way the volume control works on the CA..It has put my mind at ease .Ive just listened to the two amps side by side playing celine dions version of "first time ever i saw your face".I tried to be analytical by describing each instrument ,vocals backing vocals etc ,and overall sound and writing on paper the effect next to each category.The Rotel fails a little on bass clarity but the vocals are almost "live" though they are thrown forward quite a lot overpowering the music at times which i guess gives it that "live" feel.
After listening with fresh ears just nowto the CA ,I must say it DID sound better than yesterday.I played the same song and used the same analytical approach.The bass clarity is much better in the CA and the overall balance of the music is better.The vocals are not so in your face "live" as the rotel which is better in one way as it doesn't overpower the rest of the music ,but as some posters suggest...maybe not what im used to or prefer.I guess its time for some listening again.The guys at richer sounds are great and said i can have full refund no problems so i dont have to hurry in my descion.
Thanks everyone
ellison

 

I wouldn't discount break-in if your unit is brand new... :MILD:

 

If you have the opportunity to take your time it's worth doing so. Very often what seems impressive on initial listen can get a little wearisome long term and conversely what initially comes across as a little more mundane can sometimes be more satisfactory longer term. Not always of course, but very often

PS. Also rather than straight A/B testing the amps. If you have them in the home for a week or two, I'd suggest putting the CA in for a few days to a week and throwing as much at it as you can without trying to be analytical. Just listen to the music as you normally would. Then swap back to the Rotel. You will soon find which you prefer.

 

Thanks for the good advice...will do.
ellison

 

also - leave the CA amp powered on at least for the duration of the next couple of weeks...

 

Hi Ellisonwales

From what you are describing i think this sounds like the way in which two different designed volume controls are working.

Some amps allow most of the control in the first 1/4 and then very little further round. This type of volume control allows very little usable control,say if you are in a small room . The volume control that allows better control is to be prefered IMO i.e one that gives you control over its entire range or at least the first 3/4. If you have just moved from the first type of amp the second type can be confusing as your volume setting will appear higher but in actuality is not ,its just that you have to work further turned if its a volume pot or if its a decimal scale screen ,at a higher printed number.

Your quads are not a difficult load so what you are seeing is just a difference in operation between the two amps. Which you prefer of course is a different thing. Some amps also have a more forward sound . By this i mean that the sound stage starts at the front of the speakers or further back or further forward ,this can also throw you out a bit at first .

Regards D Louth

 

Yes apparently its designed that way,and the amps that ii have or used are the "normal" type ones.Another quirk of this amp is that when turning balance completely to left or right .sound can still be heard from both speakers though not as loud through the speaker opposite to the balance control.This of course is only quirky to me and may be the norm in other amps.Its just ive never owned an amp that doesn't silence completely one of the speakers when you turn balance control one way or the other.Ive now listened to various types music from rancid,pearljam,blink,metallica,to,roberta flack,carpenters etc and the sound is pleasing.The vocals are now exhibiting the live feel that i like.Musically it was always more balanced and controlled than the rotel especially the bass,so at this point i will probably keep it,and use the rotel upstairs.
ellison

 

Hi ellisonwales

Yes i have come across this sort of balance control issue with products from a French company called Carat . There i57 all in one system did this when the balance control was used and as you reduced volume you ended up with a lot of breakthrough/noise. The new version does not have this issue ,i should add and is otherwise fabulous ,best all in one on the
market IMHO.

Run in on amps can be as much as a 100 hours so be patient things will get better the more you use it . Imagine the sound is like a sun flower and it has still to open fully.

regards D Louth