High power amps question.

[sredmyer]

I have heard that it is better to have more power than the speakers are rated for and I understand this. I understand the whole clipping thing.

When talking about powerful amps though is the actual rated power (watts per channel) important or is it more important to get a modestly rated amp that doubles its power when the speaker load is halved. IOW is it better to feed my RF-7s (rated for 250 watts rms 1000 peak) with a amp rated at 150 watt into 8 ohm that jumps to 300 watt into 4 ohm. Or is it better to get an amp which has a 400 watt into 8 ohm rating but does not double (or is not even rated) into half the resistance? Is either senario preferable? Why?

[Speedball]

Great question........

[edwinr]

My understanding is that it's better to have an amplifier that is capable of doubling or at the very least increase it's power rated power every time you halve the impedance. A speakers' impedance tends to vary throughout the frequency range. My speakers dip to less than 2 ohms at 20Khz. I therefore require an amplifier that can output reasonable power at very low impedances.

[oldbuckster]

Does one ever have too much HEAD ROOM????????????

[sredmyer]

Does one ever have too much HEAD ROOM????????????

That is the crux of the question; What is headroom?

Is it more rated watts?

Or is it the ability to double the watts when the impeadence halves?

[stormin]

Let me just give you a little perspective with the equipment you are using.

I've powered my Chorus II's with an Adcom 555mkII which I bought when it was new. The bass was tight but was overpowered by the mids and highs because it really doesnt mate well with Klipsch because it is bright and forward sounding. I wasn't done yet. Then I bought the Adcom 565 monos. To be honest not much of a difference. Then I went to an Aragon 4004mkII. Let me tell you there is no comparing Adcom to Aragon. The Aragon which is 200wpc just completely embarrased the Adcom which is 200 wpc and the larger Adcoms which were 300wpc. Much more powerful sounding and now there was bass. The Aragon doubles down from 200@8 to 400@4 . The Adcom 555mkII is 200@8 and 325@4 . Then we go to a current amplifier in the line up which is a QSC SRA 2422. It is 425@8 and 750@4 and it smokes the Aragon in every category you can think of. As you can see the QSC doesnt quite double down and the Adcoms dont either. But I think more than doubling down for klipsch its more about voicing of the particular amplifier. Klipsch like more of a warm laid back amplifier than one that is forward and bright. And here is the kicker the Adcom 565 monos the Aragon 4004mkII and the QSC SRA 2422 all cost right at 2000.00 new. But they are light years of a difference in sound as you progress from one to the other.

Nice avatar by the way[] But as you can see I had mine mounted[]

Good Luck.

[Fish]

Great answer Stormin.After you pick a budget it's more about who makes the amp than if it doubles from 8-4 etc(which is nice but not the main factor).

[sredmyer]

I've powered my Chorus II's with an Adcom 555mkII which I bought when it was new. The bass was tight but was overpowered by the mids and highs because it really doesnt mate well with Klipsch because it is bright and forward sounding. I wasn't done yet. Then I bought the Adcom 565 monos. To be honest not much of a difference. Then I went to an Aragon 4004mkII. Let me tell you there is no comparing Adcom to Aragon. The Aragon which is 200wpc just completely embarrased the Adcom which is 200 wpc and the larger Adcoms which were 300wpc. Much more powerful sounding and now there was bass. The Aragon doubles down from 200@8 to 400@4 . The Adcom 555mkII is 200@8 and 325@4.

So why do you think it sounded so much better with the Aragon? Was this just due to "voicing" of the Amp? I have heard of a few mods to the GFA-555s which change the sonic characteristics of the amp but the power ouput is unchanged. Or was it due to the fact that had more power available as the impeadance dropped?

Then we go to a current amplifier in the line up which is a QSC SRA 2422. It is 425@8 and 750@4 and it smokes the Aragon in every category you can think of. As you can see the QSC doesnt quite double down and the Adcoms dont either. But I think more than doubling down for klipsch its more about voicing of the particular amplifier. Klipsch like more of a warm laid back amplifier than one that is forward and bright. And here is the kicker the Adcom 565 monos the Aragon 4004mkII and the QSC SRA 2422 all cost right at 2000.00 new. But they are light years of a difference in sound as you progress from one to the other.

So we are talking about "voicing" and the sound of an amp. My original question is not really about that. What I am curious about is when looking for a high power amp to work with my RF-7s which type of headroom is more important; shear watts (as indicated by an amps rated RMS) or the ability of the amp to double the power when the impeadance drops.

Nice avatar by the way[] But as you can see I had mine mounted[]

Yeah I like yours better than mine. Not only is yours framed it seems as though the picture itself is of higher quality. I use the same bmp for my HTPC destop background image. Looks kinda cool seeing this image on a 50" plasma in the listening room...kinda sets the tone for what it is all about.[]

[stormin]

So why do you think it sounded so much better with the Aragon? Was this just due to "voicing" of the Amp? I have heard of a few mods to the GFA-555s which change the sonic characteristics of the amp but the power ouput is unchanged. Or was it due to the fact that had more power available as the impeadance dropped?

Yes I believe it was due to the design of the amplifier. I do not know about the mods to the Adcom amplifiers so I really cannot give you an honest answer to that. It's not that the Adcoms do not have enough power. Those things have power to spare but compared to the likes of an Aragon they were designed with more of a budget in mind. More of a bang for the buck so to speak.

So we are talking about "voicing" and the sound of an amp. My original question is not really about that. What I am curious about is when looking for a high power amp to work with my RF-7s which type of headroom is more important; shear watts (as indicated by an amps rated RMS) or the ability of the amp to double the power when the impeadance drops.

I was just trying to help you with pairing an amplifier with your Klipsch speakers. If you are not going to go with a nice tube amplifier you are going to have to find a solid state amplifier that pairs well with Klipsch IMHO. But you might be perfectly happy with your Adcoms and thats great to. You are the one that you need to please. But I dont believe doubling down is the answer for Klipsch. It's great for some of the low impedance swings of the woofers but not a must. But I feel you absolutley have to address not only the woofers but the horns. Also shear watts mean absolutley nothing to me when it comes to amplifiers. To many companies are all over the place with how they advertise wattage. Some amps they brag about being 300wpc arent even 75wpc.

Yeah I like yours better than mine. Not only is yours framed it seems as though the picture itself is of higher quality. I use the same bmp for my HTPC destop background image. Looks kinda cool seeing this image on a 50" plasma in the listening room...kinda sets the tone for what it is all about.[]

Nah I like yours! It has that grungy rock and roll look. Too Cool[H]

[kaiser SET say]

Actually I think they both have a lot of character if you know what I mean[]

Good call on that rating system Stormin' & Wuzzer[]

My big power days where late 80's when I was running 2 NAD 2200's on a pair of JBL 4311B Control Monitors as my mains and when you start hitting those crazy watt peaks the 6db headroom on those's NAD's are what kept the system from clipping although I usually ran mine in the soft clipping mode[]

I have always thought it easier to tear up a speaker with lack of power distortion vs too much power but it really has to do (at least for me) the quality of power you are pushing also! Like Stormin' says some amps might boast 300WPC but not even put out a quality 75WPC and then some amps are under rated for what they produce. I can tell you this my 250WPC rated B&W Nautilus 804's have a 200 W max. input and they can suck the life right out of my BAT VK-200 (100WPC) amp, of course and once again IMO sound darn nice doing so[:$] (OK Max, I not an apologizing Audiophile[])

I have an old SAE RC3 receiver at 30WPC a channel I would not even consider driving the B&W's with but take these 104db Indy LaScalla's and that little 30 watts will rock you to the bone as a matter a fact it's driving the devil out of Seti's 103db Belle's right now and seems to do a little foundation shacking 4 sure.

I guess I feel it comes down to the quality of the power be it tube or SS. Good luck

[Guest " "]

"When talking about powerful amps though is the actual rated power (watts per channel) important or is it more important to get a modestly rated amp that doubles its power when the speaker load is halved. IOW is it better to feed my RF-7s (rated for 250 watts rms 1000 peak) with a amp rated at 150 watt into 8 ohm that jumps to 300 watt into 4 ohm. Or is it better to get an amp which has a 400 watt into 8 ohm rating but does not double (or is not even rated) into half the resistance? Is either senario preferable? Why?"

My take is that it is desireable, only from an impedance perspective.

My experience with home audio equipment tells me you are refering to head room, which usally is equiv to how much more power is available at a lower impedance than the rated impedeance. An example would be the SAE 501 amp (1987 vintage), rated at 250 watts per channel @ 8 ohms continus. It had a published head room value of 1.5 db, which scaled out to 375 watts. The 4 ohm rating of this amp was also 375 watts per channel. But bridged, it cranked out 750 watts. The key feature here is not all the watts, but rather the ability to drive a 2 ohm load. This basiclly allowed 2 pairs of any speakers out in the market place, with out having to worry about tripping the amp protection circuts.

10 years ago spec's look like this:

All channels: 130 watts per channel min. RMS at, 8 ohms, 2 channels driven from 20, Hz to 20 kHz with no more than, 0.05% total harmonic distortion., 170 watts min. RMS at 6 ohms, 2 channels driven from 1 kHz with no more than 0.1% total harmonic distortion.

Continuous Power output (DIN) 160 watts at 6 ohms, Maximum Power output (EIAJ) 200 watts at 6 ohms, Dynamic Power Output (Stereo) 2 ? 300 watts at 3 ohms, 2 ? 230 watts at 4 ohms, 2 ? 150 watts at 8 ohms

So does having an amp that is rated at 130 watts per channel but can drive 300 watts into a 3 ohm load sound preferable? My take is only if you are using low impedance speakers, then the ability to drive 3 or 2 ohm speakers becomes a feature. If you are running a 2 channel system, and want to drive 2 pairs of laScala's, havng an amp that can drive a 3 ohm load would likely not trigger the amps circut protection.

[sredmyer]

Ok so I am starting to get the idea that although my Adcoms are decent enough amps with plenty of power they might not be a particularly good match with my RF-7s. So what do you guys think of the newr Adcoms (ie. the GFA-7807) do they exhibit the same "bright" characteristics as the older (GFA-555) when paired with the RF-7s?

What about any of the mods done to tame the 555 such as the ones performed by these guys

http://www.musicaldesign.com/adcom.htm

Not being the slightest bit technical in electronics nor a golden eared audiophile, I am unsure about these mods. Has anyone here tried them? If not can anyone hear explain the impact of switching capacitors and resistors and such as these mods do. Any thoughts on the value of these mods. Seems a tab expensive to me. After all I could just sell of the adcoms and go for a different amp and the net out-of-pocket would be similar. But then who knows what I might think of the new amp...damned difficult these decsions.[]

[Guest " "]

"But then who knows what I might think of the new amp..."

But at least you can return a new amp until you find one that you like the sound of.

[rsp1068]

A little late in the game here, but, I had used a Rotel RB 1080 w/ 7's, and it is a great combo. It is 200 into 8 ohms. Rotel is a tad warm sounding, wich I like.

On a whim, I thought more is better, so grabbed a Rotel RB 1090, wich is 380 into 8 ohms, its a beast and a 1/2, but I quite honestly liked the way the 1080 sounded, as it became dynamic at a lower db than did the 1090.

If bragging rites are important, more is definately better, but if sound is more important, well, sample a few different amps and see where you wind up.

[heresy2guy]

Does one ever have too much HEAD ROOM????????????

That is the crux of the question; What is headroom?

Is it more rated watts?

Or is it the ability to double the watts when the impeadence halves?

My layperson's understanding of dynamic headroom is this: it's the amount of power an amplifer has to deliver on musical peaks, or bursts, above and beyond is rated RMS power. For instance, if an amp was rated at 100wpc and had 3db of dynamic headroom, then it has enough "reserves" in order to deliver twice it's maximum rated power during musical peaks. In this particular case, that would mean the amp could put out 200 watts total, for short, musical peaks, or bursts.

If a 100wpc amp had 6db of dynamic headroom (like the old NAD and Proton units of the 1980s) then it can deliver four times it maximum rated power during musical peaks. In this particular case, that would mean 400 watts for musical peaks and bursts.

You need to ensure you have enough dynamic headroom to ensure the amp doesn't clip during musical peaks. Clipping is basically just that - the amp runs out of power when the music demands more then it can offer. Amps with high dynamic headroom mean they should clip less because of their high power reserves. This means the music should sound cleaner, with less distortion due to the avoidance of clipping. This also helps to save your speakers.

You can also ensure sufficient dynamic headroom by purchasing a more power amp then you need, i.e. buying a 400wpc amp and then running it more then 100watts RMS which means the amp can still utilize it's full-rated power (in this case, 400 watts) which means that it'll be able to deliver four times its rated power (or 6db, like the above example) for musical peaks, or bursts. Of course, it's pretty difficult to know just how many watts are coming out of your amp at any given moment so this can become quite tricky.

The problem is, most amps today offer poor dynamic headroom - 1 to 2.5db - which means that if you run them towards their maximum RMS, they'll have little left for reserves and will thus clip fairly quickly. Clipping is dangerous because it distorts the waveforms and this damages your speakers. I seem to recall reading something some years back that explained it as the low-frequency waves becomming distorted and then being sent to the tweeter instead of the woofer, which is why when people usually talk of a "blown speaker," they're usually talking about damaged, or "blown" tweeters. The worst thing you can do to a speaker (other then flat-out sending more "clean," continuous power into them then they are designed to take) is to send them excessive clipping, or "dirty" power, which generally blows the tweeters pretty quickly.

High dynamic headroom - regardless of whether or not it's offered by design (i.e. high dynamic headroom built into the amp like NAD and Proton used to do) or by "smart" usage (i.e. never running a 400wpc amp past 100 watts RMS, thereby saving approximately 300 or so watts for reserves) is what is needed to avoid clipping. As a rule of thumb - the more dynamic headroom you have, the better off you are, because the amp is less likely to clip and therefore, your music will sound much cleaner.

The above is just my take on this concept; no need for any engineer wanna-bes to cut me off at my kneecaps for my layperson's approach to it all - lol.

Hope this helps.

-H2G

[sredmyer]

"But then who knows what I might think of the new amp..."

But at least you can return a new amp until you find one that you like the sound of.

Whoops I did say new...I meant new to me (ala ebay)...I am to cheap to buy new.

On a whim, I thought more is better, so grabbed a Rotel RB 1090, wich is 380 into 8 ohms, its a beast and a 1/2, but I quite honestly liked the way the 1080 sounded, as it became dynamic at a lower db than did the 1090.

If bragging rites are important, more is definately better, but if sound is more important, well, sample a few different amps and see where you wind up.

Both bragging rites and sound are important to me. I would say that sound is more important but in truth it probably depends on my mood. Since (as I noted above) I am most likely to get whatever I get from ebay or AudiogonI have to buy it to listen to it...this can get rather expensive (and as I mentioned above I am cheap). So I am just looking to get advice from other who may have been down this path before ponying up any cash (did I mention that I am cheap)[]

Just for the record I do realize that my thrifty habits (that sounds better than cheap don't ya think) are somewhat at odds with this particular hobby...but that half the fun...seeing what great deals I can find.

Thanks to all you of guys for the help and insight

Steve