I think it was the RB-981 that was recently reviewed in Stereophile. If that was the Rotel model that i'm thinking of, it was mentioned that the frequency response and overall linearity of the amp changed as power levels were varied. As such, you might be experiencing / hearing the same things that they made note of. Sean
I don't think it was the 981 if it was a recent review -- the 981 has been out of production for a couple of years. However, if a new Rotel amp had that problem, then an older one might have it as well . . . . I'll have to poke around and see if I can dig up any reviews of the 981 from when it was a current model.
How big is your room? It is possible that when the sound level increases(volume), you are hearing more of the early reflections of the leading transients (reverberation)than the primary sound from your speakers.
Proper speaker placement will help you here. I found a suggestion here at Audiogon recently about "Principles and techniques of speaker placement" it is on the net at Http://www.immediasound.com/speaker_set-up.htm
Hope this helps!
Pat, It sounds to me that you have what's called plain ole amp clipping. Your amp is 200 watts per channel into 4 ohms. That's really not that much if your speakers crave power, as you say yours do. You realy want to consider the ratio of output powers when comparing amplifier power ratings. What you should be concerned about is your dBW level. Just because your 8 ohm amp (probably 100 watts per channel, right?) can give you 200 into 4, doesn't mean anything as far as your db level. You're probably getting less than you think db wise. I'm not familiar with your speakers, but I, too, have hungry speakers. (Revel M20s) Although I can go to 2 o'clock and I still don't clip. But then, again, I'm using a YBA Passion Integre, if that means anything. You probably will do better with 200 watts per channel into 8 ohms. Big decision: change the amp or the speakers. happy hunting. warren
believe it or not but it clips! don't pay too much attention to power ratings since measuring an accurate power ratings consumes too much time for the cheapo amp.
Could you be overdriving the amp's input circuits? If so, why isn't the volume very loud? All the connections are done right, including the speaker wires? Probably a dead end here -- sorry for the incomplete thought. Good luck.
Two possibilities occur to me. The first, and I think the mostly likely, is that you simply are up against the limits of your speakers. My experience is that NHTs do get harsh and ugly as they get louder. Many less expensive (and some more expensive) speakers are like this, a notable exception on the inexpensive end being the Paradigm Reference range which usually sounds better as it gets cranking.
A second is that you are experiencing hearing loss, a sometime consequence of which is the development of rising levels of perceived distortion as SPLs increase. This would require evaluation by an audiologist but it is a very real and well documented phenomenon.
Let's hope it is the former, or one of the other possibilities identified above.
Or you hear the sonic effects of the volume pot on the passive, the impedance of which varies as you turn the volume up. I.e. a variation on what Sean suggested.
What is the output impedance and level of output of your source(probably not the problem, don't sweat it if it's not handy)? What type of cables are using and how long are they? What is the input impedance and sensitivity of your amp? What is the sensitivity of your speakers? What is the volume of space of your room and what is it's construction like? Is it "leaky"? It could be poor system synergy, inadequate system for your desires, or a faulty piece (volume pot?).
I agree, it is the amp that's coming up short. The Rotel RB-981 (130w @ 8ohms) is a fine amp but, most truly muscular amps will double their power at 4 ohms. You are only getting an additional 70wpc at 4 ohms, that's not enough. I had a similar situation when I owned a Krell KAV-500 and a pair of Revel M-20. The Krell, in its time, was considered a brawny amp at 100 wpc and a substantial toroidal transformer. The Revels are, as Warrenh mentioned above, a rather power hungry speaker, 86 db at 4 ohms. At moderate levels the sound was fine but, if I tried to crank it, the soundstage would begin to muddle and then collapse completely. I upgraded to a Plinius SA-250MkIV, a bit of overkill, but I did not want to have to upgrade my amp again and I believe, with this amp, I have accomplished my goal. For you, this may be a little more then you will want to get into but there are other excellent sounding amps with the power to handle your situation. It's also important to understand that not all 130 wpc amps are created equal. As I mentioned above, there are amps that will double down a 4 ohms. So you may want to look for an amp in that power range that will double down, that will should do the trick. I think you would be headed in the right direction if you were to consider an amp upgrade and it might not be as expensive as you might think. Good luck and happy hunting......John
Before rushing off and spending money by changing amps, I strongly recommend you examine your room setup. The Rotel is a reasonably decent amp and the NHTs are not that power hungry. In an unsympathetic room the NHTs can tend towards harshness.
Does you still have the problem if you take the passive out of the system and use the lexicon as your pre? As Gregm says the impedance of a transister based passive changes as volume changes and if you have very few steps on your volume control you could drive your amp to clip at a very low setting on the volume control. Is that passive a good match for your cdp,amp and cables?
Sounds like a mis-match to me. I don't think it's power-starved clipping at all, but a disparity between the output impedance of the passive pre-amp and a low amplifier input impedance. If the RB-981 has an input impedance of less than 47K ohms (26K, 32k ?), then it very well could be the source of distortion at moderate volume settings. This could also be made worse by long interconnects and the 86db efficiency of the NHT's. Just runs out of steam...
Wow -- thanks for the great response!!
I've got some more info:
I had an idea that I SHOULD have had earlier, but didn't think of until I saw Warrenh's post mentioned changing amps OR SPEAKERS. Well, I have three other pairs of NHT speakers in my HT rig, all of which are 8 ohm and easier loads to drive than the 2.3As. I picked the 2.1s, which are full range and with almost the same driver complement as the 2.3As, but with a slightly shorter cabinet and an 8 ohm impedence.
I moved out the 2.3As and put the 2.1s in the same spot -- didn't tweak them, and the 2.1s don't have the NHT Spike Kit bars on the bottoms, either, but I figured it would give me an idea.
It did . . . .
The 2.1s absolutely blew the 2.3As away. The soundstage started big and got BIGGER as the volume increased, the harshness was noticeably decreased, and the bass was much more solid, in spite of the fact that the 2.3A is supposed to go lower . . . .
So I think we can safely say that the problem is some sort of issue with the Rotel driving the 2.3As. I'm going to play around some with your other suggestions, including going back to A/B through the Lexicon. Gs5556, I think the input impedence of the Rotel is 27K, although I am using 2 foot interconnects with a fairly low capacitance between both CDP/preamp and preamp/Rotel.
I'm going to be annoyed if it's the preamp . . . . just bought that, and I really like the sound (or lack thereof) with it in the system as opposed to the Lexicon . . . .
I'll keep everyone posted, and again, thanks VERY much for all the help!
Used Vandy 1b or 1c can be the same price as your new NHT but they can work great with weak and low-powered amps due to the stable impedance. Also for the vertually same amount of funds you can change for small Creek integrated to replace your separates that also has passive preamplification part and there you can start to listen to the music if you love one.
test #1.Could you connect the 9000ES directly to the Rotel power amp and play a not-too loud CD (even beter does the 9000es have a variable output ?).
test #2Alternatively borrow a friend's CD player with a variable output , connect directly to the rotel, and see if it sounds better than your preamp at higher levels.
test#3 borrow an active preamp and experiment.
If any of the above experiments produce the same over-aggressive sound then it might be that the amp is underpowered. Marakanetz was correct to point out that not all watts are the same (well, they are, but the way manufacturers measure them varies). Rotel is a bit of a middle-of-the-road manufacturer ... not at all bad, good value for money, but not all that great either.
If either or both of the above produce a loud, but not so aggressive sound then it would indicate that the preamp is the probably cause of the problems. I don't know why this might be, but it could be an impedance mismatch (since it's a passive pre). In this case switching to an active preamp might solve your problems.
I very much doubt the Sony CD player is the root of the problems.
There was thread about passive preamp not long ago. Some made good points there. The purpose of have an active preamp is to have a more flat input/output resistance across the spectrum as well as input amplitude. This is more important than to provide gain, most of time you probably running pre-amp with <1 gain. For passive amp, you are changing input/output impedance while turn up or down the volume. You will get good result only when your CD player (output R) and power amp (input R) can still match the vaiation of your passive pre.
If you are not happy with the result, change it to a active preamp. Otherwises, you have to switch many CD players and power amp's to fit your passive amp. IMHO, you should get rid of bottle limited parts, not swap good parts to match your passive pre, 10 times effort and make not much sense.
Your players and power amp should not be a problem with normal active pre-amp.
When people tell you shorter path is better, you have to be careful about the statement. It is over-simplified and can be totally wrong in some cases.
I'm not familiar enough with your speakers for this to be anything more than speculation, but here goes...
There's a nasty little thing that happens to most drivers called "compression". And, different drivers introduce different amounts of compression. There's a correlation between relatively high amounts of compression and low efficiency:
Suppose you take an 85 dB efficient woofer and double the input power, perhaps going from 1 watt to 2 watts. The output goes up by 3 dB, right? In theory yes, but not in practice. In this case, the driver's output only goes up by about 2.3 dB. The rest of that energy goes into heating up the voice coil and magnet structure. That .7 dB loss is compression.
Now let's say we have a 91 dB efficient tweeter. The compression will be less - with a doubling of power, we might get 2.7 dB (still not a full 3 dB, but closer).
Because of their differing compression characteristics, these two drivers will only match up at one loudness level. Let's say we pad the tweeter down so that, at 80 dB, the relative level of the two drivers is perfectly balanced. Down at 70 dB the woofer will be about 1.7 dB louder than the tweeter, so the tonal balance will be a tad dull on top. Down at 60 dB it's even worse - the woofer is 3.4 dB louder than the tweeter, so the speakers are duller and somewhat lacking in articulation. Going in the other direction, up at 90 dB the tweeter will be up by 1.7 dB, and the sound a bit forward and a bit bright. At 100 dB, the tweeter is up 3.4 dB, and the top end becomes a bit aggressive.
I don't know if this is what's happening in your situation, but it can happen in the real world.
Best of luck,
That's really interesting . . . . could that explain why the 2.1s sound better than the 2.3As? The 2.1s have three identical 6-inch woofers and a tweeter, while the 2.3As have two identical 6-inch woofers, then a DIFFERENT midrange, then a tweeter. Seems like three different drivers would allow for more "mismatching" than two different types of drivers . . . . How do speaker manufacturers get around this issue?
Seandtaylor99 -- those are good ideas. I'll see if I can dig up an active preamp somewhere to try out. I don't think I want to experiment with running the 9000ES direct into the amp, since I don't think I have any CDs that are quiet enough for long enough to do a real test listen.
Bluefin -- Also good ideas. I think that if it DOES turn out to unquestionably be the passive that's the problem, I will swap preamps rather than trying to swap amplifiers and/or CDPs.
Marakanetz -- Thanks for the suggestions! I think I'd like to stay with NHTs, though, since my whole home theater is built with matched NHT speakers. The Creek would be an option, but that would be harder to integrate into the HT system than sticking with the Rotel amp I have (or another Rotel with more power) and changing preamps, if necessary.
Again, thanks to all!
Disregard my last post. The 2.1s do, of course, have a midwoofer that is different from the two woofers. I was thinking of the fact that their mids are the same as the OTHER NHT speakers I have . . . .