Which amp are you using to power your RTI150's ???

[Tuan Le]

Hi guys,

Currently my RTI150's are being powered by the Onkyo TX-SR800 receiver. It is very annoying, the receiver keep on getting shut off because of overload. I am looking for a 2-channel amp @ 300-500W RMS. Is there any decent one out there at around $1000?

Any help you can give me will be greatly appreciated.

Thanks
-Tuan

[jim_r]

I don't have 150's and I don't have an amp recommendation. But, I am not sure if you need 300 - 500W RMS. Maybe that for dynamic (or peak) power, but not for average power. Remember, that dynamic power is more important than average (RMS) power, since the power requirements for sounds that are very fast and dynamic (like cymbals, bass cello plucks, and explosions) are only needed for very short amounts of time. However, if that reserve power is not available when it's needed, the sound is not going to be dynamic and have that "you are there" sound. It will instead sound weak and flat. You should hear this long before your amp clips or shuts down. In fact, weak treble is a sure sign of an underpowered speaker. Even though the tweeter usually requires a relatively small average power, it's peak power requirements can be as large as the woofer's. I've heard some describe it as "the amp starves the tweeter as it attempts to drive the woofer". I had this same problem when I tried to drive my RTi70's with my old 55W Onkyo. I then upgraded to a 100W Rotel, which definitely took care of the problem. So, that's why a 200W amp will sound better than a 100W amp, even at the same low volume; i.e., because of the peak power requirements at those low volumes which the 200W amp can deliver better than the 100W amp. Anyway, I mention this because it might cost some big $$$ for an amp that can generate 300 - 500W RMS (and it might also be very heavy), when all you really need is one that can generate that kind of wattage dynamically, which should cost less.

There are several people who post on this forum who have 150's and some who have had success with bi-amping their 150's. They will most likely find this thread and give their recommendations soon.

[Dr. Spec]

The best amplifiers have relatively low dynamic headroom (peak power) ratings - typically in the 1.5 dB range or less.

While this may at first blush seem incongruous, it is not. The best amps have extremely robust power supplies that are able to deliver a higher level of continuous power than an inferior amp which is only able to do it in short bursts.

An inferior amp will have a higher dynamic range rating, like 3-4 dB. While this may seem impressive to the uninformed, it is in reality the sign of an inferior amp.

The FCC requires all amps be rated for continuous power output into a given impedance load using the RMS value of the voltage peak of the sine wave. The RMS value for a sine wave is .707 x the peak value.

Regardless, the RTi150 does indeed need an amp rated at 300-500 watts continous. That is not too much power for the RTi150. Remember, doubling the power only yields a 3 dB increase in volume. What the RTi150 needs more than anything is an amp that can deliver high current flow because those six woofers suck a lot of juice and I'm sure the impedance drops to around 4-5 ohms in the bass region of this speaker as it has developed a bad reputation of making AVR-grade amps go into protect mode at even moderate playback levels.

And the reason Rotel sounds better than the Oink is most definitely NOT because it has what you believe is a high dynamic headroom rating. Rotel does not even advertise that rating and with good reason; I'd bet money it is less than 1.5 dB.

The reason Rotel amps sound fantastic is because they use extremely high grade power supplies that can maintain a high level of continuous power into a low impedance load and that translates into a very high current delivery capability. They also have an extremely fast slew rate, and a very high damping factor both of which also contribute to sound quality.

Bottom line - Adcom, Rotel, B&K - high continuous power rating, high current capability, and the ability to drive a 4 ohm load continuously. That's what you need for the RTi150; it is a very power hungry speaker. In closing, consider that most decent subwoofer amps are in the 300-500 watt (continuous) region and that's just for one 12" woofer. The RTi150's three 6.5" woofers per side have similar (or higher) power requirements as a single 12" woofer.

Doc

[Terrax]

I am currently bi-amping my 150's with a RX-V3300 which is powering the tweets and mids, and a Parasound HCA1000a to power the woofs. This is working out wonderfully so far, and I haven't even had to use a Sub during movie palyback. At high volume levels, I have not had one single shutoff and no clipping. The 150's are being ran as large and the rest as small and the 150's are handling triple duty bass fantasticly. Enough to rumble pictures on the wall, vibrate windows, and drive my wife into shreiking (sp). (j/k) she likes the sound as much as I do. It amazes me why some are having so much trouble getting these 150's to power up like they want. I'm certainly am more than please with my current setup. But I do plan to add another 1000a, run both amps bridged to power the woofs in the near future.

[Tour2ma]

Tuan,

First, welcome to the Club.

Jim made several good points in his post. High current capacity (HCC) appears to a must for the 150's from the posts I've read. This is a common spec, but also one that is played with a bit by Manufacturers. I'd look for at least 40 amperes per channel. At minimum I'd also look for a continuous rating in the high 100's.

One of the routes to this level will be high powered amps and one will be middling powered amps. Which route is a matter of your listening preferences (material and level), your room size, do you use a sub, and other factors. For example full orchestra at concert hall levels in a large room with no sub is about as challenging as it gets. A high watt, HCC amp may be needed for the continuous output. For less demanding material a lower rated HCC amp may do just fine as the cuurent demand is shorter in duration.

I think it is going to be difficult to find a new amp for less than $1000 that fills your needs. At $1299 the Outlaw 755 is a 200 x 5 wpc is maybe the best candidate I can think of off-hand, and you can use the extra channels to bi-amp. If you are open to used amps, the field grows considerably.

jim,

A couple points in your post don't match with what I at least think I know.

Top thing is the power required for high frequency. I've never read where a tweeter's demand for power is anything but an order of magnitude or more less than deep bass going to the woofer, even peak demands. Tweeters are often protected by fuses or other circuit elements from high power bursts, which are associated with ultrasonics that accompany clipping.

Also the weak, flat sounding high frequencies are often a result of clipping, either actual or prevented by amp and/ or speaker protection circuitry in modern equipment.

Otherwise I agree with much of what you wrote about dynamic power, current capacity and so forth...

[eclypse]

Can someone put this in laymans terms? hehe.. wow.. ok.. i need something to bi-amp my new Rti12's when they come in soon.

I dont think, well i know i cant afford to drop another grand on something to do the job.. so whats the best bet for me?

I read what you guys are saying.. but can ya show some examples of what to look for in a receiver/amp? All i usually can comprehand is the wattage in the stats.. Is that not a good thing to go by? How do i figure out how many amps a receiver has?

Just wondering cause if i shot to high buying the 12's and am not going to be able to power them worth a damn then i guess i better hold onto the 70's since there new.. though my wife will be pissed cause it will cost us about a $100 bucks to send the 12's back..

[VR3]

Adcom GFA-555 -- 200 watts x 2 (400)
or
The Mono Blocks 300 x1 (700 a pair)


Mono blocks are Adcom also, just cant remember the model number

[Tour2ma]

eclypse,
Might be a little early to borrow Tuan's thread...

Doc,
For the 300 to 500 wpc you're recommending, what load is that at?

[Emlyn]

Short of spending $2K on a Rotel RB-1090 or RMB-1095 and putting 380 watts or 400 watts to each speaker, the best thing I can recommend is biamping the RTi150s or RTi12s with one of Rotel's lower end amps.

There are two ways of doing this by biamping with Rotel for around $1K for a new amplifier with a 5 year warranty. An RB-1080 (200 watts/channel x 2) can be used for the low input and a receiver's amplifiers for the high input. Or, an RMB-1075 (120 watts/channel x5) can have four of its channels biamping with one channel left over for a center channel speaker.
The RB-1080 method gets a total of about 300 watts going to each speaker, the RMB-1075 method gets about 240 watts. Be sure to remove the jumpers from the speakers when biamping.

There may be other new amps that can do the same thing in the same price range but I only have recent experience with Rotel.

The RTi150s will work with a receiver's amps up to a point that varies from one receiver to another. Although my Denon receiver gets warm when driving RTi150s by itself it has never reached shut-down point. However, the more power that can be applied to the speakers, the better they perform.

[VR3]

Adcom GFA-555 200 watts x2...

200 watts on bottum post on each speaker

Adcom GFA-555 200 watts x2

200 watts on top post on each speaker

Total?

400 watts into each speaker.

Total in price? Slightly about 800, if not in the 600-700 range.

Hmmm...

2k of the same power from Rotel or 800 of the same power of Adcom....

Excuse me for the sarcasim I placed above, but Im just missing the logic.

[eclypse]

Originally posted by Vr3MxStyler2k3
Adcom GFA-555 200 watts x2...

200 watts on bottum post on each speaker

Adcom GFA-555 200 watts x2

200 watts on top post on each speaker

Total?

400 watts into each speaker.

Total in price? Slightly about 800, if not in the 600-700 range.

Hmmm...

2k of the same power from Rotel or 800 of the same power of Adcom....

Excuse me for the sarcasim I placed above, but Im just missing the logic.

Is it possable to get away with just using one for the woofers, and just using a 100 watt receiver to drive the tweeters?

[VR3]

Yes, I believe the receiver would be driving the tweeter and midbass, the amp would be driving the subs. Rock On!

[eclypse]

Alrighty then.. Thanks! :)

[VR3]

Anytime, enjoy.

[faster100]

Yes, i have my 150's tweets and mid powered by my receiver and that is less a load then the 70's with 2 mids that it was powering, I have a 100 watt AMC amp on the woofs.. this hasnt shut down yet, although i havent kept going to see.. Im happy with the volume and that is enough for me for now.. Who cares how mych better they sound with more power

[Emlyn]

An Adcom GFA-5500 two-channel amp is about $1200. Output is about at the same specs as the Rotel RB-1080--200 watts per channel.

[VR3]

No!

The ADCOM GFA-555! A older model. It sells for a galent 400 bucks on EBay!

Can ya hear me now? Good Good!

[eclypse]

Your the man Faster! hehe.. yeah i'll be like you if my wife tells me to go to hell with the new Amp.

Man i hope i'm just tired wtih just 3 hours of sleep.. but eh.. I just got my Samsung 61" DLP today and its runing on the floor in the living room cause the damn Tv stand thats made for it was back ordered, Ofcourse!.. Anyways.. I'm starting to think i bought wayyy too big of a Tube and wayyy too big of front speakers (RTi12's) to go with it.. I mean hell my living room is only 13 feet wide.. and somehow the tv and the speakers are gona fit on that wall.. Only place it can go in the condo. The damn fronts are gona be basicly in the corners which i know is a freakin no no! So its gona be super freakin booomy.. Also i wont have no freakin room for an audio rack to store all this damn crap that i have to use to run this home theater.. hehe. man.. i really f'd up bigtime. :(

Damnit its lookin like the only thing i can do is slam some sound proof crap, diffusers,bass trap (whatever ya call it) in the corners and hope for the best..

Damn i should start a new thread for this one.. Anyone else deal with this prob before and came out ok?

[Dr. Spec]

Originally posted by Tour2ma
Doc,
For the 300 to 500 wpc you're recommending, what load is that at?

Amp should be stable and rated for continuous power at 4 ohms, BET. I agree ICC of 40 amps per side min, 60 preferable.

Because of its infamous propensity to shut down most AVR amps that are rated for 8-6 ohms, the RTi150 impedance curve probably drops down to around 4 ohms somewhere in the deeper bass region. It's a real current hog - most AVRs need not apply; I wouldn't dream of running them on large with my 3803 for example.

GFA-5503 or 5802 would be stellar in this application.

That's the problem with any big passive full range speaker - would be owners don't think about the power requirements and buy them on impulse and are frustrated when they don't peform well or send the AVR into protect mode and then they are stuck either selling them or upgrading to a big amp which was probably an unforseen (and expensive) cost at the time of purchase.

[Solaris]

Will some body listen to Sid. I use my Denon 3801 for the tweets and Adcom 555 for the sub ($400 on Ebay). It rocks for music but still lack bass for movie. I'll probably have to move up to the Adcom 5802 for more movie rumbling, but I decided against it and got an SVS PS1. THat should be more than enough.

If you want to stay under $1000 with new amps, get the Samson s700, or s1000 from SVS sub or any other place on the web to drive the subs.

One nice thing about getting a pro amp is they have level adjustments built in. One draw back, most of them have fans and look as ugly as a car radiator. The only decent pro amp without a fan that look have way decent is the Crown K1. But it will run you around $1200 new.

Take this at your own risk. These opinion are based from my own research on amps to drive my 150s.

Solaris

[Emlyn]

This is a good thread here. Solaris got me thinking about the Crown K1 amplifier that's available from SVS for $1099. It is 2 channel, puts out 350 watts/channel to 8 ohms and 550 watts/channel to 4 ohms. As a specialist amplifier for subwoofers, although flexible enough to be used full range, I'd think this may be the best if going the new amp route. A receiver should be able to power the high end of the speakers with ease in a biamp application. After all, they're just like RTi38s on top.

While Sid is right and makes a good point about the used market for amps, the Ebay market is not for me. Little Kid Sid deserves a pat on the head.

My SVS PB2-ISD arrives on Monday and, thanks to Christopher Columbus, I'll be home to receive it, set it up, and shake things up a little more.

[Tour2ma]

Could be a new contender to handle the whole chore...

http://cgi.ebay.com/ws/eBayISAPI.dll...category=39783

[jim_r]

And the reason Rotel sounds better than the Oink is most definitely NOT because it has what you believe is a high dynamic headroom rating. Rotel does not even advertise that rating and with good reason; I'd bet money it is less than 1.5 dB.

Doc

I did not mean to suggest that the Rotel sounds better than the Onkyo just because it has a higher dynamic power. My Rotel is 5X75W RMS and 2X100W RMS. Rotel does advertise it's dynamic power as 5X135W in their 2002 product catalog. Your point about dynamic ratings much higher than RMS is understood. But, there are many who do say that dynamic power is more important than RMS for some of the reasons that I state in my original post. But of course, no one is suggesting that a high, almost gimmic, value relative to the RMS is what you want, for some of the reasons that you mention. In fact, here is just one example of such a discussion of the importance of dynamic power vs. RMS: www.silcom.com/~aludwig/EARS.htm

The best amplifiers have relatively low dynamic headroom (peak power) ratings - typically in the 1.5 dB range or less.

As far as headroom or overhead is concerned, I was referring to the amount of power over the average that is required for the current listening level. For example, if you are listening to a volume requiring 20W RMS, all of the available power up to the dynamic rating is what I am referring to as reserve power. Not just the amount over the maximum rated RMS. I was just trying to address the common misconception that states that if you are only going to listen at low volumes that you do not need a powerful amp. It is because of the dynamic power requirements of the sound above the average power being used at a given volume that you do need a powerful amp to give good, dynamic, "you are there" sound, even at low volumes.

Top thing is the power required for high frequency. I've never read where a tweeter's demand for power is anything but an order of magnitude or more less than deep bass going to the woofer, even peak demands. Tweeters are often protected by fuses or other circuit elements from high power bursts, which are associated with ultrasonics that accompany clipping.

Tour2Ma, the article that I give a link to above discusses what that researcher found concerning the dynamic power requirements for the tweeter, which is where I got that tidbit of information.

Also the weak, flat sounding high frequencies are often a result of clipping, either actual or prevented by amp and/ or speaker protection circuitry in modern equipment.

You may be right about clipping being involved. I was just referring to my own experiences with underpowered speakers. When listening to such a setup, the words that comes to mind most often are "weak" and "flat", especially in the treble. I suppose that actual clipping could be involved in that.

Bottom line is that I just think that 300-500W RMS is overkill for the 150's. Moreover, most people on this forum who have 150's are not giving them near that much juice, and they all claim that they sound really good. I also think that you are going to have a hard time getting a quality amp that can deliver 300-500W RMS for about $1000, which is what Tuan stated that he has to spend. Of course, a lot of people here give examples of such amps, and those amps may sound great. I really don't know because I haven't heard most of them. But, I just think that you need to be careful about the quality of amps with such high RMS ratings at that price level. Amps do affect the sound. Maybe not as much as the preamp. But, different amps with the same maximum RMS power do sound different with the same preamp, and some inexpensive ones with a 300-500W RMS rating could sound not so good.

[tschep20]

Well, I recently upgraded to a Rotel RSP-1066 processor and the Rotel RMB-1075 amp (5x120 wpc) from an Onkyo receiver TXSR500. Right now they sound outstanding in my opinion and obviously that had a lot had to do with the pre-amp upgrade. Regarding the amp, it's putting out some nice clean power for the 150's and hasn't shut down once. I've pushed it pretty hard and loud, but it just puts out some great sound on these speakers. I do plan later down the road to add the Rotel RB-1090 amp (2x380 wpc) to really see what these speakers can do, but for now I'm enjoying them very much for my HT and 2 ch stereo music :D

Now i just have to add that svs sub to picture and my setup is complete. hopefully it will be shipping in the upcoming week ;)

[danger boy]

i'm still sold on external amps to run any speaker. i use Marantz MA500 mono blocks. two of them babies bridged together pumps out 450 W and they are so much less expensive then some other 2 ch amps in the same range. and yeah they are high current.

[Dr. Spec]

Jim:

I think we are on the same page. I misunderstood where you were coming from about peak power. I thought you were specificaly referring to the dynamic headroom rating of the amp.

Clearly, music itself is incredibly dynamic, and the truth is that even the most powerful amps can be driven into clipping by these incredibly high but extremely brief transients.

At one time there were a bunch of different power ratings floating around which were ripe for abuse of the ignorant consumer. For example, there was peak power, peak continuous power, and the more standard continuous power using the RMS value. Peak power for transients is (was) usually measured over 40 milliseconds. I hardly ever see that rating anymore, and unless it is tied to a THD rating AND the waveform is verified to be non-clipped, the number is meaningless.

That is why speaker efficiency is extremely important when you are looking at how loud they can play at say 1 watt/1 meter. Look at Klipsch and you are into the 95 dB region for some models. Plenty loud for almost all listeners. That leaves all sorts of headroom for the amp for those brief but extreme transients. Compare that to a speaker at 87-88 dB with the understanding that the dB scale is log10 and that is a HUGE difference in efficiency and it will speak volumes (sorry) about usable amp power and micro-clipping at moderate playbak levels.

And yes, I agree completely that if your are driving your speakers with say a 20 watt continuous average input and the amp is rated at 50 or even 100 watts, the amp is most assuredly clipping the waveform on transients. But also be aware that for an average efficiency speaker, 20 watts continuous is VERY loud. If you are at 90 dB for 1 watt/1 meter, that is about 103 dB @ 1 meter average sound pressure.

Overall, I was looking at this issue with the RTi150s as being about the sustained power requirements of the woofers at aggressive playback volumes for bassy HT DVDs like Titan AE DTS for example. In the planet forming scene, there is a sustained 25 Hz rumble that lasts for about 5 seconds. On my system, I can hit 116 dB (meter corrected) sustained on that scene at the seat 3 meters from the sub. I would estimate the BASH amp is delivering about 600-800 watts continuous at that point.

If you are running the RTi150 on large, the sub to off/no, and the rest of the speakers on small, that scene will trip any AVR into protect mode immediately at that playback volume. That's more what I was referring to in my original post about the 300-500 watt range being about right for the RTi150. Why buy them if you aren't going to run them on large and one could also argue (less successfully probably) that you might not even need a sub.

I wasn't really getting at the clipping issue on micro-transients in the mid and treble ranges and these can indeed be demanding on an amp in a different way and I agree can make the music sound flat and lifeless with an inferior and/or underpowered amp.

[dholmes]

Im powering my 150 with Adcom 7700 175x5, I have two of these amps for 6.1 it does the job. Its not only the watts its all about the amp being high current! Just my idea.