Power for LSi HT speakers

hydrapure05

Hi:

I'd like to know your opinions on the folowing power options I'm considering for a new LSi HT and stereo system. The LSi's I'll be running arre the LSI 15 fronts, LSiC center, PSW650 sub and either the LSi FX or LSi9 rears.

Power options I'm considering are :

Adcom GFA7607 - 125watts @ 8 ohms
Adcom GFA 7807 - 300 watts @ 8 ohms
Adcom GFA 770 - 175 watts @ 8 ohms
B&K AVR507 receiver - 150watts
B&K 200.7 Reference Series Amp - 200watts

Do you guys think these options are acceptable or are there some which will do the job and some whih won't? Thanks

Frank Z

Welcome to the forum!

I think youll find that most of the people around here are big believers in seperates when it comes to Lsi's. You've listed some great choices, but don't limit yourself to just those. A couple of others to consider are Anthem, Sunfire, and Outlaw.

I prefer the FX for surround duties. Direct firing speakers are going to localize the surround channels whereas the Bipole/dipoles will provide a more diffused sound with little to no localization at all.

hydrapure05

Appreciate it Frank. I'll look into those other options you mentioned. Are there any specific model amps and preamps among the other brands you mentioned which you like a lot?

Frank Z

Anthems PVA5 or MCA5 amps get really good reviews.
Sunfire Cinema Grand Series II is an absolute Beast!!
Outlaw 750 is a great amp for a equally great price.

There are a lot of Rotel fans around here also. I cann't comment on them cuz I've never heard one.

polkatese

hydra,
welcome to the forum! good advice from Frank. Based on your budget, the options can be quite numerous. Here are some:

Pre/Pro:
Anthem AVM20
B&K Reference 50
Rotel RSP-1066, RSP-1098
Outlaw 950

Power amp:
Rotel RMB 1075, RMB 1095
B&K Ref 200.7
B&K AV125.7
Outlaw 7100
Sherbourn 5/7100

Receivers:
Rotel RSX-1055, RSX-1065
B&K 507

btw, at 4 ohms, B&K ref 200.7 will produce 375 watts, at damping factor of about 400. A powerful option, along with Sherbourn 7100 with its monoblock design.

I also agree with Frank on LSiFX choice for surround, especially with the size of your listening area. Have fun!

jdavy

FYI the LSI series is a great but it is a 4ohm speaker. You should be looking at high quality 4ohm amps. What does the dealer recommend where you are buying them? Test the speakers out with the amps.

Good luck.

hydrapure05

This will sound stupid of me, but how do you tell if an amp can handle 4 ohms? How many watts should it be rated at at 4 ohms to effectively power an LSi15 speaker set?

Frank Z

You'll need to look at the manufacturers published spec's for the piece of equipment. Most manufacturers will have the specs listed on their websites, product brochures, manuals, etc.

The recommended amplification for the Lsi15's is 20-250 watts, obviously more watts equals a louder speaker. More watts also means you'll have less of a chance of damaging your speakers. Under-amplification can do a lot more damage than over amplification. Think of it this way, If you have an amp that is rated at 400 watts, your ears will never let you use 100% of the available power.

madmax

Forget the new stuff, spend half the cash and buy twice the horsepower used on ebay or audiogon. Carver in particular is a good popular option, especially for great prices on used equipment.
madmax

turbogeek

All the options you mentioned are good ones, although I'd favor the separates versus the receiver path. Any good quality 100 watt at 8 ohm amp which can put out 150-175 watts at 4 ohms with a good signal to noise ratio and decent overhead numbers will drive those speakers just fine and as loud as your ears would want. A good 100w amp will be able to put out well over 100dB's of sound in your HT listening area and lots above that you'll need to be holding a pillow over your head to stop the pain. Most home theater systems, can get along fine with a good 100w amp so long as it can reach down to the lowest rated ohm levels of the speakers.

Just looking at watts is very deceptive. There are a good deal of amplifiers out there which look great watts wise at 8 ohms, only to have pretty bad numbers at 4 ohms. If the amp has a poor overhead or S/N ratio figures these also will affect its ability to deliver good clean power. A well built 100 watt amp with good S/N, overhead, ,etc... will actually outperform an amp rated at a much higher wattage with poorer numbers in other important amp power parameter categories.

Look at the B&K AVR507 receiver listed above for example. This receiver looks great with its advertised 150w/channel number, but at 4 ohms it's only putting out 175 watts. That basically means it's not a true big power sourced amp. A true big powered sourced amp should almost double it's rated wattage when you go from 8 ohms to 4 and 4 to 2 and 2 to 1. If it isn't coming at least in the neighborhood of doubling its wattage, it really isn't as powerful as it appears. On the other hand, look at the Rotel 1075 amp. Only rated at 120 watts at 8 ohms, but a very good 200 watts at 4 ohms. On the surface the B&K AVR507 looked better with its advertised 150 watts per channel versus the Rotels 120 per channel. But look at the amps at 4 ohms and go check out their S/N ratios and overhead figures and tell me if you think you'd rather have the AVR507 pushing power hungry speakers like the LSi's?????????

I'd take the Rotel in a heartbeat matched with a good preamp like the B&K Ref 50!!! And the 120 watts at 8 ohms and 200 at 4 ohms will be plenty of power to give your LSi's good clean power. More than your ears can handle unless you plan on going deaf in the next couple months.

Also remember that when looking at amps of comparable S/N ratios, the higher powered amp will actually sound a good deal worse than a lower powered amp at low to moderate listening levels. you will absolutely hear more hiss in such a situation coming from your speakers with the higher powered amp in this scenario. This is why you should in fact be careful not to "overwatt" your HT system. Unless you are buying a supremely expensive amp with awesome S/N ratios and other parameters like a Krell, at the lower volume levels the higher powered amp setup will produce more unwanted noise through your speakers than a comparable S/N lower amped setup, hope this helped.

hydrapure05

Thanks turbo, that does help. Should I also be looking at NAD products. A friend I work with today, recommended them, but I have never heard of them before, are they good?

madmax

Originally posted by turbogeek
Also remember that when looking at amps of comparable S/N ratios, the higher powered amp will actually sound a good deal worse than a lower powered amp at low to moderate listening levels.

I have never found that to be the case.

madmax

turbogeek

Have you tested such a scenario or listened to it back to back with a higher versus lower powered amp of approximately the same quality and noise ratios?

Most people watch movies at a loudness averaging from 75dB to 85dB. You don't need more than 1 watt from your amp to sustain those averages. However the peaks will be much higher than the average. So, if you have a 100 watt amp (and a speaker with a sensitivity of 93dB), you can generate peaks of over 113dB at one meter - slightly less at 2 or 3 meters. These are high sound levels for any person with functioning ear sense.

The drawback to larger amps is that most have a higher noise floor at one watt than smaller amps. Basically, if your 100 watt amp has a signal to noise ration os 94dB, that means the noise is 74dB quieter than the signal at one watt. If a 200 watt amp has the same s/n ratio, the noise is 71dB quieter than the signal at one watt. The larger amp will have twice the hiss at the same volume level. There are exceptions - some very expensive high power amps have less noise than most affordable moderate powered amps. But with standard, run-of-the-mill amplifiers, the s/n ratio tends to remain about the same regardless of the output power. And at the 1 watt level, the scenario stated above is an acoustical fact assuming the higher powered amp does not have different noise reduction capabilities with the accompanying typically higher noise floor.

kn505

Onecall.com has the ATI 2505 amp on sale at $1550 ($1000 off from regular price). This amp is 250 watts at 8 ohm for each of the 5 channels. It weights at 110 lbs and requires 20 amp wall socket.

madmax

Originally posted by turbogeek
Have you tested such a scenario or listened to it back to back with a higher versus lower powered amp of approximately the same quality and noise ratios?

I've done back to back tests between my Soundcraftsmen amps (160w vs 600w) and between my Carvers (625w vs 1000w). Absolutely dead quiet with zero level input from the preamp. As you turn the preamp way up with no input signal you can get a little noise but it seems the same whether the 160w SC or the 1000w Carver is hooked up. I'm not sure what exact scenerio you have tried but I just have not experienced it.
madmax