Underpowered situation with LSi15

Big Daddy

I've been informed by the Polk guys that my Harman Kardon AVR 630 (90wX 2channel or 75wx7) is severely under powering my LSi15s, resulting in blown cross-overs. It seems my LSi are starving for additional power and the power supplied by my receiver at higher ranges are causing a major problem.

My HK has Preamp output jacks. First of all what is a pre-amp? and may this be the remedy to my problem? If it is what kind of things shall I look for as for as options on a preamp. I'm having no luck finding clear answers on the web and my HK owners manual is no help either.

Thanks for all of your help

dkg999

The pre-amp outputs on your receiver will run to the inputs on an external power amplifier. You will use the main left and right pre-amp outputs on your receiver. You would use a 2 channel power amplifier, probably a good quality brand with 125 to 250 watts of output power for your LSI's. For some examples go to audioadvisor.com and click on the Adcom or Parasound links on the left side of the page and look for power amplifiers.

And welcome to Club Polk!

Early B.

Blown crossovers? Where did you buy the speakers?

Not sure if this was your experience, but it's a damn shame to go in a store like Tweeter and they typically demo the Lsi series off receivers, but don't inform the buyer that a receiver should not be used to drive the Lsi's. The danger, of course, in informing the consumer approriately would be a significant drop in sales. Is this issue a question of business ethics or ignorance?

2+2

you must be listening pretty loudly to blow crossovers....HK power is pretty strong. As mentioned, get a 2 ch amp and connect it to the pre-outs of the 630. I recommend 200watts/ch at least....I would also look for high damping factor to control the woofer...although some here say it means nothing, it definately couldnt hurt.

mantis

Why people go around buying such nice speakers only to power them with a receiver which doesn't even meet the power requirements????

I'll never understand it. People do your homework before you spend you money.

Dan

Big Daddy

Thank you all for your valued advice, as you as probably well aware of, I do not know much about these things. So what I'm being told is I need to get a separte amp to power my unit? My HK system has output plugs which state "pre-amp", if I plug in amp into these output plugs, won't this cause a major explosion?

Refering to the person who asked where I bought the system. I bought both of them on line through Crutchfield and HK, however I did not speak to an advisor. I researched both the speakers and the Hk individually and both receive very high marks. Regretably I didn't see if they would both match each other. Again I do not know too much about these things, but thanks to you guys I am learning.

Looking forward to your response.

RM

hoosier21

You've got it.

Buy a stereo power amp, new or used, use an interconnect cable to connect the HK's preamp outputs to the power amps inputs, connect your speaker wires to the power amp, no explosion.

Good luck

hoosier21

mantis wrote:

Why people go around buying such nice speakers only to power them with a receiver which doesn't even meet the power requirements????

I'll never understand it. People do your homework before you spend you money.

Dan

Nice and helpful there Dan, glad your still around :rolleyes:

Big Daddy

Dan

You need to chill out! I bought them because I can afford them and I intend to solve this issue, because I can afford to do so. If I didn't do the research it's simply because I do not have the time to do so. Since I own a a multi-million dollar insurance agency I do not have the luxury to conduct a lenghtly research project on compatability. Based on you 6600+ reponses on this forum you obviously have nothing better to than print arrogant and inane remarks. Do us all a favor and use your technical knowledge, if you actually poccess it, to help people out of their dilemas, instead of coming accross like a jerk.

RM

Big Daddy

Hoosier,

Many thanks for your input! I'll check and act on your advice

P.S. I'll by in Indy next month for the US Grand Prix. I go there at least 2 time a year you folks are great!

RM

hoosier21

Have a good time, Indy is a great town.

I moved to Georgia in 1986.

Have you got a budget in mind for a power amp? Many here can give you some suggestions based on how much you want to spend. Is this for 2 channel of part of a home theater?

Russ

Big Daddy

Russ,

Sorry for the delay, I'm at my office and it's been a bit hectic. My Hk is a 7.1 unit and I do utilize it for mainly theater, so I do employ all the speakers. I'm looking anywhere between $1000. to 1500. I'm not sure wheter to go 2 channel or multi-channel, since my problem only seems to affect my LSi15's

polkatese

Big Daddy,

welcome to the club. Check out this amp: B&K AV125.7, it is 4 ohms stable (for your LSi15), ample power for 7 channels,

MSRP is in $1800 range, but you should be able to get one at around $1500 from your local authorized dealers.

http://bkcomp.com/av125.asp

have fun shopping!

DarqueKnight

mantis wrote:

Why people go around buying such nice speakers only to power them with a receiver which doesn't even meet the power requirements????

I'll never understand it. People do your homework before you spend you money.

Dan

This is a direct quote from the LSi15 specifications:

"Recommended Amplifier Power: 20 - 250 w/channel"

So, according to the manufacturer's specs, if I get a 75 or 100 watt receiver, I should be OK, right? WRONG!!

Most of the people who buy audio gear, even very nice, high performance gear like the LSi15's, are not knowledgeable audio enthusiasts. They don't don't know about all the little "unwritten" audio pitfalls, like blowing up your speakers with an underpowered amp. Really, the consumer should not have to undertake a research project in order to obtain such crucial performance information. It should be spelled out up front.

When I purchased my LSi speakers, I didn't receive any caveat that they should be used with a good quality, high current amplifier with a minimum of 200 watts. Stating such would negatively impact sales and would force retailers to provide proper demo facilities. That wouldn't go over too well with today's mass market/appliance megastore type retailers.

It's sad really. The consumer takes his glossy new set of LSi's home, hooks them up to his 50 watt Sony receiver, and all hell breaks loose. Then, Polk gets blamed for making crappy speakers. Think of all the posts you have seen concerning blown crossovers, drivers, or tweeters.

DarqueKnight

Big Daddy,

Here are a some things to consider for best performance from the LSi15's:

1. You need a good quality, high current power amplifier. Less than 200 watts per channel will work, but 200 watts or more is better. Why? The more power the amp is capable of, the less strain will be put on it under normal and peak load operating conditions.

2. The amplifer must be rated for 4 ohm loads.

3. Replace the flat, gold-plated binding post straps with good quality, heavy gauge speaker wire. You should hear an improvement in high frequency detail after doing this.

shack

DarqueKnight wrote:

This is a direct quote from the LSi15 specifications:

"Recommended Amplifier Power: 20 - 250 w/channel"

So, according to the manufacturer's specs, if I get a 75 or 100 watt receiver, I should be OK, right? WRONG!!

Most of the people who buy audio gear, even very nice, high performance gear like the LSi15's, are not knowledgeable audio enthusiasts. They don't don't know about all the little "unwritten" audio pitfalls, like blowing up your speakers with an underpowered amp. Really, the consumer should not have to undertake a research project in order to obtain such crucial performance information. It should be spelled out up front.

When I purchased my LSi speakers, I didn't receive any caveat that they should be used with a good quality, high current amplifier with a minimum of 200 watts. Stating such would negatively impact sales and would force retailers to provide proper demo facilities. That wouldn't go over too well with today's mass market/appliance megastore type retailers.

It's sad really. The consumer takes his glossy new set of LSi's home, hooks them up to his 50 watt Sony receiver, and all hell breaks loose. Then, Polk gets blamed for making crappy speakers. Think of all the posts you have seen concerning blown crossovers, drivers, or tweeters.

There are no unwritten specs. A high current amp with 200 watts of high quality power is not necessary. What is necessary is an amp with at least 50 watts of power rated for 4ohms. Information clearly stated in the manual. I have heard the LSi15s driven by a NAD 50wpc integrated that sounds great, even pushed to fairly loud levels. There's no danger of clipping or distortion, unless pushed to insane levels if you follow those guidelines.

jcaut

I'm a bit surprised that you're blowing crossovers and not tweeters--

Did Polk confirm that the crossovers were blown? What symptoms did you experience and what were the conditions during which the problem occurred?

I'm not questioning any of the advice given in the other replies, and I'm well aware of underpowering/clipping's ability to destroy drivers. It's just that, to me, it looks like it would be hard to tear up a crossover short of overpowering it. Like exceeding the voltage rating of the capacitors or the wattage of the resistors, etc..

Jason

Big Daddy

The crossovers where blown. The circuit board was slightly charred and one of the transistors was brittle to the touch, as soon as the crossover was replaced the speaker worked fine. This is the second crossover and the symptoms where the same as the previous one.

nankerphelge

i've never heard of crossovers blowing. you are severely underpowered, but are you sure this is what caused it? i totally agree with jcaut on this one. the tweeters should have blown, not the crossovers. also did they both blow at the same time? this seems very strange to me. it just seems to me that something else is going on here.

jcaut

It's hard to argue with 'charred'-

I wasn't trying to take this off-topic, either. Sorry. It's just that crossover components are almost always more robust than the drivers that are connected to them- particularly the tweeter. I'd be interested in hearing Ken's input as to why this might have occurred, and/or how common it is.

Shouldn't be a transistor on a passive crossover. Sounds like an overheated resistor, because I think caps will usually blow up. True, the resistors are probably either 5 or 10 Watts, but those wirewound types will sustain significantly more than their rating for some time before they would become charred and brittle. I guess it could be a shorted cap that got hot- it's not something I have experienced, so I'm just guessing. I'm having trouble thinking of how clipping or distortion- the result of overdriving an underpowered amp- would cause damage to the crossover without at least taking a tweeter out with it. Never heard of that happening, in my limited experience.

Jason

Big Daddy

After conversing with Polk guys they all seem to agree that my HK 630's underpower is causing my crossover to overheat, thus evenyually charring. I'll be happy to send Ken my crossovers for futher inspection and his advice would greatly be appreciated. Jcaut was right it was a resistor and not the transistor.

wingnut4772

When I bought my 15s the Tweeter sales guy had no idea what I was talking about when I asked him if my Onkyo reciever was enough for them...so of course he said yes. He was wrong...(in a real world sense anyway for a complete HT set up) and now I have a monster amp! Mwah ha ha:D

dorokusai

Big Daddy - I'll be posting a B&K 2140(2x140) 2CH amplifier in the Flea Market, along with a bunch of other gear, this weekend. It would be WAY within that aforementioned budget. If you're interested keep your eyes peeled.

Big Daddy

After doing some preliminary research, I'm seriously contemplating in purchasing a Monster MPA3250 3 channel amplifier. At 4 ohms it pushes 400 watts per channel. I sense that kind of power will feed my power hungery LSi15's aswell as my LSiC and most of all spare my crossovers. Reviews on these units appear to be good. EBay has them listed below $900.00 new, what do you guys think?

RM

janmike

Welcome Big Daddy.
Just ignore the folks who criticize instead of offering advice. One thought you may want to keep in mind. I for one went down the 2CH amp road and recently purchased a 5CH amp. Keep in mind that if HT is your kick, what will power the centre and rears if you purchase additional LSi speakers? Good luck in your quest.

polkatese

Big Daddy,

Michael's point is right on. If you are into HT, your amp "clutter" and heat dissipation will need to be considered. If you go 7 channels route, a 3 channels amp might not be optimal. Btw, those Monster amps that you can get from eBay new, make sure they come from authorized dealers, otherwise, warranty will not be honored. Have fun!

cfrizz

Hi Big Daddy, welcome!

I concur with both Michael & Polkatese. Sooner or later you will be wanting to feed all of your speakers with lots of power, so you might as well just get on big amp to feed all of them!

Have fun & let us know what you end up getting!

Cathy

Early B.

Big Daddy wrote:

After doing some preliminary research, I'm seriously contemplating in purchasing a Monster MPA3250 3 channel amplifier. At 4 ohms it pushes 400 watts per channel. I sense that kind of power will feed my power hungery LSi15's aswell as my LSiC and most of all spare my crossovers. Reviews on these units appear to be good. EBay has them listed below $900.00 new, what do you guys think?

Nah. As mentioned, you can buy a used 5-channel or 7-channel amp in the same price range. Check audiogon.

Skynut

Another multi amp vote here.
Check out some seven channel models and leave two empty for a while.

George Grand

And nobody tells the man what a pre-amp is. That WAS his question.

BD, the preamp stage of your receiver is the "brain" for lack of a better term. It is the stage where all the decisions are made. For example, louder volume, lower volume, more treble, less bass, switch to FM radio from CD, balance controls. These are all functions of the preamp stage in any receiver, and are the functions of a stand alone preamp as well. The power amp stage is nothing more than the "brawn" or "muscle". Your brain tells you to lift up a heavy box, your body responds like the power amp. It just does what the brain tells it to do.

amulford

Forget the Monster. Overpriced hype.

Go pre owned...