4-Ohm Amp Question relating to LSi-15s

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sdurfee
sdurfee Posts: 8
edited April 2004 in Electronics
Hi. Here's the deal. I have a Pioneer Elite 35TX receiver that is 90W x 5ch at 8ohms. Needless to say, the 4-ohm Lsi-15s that I bought don't sound that good. I'm really dissapointed but it's probably my own fault since I didn't really plan or know what I was doing. My inexpensive Wharfedale bookshelf surrounds and center our rated at 100W, 8ohms. I think the Pioneer handles them fine. Since the Pioneer has pre-amp RCA connections to run additional amplifiers, can I just hook up a 250w x 2ch 4-ohm amp for the Lsi-15s? The Lsi-15s recommend 20 to 250W per channel at 4-ohms. Should I go with the highest allowable (250w x ch)?

My second question is regarding designer, high-cost amps. I don't have the money to be buying a new Carver, Rotel, B&K, etc. and I'm not that big of a spender or audiophile to justify the cost. I'm looking at amps that are typically used by musician types (Peavy, Nady) and they are SERIOUSLY cheaper. For $300, I can get a Nady SRA-2250 that is 2-4-8 ohm compliant, convection cooled, low cut filters, 2 x 250w at 4ohms, THD <.05, RCA inputs, headphone jack, etc. Check out this link and tell me if this is suitable or if I'm crazy

Last question is what is the term "bridged" mean?

THanks for your help.

- Steve
Post edited by sdurfee on
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  • organ
    organ Posts: 4,969
    edited March 2004
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    Yes, you can use the RCA out's to connect to an external amplifier. You don't need 250w/ch. The gain achieved by going 250w/ch compared to a 125w/ch is only 3db. So even a good quality 100w/ch can drive them nicely.

    I wouldn't go for the amp you provided on the link. While looking at the specs, the amp uses a switch for the 2/4/8 ohms speakers. The switch acts as a current limiter, thus you won't get the juice needed to make the LSi sing. The current limiter is there to prevent the amp from overheating while driving low impedance speakers. Impedance swithing can be found in low quality receivers. I bet the amp section of the 35TX is better than that amp. A good amp should increase power output as the impedance goes lower without any impedance switching.

    I know your budget is $300 but if you save up a bit, there are plenty of great sounding amps in the $500 range. You should also look for a used amp.

    Bridging is the ability for the amp to become a mono block. The power output will double but it will only be able to power one speaker. So a 150w/ch could put out 300w into ONE speaker. You'll need two amps if you want to bridge.

    DO NOT bridge the LSi speakers. When bridged, the load seen by the amp is reduced by half. So a bridged amp will see the LSi15 as 2ohms nominal instead of 4. Bridging should be done with 8ohms or higher speakers.

    Maurice
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  • sdurfee
    sdurfee Posts: 8
    edited March 2004
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    What would you recommend ? Is a B&K ST-140 (105w ch) for $300 a good deal? Are the used dealers that provide better prices than eBaY for quality amps? I appreciate your input about the only 3db difference .... still, the Lsi-15s have passive subwoofers and I'm just afraid of not having enough power.
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  • organ
    organ Posts: 4,969
    edited March 2004
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    I have no experience with B&K but there are several members here who own B&K amps and love them. Is the $300 price tag retail price? You should be able to find lower than retail prices if you go to a dealer. I'd rather buy from a used dealer than ebay. You can have a look at the amp and test it out before buying. I"m sure the 105w/ch should be enough unless you're planning to pump them to ear piercing levels.

    Good luck

    Maurice
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  • organ
    organ Posts: 4,969
    edited March 2004
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    Originally posted by sdurfee
    What would you recommend ?

    I ran my LSi9 with a NAD C270 and loved the sound. It has been replaced by the C272 http://www.nadelectronics.com/hifi_amplifiers/C272_framset.htm Great sounding and very powerful amp. It has their "Impedance Sensing Circuitry" to maximize power transfer to your speakers. A good thing for the LSi IMO. Retail is around $500 but you should be able to find it cheaper at a dealer. If they still have the CS270 leftovers, I'm sure you'll be able to get them at a clearence price.

    Maurice
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  • VR3
    VR3 Posts: 28,050
    edited March 2004
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    Adcom GFA-545 or 545 II...

    200 bucks, 125watts or 150 watts into 4 ohms.
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • LuSh
    LuSh Posts: 887
    edited April 2004
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    Don't be so concerned with the "wattage" this number is not usually realistic anyways. I wouldn't suggest a Tube Amp but by the same token 80-100 will be just fine.

    Consider buying an entry level intergrated from a host of higher end makers like classe', SimAudio, or Arcam.

    A used Classe or SimAudio from Audiogon can be had for about $700 US. These have hometheatre bypassable switchs. Allowing you to use the amp section for home theater and both the pre and amp sections for two channel music. The gain control is fed via the Elite.

    While the power of an amplifer is important, the most overlooked part, aside from the source, is the pre-amp.
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  • criverajr
    criverajr Posts: 1,675
    edited April 2004
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    Sdurfee,

    I would check audiogon, they have just about every amp for sale at some good prices, you could probably drive those 15's with a good RB980BX amp from Rotel, I have the 960BX, which Russman also has and it'e a great amp, give it a try and see what you think, I can't speak as to B&K because I have never owned one but I live my Rotel.

    CRj:)
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  • sdurfee
    sdurfee Posts: 8
    edited April 2004
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    This is a dumb question but I've never hooked up a 4-ohm amplifier to a 8-ohm receiver. Beyond hooking up the RCA left and right to the amplifier from the receiver's outs, my question is this:

    In 5 channel channel stereo mode (I'm not a big fan of surround sound on DVDs but I do like multi-channel sound on CDs), does this receiver use the entire 90w x 5 ch at 8 ohms *in addition* to a 150w x 2 ch at 4 ohms for the amplifier I'm going to add? .... Or, does it say "hey, there is an amplifier hooked up to the dude's main front 2 channels and we will bypass those channels alogether and focus the energy on the centers and surround which are 8-ohm speakers? Will I still set up receiver's front speakers to LARGE and all that jazz.

    Thanks for the insight.

    - Steve
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  • Frank Z
    Frank Z Posts: 5,860
    edited April 2004
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    Let me try to clarify. The amp and receiver are not 4 or 8ohm, rather they are rated to drive a speaker with a given nominal (average) resistance (measured in ohms).

    The connection is simple, 2 pair of RCA interconnects from the receiver preouts to the amplifier inputs. At this point the signal leaving the receiver is the same as the signal that would normally be sent to the receivers internal amplifiers. The signal being delivered to the amp will then be boosted (amplified) and delivered to the speakers. All you are really doing is removing 2 of the receivers internal amplifiers from the equation. The receiver will no longer be affected by the lower resistance of the Lsi15's because they are being powered by the separate amp.

    Calibration with an SPL meter after installing the new amp is really important. The idea is to use a Sound Pressure Level (SPL) meter to insure that all of the speakers are set to provide the same output (measured in Decibels). Here's a link that you might want to check out.

    A little warning. Once you connect a separate amp you're going to start wondering how the rest of your system will sound with a separate multichannel amp driving the balance of your speakers. Then you're going to start asking about a separate preamp instead of a receiver, etc, etc, etc.

    It's sickness I tell ya!!! And there ain't no stinkin' cure!!!;)
    9/11 - WE WILL NEVER FORGET!! (<---<<click)
    2005-06 Club Polk Football Pool Champion!! :D
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  • sdurfee
    sdurfee Posts: 8
    edited April 2004
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    I can get a used Adcom GFA-545 in the $200 range and a 555II in the $300 range. Should these be adequate to drive just the pair of Lsi-15's or should I be look at something else? My main objective here is to not spend over $500. Maybe someday. But not now.

    - Steve
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  • Frank Z
    Frank Z Posts: 5,860
    edited April 2004
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    The Adcom Manual for the 545 only listed the output into 8 ohms, not 4.

    The bottom of page 5 of the 555ii manual states that it can drive a speaker with an impedance (resistance) as low as 2 ohms, so the 555ii would be the better of the two.
    9/11 - WE WILL NEVER FORGET!! (<---<<click)
    2005-06 Club Polk Football Pool Champion!! :D
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  • VR3
    VR3 Posts: 28,050
    edited April 2004
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    The 535, 545, 555 all can power 4 ohm loads.

    Look at the *COMPLETE* Manual eh??

    http://www.adcom.com/pdfs/gfa545iimanual.pdf

    150 watts into 4 ohms :D Have a great day!

    The 545 manual also states it has the capability to drive low impedence loads. (They only show like 5 pages of the manual...)

    If you were to use the Adcom GFA-545 for the LSi.

    Either 545 can handle your LSi. the 555 is harsh on the top end. (according to a reviewer on Adcom's site)
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Frank Z
    Frank Z Posts: 5,860
    edited April 2004
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    Originally posted by Vr3MxStyler2k3
    The 535, 545, 555 all can power 4 ohm loads.

    Look at the *COMPLETE* Manual eh??

    http://www.adcom.com/pdfs/gfa545iimanual.pdf

    150 watts into 4 ohms :D Have a great day!

    The 545 manual also states it has the capability to drive low impedence loads. (They only show like 5 pages of the manual...)

    If you were to use the Adcom GFA-545 for the LSi.

    Either 545 can handle your LSi. the 555 is harsh on the top end. (according to a reviewer on Adcom's site)

    Before you take your pacifier out and start spouting bullcrap, the way you normaly do...
    perhaps you better clean your freakin glasses and re-read the post. 545, not 545ii, is what he was asking about.

    Children should be seen and not heard!
    9/11 - WE WILL NEVER FORGET!! (<---<<click)
    2005-06 Club Polk Football Pool Champion!! :D
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  • VR3
    VR3 Posts: 28,050
    edited April 2004
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    The 545 and 545 II are basically the same thing.

    The 545 can handle low impendence loads as the manual says it can. The 545 manual, not the 545 II.

    The 545 II has a spec sheet on it.

    Both the 545 and 545 II can be had for 200 or so dollars, and both can handle the LSi line.

    I'm saying the same dang thing I said above. Maybe with less sarcasim, sorry I offended you in anyway Oh obi wan co nobi!

    I think the guy gets my point though! Either will work, for safety go with the 545 II.

    In the 545 manual, read the wattage rating on the 2nd or so page, then read below it *ability to handle low impendence*

    Frank,
    I own the 545, and the 545 II. I am here to tell you that their differences are nothing big. They weigh about the same, they look the same. They perform the same. The differences in them are little.

    Which is why I said look at the 545 II manual. The 545 and the 545 II are NOT that different. BOTH can handle lower loads.
    - Not Tom ::::::: Any system can play Diana Krall. Only the best can play Limp Bizkit.
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  • Tour2ma
    Tour2ma Posts: 10,177
    edited April 2004
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    Yes, there a number of used choices in te $200 to $300 range.

    Back to an earlier question... The ST140 is a nice amp, but not at $300 for a used one. $200 is more like the going ebay rate, maybe a tad more, $220, if the bidding heats up.

    Do consider though that any ebay, audiogon buy is plus shipping, so you can go a bit more if local to you. Of course then sales tax kicks in...

    Good luck and welcome to the Club...
    More later,
    Tour...
    Vox Copuli
    Better to remain silent and be thought a fool, than to open your mouth and remove all doubt. - Old English Proverb

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  • sdurfee
    sdurfee Posts: 8
    edited April 2004
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    I won an Adcom on eBay (GFA-545) for $152.50. Hopefully, this will do the trick in driving the Lsi-15s.

    Thanks for everyone's opinion and suggestions.

    - Steve
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  • organ
    organ Posts: 4,969
    edited April 2004
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    Congrats. Your LSi should open up and sound more dynamic. Let us know how it turns out. I don't think there's anyone here using the 545 for LSi.

    Maurice
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