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Old 02-13-2010, 08:28 AM   #1
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Default Need help choosing an amplifier

I have 4 Sony speakers (2x 6ohm LBT-LX9AV, roughly 100W each, and 2x 8ohm LBT-XB800AV roughly 100W again). My current amplifier seems to power them alright, but it is on the way out and I need a replacement. I don't have much money to spend on this so I'm not sure if this will be do-able or not. Would it be best to get a home amplifier (like a sony, denon, pioneer etc) or manybe like a professional amplifier? I was looking at this for example http://cgi.ebay.co.uk/SONY-STR-DB925...item20af688b33 (it would be nice to be sony as it matches the speakers) but would that be capable of powering my speakers? I used an online calculator to work out the parallel resistance of ym 4 speakers and it came to under 2ohms! So maybe this will not cut it. Thanks for any help.
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Old 02-13-2010, 08:50 AM   #2
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Default Re: Need help choosing an amplifier

That will power the speakers fine.

100W DIN per channel is going to fine for your speakers. You want to plug a single speaker to each terminal on the amp. To start wiring speakers in parallel and stuff will complicate things.

Ideally you want a preamp with some high power amps to drive your set up.
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Old 02-13-2010, 09:04 AM   #3
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Default Re: Need help choosing an amplifier

Hi thanks for the response, it has 4 speaker terminals (excluding the surround terminals) but wouldn't that be parallel as well?
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Old 02-13-2010, 09:11 AM   #4
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Default Re: Need help choosing an amplifier

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Originally Posted by vaio-fx View Post
Hi thanks for the response, it has 4 speaker terminals (excluding the surround terminals) but wouldn't that be parallel as well?
Yes which is why you should use a pair of fronts and a pair of surrounds to connect to your speakers. Connecting them to the A & B fronts and running them at the same time is creating a load of 3.4 ohms per channel across the front channel power amps. It will run this at moderate levels but it will suffer as you turn up the wick.

To use the A & B front outputs you will need speakers rated at 8 ohms.
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Old 02-13-2010, 03:16 PM   #5
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Default Re: Need help choosing an amplifier

Keep in mind that A Newer amplifier isn't nesicarily better than an old one.
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Old 02-13-2010, 03:23 PM   #6
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Default Re: Need help choosing an amplifier

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Originally Posted by vaio-fx View Post
...manybe like a professional amplifier?
To power those Sony speakers you had?
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Old 02-13-2010, 07:02 PM   #7
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Default Re: Need help choosing an amplifier

I got some new speakers since then, they are similar to the ones I had before. I currenlt have an old Denon amp which seems to be able to power all for no problem but it keeps crackling, then I have two full stereos (one for each set) but these take up so much space so it would be ideal if I could get a single amp to power all 4.
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Old 02-15-2010, 03:34 AM   #8
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Default Re: Need help choosing an amplifier

the big trouble is those 6ohm speakers.

if you're putting them in parallel with the 8ohms, you;re getting a 3.something ohm load, which is less than 4, get an amp that will go down to 2 ohms, and you're probably fine. but it's not common for home amps to go down that low, more common for car amps, (and that's usually just to fudge the power ratings so that you can have a 2000W amp running in your car).

if you wire them in series you're only getting 14ohm, so amps designed to drive into 16ohm loads are no good. if you get am amp with dual channels then you;re probably looking at getting 8 ohm loads, so channel a is fine where you have your 8 ohm loads, but channel b has the 6ohm ones on it and is driven too hard.

or you get amps designed for powering 4 ohm loads, and you;re consistently not getting the best out of the speakers at all. as you're attaching either 8 or 6 ohm loads to the channels.

the 6 ohm speakers, I think were most likely sold as consumer speakers that went with a matched hi-fi, and the speakers have probably outlasted the hi-fi...

best advice, get rid of the 6ohm speakers on ebay and use the money to shop for a second pair of 8ohm speakers that match the ones you already have in terms of power.

then you'll find it a lot easier to get an amp. (or the range of amps that are suitable will be greatly improved).
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Old 02-15-2010, 09:23 AM   #9
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Default Re: Need help choosing an amplifier

Thanks root for the help. Thing is the 6 ohm speakers are newer and better than my 8 ohm ones so I don't really want to get rid of them. I do have the orginal stereo systems for both sets of speakers, I have linked both of these together before with a splitter and it sounds great, its just 2 full size stereos take up a ridiculous amount of space. I see what you mean about that low ohmage though, I have been searching all over ebay and can't seem to find a home amp which is affordable and able to cope with that load. I guess all i can do for now is either put up with the crackling noise on my Denon amplifier or wire up both stereos together.

EDIT: Also I was just wondering if anyone has any idea how my Denon amplifier is able to power all 4 of these speakers without even getting slightly warm for ages (although it starts getting hot after 30mins - an hour if you have them on full volume (well about 10/40 as thats all the speakers can take), full bass constantly etc) Although it does this whether you have 2 or 4 speakers playing, seems to make no difference. It is an ancient amplifier, 1988 I think and I think if you have four speakers connected it can only supply 70W per channel (although i can't notice any difference) and It sounds way better than playing the speakers through their orginal matching stereos. Just a shame it crackles every so often (and it has been doing this way before I got these speakers). The model is Denon PMA-520 and it says on the front "High Power Low Impedance Capability" but surely not as low impedance as these speakers need. I'm really confused by this.

So to sum this up, I have this really old 1988 amplifier powering 4, 4 way speakers (all have built in 7 inch subwoofers) and it seems to show no sign of straining. But it surely must be, is it just going to burn out on me when I least expect it or something?
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