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pre amp for 7 channel, multi room system?

John Parkey

John Parkey

Member
Greetings everyone. Some sales guy at Magnolia HiFi set up a system for my friends. In wall speakers in 7 rooms, separate volume control in each room, B&K 2 channel pre amp and then B&K 2 channel amp. Originally another amp, that that amp stopped working. Now the B&K amp has stopped working. I am pretty sure it is because the speakers are coming in parallel and presenting a very low ohm impedance to the amp. The only reason it has worked at all is because the volume control in most of the rooms is at zero at any given time. So, I am trying to help them but have never worked with multi channel systems. We can get a 7 channel power amp. The question is how to set up the pre amp
1) is it safe to drive 7 channel using a 2 channel pre amp? I would think not, and it would take quite a custom RCA cord to go from 1 to 7.
2) does anyone know of a pre amp or even receiver that will allow all 7 channels to be driven in stereo? We want stereo in each room.

Thank you for your help!

John
 
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The Magnolia guys have access to switching boxes like donprice is alluding to. Your friend needs to make them get in their pocket and install one after the amp so that each pair of speakers are a separate zone. With the equipment they sold him he will only be able to play in one room at a time without risk of taking out another amp. If this setup is still in the warranty period and the store seems hesitant or not capable of fixing the problem he needs to contact the Management level at Best Buys corporate offices.
 
If there are that many volume controls they should be or, I should say, they should have used impedance matching volume controls.

Check to see what they actually used (brand and model) and how they're set BEFORE more money is thrown at it.
 
The friend shouldn't throw any money at it. It is fairly obvious the "blue shirts" who sold him the system and installed it were fairly clueless so Best Buy needs to resolve the problem on their dime. If they did in fact install impedance matching controls the system as sold would still work optimally only if all volume controls installed were turned to their all the way to the left "off position" except in the one room in use. Unless you are dealing with one of the stand alone Magnolia locations assume that the BB employees in that section of the store don't know any more than you do and maybe even less.
 
seminole54 said:
..If they did in fact install impedance matching controls the system as sold would still work optimally only if all volume controls installed were turned to their all the way to the left "off position" except in the one room in use. ...
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How do you figure that?

The ones I've seen are set based on the speaker (nominal) impedance and the number of speaker pairs in the system. You set a multiplication factor on each volume control to make the parallel string net out at a normal nominal load appropriate for the amp of topic.
 
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How do you set up a system with 7 pairs of speakers that just for the purpose of discussion have an impedance of 8 ohms to work with a two channel amp that on it's best day will drive a "friendly" pair of 4 ohm speakers no matter the amount of "electronic wizardry" you use. If "the friend" is moving the system from room to room without turning the volume controls to the off position their will eventually be an unacceptable load no matter what the maker of the impedance volume control claims in it's literature. It's not like BB is selling amps in this type of system setup that are designed to take this kind of loading. There was no mention by the OP that the friend bought one of the High Dollar Mac amps that you can buy from Magnolia that would have just shut down with no damage. The "Friend" was taken to the cleaners and he needs to make the store or the company resolve the issue. If the OP puts himself into the equation by trying to "resolve" the problem then he is taking BB out. Not a problem for AK to resolve, but one for BB to address or if in the acceptable time frame for the "Friend" to address with his CC company.
 
seminole54 said:
How do you set up a system with 7 pairs of speakers that just for the purpose of discussion have an impedance of 8 ohms to work with a two channel amp that on it's best day will drive a "friendly" pair of 4 ohm speakers...
Click to expand...

It's pretty straightforward, actually.

I will use eight 8 ohm speakers just because the math is easier. :)

Speaker is 8 ohms, you have 8 of them. The volume control has a multiplier setting that you choose based on the number.of speaker pairs. In this example eight pairs so 8x multiplier setting. The 8 ohm impedance of the speaker is multiplied by 8, giving 64 ohms net per channel.

Now, you have 8 of those 64 ohm equivalent setups in parallel. When impedances are equal it's straight division so 64 / 8 = 8 ohms load at the amp.

Now, it's possible they didn't install correctly, or that something has happened to the wiring, or even that despite all that being correct, they just tried to ask more from the amp on a long term average power basis than it could handle. Who knows, maybe even the amp is installed with poor cooling/ventilation.
 
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Greetings everyone. I finally made the trip over to my friend's house to see the system in person. So they did have an impedance matching device, as DonPrice suggested in this thread, but it did not work correctly and the mfg told them they had too many speakers for that device. The builder or whoever placed the speakers in the ceilings so that they are centered and look nice, but not correct for any kind of stereo presentation. I told them they could get a Nile or Crown PA multi channel amp and play mono everywhere as background music or they could pick 2-3 rooms and set up Sonos, receiver/amp, speaker systems in those rooms and link them together when they wanted to through the Sonos system. They are thinking about it. It turns out my initial information was incomplete. Magnolia HiFi sold them the equipment but then a combination of the builder and a "smart home" vendor (alarm system, hvac, etc) did the final wiring and hookup. They just want to move on and not try and get any one of them to fix it as they have little faith it would be or could be fixed. Their choice. I think even if they put in a single system in the family room (which they could hear in the kitchen and dinning room and living room), they would be so much happier. Thank you again, everyone, for your help with this. I was reluctant at first to even try to help since I have never had a multi channel system before myself.
 
John Parkey said:
... I was reluctant at first to even try to help since I have never had a multi channel system before myself.
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Yeah, always risky to take ownership of someone's pile of do-do. Really easy to get married to the mess, so to speak.

FWIW, I picked up a couple Elan Z660 amps for reasonable prices. While their intent is primarily for distributed sound, I was going to use them for active bi/triamping a pair of speakers.
 
quick follow up. As you would expect, they were absolutely blown away with the stereo presentation provided by well placed floor standing speakers in the family room (Infinity RS4B with Pioneer SA-708 amp, good CD player). I untangled the wire bundles from all of the in ceiling and in wall speakers and found that all rooms had only either the right or the left channel in both speakers, nice. I used the tape out on the Pioneer amp to drive a Techniques receiver and then to drive, in stereo, the in ceiling speakers in the kitchen and the dinning room. The sound blends reasonably well as the bass from the family room fills in nicely in the kitchen and dinning room. They could not be more pleased. Not too expensive and so much better than what they had. The level of detail, the tone quality, and the dynamics are surprising and I think better than what they would have experienced with one of those impedance matching devices. Happy holidays to all of you.
 
John Parkey said:
I untangled the wire bundles from all of the in ceiling and in wall speakers and found that all rooms had only either the right or the left channel in both speakers, nice.
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Good grief! Hard to call that a rookie mistake. More like someone didn't even try to get it right.
 
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