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PostPosted: 18 Feb 2010, 14:09 
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Hello, I am new to this forum.None of the posts asked this exact question so here goes.
I need to build several amplifiers to power 5 rooms worth of audio. I moved into a house with ceiling speakers in 4 rooms ( Infiniti 8" round, 89dB sensitivity), and a 5.1 speaker system in the "TV room" ( again Infiniti, 86 dB sensitivity, with a powered subwoofer). Thus there are 10 speaker pairs, plus the center speaker and subwoofer for a total of 11 mono amplifiers required, as the subwoofer has its own amp.
The expected listening level in the 4 rooms is just background, so not a lot of power is required. Things will get quite loud in the TV room, so more power is desired for these 5 speakers.
What would be a target amplifier output rating be for the two types of speakers? What about 40W/ch for the background speakers and 100W/ch for the movie speakers? Each speaker should have its own volume control.
How many power supply elements is suggested?
Can all this fit and work in one box?
The inputs will be CD/DVD, cable TV audio, and iPod. Only one input at a time. I will need to investigate a simple switching pre amp next. probably not so simple.! could live with one set of tone controls, bass and treble, for all the speakers at once.

There are many kits available from Vellemans or Carl's electronics with vaunted distortion ratings. I would need to buy 6 stereo or 11 mono amps. The solid state kits/designs on this web site look pretty interesting , though. Is there one or two you think would satisfy my needs?

My experience level is new. But I've built a scope , signal generator and power supply from kits, so I'm ready to test my new amps.
Thanks


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PostPosted: 19 Feb 2010, 19:36 
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Chipamps / gainclones are likely well suited to fit that role and are available as kits (parts and pcb).
LM1875 ~ 20-25W
LM3875 ~ 45-55W
LM3886 ~ 50-60W
LM4780 ~ 60-120W
These kits sound good. Which kits were you considering?
Cheers and welcome to the forum.

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PostPosted: 24 Mar 2010, 20:06 
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Thanks for your answer. I have been reading since the last post, and agree that chip-amp kits are the way to go with so many amplifiers required to power 4 rooms. Differing to the discussion below, my rooms are small and normally I'd think 40W would be sufficient.
I think my issue boils down to one question. The one thing I have not been able to find online or in the audio circuit books I have is what are the requirements for one pre-amp to feed 12 amplifiers. The output voltage will not change but the current will be 1/12 of the output of a preamp to a single amplifier. Then, the amplifier risks higher distortion if it has to compensate for the small input signal with maximum gain. Am I reasoning correctly?

Would the audio gain specification for a pre-amp give me an answer? By my reasoning I need at least 10dB gain in the pre-amp.

This system will let me play one audio source in all 4 rooms. For home theater, I'll still have to rely on my 20 year old Yamaha RX-V850 stereo receiver.


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PostPosted: 25 Mar 2010, 08:46 
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So you have a 5.1 setup for your TV and three other rooms for 2ch that will be low level listening.

You will need some sort of 5.1 processor for the TV room which leaves the three 2ch rooms. Since you are already using chips, opamps in a simple buffer circuit seem like a reasonable choice.

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PostPosted: 27 Mar 2010, 20:30 
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the way I was thinking of it was the TV room speakers would bew hooked up to both the DSP receiver and the pre-amp/4 room system. I can make a switch box so they receive a signal either from DSP receiver or the new system I intend to build.
I understand there is some redundancy in this plan- amplifiers sitting around doing nothing.
Gio, I don't understand what you are saying in your post.


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PostPosted: 30 Mar 2010, 22:29 
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When you split signals, you need to be aware of possible impedance issues; output impedance of the split signals and the input impedance at the amp.

Here is a good article: http://sound.westhost.com/impedanc.htm

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PostPosted: 07 Apr 2010, 19:55 
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Thanks for the reference to Rod Elliott's article and website. Let's see if I understand the problem with impedance.
I was unable to find a specification for amplifier input impedance for kits online, but Elliotts' article gives the range as 20K-47K. Let's use 36K. I found a Velleman pre-amp kit, the K8021, which lists 360 ohms as the output impedance. Under normal circumstances, feeding one amplifier, the impedance ratio is 100:1. The high ratio preserves the supply voltage to the amplifier.
Now I want the left and right channel of my pre-amp to feed 6 amplifiers each, for a total of 12 speakers in 4 rooms. If each amplifier's input impedance is 36k, than 6 amps in parallel would present 1/(6/36K) or 6000 ohms to the pre- amp. The pre-amps output impedance of 360 ohms, split 6 ways, would have each amplifier seeing 1(6/360) or 60 ohms.
I still maintain a 100:1 ratio, but now the current required for an equivalent power level varies as P=I*I*R/6. The current required would be 2.5 times higher ( square root of 6).
Beyond choosing components for the circuits with higher current handling ability, what else is changed? I'm at a loss to further explain the ramifications of splitting the signal.

I believe I have found one solution. The book "The Audiophiles Project Sourcebook" by Randy Slone, 2002, has a simple pre-amp/ tone control circuit I can breadboard to experiment with. JFet op-amps, TL-084 series, are specified. In the data sheet for a TL-084CNE4, a diagram has the signal from the pre-amp feeding parallel similar TL-084s in parallel- an Audio Distribution Amplifier. . See the attachments. I won't build the phono section of the pre-amp, not having a turntable.
The Audio Distribution Amplifier diagram circuit has no buffering components before or after the row of output op-amps. If I want individual volume control for each amplifier, I would have to insert a pot before each output pre-amp. Can the output of the op-amp go directly to the amplifier's input?


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PostPosted: 07 Apr 2010, 20:36 
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Yes, that will do the trick. That book is a good resource. I think the volume control would be best placed in front of the amp, that way you can adjust the level in the various rooms.
Cheers

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PostPosted: 08 Apr 2010, 16:43 
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Great, thanks. I'll re-post when i have first breadboard prototype.


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