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Old 4th November 2006, 07:46 PM   #1
diarav is offline diarav  India
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Default Multi-channel, single transformer

Hi,
I have read posts where people have used a single transformer and powered multi channels.

I am planning such an arrangement with 6 LM3886 non inverting amps at +/- 35V and would like to know the implications:

Would loads get evenly distributed assuming all speakers are connected? What would happen if one or two speakers were disconnected? Would the other connected speakers get louder? If so how can we avoid this situation.

Going by a "a trafo for each amp" is not the solution I am looking for.
Any other suggestions are welcome.

Thanks in advance.
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Old 4th November 2006, 08:10 PM   #2
v-bro is offline v-bro  Netherlands
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One power supply will do just fine to most peoples needs. The other channels probably won't get noticeably louder. The amplifier is set to a certain gain and will do this within the suggested operating voltage range equal on all channels disregarding what is connected to the other..(providing you have enough current, which WILL have to be six times the value of only one amp).
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Old 5th November 2006, 11:58 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
using multiple PSUs run from a single transformer is an excellent way of achieving value for money and good quality power into the amplifiers.

A single centre tapped transformer feeding a single rectifier dedicated to EACH amplifier is the starting point.
Then add smoothing caps rated for the voltage and current expected from them.
The cap size I recommend is +-2mF/Apk to 3mF/Apk of output current
Your +-35V rails will give an output of about 28Vpk into an 8ohm load. That results in a peak current of 3.5Apk.
Using caps of +-7mF will just about do for 8ohm speakers. Using 4ohm speakers demand doubling the cap values!

So each amplifier needs a 25A 200V bridge rectifier and two 6800uF or 10000uF caps rated at 50Vdc.

However, the RC time constant of the PSU affects your choices for the amplifier design. The proposal above results in an RC=10mF*8r=80mS. the input filter must be set at least one octave above this leading to 40mS and a -3db frequency of 4Hz. the bass rsulting from this will not be as good as from an amplifier with the input filter set to 80 to 90mS. But this philosophy requires a further doubling of smoothing capacitance. Now you are into big money and big space requirements. make your choices. Me, I would build stereo amps and place them near the speakers they are driving, with long interconnects.
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Old 6th November 2006, 03:05 AM   #4
diarav is offline diarav  India
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Hi,
Thank you for your inputs.

This being my first attempt, I guess I'll start on what I have and make changes as required.
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Old 7th November 2006, 02:01 AM   #5
v-bro is offline v-bro  Netherlands
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May I give you a hint when you're looking for a cheap AND high quality DIY amp check this out (AMP6 and AMP9 are a really eay build )

http://www.41hz.com

I've always had real good support through mail too. And Jan is a really nice guy to deal with..
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Old 7th November 2006, 02:04 AM   #6
v-bro is offline v-bro  Netherlands
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Offcourse I ment to say "easy build"...
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