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Old 3rd September 2010, 05:29 AM   #1
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Default Where to place amp: Inside a common cab or inside speakers?

I am about to build an active HT setup with 3886 based amps. The source is going to be a PC. I am in a dilemma regarding the placement of amps.

There are two options as below:-
1) Place the amp in an a common cab just like AVRs. In this case, the signal carrying cables between the PC and amps are going to be quite short but the cables between the amps and the corresponding speakers are going to be long.
2) Place the amp inside each speaker cab. This way the speaker cables are shorter but the signal carrying cables are much longer.

Which is better, in terms of sonics, assuming decent cables are used for both the speaker cables as well as signal cables?


Thanks,
Goldy
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Old 3rd September 2010, 11:34 AM   #2
AndrewT is offline AndrewT  Scotland
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In general I recommend that the Power Amplifiers be located right beside the speakers they are driving.

An active set up links the Amps more closely with the Drivers in the speakers. For this reason I think you must locate the amplifiers beside or very near the drivers with the shortest possible cables.

But, take account of the heat generated by both the driver and the amplifier.
You must allow this to be dissipated in a way that does not overheat any components. Remember that 80% to 99% of the power sent to a driver is dissipated as heat. If you add two or three amplifiers that are averaging 30% input to output efficiency you should soon realise you cannot mount the amplifiers inside the (thermally insulated) speaker box.
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Old 3rd September 2010, 12:16 PM   #3
sangram is offline sangram  India
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Even an input cable presents a load to the driving stage. I would suggest trying out a single long length of your selected input cable with one channel and its associated amplifier and driving stage to reach a conclusion for yourself.

A PC isn't really a great audio source to start with, and I suspect loading its output with a long and possibly highly capacitative cable isn't going to do your ears any favours, specially for the rear channels.

And then you have to provide for power as well, five points at remote locations. May I suggest you keep everything in a single box, the runs to the front/center speakers are normally pretty short as it is, and you'll be listening to those most of the time. The rear speakers will need longer wires, but a 3886 should have no problems at all with that.

If you decide to run 'monoblock' style you will be better off using balanced signals, specially for the speakers at large distances. I suspect your PC will have problems with this, so you can use a virtual balancing circuit like Rod Elliot shows on his site, but you will definitely need a summing amplifier.

I've used a similar setup before and since my Delta66 uses a virtual balancing output, I had no problems with noise or interference even with a ~30 feet run of signal cable. However, moving to a shorter input cable by relocating the source improved sonics considerably.
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Old 3rd September 2010, 12:39 PM   #4
AndrewT is offline AndrewT  Scotland
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if your PC cannot drive cables then improve it.
Add a buffer at the output of the PC.
That buffer must have the current capability to drive the capacitance of the interconnect cables.

There are cheap and cheerful buffer design by the dozen.
Or you could use high quality headphone amps as your buffers or even the B1/DCB1/bf862 jFET based buffers.

You will need one buffer for each audio output from the source. One good PSU could supply all the buffers. Power this PC buffer from a separate mains supply, not from the PC.
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