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Old 3rd March 2014, 10:58 PM   #1
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Default Amp advice prior to purchase -

T&me sa8200 would this amp be OK to bridge even though no bridge mode?

Thanks.

Last edited by bushmeister; 4th March 2014 at 06:29 AM.
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Old 4th March 2014, 06:18 AM   #2
CBS240 is offline CBS240  United States
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It appears in the owners manual that there is XLR input sockets. It seems that each pair of output channels use the same power supply circuit and that the SA8200 is just two SA4200 in one enclosure. It makes sense that under heavier load that the power supply rail voltage will sag a bit. Many designers count on this to limit Pd max so as not to push the output devices beyond their SOAR (safe operating area range). If the particular model in question does not have a XLR input, then you could apply the + & - phase input to each of the single end inputs of the two channels in one of the modules and connect the speaker to the +output terminals of each output. The +speaker terminal would go to the output which has the positive signal in, and the -speaker terminal would go to the output which has the negative input signal.

It is important to note that you cannot get any more power out than the maximum that is designed for. If you bridge the two amplifier channels, you have doubled the output voltage as seen by the speaker. This means the minimum speaker impedance must be doubled so as not to overload the output stages with excess current flow.

With reference to page 8 of the manual: It seems that if you connect only one 8R speaker to only one of the channels in the module containing two channels with shared power supply, you can get 140W. If you connect an 8R speaker to both channels of the same module you will only get 125W per speaker due to PS rail sag. Connecting one 4R speaker to only one channel of a module yields 250W with the rail sagging. Connecting a 4R speaker to both channels of the same module results in only 200W per channel due to excessive PS rail sag. Bridging one 8R speaker between the two channels of one module equates to connecting a 4R speaker to each output and thus due to the excessive rail sag, can only output 200W per channel, which is summed for 400W @ 8R. I suppose if you bridge one channel from one module to another channel from another module then you might be able to squeeze a few more watts out because of less rail sag but that would be quite a waste to buy an 8 channel amp and use only half of it. It is possible that there could be minor stability or distortion issues created by bridging two separate modules with separate power supplies. I would guess the design is intended to be bridgeable between the two channels of one module, hence the common power supply for two channels.

Just to reiterate, bridging one 4R speaker across the module will equate to connecting a 2R speaker to each output and would overload the amp, hopefully causing the protection circuit to engage before magic smoke erupts.

Clear as mud in a swamp, eh?
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Last edited by CBS240; 4th March 2014 at 06:40 AM.
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Old 4th March 2014, 06:32 AM   #3
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Fantastic answer, thank you so much. that tells me what i need to know. I will look elsewhere for an amp!

cheers!
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Old 4th March 2014, 09:34 AM   #4
AndrewT is offline AndrewT  Scotland
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There is something wrong in the technical specifications.
I have only looked at the maximum power output figures.

8 x 140W into 8r0
8 x 250W into 4r0
4 x 400W into 8r0

The last figure should be exactly double the 4r0 values i.e. it should state 4 x 500W into 8r0.

I wonder why this discrepancy?
Which is wrong?
Why is it wrong?
Do the retailers not know what they are selling?
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Old 4th March 2014, 10:56 AM   #5
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Don't worry, I have decided to give it a wide berth!

I have some DIY active three way speakers, and need 6 channels of amplification, min 200W for woofers, and 100w for mid/tweets.

Trouble is unless I get three separated amps, I am struggling to find a decent multiway, which will fit the bill.

I was thinking DIY, but am a complete amp novice, so this fills me with trepidation!

Any suggestions?
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