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Old 10th April 2006, 04:46 AM   #1
Nathan2 is offline Nathan2  United States
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Question how to bridge 4ch to 2ch?

Hi,
I have a PowerAcoustik HMR240-4 240 watt (max) 4ch 2 ohm amp and was wondering if I can bridge it to 2ch? and how to bridge it?



P.S. The speakers are Blaupunkt RL6937 6x9 4ohm 170 watts (peak) 85 watt (RMS)



Thanks,
Nathan
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Old 10th April 2006, 07:59 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
if you add on a phase inverter to a channel then the outputs from the inverted and the normal will be out of phase.

The power available from the two out of phase channels will be double the power into double the impedance.

If you start with 240W into 2ohm load, then bridged will give you 480W into 4ohm.
That's a lot of overdrive for a 75W speaker.
The 240W into 2ohm amp will give about 120W into 4ohm and probably a bit extra (about 130W to 150W) and at lower distortion.

The answer is yes, invert two channels and your 4channel have become 2 bridged channels.

However an amp that is already bridged cannot be bridged again.
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Old 10th April 2006, 03:09 PM   #3
Nathan2 is offline Nathan2  United States
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Ok,
the output side looks like this
L R L R
+ - - + + - - +
CH1 CH2 CH3 CH4


So if I do this it will work?


+ - - + + - - +
| \ | /
\ \ / /
\ \ / /
\ \/ /
\ /\ /
\ / \ /
CH 1 CH2
Left Right
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Old 10th April 2006, 10:11 PM   #4
Nathan2 is offline Nathan2  United States
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well that didn't come out right

so if i tie CH1 & CH3 together, and CH2 & CH4 together that will work? L L R R




Thanks,
Nathan
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Old 10th April 2006, 10:56 PM   #5
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You haven't answered the question yet as to what you are doing on the input side of things.

EDIT: I found this link which basically says that your amp isn't bridgeable: http://www.bestamp.com/electronics/c...2_hmr800_4.htm
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Old 11th April 2006, 02:28 AM   #6
Nathan2 is offline Nathan2  United States
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Input side
can't I just take the left out of the stereo and splice it into two and same on the right?
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Old 11th April 2006, 05:38 AM   #7
clem_o is offline clem_o  Philippines
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No you can't. If it were that simple then anyone would have advertised their amp as bridgeable. Read leadbelly and AndrewT's posts again...

Cheers!
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Old 11th April 2006, 01:35 PM   #8
Nathan2 is offline Nathan2  United States
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Ok,
what is a phase inverter?
and so basically what you all are telling me is, no it can't be bridged.




Thanks
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Old 11th April 2006, 01:44 PM   #9
AndrewT is offline AndrewT  Scotland
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Hi,
yes, it tells you that in the spec sheet.

It drives 40W into 4ohm. It is unsuitable for 2ohm speaker duty.
The spec says it is stable into 2ohms, presumably resistive only. Check the power into 2ohms the voltage is down by -2.03db.
A good amp would be down -0.5db, reasonable -1db and poor -1.5db. This model is bad into 2ohm.
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Old 11th April 2006, 03:01 PM   #10
JWZ is offline JWZ  Malaysia
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Your amp is still possible to bridge although there is no built in
facility to do that as stated in the spec. You can add external phase inverters in between the signal source and the input terminals to the amp. and also need to reassign the meaning of the speaker out terminals of the amp. If you need any schematic to do it, I will email to you.
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