bridged amp please help

Dan2 · 24th April 2008, 08:51 PM

I guess u should have seen this coming

i bridged a 2 channel amp (4ohm min per channel, 30W RMS) and ran one 4R sub off it. it was a (sound quality wise) crappy amp so i had no other use for it other than to use it for a subwoofer amp.

I also figured that the protection circuit (thermal, short circuit) would kick in if there was any problems, so i thought i was safe using a low load (bridged = 2R per channel) I also put a fan on the heatsink and it was cool to the touch even when driven hard.

it has been working fine for a couple of days, and today i turned it up (not as loud as it can go) and it started sounding like it wasn't getting enough power from the supply - and then when i turned it down (to zero) it carried on buzzing for about 10 seconds, then stopped. then i could turn it up a bit (not loud) and it will be fine - but if i turn it up some more it starts again.

Any ideas on where i can start looking for the problem?? or have i destroyed the amp?

Dan2 · 25th April 2008, 09:10 AM

well - as always - after hooking it up again at home it works fine.

one thing i did notice though - the transformer is 28v - 0v - 28v and is connected in parallel to the amp (i remember not so long ago one of the 28v wires came loose and the amp was still working fine on both channels)

and when i moved the 28v wires around i heard a soft pop on the speaker. so please tell me if this makes any sense:

if the 28v line came loose, the transformer would only be able to supply half the current (1.5A) to the amp - so when i turned the amp up, the supply caps discharged too quickly and the amp kind of started ocsilating - until the caps charged up again and it went back to normal.

does it sound fesable??

Andre Visser · 25th April 2008, 12:54 PM

A loose power connection can do that yes.

DRC · 25th April 2008, 01:54 PM

an amp rated at 4 ohm per channel should have its load increased to 8 ohm in a bridge configuration

Dan2 · 25th April 2008, 02:40 PM

i know about the load being too low - but i am just using what i got. i don't hear any distortion on the sub though.

thanks for your replies - i am just gonna resolder the wire and hopefully it will make a better connection.

Dan2 · 27th April 2008, 12:34 PM

well its all working like it was - so it must have been a loose power wire. i ran it last night for about 5 hours and there were no problems

24th April 2008, 08:51 PM	#1
Dan2 diyAudio Member Join Date: Sep 2005	bridged amp please help I guess u should have seen this coming i bridged a 2 channel amp (4ohm min per channel, 30W RMS) and ran one 4R sub off it. it was a (sound quality wise) crappy amp so i had no other use for it other than to use it for a subwoofer amp. I also figured that the protection circuit (thermal, short circuit) would kick in if there was any problems, so i thought i was safe using a low load (bridged = 2R per channel) I also put a fan on the heatsink and it was cool to the touch even when driven hard. it has been working fine for a couple of days, and today i turned it up (not as loud as it can go) and it started sounding like it wasn't getting enough power from the supply - and then when i turned it down (to zero) it carried on buzzing for about 10 seconds, then stopped. then i could turn it up a bit (not loud) and it will be fine - but if i turn it up some more it starts again. Any ideas on where i can start looking for the problem?? or have i destroyed the amp?

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25th April 2008, 09:10 AM	#2
Dan2 diyAudio Member Join Date: Sep 2005	well - as always - after hooking it up again at home it works fine. one thing i did notice though - the transformer is 28v - 0v - 28v and is connected in parallel to the amp (i remember not so long ago one of the 28v wires came loose and the amp was still working fine on both channels) and when i moved the 28v wires around i heard a soft pop on the speaker. so please tell me if this makes any sense: if the 28v line came loose, the transformer would only be able to supply half the current (1.5A) to the amp - so when i turned the amp up, the supply caps discharged too quickly and the amp kind of started ocsilating - until the caps charged up again and it went back to normal. does it sound fesable??

25th April 2008, 12:54 PM	#3
Andre Visser diyAudio Member Join Date: Sep 2007	A loose power connection can do that yes.

25th April 2008, 01:54 PM	#4
DRC diyAudio Member Join Date: Jan 2003 Location: UK (south west)	an amp rated at 4 ohm per channel should have its load increased to 8 ohm in a bridge configuration

25th April 2008, 02:40 PM	#5
Dan2 diyAudio Member Join Date: Sep 2005	i know about the load being too low - but i am just using what i got. i don't hear any distortion on the sub though. thanks for your replies - i am just gonna resolder the wire and hopefully it will make a better connection.

27th April 2008, 12:34 PM	#6
Dan2 diyAudio Member Join Date: Sep 2005	well its all working like it was - so it must have been a loose power wire. i ran it last night for about 5 hours and there were no problems

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