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Old 20th October 2006, 02:45 PM   #1
kinser is offline kinser  Israel
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Default OPA541 Parallel Problems

Hey all,

i just powerd up a pair of OPA541 NI amps, both working fine, tested each one buy it own, while both being conected. paralleled, using 0R33 5W resistors at the output, input tied together, and when i hit the switch the fuses on the power supply blew, i have two more fuses left, and its friday night (shops are closed, cant get more fuses. does any one have any idea what the problem could be?

Thanks,
David Resnik


P.S.
I need the amp for tonight, so i need it working in about 3 hours, so if someone know anything, a quick reply would be great!
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Old 20th October 2006, 03:18 PM   #2
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Check you haven't shorted anything during assembly, like the OPA cases to the heatsinks. If that isn't the problem, then run your amp with just one chip for tonight, then come back to us with a full schematic and pictures tomorrow. Don't rush a repair! You will likely just blow something up!
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Old 20th October 2006, 03:27 PM   #3
kinser is offline kinser  Israel
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Thanks pinkmouse

Ill check all the wiring from the psu to the amps, test again, if it works ill connect them to the 300va PSU, if the fuses blow again ill just have to use one amp with the 300va PSU.
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Old 20th October 2006, 04:01 PM   #4
kinser is offline kinser  Israel
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okay,
so i resolders the psu wires to the amps, and unsolderd the output resistors (like a 2ch amp now) i put the new fuses in, and it worked! but this is not in parallel mode, each amp on its own. all worked ok, now what do i do? do i reconect the 5w resistors and hope that it dosent blow?


Thanks,

Kinser
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Old 20th October 2006, 04:29 PM   #5
paulb is offline paulb  Canada
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Measure the voltage directly between the two outputs (where you would be connecting the 5W resistor). This voltage divided by 0.33 ohms is the current that will be wasted between the two amps. It could be enough to blow the fuses.
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Old 20th October 2006, 04:39 PM   #6
kinser is offline kinser  Israel
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How would that affect the fuses? how would the wasted current get back to the power supply fuses? the fuses are betweern the transformer and the rectifier.

BTW i did not have any load conected


Thansk,
David Resnik
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Old 21st October 2006, 12:04 PM   #7
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Hey again,

So the amp is working!! not sure what caused the fuses to blow, but thanks to a member from the forum (SSS_Thug), he took me step by step, power up, test, connect, test again, power up, connect a source, connect a load, test again, and so on, and it was very helpfull!

I didnt need the amp after all last night, but im happy i got it done already! put both amps in a PC case, put the filter and inputs (speaker level and low level) in the front were the cd-rom's go, looks real awsome. The sub soundd soo much harder, u can hear that there is more power, and u can feel it too! im happy with the results!

Will post some pics as soon as the camera gets back here!

Thanks to evryone who help me build these amp, and my subwoofer of course! its taken me nearly a year to finish this project!

David Resnik
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Old 21st October 2006, 12:28 PM   #8
Bone is offline Bone  United Kingdom
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What sort of output power are you getting from your amplifier?

Tony
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Old 21st October 2006, 12:38 PM   #9
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Tony,

Well, before i was using only 1 chip @ 4 ohm load and rail voltage was 28+/- Vdc 100VA IE Xformer. so i was getting no more than 65 watts.

Now i paralleled 2 amps, running into a 4 ohm load, each amp is seeing 8 ohms, but now running on 35+\- Vdc 250VA toroid. now im getting about 100-120 watts @ 4 ohms. (i think)
Ididnt bridge becuase most chip amps wont handel a 2 ohm load at 25 volts and over, so my only option was to parallel, so now i can go as low as 2 ohm loads (each amp seeing 4 ohms)

Hope this helps, if u need anything just ask

David Resnik
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