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infobot 27th September 2008 04:12 PM

LM3886 fuse
Boy, my LM3886 (BrianGT kit). At first fine with 2A fuses. Then started going through them. Tried 3A then started eating those too. 4A maybe not always, 5A seems fine.

Just surprised was able to use 2A for so long.

Amp checks out fine, just current inrush at turn on. Added xformer for dual mono - really started eating fuses. Worked sometimes using 2A in dual mono amazingly. Maybe summer apartment air conditioners or something.

Used 18V + 18V, 250VA Avel Lindberg transformers, US voltage. First one then two for dual mono.

Mooly 27th September 2008 04:25 PM

Is the fuse/s on the primary or secondary side ? Are you using anti surge fuses ? Do you mean it blows on switch on or when in use ? :)

Ted205 27th September 2008 04:53 PM

do you switch your source on when the amp is already on?

kevinkr 27th September 2008 04:54 PM

Changing to dual mono means that your inrush current has just about doubled. At time 0 the inrush current drawn by a toroid is almost entirely determined by the dcr of the winding so to prevent nuisance blowing you would need double the fuse rating or a time delay fuse.

Toroids have ridiculously high inrush current and it is not unusual to see single transformers of just a couple of hundred VA with up to 6A slow blow fuses..

You need time delay type fuses designed for inductive loads, and a 5A - 6A fuse with your 2 transformers is an acceptable choice - just don't expect it to provide much protection in the event of a component failure. Even better would be a separate fuse for each power transformer - this would provide almost reasonable protection in the event of a malfunction on one channel.

richie00boy 27th September 2008 05:00 PM

500VA total load, really needs a soft start. Then you can get back to using correctly sized fuses.

infobot 27th September 2008 06:04 PM

LM3886 fuse
Thanks glad I asked. Will try the separate fuses per side and check into soft start.

Fuses blow only on startup, no problems when in use.
Fuse is on primary side.
Used all time delay (slo blo) fuses.

Switch amp on before source a lot but it varies. Like esp if using another amp then change to gainclone amp.

enzoR 27th September 2008 07:36 PM

I have 2x 330VA avel lindberg's. Turning them on blows my 16A circuit breaker :hot:

Use a soft-start circuit!! Much better for your rectifier/capacitors aswell, and you can get by with your 2A fuse again (also safer).

i use this one for mine. sorry that its in dutch, but the schematic is very simple and works well. Another option is this one but it is more complex and not necesarily better. Ofcourse there are other options out there aswell....

infobot 28th September 2008 05:25 PM

LM3886 fuse
Thanks for the links.
Actually we're 120 volt out here but thanks still helpful.

Anyone thoughts on fusing after primaries? Is it a good idea to put a fuse before the power supply boards and the amp boards?

(i assume audiophile materials fuses if used come quite after a project been proven to be more reliable)

enzoR 28th September 2008 05:30 PM

its best to put the right sized fuse before the primary.

infobot 28th September 2008 05:59 PM

LM3886 fuse
Makes good sense. Think using separate fuses and adding soft start should help with that one.

Sorry guess what I meant was in addition to before the primary. Heard it mentioned, some folks fused everything, just wondered.

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