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Old 12th January 2009, 05:41 PM   #381
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Quote:
Originally posted by AndrewT

No, Bi-amp your speakers.
Use one amp to drive the Bass half of the passive crossover, use a second amp to drive the Mid/Treble half of the passive crossover.
I see what you mean, thanks!

Joshua
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Old 12th January 2009, 05:46 PM   #382
AndrewT is offline AndrewT  Scotland
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and optimise the bass amp to produce the best compromises for bass quality.
If the passive crossover split is Bass/Mid and Treble, then there is less to gain, because you don't want to lose the Mid performance you currently have.
The Treble amp could go all film/foil caps for increased fidelity. It would not need any electrolytics.
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Old 12th January 2009, 05:49 PM   #383
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Additionally, you could use 1st order filter caps (of higher quality as the much smaller size is needed) before tweeter or midrange amp, eliminating some caps in a crossover.
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Old 12th January 2009, 06:12 PM   #384
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Default Problem with fuses blowing

I've just got to the stage of checking my power supply/rectifier board, but I'm hitting problems with the fuse in the IEC blowing, and also not getting anywhere near the DC voltage I should have (35V). I suspect the latter is because the fuse is blowing.

Decibel Dungeon suggests a 1.6A time delay fuse is adequate for Gainclones running at 230V, which mine is.

So I have a 1.6AT fuse in the switch, a 300VA primary with 2*25V secondaries, but the fuse is blowing all the time.

I've got DC measurements of 11.2V the first time (both 11.2V, and both positive), and 1.2V the second time I tried measuring (and to check it wasn't a dud fuse the first time). The 1.2V was positive for both measurements.

Now I'm pretty sure all of my problems are because the fuse keeps blowing, but if DD suggests a 1.6AT fuse to be adequate then what's going on with mine to keep blowing the fuses?

I've checked the joints - everything seems fine - blue to live and brown to neutral, plus earth to ground.

On the secondaries the black and red wires are to one AC input (black 0V, red 25V) and yellow and orange to the second AC input (yellow 25V, orange 0V).

I'm wondering if I've damaged the switch - I soldered the primary wires to the switch contacts, so perhaps I've done something to the switch with the heat?

Each secondary is rated at 6 amps.
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Old 12th January 2009, 06:20 PM   #385
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With 300VA toroids and 115V mains I found 5A fuses a minimum to avoid inrush blowing at turn on. With your double mains voltages it would be closer to 2.5A. Try bigger fuse and see if it blows.
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Old 12th January 2009, 06:31 PM   #386
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Default Re: Problem with fuses blowing

Quote:
Originally posted by westers151
I've checked the joints - everything seems fine - blue to live and brown to neutral, plus earth to ground.
Blue is Neutral, Brown is live. I doubt that is the problem - but better to reverse the wires and check both ends (plug and amplifier).

Alan
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Old 12th January 2009, 06:37 PM   #387
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Sorry, that's a typo - blue is connected to neutral and brown to live.

I'll try larger fuses - if you had problems with them blowing then that gives me a bit more hope that I've not made a big mistake.
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Old 12th January 2009, 07:00 PM   #388
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Default fuse rating

Wattage times 3 for an inductive load divide by voltage to find the start up fuse rating.
This applies to motors and transformers.
300VA * 3 / 240 = 3.75A. Use an T4A fuse.

But, this will pass 4A for days even though something has blown inside.
It is far safer to close rate the fuse as Nuuk has suggested. This requires you to fit a soft start circuit. Again Nuuk gives all the details.

Why did you start up without using a mains light bulb tester?
This would save the fuse and prevents other damage if you have wired up something wrongly.
Build the tester and use it! Nuuk has given you all the details for this as well.
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Old 12th January 2009, 07:15 PM   #389
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Because I thought I knew better, but obviously I didn't.

I still think it's just the in rush of current that's blowing the fuse, but haven't seen the soft start circuit at DD. I'm just following the build in the basic Gainclone section - no mention of soft starts there.
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Old 12th January 2009, 09:05 PM   #390
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Ok, tomorrow I will build the tester, dismantle the switches and start again.

However where is the soft start circuit at DD? I've looked everywhere and can't find it at all.

Thanks
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