Hello, I've finally assembled my first amp, you can see it on the picture.
Now I'm using 1A 30mm fuse between and transformer and 110v, and 2 1.5Amp 20mm fuses between the transformer and the bridge.
However one of the small fuses always glows for 1 second when I turn the amp on. ¿Should I replace those fuses for 1.5A ones? I can't see the mains fuse so I don't know if it's glowing too. I guess I'll have to wait to see if it gets burnt and if that's the case replace it for a bigger one, am I right?
Does it matter in which one of the main lines (phase and neutral) do I place the big fuse?
Thanks a lot again!!!
An externally hosted image should be here but it was not working when we last tested it.
Now I'm using 1A 30mm fuse between and transformer and 110v, and 2 1.5Amp 20mm fuses between the transformer and the bridge.
However one of the small fuses always glows for 1 second when I turn the amp on. ¿Should I replace those fuses for 1.5A ones? I can't see the mains fuse so I don't know if it's glowing too. I guess I'll have to wait to see if it gets burnt and if that's the case replace it for a bigger one, am I right?
Does it matter in which one of the main lines (phase and neutral) do I place the big fuse?
Thanks a lot again!!!
The mains fuse should sit *before* the main switch (in case the switch fails) and the fuse should be a slow-blow.
Phase or neutral ? That depends on wether you can tell the differens. If you can rotate the power-plug 180 deg, it doesn't matter. If you can't then it should sit on the phase.
The fuses on the secondary side should sit between the reservoir capasitors and the amplifier, *not* between the xformer and the bridge. As you have noticed, the initial surge current can quite large.
Remember, these fuses are there to protect 1 ) you speakers and 2) the transformer. Not the amplifier. Say in case you accidentially short the output (and there is no current limit in the amplifier itself) the output transistors will most likely blow before the fuses do in a few milliseconds.
Lars
Phase or neutral ? That depends on wether you can tell the differens. If you can rotate the power-plug 180 deg, it doesn't matter. If you can't then it should sit on the phase.
The fuses on the secondary side should sit between the reservoir capasitors and the amplifier, *not* between the xformer and the bridge. As you have noticed, the initial surge current can quite large.
Remember, these fuses are there to protect 1 ) you speakers and 2) the transformer. Not the amplifier. Say in case you accidentially short the output (and there is no current limit in the amplifier itself) the output transistors will most likely blow before the fuses do in a few milliseconds.
Lars
Hello, thanks a lot for your answer. I can move the mains fuse easily but for the smaller ones I'd have start from scratch again, is it risky to leave them in the place they are?
Nobody in this town knows about slow blown fuses, they actually laugh at me when I asked, should I use higher capacity fuses?
Is there any way I can protect the amplifier itself?
Thanks again.
Nobody in this town knows about slow blown fuses, they actually laugh at me when I asked, should I use higher capacity fuses?
Is there any way I can protect the amplifier itself?
Thanks again.
It's not a major risk and as far I can see in the picture in #21 your amplifier is an integrated one. These have some form of current limit build in. So, if you can't get slow fuses, use a larger one. If it still glows up clearly, try the next larger one. If they glow up every time you turn it on, the fuses will blow at some point. The real problem is if one of the fuses blow then your amplifier only gets supply for one side (plus or minus) - how it will react to this I don't know.
What you could do is to put a soft start circuit before the transformer e.g.:Soft-Start Circuit For Power Amps . For a few seconds , there will be a resistor in series with transformer thereby limiting the inrush current.
This is allways a good idea, as it ensures a longer life for the reservoir capacitors.
Lars
What you could do is to put a soft start circuit before the transformer e.g.:Soft-Start Circuit For Power Amps . For a few seconds , there will be a resistor in series with transformer thereby limiting the inrush current.
This is allways a good idea, as it ensures a longer life for the reservoir capacitors.
Lars
Moving from 1A to 1.5A completely removed the glow, but I had never thought what would happen if one of them failed but not the other one (very likely, actually only one of them, always the same, was glowing).
The IC's (STK4172II) datasheet doesn't say anything about it either ¿Do you think those little fuses could do more harm than good? ¿Should I remove them and rely in the mains fuse only?
Thanks again!
The IC's (STK4172II) datasheet doesn't say anything about it either ¿Do you think those little fuses could do more harm than good? ¿Should I remove them and rely in the mains fuse only?
Thanks again!
Leave them in, maybe increase to 2A. The mains fuse will not protect anything past the secondary, it's job is to protect the transformer from catching fire (!) in case of a melt down, and make sure you don't blow the fuses for the house.
The fuses will blow if you accidently short the output for a longer period (seconds) with signal at the input. The amplifier will limit the current, but it will get mighty hot which is not good in the long run.
Lars
The fuses will blow if you accidently short the output for a longer period (seconds) with signal at the input. The amplifier will limit the current, but it will get mighty hot which is not good in the long run.
Lars
Hello and thanks for your answer, my last concern is about transformer's temperature, after 30 - 40 minutes at low volume it gets very warm, not enough to hurt but very warm.
The IC I'm using is STK4152II, I'll upgrade to STK4172II as soon as I can get one.
Thanks again.
The IC I'm using is STK4152II, I'll upgrade to STK4172II as soon as I can get one.
Thanks again.
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