Hi all,
My son and I are building (assembling) an amplifier for our living room. It will drive the sub when completed. The board we purchased has all the rectifier & power supply rail caps already on it, all I had to do was source a transformer (+34/-34 secondary @ 300VA). When I connect the primary winding to AC power I'm blowing a fuse even with the secondary unconnected. I've stepped up from a .125 to a .25 to a .5 amp fuse, but the fuse keeps blowing. I don't I put a 100 watt incandescent bulb in series with the primary, and leaving the secondary unconnected, the fuse does not blow and the voltage on the secondary is correct - so I do not believe there's an issue with the transformer. Is there a component that I can leave in series with the transformer primary which will accomplish the same thing as the light?
I apologize to the audience here to post such a novice question, but I'm hoping for a solution so that we can button up our project and move on to another.
Thanks in advance,
Joey C
My son and I are building (assembling) an amplifier for our living room. It will drive the sub when completed. The board we purchased has all the rectifier & power supply rail caps already on it, all I had to do was source a transformer (+34/-34 secondary @ 300VA). When I connect the primary winding to AC power I'm blowing a fuse even with the secondary unconnected. I've stepped up from a .125 to a .25 to a .5 amp fuse, but the fuse keeps blowing. I don't I put a 100 watt incandescent bulb in series with the primary, and leaving the secondary unconnected, the fuse does not blow and the voltage on the secondary is correct - so I do not believe there's an issue with the transformer. Is there a component that I can leave in series with the transformer primary which will accomplish the same thing as the light?
I apologize to the audience here to post such a novice question, but I'm hoping for a solution so that we can button up our project and move on to another.
Thanks in advance,
Joey C
Don't be tempted to throw in the big oneAlready ordered an assortment.
Did you do a simulation with your set-up to determine the surge of current with X capacitance upon..."zero-time" forward?
Don't be too trusting with these so-called "recommendations" for power supplies...many seemingly don't bother with crunching the numbers.
-------------------------------------------------------------------------Rick..........
Don't be too trusting with these so-called "recommendations" for power supplies...many seemingly don't bother with crunching the numbers.
-------------------------------------------------------------------------Rick..........
WHAT COUNTRY ARE YOU IN? ..... WHAT IS YOUR MAINS VOLTAGE?a transformer (+34/-34 secondary @ 300VA). When I connect the primary winding to AC power I'm blowing a fuse even with the secondary unconnected. I've stepped up from a .125 to a .25 to a .5 amp fuse, but the fuse keeps blowing.
Impossible to answer without that BASIC data.
As usual, DIY Audio Members JUMP to answer without enough data
I did not. Sounds like I have some math to do as far as that goes.
I initially started with low value fuses (fast blow) because I really didn't know what the unloaded current would be and I just wanted to test the transformer outputs. When I got to a half amp fuse, I knew I was missing something because even though my knowledge is admittedly limited, I know Ohms law and that a half an amp at 110 volts is fairly considerable. And I didn't want to damage anything through ignorance.
I have another question if you guys will indulge me, The board I bought has a trace from the input of the secondary transformer center tap to ground through the mounting holes on the edge of the board. If I use brass standoffs as we were planning, this would mean the secondary would literally be frame grounded - and I'm grounding the actual ground wire from the wall plug to the chassis as well. Something seems wrong about that to me. There's a bridge rectifier in the circuit with the common also connected to the same trace. Here's the question: Is grounding the secondary center tap typical or am I about to let all the smoke out of this when I connect the amp board in this configuration (grounded secondary center tap)?
Again, thanks in advance and apologies for such elementary questions.
JC
I initially started with low value fuses (fast blow) because I really didn't know what the unloaded current would be and I just wanted to test the transformer outputs. When I got to a half amp fuse, I knew I was missing something because even though my knowledge is admittedly limited, I know Ohms law and that a half an amp at 110 volts is fairly considerable. And I didn't want to damage anything through ignorance.
I have another question if you guys will indulge me, The board I bought has a trace from the input of the secondary transformer center tap to ground through the mounting holes on the edge of the board. If I use brass standoffs as we were planning, this would mean the secondary would literally be frame grounded - and I'm grounding the actual ground wire from the wall plug to the chassis as well. Something seems wrong about that to me. There's a bridge rectifier in the circuit with the common also connected to the same trace. Here's the question: Is grounding the secondary center tap typical or am I about to let all the smoke out of this when I connect the amp board in this configuration (grounded secondary center tap)?
Again, thanks in advance and apologies for such elementary questions.
JC
I
I initially started with low value fuses (fast blow) because I really didn't know what the unloaded current would be and I just wanted to test the transformer outputs. When I got to a half amp fuse, I knew I was missing something because even though my knowledge is admittedly limited, I know Ohms law and that a half an amp at 110 volts is fairly considerable. And I didn't want to damage anything through ignorance.
JC
300VA on secondary also gives 300VA on primary.
So with 110VAC that gives approx 3 amps.
Add a bit more for power on surge into capacitors and a 5 amp slow blow fuse will be about right.
I have another question if you guys will indulge me, The board I bought has a trace from the input of the secondary transformer center tap to ground through the mounting holes on the edge of the board. If I use brass standoffs as we were planning, this would mean the secondary would literally be frame grounded - and I'm grounding the actual ground wire from the wall plug to the chassis as well. Something seems wrong about that to me. There's a bridge rectifier in the circuit with the common also connected to the same trace. Here's the question: Is grounding the secondary center tap typical or am I about to let all the smoke out of this when I connect the amp board in this configuration (grounded secondary center tap)?
See pages 43 to 45 http://hifisonix.com/wordpress/wp-content/uploads/2019/02/Ground-Loops.pdf
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