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Old 14th January 2009, 08:47 AM   #411
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Thanks Peter, I think I'll do what you say for the testing side of things, but look at a soft start circuit for when it's put in a case.

By the way, my search for a proper soft start schematic is over - there's one in the Gainclone Power Supply thread in the National PDF file.

I've just got to adapt the resistor values accordingly for my voltage, but I know how to do that.

It is strange that my 300VA supply is blowing fuses when others have no problems. I can't think why it would do it, unless the windings in my torroid don't have sufficient resistance to limit the amount of current coming in.

It's a Noratel torroid, brand new from Farnell.
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Old 14th January 2009, 10:32 AM   #412
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you need a T3A or T4A for a 300VA transformer.
But, this is not a close rated fuse like Nuuk and I recommend.
If you want to use a close rated fuse then you must use a soft start.

Carry on using the bulb tester for the time being. The amp will work with the bulb tester in place . The bulb will glow if you ask for too much output power. But, you still have the protection of the bulb while doing testing.

You can fit a manual bypass switch across the bulb tester to allow full power to the mains transformer. But if this is inadvertently left closed it completely defeats the bulb tester function. Take care to label this bypass switch.
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Old 14th January 2009, 02:29 PM   #413
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Quote:
to use the amp in bridged mode you need to supply balanced signal to the amp
thanks peter - in another thread you suggested some cheap transformers for this - do you know where i can get details of a suitable circuit?
-ben
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Old 14th January 2009, 02:29 PM   #414
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Yes, I built the bulb tester exactly as Nuuk describes on his site and then got confused with what the various switches did, so much so that when I first measured the bridge output I was only getting 1V !!

After scratching my head and thinking about it I started pressing the switches and lo and behold, 24V - obviously I had left the bypass switch turned off at first, hence the low Voltage reading.
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Old 14th January 2009, 02:34 PM   #415
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Quote:
Originally posted by presterjohn

thanks peter - in another thread you suggested some cheap transformers for this - do you know where i can get details of a suitable circuit?
-ben
I will post a drawing later today.
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Old 14th January 2009, 03:03 PM   #416
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by westers151
Yes, I built the bulb tester exactly as Nuuk describes on his site and then got confused with what the various switches did, so much so that when I first measured the bridge output I was only getting 1V !!

After scratching my head and thinking about it I started pressing the switches and lo and behold, 24V - obviously I had left the bypass switch turned off at first, hence the low Voltage reading.
my bulb tester has no switches, keeps it simple.
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Old 14th January 2009, 05:58 PM   #417
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This is how I had Edcor transformer wired to convert unbalanced signal into balanced, to use with LM4780 in bridged mode.

http://www.edcorusa.com/products/tra...sm10k-10k.html
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File Type: jpg balanced.jpg (24.4 KB, 2072 views)
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Old 15th January 2009, 12:36 AM   #418
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Quote:
Originally posted by Peter Daniel
This is how I had Edcor transformer wired to convert unbalanced signal into balanced, to use with LM4780 in bridged mode.
that simple! i'll give it a go
-ben
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Old 16th January 2009, 05:47 AM   #419
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Question Coaxial copper

Ok, I'm a beginner.
What about the copper of a coaxial cable for ground bridge?
I also found an anamel copper from a transformer. Is it better?
CAT5 copper for R1 bridge is ok or standard awg wire is preferred?
Thank you very much for your work and sorry for my very bad english.
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Old 17th January 2009, 10:05 PM   #420
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So... I could build a box with two unbalanced inputs, run across a couple of transformers to two balanced outputs and I'm off and running???
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