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Old 13th December 2009, 03:58 AM   #471
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Quote:
Originally Posted by Tripmaster View Post
Hello

I have a soft-start circuit, and I am using a T1.6 fuse in the mains inlet, and a 3A fuse in the mains plug as per Andrew's recommendation. I just wanted to know if I needed to untwist the two primary Lives and Neutrals and insert a 800mA fuse per each transformer Live wire, rather than leaving the two neutral and live wires (two transformers connected together) connected and fusing each twisted pair with a 800mA fuse.

I hope that makes sense

Thanks again
if you already have fuses T1.6 (neutral/hot)before the soft start.I would leave those twisted wire alone.try to twist the ac wires as much as you can.
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Old 13th December 2009, 09:05 PM   #472
tvrgeek is offline tvrgeek  United States
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Any recommendations for high speed diodes to replace the usual 1N4xxx series? Shottcky or "fast"? I am not sure I believe the hype that they can make a difference in the sound of an op-amp based circuit providing proper cap size and location, but worth a try.
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Old 18th December 2009, 08:15 AM   #473
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Hi there

I have just added a winding to one of my 300VA transformers. The new winding outputs 7 VAC. As you can see I have crudely soldered a 400R resistor to the LED anode pin and have soldered a diode across both LED legs, the diode anode leg is soldered to the LED anode.

Click the image to open in full size.

Click the image to open in full size.

I'm guessing it doesn't matter having too much resistance providing the resistor is of a suitable wattage and I am happy with the degree of illumination.

The LED lights up and is not overly bright so I guess everything is OK.

Can you see any potential problems?

Thanks
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Old 18th December 2009, 10:06 AM   #474
AndrewT is online now AndrewT  Scotland
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Hi,
have you really wired the LED to diode, anode to anode?
This would limit the LED voltage to ~650mV and the LED would not light up.
The LED would also see the full 10Vpk in reverse direction and probably fail.

If the diode is passing current in one direction and the LED is passing current in the other direction then all the problems go away.
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Old 18th December 2009, 12:20 PM   #475
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Hi Andrew,
Richard has confused the name of the end of the diode with the line marking. He has actualy conected cathode of diode to anode of LED, this is shown in the pic's.
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Old 24th December 2009, 10:53 AM   #476
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This has become cringe worthy!

I've been running my dads newly built amp for 12 hours a day over the last week without a problem.

Click the image to open in full size.

The mains inlet is switched, but is a little awkward to get at so I have been switching the amp on and off via the 6 way gang socket. I switched it on this morning and nothing happened. There was a faint twinkling front the led on the front, but nothing else. I then removed the lid to find that the T1.6A mains inlet and the two T800mA transformer primary fuses had blown.

I've visually checked over the parts in the amp and I cant see any component faults or shorts. I've just replaced the three fuses and powered up the amp using the light bulb tester and the 40w bulb glows like it has always done, dimly. The amp still works OK.

Click the image to open in full size.

Can I put this down to nuisance fuse blowing or do you think it could be something serious?

Sorry to hog this thread!

Thanks
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Last edited by Tripmaster; 24th December 2009 at 11:02 AM.
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Old 24th December 2009, 12:42 PM   #477
AndrewT is online now AndrewT  Scotland
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All three fuses blown at the same time says something drew excessive current.
Check the 47r resistor is still in spec.

Can you disconnect both amplifiers from their PSUs?
If you can, do the bulb test with just the transformers and the PSUs online.
Then add one amplifier. bulb test, then the other amp, bulb test, then both amps, bulb test.
What is the bypass relay time delay? I wonder if you could series connect a pair of 47r Power resistors to slow down that initial start up?
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Old 24th December 2009, 01:09 PM   #478
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Quote:
Originally Posted by AndrewT View Post
All three fuses blown at the same time says something drew excessive current.
Check the 47r resistor is still in spec.

Can you disconnect both amplifiers from their PSUs?
If you can, do the bulb test with just the transformers and the PSUs online.
Then add one amplifier. bulb test, then the other amp, bulb test, then both amps, bulb test.
What is the bypass relay time delay? I wonder if you could series connect a pair of 47r Power resistors to slow down that initial start up?

The 47R power resistor is still in spec and the relay clicks at about 2 seconds.

I can disconnect the amps and PSUs, they are soldered so the solder pads may or may not withstand another two heatings. Should the bulb filament remain off until I connect the faulty amp/psu?
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Old 24th December 2009, 01:31 PM   #479
AndrewT is online now AndrewT  Scotland
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the bulb should be completely off when only the transformers and the PSUs are coupled.

The bulb may glow very dimly with one good amp connected. Check to see that both are OK.

Soldered joints. Pity that. Consider cutting the wires and inserting a terminal block at least until all the checks have been done.
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Old 24th December 2009, 02:22 PM   #480
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I disconnected both amps and tested the PSUs together, and individually and it lit the bulb every time. I've just tested the soft start circuit and it also lights the bulb, so does this mean there is a fault with soft start circuit?
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