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Old 20th August 2010, 12:03 AM   #381
Eva is offline Eva  Spain
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It's by far not as bad as you imagine. And his imagination tells a lot about how things are going in life for somebody...

The protection that tripped was in the power supply and involves a current sense transformer with 200 turns and inherent antenna properties. Ironically, this transformer is working at mains frequency, it's a linear circuit involving op-amps and a PIC. It's calling for a couple of ferrite beads and caps to avoid rectification of ambient RF in the input LTP of a bipolar op-amp.

Protection against wrong oscillation modes is very useful as the product ages. Imagine the result of an open feedback resistor or a cold joint somewhere. Bang! or immediate shutdown.

btw: No, it does not make funny noises unless the phone is placed crazy close to the modulator

btw2: That's without an enclosure, bare pcbs on a wood bench
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Last edited by Eva; 20th August 2010 at 12:32 AM.
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Old 20th August 2010, 12:56 PM   #382
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Today i built a little circuit that provides a delayed turnon to let the caps charge before the amp goes active.

Heres a short vid of the cir in action:
YouTube - Delayed turnon circuit
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Old 20th August 2010, 01:13 PM   #383
luka is offline luka  Slovenia
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now that is great, starting to be a good amp, keep at it
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Old 20th August 2010, 02:09 PM   #384
qsa is offline qsa  Germany
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Quote:
Originally Posted by Tekko View Post
Today i built a little circuit that provides a delayed turnon to let the caps charge before the amp goes active.

Heres a short vid of the cir in action:
YouTube - Delayed turnon circuit
can you provide schematic for delay turn on ?
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Old 20th August 2010, 02:27 PM   #385
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This is the schematic for the delayed poweron board:
Click the image to open in full size.
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Old 20th August 2010, 08:04 PM   #386
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It have turned out im still below 200kHz, had moved a knob on the scope without knowing it, so that it looked like the frequency had increased to 300kHz.

And now i noticed there were too many resistors in the input part so when i removed those i actually did climb to 250kHz, and it sounds like it improved ther sonics as well.

Last edited by Tekko; 20th August 2010 at 08:20 PM.
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Old 20th August 2010, 08:23 PM   #387
AP2 is offline AP2  Italy
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Hi tekko,
I'm curious to know ... tr1 puts down pin SD IR210? If so, there was no need to use transformer IC + bjet +parts
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Old 20th August 2010, 08:38 PM   #388
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AP2, i used the enable/disable in the current source like in the philips ucd schematic: http://www.nxp.com/documents/user_manual/UM10155.pdf

pad 3 and 4 in my schematic, tho i guess using the sd pin on the IR2010 would yield similar results, i chose what i chose because i dident feel like digging up the ground plane around the SD pin.
Click the image to open in full size.

And here are two new pics of the updated startup delay:

Amp in standby, no oscillation:
Click the image to open in full size.

Amp active:
Click the image to open in full size.

The white led was supposed to be yellow, picked the wrong bag.
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Old 20th August 2010, 10:37 PM   #389
AP2 is offline AP2  Italy
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Hi
well, maybe...this running for

Regards
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Old 20th August 2010, 10:52 PM   #390
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well i use not only a delayed poweron but a more or less instant power off rather than having it keep oscillating as the psu drains out with a pop of squeek as the end result.
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