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Few LM3886 Chipamp questions (hopefully differnt)
Few LM3886 Chipamp questions (hopefully differnt)
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Old 13th May 2021, 04:54 AM   #31
Sangram is offline Sangram  India
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Few LM3886 Chipamp questions (hopefully differnt)
Quote:
Originally Posted by Hiten View Post
The bulb I plan to use are neon ones Which comes in DP switches here in India. I also have some chinese power switches with bulb in them. Bulb is just a reminder to turn amplifier off when not in use.

I will connect AC mains Earth Wire to enclosure metal chassis and Power supply 0V reference (On rectifier-Filter board) to different point on same metal chassis. Is that Correct ?
regards.

1. That bulb connects in parallel to the mains, not series. It cannot handle the entire load of the amplifier.

Same goes for all power switch illumination.

2. 0V and mains earth have to connect to chassis at practically the same point. You cannot use the chassis to conduct any sort of current, let alone a mains fault current.
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Old 13th May 2021, 05:54 AM   #32
Hiten is offline Hiten  India
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OK understood.
Thanks gentlemen. Will implement these things.

Edit : just thought about this. Can I use transformer AC secondary* for neon bulbs. (I will have either 18v or 36v) Reason being the way I will be arranging PS boards the wires to front panel will be short and closer so I can avoid clutter in already my crammed amplifier enclosure.

* Or will that be counter producting of amplifier functioning. I mean any imact of secondary impedance changing etc.
thx.

Last edited by Hiten; 13th May 2021 at 06:15 AM.
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Old 13th May 2021, 06:47 AM   #33
tomchr is offline tomchr  Canada
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Quote:
Originally Posted by joensd View Post
Isn't that a bit too generous?
A slow blow fuse can sustain 150% of it's rated current for an hour.
So for a 230VA transformer you'd use a 2A fuse.(230v input assumed)
150% current is 3A, input power for an hour would be almost 700VA. The transformer will either be very hot or melting already if exactly 3A would flow.
It's actually a bit more complicated than that. You have to deal with the current required to magnetize the transformer core and to charge the reservoir caps. That current can be substantial.

I write quite a bit about it here and show some measurements that I think will interest you: The Ultimate Guide to Soft Start Design – Neurochrome

Tom
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Old 13th May 2021, 07:01 AM   #34
Sangram is offline Sangram  India
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Few LM3886 Chipamp questions (hopefully differnt)
Hiten, The neon 'Bulb' is probably 110V. It has a large series resistor and will not operate properly from low voltage. It is designed to connect to the mains and should be powered from there. I would still advocate LEDs because they're more reliable, brighter and efficient than neon.

If you post a photo of what you're trying to use, it would be possible to give you better advice. Front-panel mounted lighting fixtures using inbuilt neons are not a great choice for indication. I thought you talked about it being in the switch, the examples I've seen of these are already connected to the rocker switch and need no further user intervention.
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Old 13th May 2021, 07:31 AM   #35
Hiten is offline Hiten  India
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Yes I do have some iluminated power switches. But they are filmsy with thin lugs. I have vintage Indian robust tight spring action switch (No light though) which I intend to use. So was thinking of salvaging neon lamps from filmsy switch and use them as indicator.
Will use LEDs as recommended.

But out of curiosity. Will a resistor-Neon bulb on primary have any ill effect on functioning ?
thanks
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Old 17th May 2021, 08:25 PM   #36
joensd is offline joensd  Germany
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Quote:
Originally Posted by tomchr View Post
It's actually a bit more complicated than that.[/url]

Tom
Thanks for the hint. Goes to show I still haven´t read all of your well researched and well-written page.
It sure is not a trivial subject as one could easily/naively guess.
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Old 18th May 2021, 03:31 PM   #37
tomchr is offline tomchr  Canada
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I have a lot of information available and much of it is pretty dense, so I understand.

Littelfuse has a good app note on the topic as well:
https://www.littelfuse.com/~/media/e..._guide.pdf.pdf

If the link breaks, just search for it by title, "Fuse Characteristics, Terms and Consideration Factors".

Tom
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Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
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Old 19th May 2021, 03:27 AM   #38
PRR is offline PRR  United States
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Few LM3886 Chipamp questions (hopefully differnt)
> Littelfuse has a good app note..... If the link breaks....

It is small enough to attach here.
Attached Files
File Type: pdf Littelfuse_Fuseology_Application_Guide.pdf.pdf (1.13 MB, 22 views)
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Old 6th June 2021, 02:20 AM   #39
Hiten is offline Hiten  India
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I though I should update.
Pardon me for slow progress. (Little home repair work going on) But I managed to make chassis, Drilled holes, made front some panels. Disconnected all parts meant for temporary testing setup. Probably will need help in routing wires. etc.
regards.
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Old 25th July 2021, 05:08 AM   #40
Hiten is offline Hiten  India
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Hi,
In attached picture
1) Only one channel and Only ground connection in green is shown and other channel will be replicated.
2) My source always will be Mains 2 Pin CD player (No earth connection on it)
I have made front/back panel, drilled the holes in chassis for components, Before I start fixing in component and wiring would like to know

for start ground I will take EXTRA wire from (1) Speaker terminal pin ground (2) Signal input pin ground (3) Amplifier Module Speaker Out ground (4) Power supply board Rectified 0v Ground to the Center point shown in green circle Which will have Mains Earth wire connected to metal chassis. Tell me if this is correct ?

As this is my frugal, learning and getting hands dirty DIY the chassis is small and not much space left. However I have second option (shown in grey) for Star Ground near power supply board. So where would it be better ? Near Back panel where all input and outputs are OR near Power Supply Rectifier Filter Board as shown in OPTION 2

On the Amplifier module (XY Chinese brand). My multimeter shows All the output, input and PS ground as short. So why not take only one PS ground to the chassis Star ground where mains earth wire is ? Do tell if any wire can be eliminated to have less clutter.

Thanks very much
Attached Images
File Type: jpg star ground.jpg (106.1 KB, 84 views)
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