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Chip Amps Amplifiers based on integrated circuits

LM1875 Amp layout
LM1875 Amp layout
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Old 2nd June 2019, 05:03 AM   #21
ubergeeknz is online now ubergeeknz  New Zealand
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Originally Posted by Dunk02 View Post
I suspect you may be right, especially since the chassis is completely metal and screwed together tightly.
That is way better IMO LM1875 Amp layout now your signal path is nice and clean.
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Old 2nd June 2019, 05:04 AM   #22
ubergeeknz is online now ubergeeknz  New Zealand
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But put protection circuit in the middle I think if you can. Give the amps more room
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Old 2nd June 2019, 05:12 AM   #23
Dunk02 is offline Dunk02  Australia
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Sure, for better heat distribution. I am going to keep uploading photos to keep track of setup.
Should I make a steel shield to isolate the transformer?
Could someone sketch in a mains earth and ground wiring layout? I am not sure if they are to be joined at the same point on the chassis.
I almost forgot that I have some inline or PCB fuse holders to install between the toroid and power board and maybe between power board and amplifier boards, not sure what is best practice.
Thanks
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Old 2nd June 2019, 06:03 AM   #24
ubergeeknz is online now ubergeeknz  New Zealand
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I would fuse the mains input, and the DC to each amp channel. Layout looks good.
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Old 2nd June 2019, 06:05 AM   #25
Dunk02 is offline Dunk02  Australia
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Thanks Bro
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Old 2nd June 2019, 06:33 AM   #26
ubergeeknz is online now ubergeeknz  New Zealand
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Originally Posted by Dunk02 View Post
Thanks Bro
Look forward to seeing the finished product!
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Old 2nd June 2019, 02:24 PM   #27
ubergeeknz is online now ubergeeknz  New Zealand
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Should I make a steel shield to isolate the transformer?

Toroidal transformers hardly emit any field, unlike EI transformers. Just keep your audio path as far from it and the AC lines as possible, and you should be fine.

Twist any AC lines to reduce their emission and keep them close to the chassis.

Could someone sketch in a mains earth and ground wiring layout? I am not sure if they are to be joined at the same point on the chassis.

Grounding is a much contended issue... here are my thoughts but others may have different suggestions In the end, do what works for you.

* Take mains earth to chassis as close to the inlet as practical. Make it very secure (crimp lug + soldered) as this is for safety.

* Run 0v or power ground independently to both channels from the transformer secondary (or power supply board if single rail). Keep it isolated from chassis ground. If you like, twist it with the DC supply.

* I generally prefer to leave audio ground floating - to sidestep ground loops in the system - but if you feel that is unsafe (and it does have potential to be in certain circumstances), then ground it securely to the chassis at the inputs, not to the same point as the mains ground.

* Take the audio ground from there to the volume control and from the volume control to the amplifiers, using shielded cable.

* I am not sure what potential the chips' bodies are at but you will almost certainly want to isolate them from the heatsink with a mica washer or similar regardless.
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Old 2nd June 2019, 08:41 PM   #28
Dunk02 is offline Dunk02  Australia
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Thanks for the tips.
Star washer on the mains earth screw.
I’ll start sketching it out.
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Old 9th June 2019, 06:19 AM   #29
Dunk02 is offline Dunk02  Australia
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I have started sketching out the wiring but have got stuck with wiring and mounting of the separate 18v encapsulated transformer for the speaker protection board.
VB 3,2/1/18 | 18V ac 1 Output Through Hole PCB Transformer, 3.2VA | RS Components

I was going to put it on a double sided PCB with spade connectors, and a fuse on the 18v side. Then got worried about arcing across the tracks in the 240v end. Tried creating space by removing some tracks but I donít like the outcome.

Not keen on just gluing it upside down to chassis floor.

Suggestions please.
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Old 9th June 2019, 06:29 AM   #30
ubergeeknz is online now ubergeeknz  New Zealand
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IMO if you want to do it right... Get a PCB made

Not too hard to design one on EasyEDA and get it manufactured at jlbpcb. There are likely the footprints you need already, otherwise making them isn't too hard. The software is free to use and the PCB manufacture is very reasonable.

There's other software and vendors too but I've used these and they did a nice job, also pretty fast.
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