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Chip Amps Amplifiers based on integrated circuits

Can I lengthen legs of chipamp?
Can I lengthen legs of chipamp?
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Old 6th December 2017, 06:59 PM   #1
Kshishtoff is offline Kshishtoff
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Default Can I lengthen legs of chipamp?

Hi everybody!
I've made my own PCB for stereo LM1875 gainclone. I've soldered only one channel for check if it works fine. Later I decided I want compact case and now that nesting of components is not very practical because of heatsinks which will take additional place in a case.
I now I should to think about this earlier, but...
I think about 2 options of heatsink placement. In both cases I have to lengthen my chipamp legs with wire. Shall I have any problems because of it? For example oscillation or noise or something like that?
PS I know about unwashed rosin. I shall have washed my PCB after I have all components soldered.
Attached Images
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File Type: jpg 18751chan.jpg (946.8 KB, 231 views)
File Type: jpg 18751var.jpg (732.0 KB, 231 views)
File Type: jpg 18752var.jpg (720.1 KB, 222 views)
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Old 6th December 2017, 07:06 PM   #2
Mooly is offline Mooly  United Kingdom
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Can I lengthen legs of chipamp?
Welcome to diyAudio

It is possible you might introduce problems... these things are hard to predict though.

You should add a single small electrolytic cap of say 10uF between the two supply pins of the chip soldering the cap directly to the pins of the IC. That will help maintain stability.

Keep the main output wire as far away as possible from the wires to the input pins. This will help avoid any capacitive coupling between them.
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Old 6th December 2017, 08:15 PM   #3
Kshishtoff is offline Kshishtoff
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Quote:
Originally Posted by Mooly View Post
electrolytic cap of say 10uF between the two supply pins of the chip
May be 0,1 uF ceramic capacitor will fit better? The datasheet recommends to use them for stability.
Till now I haven't got any suitable case.
And I have one more option. I can cut my board in half and I'll get two mono amplifiers.
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Old 6th December 2017, 11:41 PM   #4
tomchr is offline tomchr  Canada
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You will likely invite oscillations if you extend the leads on the chip. I recommend extending the heat sink instead. Find a good chunk of aluminum and machine it to connect the IC to the heat sink through as much aluminum as you can fit.

Tom
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Old 7th December 2017, 04:50 AM   #5
Fast Eddie D is offline Fast Eddie D  United States
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I would cut and file the board until you can fit the heat sink against the chip, if possible.
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Old 9th December 2017, 06:34 PM   #6
Kshishtoff is offline Kshishtoff
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Fast Eddie D
I'm sorry, but English isn't my native language. Please say what you mean with another words.
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Old 9th December 2017, 07:05 PM   #7
Fast Eddie D is offline Fast Eddie D  United States
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Cut with a saw or dremel.

File with a - file?

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Old 9th December 2017, 07:28 PM   #8
Kshishtoff is offline Kshishtoff
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Oh, I understand now
I have got an file, but it isn't needed in this case.
I think of to place the heatsink above or under the PCB.
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Old 14th December 2017, 10:20 AM   #9
ICG is offline ICG  Germany
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The extension of the legs is one way, hacking off the board is another (well, there might be some who see that differently though) but I would like to suggest yet another which avoids any electrical problems. You could mount the IC to an L-shaped aluminium profile or aluminium block and mount the heatsink on it. The heat transfer isn't as good as the IC directly mounted on the heatsink but with a decent size the loss in heat dissipation can be neglected, the big contact surface helps there.

Just in case you didn't understand that, again short and simple:

Put the IC on a big L-shaped aluminium part or aluminium block. Screw the heatsink/cooler onto the Aluminium part. The L-profile should be wide and thick and don't forget the thermal conductive paste.
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Old 14th December 2017, 07:23 PM   #10
Kshishtoff is offline Kshishtoff
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Quote:
Originally Posted by ICG View Post
Put the IC on a big L-shaped aluminium part or aluminium block.
Yes, this option is probably the most optimal. The only thing I shall have to find a thick aluminium bar and accurately adjust an additional mounting of a heatsink.
Thank you for your advice
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