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Old 28th March 2006, 10:23 PM   #1
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Default Help needed for LM3875 design + simple single-sided PCB.

The design is pretty simple; it's a Chill-Amp with 100uf capacitors in place of the 1000uf capacitors, 0.1uf MKT's bypassing the 100ufs in place of the 1uf from + to -, and designed to be powered by a "CarlosFM" snubberized PSU. It's nothing special, as far as Gainclones go.
I have, though, managed to create a simple 1-sided PCB with really big copper traces. I've got access to unetched PCB and ferric chloride, so making them should be no problem, and I can afford to spend some time drilling the holes.
I was hoping to let you have a look; however, the PCB's still stuck in Eagle format. Anyone know how to export it to Jpeg or a bitmap?


Thanks,
Joe.
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Old 28th March 2006, 10:32 PM   #2
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If you look in the drop down menus, under export, there is a bitmap option.
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Old 29th March 2006, 02:28 AM   #3
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Here's the PCB. You can (sort of) see how its laid out; the .1uf MKT caps are soldered directly across the leads of the 100uf caps. The holes in the center are the output, those on the left for the power, and those on the right for the 4.7uf input cap. It's not the best design ever, but I just learned how to use the software.
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Old 29th March 2006, 04:46 AM   #4
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Hi 'teapot,

Have you generated the PCB from a schematic? Some of the connections to the LM3875 seem wrong to me. V- should be pin 4.

It looks to me like you missed the 22k resistor from in+ to ground and the input cap should be in series with the in+. You need to look at power ground.

I might not be squinting quite right.

regards
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Old 29th March 2006, 06:31 AM   #5
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Quote:
Originally posted by Greg Erskine
Hi 'teapot,

Have you generated the PCB from a schematic? Some of the connections to the LM3875 seem wrong to me. V- should be pin 4.

It looks to me like you missed the 22k resistor from in+ to ground and the input cap should be in series with the in+. You need to look at power ground.

I might not be squinting quite right.

regards

The 22k resistor will be soldered directly to the leads. You're right about the other two mistakes, though; I'll have to fix those!
Can anyone reccomend a possibly neater way of doing this? My implementation seems a bit messy.
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Old 29th March 2006, 09:39 AM   #6
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Quick glance - the PSU caps need to be as close to the power pins as you can get them.
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Old 30th March 2006, 03:36 AM   #7
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Yet another version!
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Old 30th March 2006, 05:03 AM   #8
dfdye is offline dfdye  United States
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Careful of the short between the V+ pin and the output pin. That will cause you more than a few headaches in the future!
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Old 31st March 2006, 01:42 AM   #9
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Quote:
Originally posted by dfdye
Careful of the short between the V+ pin and the output pin. That will cause you more than a few headaches in the future!

Oops! I'll have to fix that. (I figured I'd just seperate them with an X-acto knife.)

Any thoughts? I'm hoping to make them up on Monday; I've got access to all the stuff I need, including some rather high-quality PCB material.
Also, can anyone reccomend a good way to drill all the @#$#$ing holes?
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Old 31st March 2006, 05:11 AM   #10
Nordic is offline Nordic  South Africa
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Those holes will kill ya.... I start them off with a small hand-drill just to form the indentation on the right places, then I put the small handdrill in the electric drill's chuck and complete all the holes...
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