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Old 7th December 2008, 10:34 AM   #101
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Quote:
Originally posted by danielwritesbac


OMG! I just got quoted by a guru. I'm smiling like the cheshire cat.

Wow. Thanks man!


P.S. It seems that the computer software that Nordic used, had partially obscured the polarity markings for V+ and V- power inlet terminals, which is what led to the error. This could have happened to anyone if using that software. This reminds me. I need to go buy a new automatic pencil.
Hi Daniel,

You must be confusing me with someone else.

BTW: There is nothing wrong with Eagle, the error is a human error not software. Either the LM1875 component is made incorrectly or the schematic was drawn wrong. This highlights a important point, people should always post the schematic as well as the generated PCB.

regards
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Old 7th December 2008, 10:38 AM   #102
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Quote:
Originally posted by sneih
^
thx for this information!!

btw that is my first homemade 1875. . .

Pretty job there!!!
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Old 7th December 2008, 11:06 AM   #103
AndrewT is offline AndrewT  Scotland
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Default schematic post 97

c2 =22uF ( C7 on the PCB) is far too small.
It must be bigger than or equal to 1.4 * C1 * R2 / R3. i.e if C1=2u2F, r2=22k and R3=1k, thenC2>=68uF. Use 100uF. If you want deep extended and phase coherent bass then increase this to either 150uF or 220uF.
If you use an electrolytic then protect it by adding a diode across the cap pins to prevent reverse DC destroying the cap.
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Old 7th December 2008, 11:12 AM   #104
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Quote:
Originally posted by AndrewT
c2 =22uF ( C7 on the PCB) is far too small.
It must be bigger than or equal to 1.4 * C1 * R2 / R3. i.e if C1=2u2F, r2=22k and R3=1k, thenC2>=68uF. Use 100uF. if you want deep extended and phase coherent bass then increase this to either 150uF or 220uF.

220uF there. A bit more heat and much more fun.

So, I take it that the textbook values in the range of 45uF to 100uF (center 68uF) are actually -3db where we'd like flat response instead, so we need to double the capacitor size to get our bass?
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Old 7th December 2008, 11:21 AM   #105
AndrewT is offline AndrewT  Scotland
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no,
if we require flat down to 20Hz, then the amp should have a frequency response a full decade below the flat frequency requirement, i.e. 2Hz F-3dB (RC input filter >=80mS). This will give F-1dB ~ 4Hz which is the most common minimum standard for power amps. I prefer to go slightly lower than that. Pre-amps should go at least an octave below the power amp passband.
I see other designers of repute suggest we go even lower, F-3dB @ 0.6Hz, but I have not experimented that low.
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Old 7th December 2008, 01:01 PM   #106
sneih is offline sneih  Indonesia
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Default Re: schematic post 97

Quote:
Originally posted by danielwritesbac


Pretty job there!!!
thanks daniel!!
btw just a few minutes it's sounding hehe


Quote:
Originally posted by AndrewT

If you use an electrolytic then protect it by adding a diode across the cap pins to prevent reverse DC destroying the cap.
the schematic like this?
Click the image to open in full size.

what dioda can i used?

thx
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Old 7th December 2008, 01:04 PM   #107
AndrewT is offline AndrewT  Scotland
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yes, just like that.
Two diodes in series could be considered giving 1.2Vdc of reverse peak ability and still protect the electrolytic.
The currents are tiny. A signal diode like 1n4148 could be used.
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Old 7th December 2008, 01:13 PM   #108
sneih is offline sneih  Indonesia
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thanks guys for ur kindness
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Old 7th December 2008, 03:18 PM   #109
sneih is offline sneih  Indonesia
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Default Re: schematic post 97

Quote:
Originally posted by AndrewT
c2 =22uF ( C7 on the PCB) is far too small.
It must be bigger than or equal to 1.4 * C1 * R2 / R3. i.e if C1=2u2F, r2=22k and R3=1k, thenC2>=68uF. Use 100uF. If you want deep extended and phase coherent bass then increase this to either 150uF or 220uF.
If you use an electrolytic then protect it by adding a diode across the cap pins to prevent reverse DC destroying the cap.
update:
c7= 68-100uF:

Click the image to open in full size.
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Old 7th December 2008, 11:09 PM   #110
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A couple of notes.

You can update the photo to show 68uF-100uF

You can eliminate the "Out -" trace because 220uF power caps aren't large enough to deal with return AC from the speaker. Therefore the speaker ground should be located at the 0v output terminal of the power supply board in the completed amplifier. That (a single groundpoint for speakers) will also help if you decided to add a headphone jack to the project.
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