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Chip Amps Amplifiers based on integrated circuits

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Old 22nd May 2008, 03:23 AM   #41
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Here's the "color" marked photo showing the RF blocker and the 1M resistor.

Green is ground
Yellow is input signal +
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Old 22nd May 2008, 03:42 AM   #42
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Here's the speaker hookup.
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Old 22nd May 2008, 04:16 AM   #43
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Optional Component, Output Zobel

Because a speaker wire is like a big antenna, and it leads directly into the NFB, then an amplifier could get some noise in through the speaker leads. A speaker output zobel helps block some of that. This is a noise reduction component.

In addition, the Speaker Output Zobel serves to enhance the stability of the amplifier.

This zobel shouldn't be within the audio band, but rather, just above.

For this, I've selected:
10R (10 ohms) and this one is brown, black, black,
plus
10nF, which is 0.01uF and probably has "103" printed on it.

Zobel. That's a resistor and capacitor, "RC," as a load.
This load is upon the speaker output.

See picture.
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Old 22nd May 2008, 04:28 AM   #44
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And now, the complete amplifier in "dazzling technicolor"

Hey, don't worry! I'll put a nice clean photo up after this one.
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Old 22nd May 2008, 04:34 AM   #45
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Complete.

Please do trim the connection wires short.
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Old 22nd May 2008, 05:05 AM   #46
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Here's an example on how to connect the external components (such as the power supply board). Tie the connections up tight, prior to soldering. See photo.
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Old 22nd May 2008, 06:13 AM   #47
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Quote:
Originally posted by Edits
Hi Dan,
Can not wait the sequel! Compiled those parts, but still miss the 27K feedback resistor. Can I substitute with 20k, 22k? or 33k?
That is the one I'll try.
Okay! Now that its done, we can mod it if you like.

Its cross-compatible with the AudioSector resistor values, so 22k with 680R can work for the NFB. That's gain 32.

If your source/preamp is really strong or if you've used less than the recommended voltage, then you can use:
20k with 680R = Gain 30
22k with 820R = Gain 28
20k with 820R = Gain 26

*There may be slight differences in DC offset with different gain settings, and the chipamps do vary between individual samples.
Do check with your meter, at the amplifier's speaker output.

**I set a rather high gain of 35 (that's 27k with 820R) to help modern sources with digital volume controls that shouldn't be run "maxed out" because they are often op amp chips.

The National Semiconductor Overture Design Guide spreadsheet does work with with LM1875. Dial in LM1876, which is two LM1875's and an extra circuit crammed onto one LM1876 chip. The resulting designs will work for LM1875.
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Old 22nd May 2008, 02:13 PM   #48
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Daniel you have made an excellent and helpful article .

Why don't you upload it in a website or a blog .It will be very helpful for us .

Please keep it up .

Somak
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Old 24th May 2008, 05:32 AM   #49
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hi Daniel,

personally i like my input cap to be poly film, i dont know about anybody else, but my guitar sounded much better.
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Old 24th May 2008, 10:22 AM   #50
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Quote:
Originally posted by casiomax
hi Daniel,

personally i like my input cap to be poly film, i dont know about anybody else, but my guitar sounded much better.
Oh yes! You can use Polypropylene, Polyester, Ceramic, Electrolytic, and botique types. And, you can use them solo or in combination.

One combination, was recommended by "that very helpful guy who earth-grounds everything very thoroughly," and that suggestion was 4.7uF + 0.47uF.
I haven't tried it yet, because I was pretty happy with just 0.47uF part.

So, do what ever sounds good.
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