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Chip Amps Amplifiers based on integrated circuits

Beginner's Gainclone, HiFi LM1875, The Amplifier Board
Beginner's Gainclone, HiFi LM1875, The Amplifier Board
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Old 21st May 2008, 04:36 AM   #31
danielwritesbac is offline danielwritesbac  United States
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It wasn't talent. It was tools.

See these two posts:
http://www.diyaudio.com/forums/showt...01#post1509701
http://www.diyaudio.com/forums/showt...79#post1509879
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Old 21st May 2008, 05:15 AM   #32
danielwritesbac is offline danielwritesbac  United States
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Its time to attach the onboard power capacitors.

Notice the orientation in the photo below.

You can use 470uF or 330uF.
A 50v model is recommended.

See that the centerpoint between the two power caps does connect to the ground (0v) lead.
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File Type: jpg lm1875 on veroboard power caps 001.jpg (58.7 KB, 3222 views)
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Old 21st May 2008, 05:29 AM   #33
danielwritesbac is offline danielwritesbac  United States
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Here's some details about the power circuit.
(click the photo)
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File Type: jpg lm1875 on veroboard power circuit.jpg (58.8 KB, 3168 views)
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Old 21st May 2008, 06:57 PM   #34
danielwritesbac is offline danielwritesbac  United States
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Its time to do the input circuit! Whee!

The first, and most important part of the input circuit, is the 15k input impedance resistor.
This one is brown, green, orange.

It runs from the input + to the 0v (ground), thereby presenting a load.

Now, in the photo below, the "input star ground" has started to form. Have a look at the photo below and see that the NFB and the input will ground at the same point (marked in green).
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File Type: jpg lm1875 on veroboard input impedance 15k.jpg (96.6 KB, 3060 views)
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Old 21st May 2008, 08:21 PM   #35
danielwritesbac is offline danielwritesbac  United States
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The following photo will show the hookup from Power ground to Input ground.

Compare this with the photo above. We have added just the one wire to make this connection.

This will complete the "input star ground" See photo--its marked in green.

EDIT: Notice that only one end of the 15k resistor connects to ground. The other end (marked yellow in the photo) is your signal + line.
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File Type: jpg lm1875 on veroboard input star ground.jpg (80.4 KB, 3019 views)
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Old 22nd May 2008, 12:39 AM   #36
danielwritesbac is offline danielwritesbac  United States
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Here's a bit clearer picture.

Notice the input star ground.

Green = Ground
Yellow = Input signal
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File Type: jpg lm1875 on veroboard input star ground 001.jpg (80.5 KB, 2937 views)
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Old 22nd May 2008, 01:16 AM   #37
danielwritesbac is offline danielwritesbac  United States
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Optional Component

This post is about an optional component called the "groundlift" resistor. It can be from 2.2 ohm to 8 ohms.

What it does it to make your input circuit "less attractive to hums" because a bit of added resistance prevents, "point of least resistance."


Compare the photo above with the photo below.
Notice the optional component has been added--the groundlift resistor.

This one is 2.2R (2.2 ohms) and its red, red, gold, as shown.
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File Type: jpg lm1875 on veroboard groundlift 003.jpg (92.6 KB, 1460 views)
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Old 22nd May 2008, 02:15 AM   #38
danielwritesbac is offline danielwritesbac  United States
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Hey, let's add our input filter cap and its compensation resistor.

The input filter cap blocks DC from entering the amplifier.
This particular input filter cap, I spec'd for 2.2uF.
*See previous discussion at post #8 and post #10.

Use either a "made for audio" electrolytic or any "poly" cap.

And, because source equipment generally dislikes a capacitive load, we have a compensation resistor. This compensation helps prevent the "endless search" for the "perfect" input filter cap. So, putting a resistor here is so much easier.
This resistor is 470R (470 ohms) and this one is yellow, purple, brown.

These are in-series with the input signal line.
See this photo and the next photo.
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File Type: jpg lm1875 on veroboard input filter cap d.jpg (82.6 KB, 1364 views)
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Old 22nd May 2008, 02:19 AM   #39
danielwritesbac is offline danielwritesbac  United States
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Here's the "color" marked photo, showing the input filter cap and its compensation resistor.

Ground is shown in green
Input signal is shown in yellow
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File Type: jpg lm1875 on veroboard input filter cap.jpg (74.7 KB, 1342 views)
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Old 22nd May 2008, 03:12 AM   #40
danielwritesbac is offline danielwritesbac  United States
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Optional Component, RF blocker
This is a tiny capacitor, 330pF (says "331" on it), that is added onto (parallel) the 15k input impedance resistor.

The RF blocker is a noise reduction component, thereby increasing the efficiency of the amplifier.

And. . .


Optional Component, input cable load
This is a 1M (1 megaohm) resistor.

It goes from signal input + to signal input - (as a load).

This resistor presents a tiny load, and its helpful that your input cords shall have a resistive load at the amplifier.
So, the 1m resistor is also a noise reduction component.
This one is brown, black, green.
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File Type: jpg lm1875 on veroboard rf blocker 002.jpg (64.0 KB, 1359 views)
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