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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 20th December 2017, 11:17 AM   #781
kurtvisti is offline kurtvisti  Denmark
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Thanx a lot Mooly!
I shall make my next component shopping according to your guidelines.
First prototype channel though now playing without any explosions
Regarding the 220R VR potentiometer at the input, I wonder what function this component has?
Regards Kurt
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Old 20th December 2017, 01:41 PM   #782
Mooly is offline Mooly  United Kingdom
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Beginner's Gainclone, HiFi LM1875, The Amplifier Board
You're welcome and pleased to hear you have one channel working.

The 220 ohm... only Daniel can explain that one

What it does do is interact with the 220pF cap to form a low pass filter although imo the effect of it is minimal with those values. If you turn the pot to a low value resistance, or even to zero ohms, then the 220pF cap effectively appears in parallel to whatever you connect to the input and in certain cases that might cause problems rather than help matters.

I would recommend fitting something like a fixed 1k resistor in place of the preset.
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Old 20th December 2017, 05:19 PM   #783
kurtvisti is offline kurtvisti  Denmark
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You mean leaving the 220p cap and just replacing the 200R pot with a 1k resistor?
I trust that Daniel will enlighten us at some time.
I also asked him about the sound quality of the original schematic vs the Turbo II.
Do you know about the differences between the 2?
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Old 20th December 2017, 06:30 PM   #784
Mooly is offline Mooly  United Kingdom
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Beginner's Gainclone, HiFi LM1875, The Amplifier Board
I've no idea on sound quality at all I'm afraid as I've never even built a chip amp for serious listening.

The 1k and 220pF form a filter with a -3db point of over 700kHz and so any effect it has will be marginal. Its Daniels choice of how he wanted to do it though.
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Old 20th December 2017, 06:32 PM   #785
Mooly is offline Mooly  United Kingdom
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I should have said that Daniels 220 ohm and 220pF form a filter with a -3db point of over 3MHz, and even higher if you turn the pot down.
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Old 20th December 2017, 08:17 PM   #786
kurtvisti is offline kurtvisti  Denmark
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Now I better understand, why I couldn’t hear any difference no matter the position of the potentiometer
My testspeakers are not the best but still.
With your explanation of the function of the cap and resistor I wonder why he put a potentiometer there instead of a fixed resistor.
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Old 21st December 2017, 07:58 AM   #787
Mooly is offline Mooly  United Kingdom
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You would have to ask Daniel that one

This shows graphically how the filter shapes the response. Look at the scale at the left. The second example would be more typical of values used in other designs.

One of the main functions of such a filter is to keep out interference.
Attached Images
File Type: jpg LPF1.JPG (226.8 KB, 333 views)
File Type: jpg LPF2.JPG (226.9 KB, 320 views)
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Old 18th March 2018, 08:10 AM   #788
Jishu is offline Jishu
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Dear Gurus, I would be using 18v-0-18v 3A transformer; I would like to use fuses on the power supply module as well as on the amplifier modules. How much amperage should the fuses be rated at? Should they be the same? Also should I use slow-blo or fast-blo versions?
Thank you.
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Old 19th March 2018, 09:26 PM   #789
FauxFrench is online now FauxFrench  France
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At least I am first with a suggestion:
1A "slow-blo" for the transformer primary and 5A or 6A "slow-blo" for the amplifier board.
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