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Chip Amps Amplifiers based on integrated circuits

Beginner's Gainclone, HiFi LM1875, The Amplifier Board
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Old 5th July 2016, 08:52 AM   #681
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Nag View Post
Dear Andrew,
I am completely newbie on amp/audio circuits. Some times even I don't understand technical words like feedback/zobel network/star earth ground bla bla. So as per your reply PSU is ok except c5 and c6. Can I through that amp and start build own amp form National semiconductor or form this DAN reference circuit. Which one is good ?. Speakers have efficiency 85.5dB 8ohm.
Thanks,
Nag.
To that, I would have to ask, what power voltage have you planned to use?
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Old 5th July 2016, 09:26 AM   #682
Nag is offline Nag  India
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Dear Daniel,
Input 230 AC,
OUT PUT 15V-0-15V 5AMP 150VA as per Andrew suggestion.
Thanks,
Nag.
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Old 11th July 2016, 03:51 PM   #683
Nag is offline Nag  India
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Originally Posted by AndrewT View Post
remove S1 & S2 Fuses here need to be so big to survive start up that they offer no safety advanatge when something goes wrong. A close rated mains fuse is far better at giving the required safety.
remove C5 & C6. They are more likely to increase ringing on the supply lines.
They cannot offer lower impedance seen from the amplifier because they are too far away. Local Supply Rail Decoupling has to be LOCAL to where the currents change.This sch is completely ****** up. Is that an interpretation of what Daniel is giving you?
Go back to the datasheet from National and start with that.
Then add in filters at the input and Thiele Network at the output and proper Local Supply Rail Decoupling.
Dear Andrew and members,

Now I am going to build with official schematic, Please let me know what changes need to done like capacitors/resistors. and any modifications or valuable suggestions.
Click the image to open in full size.Click the image to open in full size.
Click the image to open in full size.

Click the image to open in full size.

Last edited by Nag; 11th July 2016 at 04:01 PM. Reason: images not loaded properly
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Old 13th July 2016, 10:28 PM   #684
AndrewT is offline AndrewT  Scotland
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add an RF filter to the input.
Change C2 to 100uF
Make sure that R1, R2 and C2 connect to input signal return.
Why is 2200uF fitted to output? It has no C number ! Did you add it to the sch?
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Old 14th July 2016, 04:31 AM   #685
Nag is offline Nag  India
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Quote:
Originally Posted by AndrewT View Post
add an RF filter to the input.
Change C2 to 100uF
Make sure that R1, R2 and C2 connect to input signal return.
Why is 2200uF fitted to output? It has no C number ! Did you add it to the sch?
I added 2200uF as per previous suggestions as protection to speaker.
I didn't get you exactly "add an RF filter to the input"
I didn't get you exactly "Make sure that R1, R2 and C2 connect to input signal return". I have 3 wires as input "left channel wire , right channel wire, ground wire"
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Old 14th July 2016, 04:39 AM   #686
keith_correa is offline keith_correa  India
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Quote:
Originally Posted by Nag View Post
I added 2200uF as per previous suggestions as protection to speaker
Who suggested this and where was this suggested?
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Old 14th July 2016, 06:08 AM   #687
Nag is offline Nag  India
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Quote:
Originally Posted by keith_correa View Post
Who suggested this and where was this suggested?
I red in diyaudio forums as decouplig capacitor will improve bass and it protects speaker.
If it is not required I will remove no issues.
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Old 14th July 2016, 12:50 PM   #688
AndrewT is offline AndrewT  Scotland
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A decoupling capacitor is completely different.

You have fitted a DC blocking capacitor. This blocks an output stage failure generated DC damaging you speaker.

Instead of a DC blocking capacitor you can fit some form of speaker protection.
I do recommend some form of speaker protection !
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Old 14th July 2016, 12:58 PM   #689
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Nag View Post
I added 2200uF as per previous suggestions as protection to speaker.
I didn't get you exactly "add an RF filter to the input"
I didn't get you exactly "Make sure that R1, R2 and C2 connect to input signal return". I have 3 wires as input "left channel wire , right channel wire, ground wire"
I always recommend that the input to our equipment be fitted with band limiting passive filters.
These come in two forms and both are required.
A low pass passive filter attenuates very high frequencies.
A high pass passive filter attenuates very low frequencies.

The High Pass filter needs two components A capacitor in series with the input signal Hot line and then a signal grounding resistor from Signal Hot to Signal Return. You have both these components (C1 & R2) shown in the sch.

The Low Pass filter needs two components A resistor in series with the input signal Hot line and then a signal grounding capacitor from Signal Hot to Signal Return. You have neither of these components shown in the sch.
Typical values are 200r to 3k for the series resistor and 220pF to 2n2F for the grounding capacitor.

Both filters need some fine tuning to get their roll-off frequecy to meet your needs. You expect ALL the audio signalto pass and expect ALL the interfering signal to be blocked. You cannot meet this idealised performance requirement. You adjust till the compromise is acceptable. Allowing an F-3dB for each filter about a decade outside the required audio bandwidth satifies most Builders/Listeners.
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Last edited by AndrewT; 14th July 2016 at 01:01 PM.
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Old 20th July 2016, 09:17 AM   #690
danielwritesbac is offline danielwritesbac  United States
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Quote:
Originally Posted by Nag View Post
I added [series] 2200uF as per previous suggestions as protection to speaker.
If the speaker is bigger than 4 inches, double that capacitance. Match it to your speaker's needs.
Also, if you have a split-rail powered amp, it would be nice to put the series capacitive speaker filter close to (nearby) the speaker, not close to the amp; and, in the case of a split-rail powered amp, put your series capacitve speaker filters at groundside (speaker negative).
Quote:
Originally Posted by AndrewT View Post
The Low Pass filter needs two components A resistor in series with the input signal Hot line and then a signal grounding capacitor from Signal Hot to Signal Return. You have neither of these components shown in the sch. Typical values are 200r to 3k for the series resistor and 220pF to 2n2F for the grounding capacitor.
When the source is a modern computerized sort, I'd add 470p~560p parallel to the ~22k input load resistor. Round about that much loading does seem to clean off what I didn't want to hear, without reducing what I wanted to hear.
I can't tell you very much about it, except that I'm sure it is worthwhile to add the parts for it. Thanks for suggesting it.
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