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Old 7th March 2012, 05:49 AM   #151
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Join Date: Sep 2011
Location: El Triunfo
Question Audio Amplifier with LM1875

Hi all!
Here are two seeds on the internet where different feedback: Av=(22k/1k)+1 and Av=(180k/10k)+1 !?
Which schematic better?
And here's how I made audio amplifier ​​with the LM1875 .
thank you!
Attached Images
File Type: jpg Shematic-1.jpg (55.6 KB, 903 views)
File Type: jpg Figure-F.JPG (98.3 KB, 909 views)
Attached Files
File Type: pdf Shematic and texst.pdf (20.7 KB, 180 views)

Last edited by formula 22; 7th March 2012 at 05:58 AM.
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Old 7th March 2012, 09:27 AM   #152
bcmbob is offline bcmbob  United States
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Location: Bay City, Michigan
JohnnyPOO, Please take a look at this thread. A new approach.
Bob M.
"Arrange Whatever Pieces Come Your Way."
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Old 7th March 2012, 12:01 PM   #153
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
There is much to commend post151 schematic.
It shows:
Input filters
AC coupled.
Local decoupling
Output Zobel
Fused supply rails
Separate Signal and Power Grounds.

All that's left is ON/OFF muting and selecting component values.
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 7th March 2012, 05:42 PM   #154
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Originally Posted by JohnnyP00 View Post
Would it be possible to replace the 22k resistors on BrianGT's amp boards with 1/4 watt instead of 1/2 watt. Having a hard time sourcing 1/2 watts that small in Canada. Thanks for your help.. JohnnyP
That is a low current area and thus 1/4w will do fine.
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Old 4th March 2013, 12:14 AM   #155
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Join Date: Mar 2012
Originally Posted by BrianGT View Post
I haven't had a chance to work on the manual yet, but here are some board pictures, and info:

Amp board:
Click the image to open in full size.Click the image to open in full size.
R1 - not used (optional resistor to ground before C1)
R2 - 22k (input to ground resistor)
R3 - 1k (gain resistor , gain = 1 + R4/R
R4 - 22k (nfb resistor - on bottom of pcb)
R5 - 2.7 2w (optional - zobel network)
R6 - jumper (optional resistor between input ground and output ground)
C1 - 2.2µF (optional input capacitor)
C2 - 22µF bipolar (optional)
C3 - 0.1µF (power supply decoupling)
C4 - 0.1µF (power supply decoupling)
C5 - 0.1µF (power supply decoupling)
C6 - 47µF (power supply decoupling)
C7 - 0.1µF (optional - zobel network)

PSU board:
Click the image to open in full size.Click the image to open in full size.
R0 - 10k (series resistor for LED)
R1,R2 - 1 2w (optional "snubber" network capacitors)
C1,C2 - 1500µF (main power supply caps)
C3,C4 - 0.1µf (power supply decoupling)
C5,C6 - 0.1µf (optional "snubber" network capacitors)
D0 - blue LED
D1-D4 - MUR860

Transformer wiring:
For the PSU transformer connections, AC1 denotes the first secondary winding of the transformer, and AC2 denotes the second secondary winding of the transformer. It is also possible to use a center tapped transformer with this PSU board by wiring the center-tap to either AC1(bar over top) or AC2.

As for size, the LM1875 amp boards are almost half the size of the original LM3875/LM3886 amp boards.

Basic Assembly Info:
Solder components on board in order from lowest profile to highest profile, with the PSU diodes and LM1875 chip being soldered last.

As the pics show, the boards were made on the 11th week of 2007... over a year ago. I believe I mailed 10-15 boards out to various people, so let me know if you have any additional questions,

Thanks to Allan for transcribing his component notes and taking pictures!

Does anyone have the original pictures for this? Was a guide ver made?
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Old 4th March 2013, 11:12 AM   #156
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Originally Posted by magomago View Post
Does anyone have the original pictures for this? Was a guide ver made?
Brian's kit is here: LM1875 Amplifier Kit |
It seems that there's no published manual nor pictures on the site at this time. That site needs some maintenance. However, the boards may still be available.
DIY Models & AppsClipNipperLM1875TDA7293Powerful Parallel TDA7293 kit ♦ My post has opinion.
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Old 10th July 2014, 08:49 PM   #157
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I just discovered these chipamps because of my dedication to the great sound of the Renkforde E-SA9 amp.
It had a lot of distorsion but it sounded great and i found out that the distorsion came from the JRC 4558 chips that took care for the bass and treble adjustment.
Now i am left with the great sounding LM1875, thats the reason it sounded great.
I will rebuild this amp in a chipamp in this way and i asked myself the last days what the best parts are to use.
I came with Elna Simic 2 caps for the PSU, (those might be better than the Panasonic caps) and also this type for all other other electrolitics.
In the signal path i will use Caddock MP resistors.
Also i will use Evox Rifa MMK5 capacitors voor coupling, the 2.2 uF.
Also a ALPS potentiometer of cause.

Are there any other advices in what type components to use ?
And i ask muself why the power capacitors are only 1400uF, why not bigger ?
In the original Renkforce E-SA9 its 3300uF.
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Old 10th July 2014, 09:35 PM   #158
jemraid is offline jemraid  United Kingdom
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Location: NE Derbyshire
Hello Thed,

Have a look at Mick Feuerbacher Audio Projects Mick Feuerbacher's site. If you want an austere (and to my mind rather thin and weedy) amp make his 'Copper' one, if you want one with a big fat warm sound build one with a snubberized PSU. They are both on there.

Cheers - Jim
FH3 build using very simple tools and a point to point Gain Clone with largish power supply.
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Old 11th July 2014, 12:14 AM   #159
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MMM, Sounds like mono blocks.
Is it mentally ?
All the discussions about best sounding components will be like this.
Just good schielding i would say in a enclosesure.
I will snubber !
Is there no good power regulator that wil go to 18 volts ?
So stupid..., i will go in a humm any minute now.
But there is !!! but no one found above 48volts if i am correct.
For other aplications you could them connect them in series like batteries.

Last edited by Theduboracle; 11th July 2014 at 12:44 AM.
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Old 4th September 2014, 01:14 PM   #160
gychang is offline gychang  United States
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Location: Davis, California
Originally Posted by AndrewT View Post

If the surfaces are "hard" then compound must be used eg. mica, metal, Kapton etc.

If one of the surfaces is "soft" then the insulator itself fills all the gaps thereby eliminating the air.
if metal is used would conduct, original question is applying heat sink without conducting electricity but with conduction of heat...
Good sound from Davis, CA
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