LM1875

They say LM1875 is the low-power version of famous LM3875 (which is the heart of Gaincard power amplifier). Someone say, the sound is very good, and very alike tube-amplifier. I am not good at listening, so I am not sure if they are right or wrong. But still, I like this one.


The first purpose of making this one is kinda odd: use it as head-amp. Hmm, this IC is just like an opamp but it can provide good power for loud speaker. To use with head-phone I guess I need to reduce the gain to 3 or 5 and use lower voltage (dual 12v), and some other tweak. But I think I will save that for another day.

Schema from datasheet (I ripped some filter out of schema)
lm1875sch.png

PDF file for printing:LM1875_pcb.pdf

lm1875-pcb.jpg

This one can be use with the simple dual power supply.

Put in a box:
lm1875_box1.jpg
lm1875_box2.jpg

 
  1. mike000

    Sunday, August 5, 2012 - 20:53:15

    #1

    how does it sound?

  2. ceez

    Saturday, August 11, 2012 - 03:48:01

    #2

    Quite OK, lack of bass low and treble high. Mid low and bass are floating but blur and sticky. I don’t have a good pair of speakers to test with, just with my DIY speakers from some old chunky drivers.

    So, I can’t tell much. But it cheap and fun to make one :D

  3. Sylvie Ventura

    Wednesday, December 18, 2013 - 11:23:39

    #3

    I’m just print and assembled the pcb you attach here and…

    Hey man, do not invalidate your work, its sound good, very good, need more than 12V (a 22V ac to reach about 27,5V+ 27,5V-) and two very very hi capacity condenser on the power supply.
    The Hi freq still sound to “aggressive” but we can fix easily. with a 800pf condenser on the incoming + signal to ground
    So man, great job!

    I’m wondering if you have something to increase the current drive on this little amplifier, i’m thinking about about a buffered preamplifier with low gain (1 to 3), but I’ve no idea to start.
    Could you help me please?
    You can reach me here: “sylvieventura at tiscali dot it”

  4. ceez

    Saturday, December 21, 2013 - 12:12:48

    #4

    Yeah, I use this 220v - 18v(x2) AC transformer, therefore I have ~ ±24v DC . Main power capacitors are ELNA 6800uF x2 (each for one power rail). But I think it is not enough.

    You can start with Cmoy for buffered preamp http://tangentsoft.net/audio/cmoy-tutorial/ but R3 (1k) in the schematic should be replace by 4k7 or 10k to set the gain from 11 down to 3 or 2. For better one, you can try A47 buffered headamp http://benfeist.com/how-to-build-the-apheared-47-headphone-amplifier-for-grado-headphones/

    Some documents I read on the internet indicate voltage peak of an audio lineout should be about ±1v (peak) up to ±1.6v (peak) for pro equipment. Depends on the Power you run (say ±25v) you can set total gain about 25v/1v= 25 (we don’t use pro equipment in the sutdio, right?), so maximum gain of buffered preamp should be 25 - 21 = 4 (21 is the gain factor of this LM1875 circuit). So, as long as you keep gain factor of buffered preamp below 4, it would be fine.

    And, you have to make another power supply for buffered preamp circuit.

    I use this with my USB DAC from my very first DIY project http://ceezblog.info/2008/07/07/usb-dac-pcm2707/ which include a headphone driver circuit using IC TDA1308 (taken from an old CD-ROM), it also works as buffered preamp since the gain factor is 2 which just fit my need.

    Hope, you can find it useful :)

  5. Sylvie Ventura

    Friday, December 27, 2013 - 07:43:04

    #5

    Yes,u did!
    I will try something like these..
    TnX Ceez!

  6. gobrogobro.ru

    Monday, January 11, 2016 - 05:36:16

    #6

    Heya! I just wanted to ask if you ever have any problems with hackers?
    My last blog (wordpress) was hacked and I ended up losing months of hard work due to no back
    up. Do you have any methods to prevent hackers?

  7. ceez

    Monday, January 11, 2016 - 06:58:45

    #7

    Yes. I had a few problem with hackers. The only things I could do are change password, backup database, then completely delete everything and upload new source code of the website and reconfig the website to run with the existing database.