Hi, Im making lm1875 amp and I want to make xlr and rca input and also volume control but I have no idea how to do it. I dont really know how op amps works so I would be very glad if you can help me. Thank you 🙂
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Do you mean LM1875 instead? Use the pcb layout as shown in the data sheet.
You first have to decide single supply or dual supply.
https://www.ti.com/lit/ds/symlink/lm1875.pdf?ts=1656863800052&ref_url=https%3A%2F%2Fwww.google.com%2Fsearch%3Fsxsrf%3DALiCzsaG1z0Xt9eO9vuGkio5yt0R7K-sJw%3A1656863767544%26q%3DLm1875+pdf%26oq%3DLm1875+pdf%26aqs%3Dheirloom-srp..
You first have to decide single supply or dual supply.
https://www.ti.com/lit/ds/symlink/lm1875.pdf?ts=1656863800052&ref_url=https%3A%2F%2Fwww.google.com%2Fsearch%3Fsxsrf%3DALiCzsaG1z0Xt9eO9vuGkio5yt0R7K-sJw%3A1656863767544%26q%3DLm1875+pdf%26oq%3DLm1875+pdf%26aqs%3Dheirloom-srp..
Agree, except...... hasn't some junior draftsperson let the parts and traces layout slip down and to the right?
have a look at rod elliott's site, including several schemes and PCBs for pre-amps:
https://sound-au.com/p-cat.htm#pre
by the way, you will need a balanced input circuit for XLR.
https://sound-au.com/p-cat.htm#pre
by the way, you will need a balanced input circuit for XLR.
this depends on the voltage of your source and the gain of your LM1875 amp.
the volume regulation should probably allow maximum amp output but also allow sensible volume regulation. that means you should not driver your amp into clipping with the volume pot just slightly above minimum.
have a look at pano's gain structure explanation: https://www.diyaudio.com/community/threads/what-is-gain-structure.186018/
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This is a small PA mixer input channel, I stripped it down, removed Phantom power, to match your requirements.
Balanced microphone straight to XLR; original Line input uses a typical 6.35mm Guitar jack but of course you can use a RCA jack there.
If you want to mix stereo RCA signals into a single Mono one, use 2 jacks (Left-Right), each with its own 10k mixing resistor, connected to R77 top.
It has a Tone Control stage which you might find of use, if not, remove everything inside the red box and connect U1b output (pin 1) straight to W3 volume control.
Not strictly needed but to avoid possible scratchiness leave either C9 or C72 in the path.
I also suggest you try to find and use an Audio/Log pot for W3; a linear one is easier to find but harder to use.
Balanced microphone straight to XLR; original Line input uses a typical 6.35mm Guitar jack but of course you can use a RCA jack there.
If you want to mix stereo RCA signals into a single Mono one, use 2 jacks (Left-Right), each with its own 10k mixing resistor, connected to R77 top.
It has a Tone Control stage which you might find of use, if not, remove everything inside the red box and connect U1b output (pin 1) straight to W3 volume control.
Not strictly needed but to avoid possible scratchiness leave either C9 or C72 in the path.
I also suggest you try to find and use an Audio/Log pot for W3; a linear one is easier to find but harder to use.
Mic input: 47k/510=92X
Line input : "same but attenuated by R58/R77" so about 7.5X
It will work fine straight driving your LM1875 input, when set to datasheet suggested values.
EDIT: same gain with/without tone control since it is unity gain when set flat.
Bonus points to PRR for his hawk eye discovering Datasheet drawing error 🙂
Line input : "same but attenuated by R58/R77" so about 7.5X
It will work fine straight driving your LM1875 input, when set to datasheet suggested values.
EDIT: same gain with/without tone control since it is unity gain when set flat.
Bonus points to PRR for his hawk eye discovering Datasheet drawing error 🙂
i want to use it as studio monitors and i will connect the balanced xlr input to sound card. isn't the gain too high for xlr?
You should have said so in the first post 😉
Unless expressly stated otherwise, XLR is assumed to be Balanced Microphone input (where it´s needed) and not short distance high level signals where it´s not.
Lots of devices include that needless "feature" only because most people associate XLR-balanced to "Pro" equipment so it helps sales.
Oh well.
Within normal Home Studio distances, just use unbalanced RCA from your sound source to LM1875 input, period.
Shielded cable of course.
Levels match, impedance too, just add a 10k to 50k Audio/Log volume pot at LM875 input for your convenience or last minute adjustments.
Balanced XLR was invented to send weak low impedance microphone signals up to 200 meters away without loss or interference, not the case here.
Unless expressly stated otherwise, XLR is assumed to be Balanced Microphone input (where it´s needed) and not short distance high level signals where it´s not.
Lots of devices include that needless "feature" only because most people associate XLR-balanced to "Pro" equipment so it helps sales.
Oh well.
Within normal Home Studio distances, just use unbalanced RCA from your sound source to LM1875 input, period.
Shielded cable of course.
Levels match, impedance too, just add a 10k to 50k Audio/Log volume pot at LM875 input for your convenience or last minute adjustments.
Balanced XLR was invented to send weak low impedance microphone signals up to 200 meters away without loss or interference, not the case here.
Ye i know i dont need it but i already have balanced output and xlr cables so I decided to add it so that I don't have to use the reduction
