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I realize it doesn't seem so to a newbie, but this is a ridiculously simple circuit. Please note FYI:
C1 and C2 are both intended to prevent DC offset at the output. That is, with the input (left-hand side of R1) grounded there should be no output. Are these capacitors present? Never mind measuring anything, just are C1 and Cs present.
C3, C4, and C5, C6, are all associated with the power supply, not with amplification directly.
R6 and C7 are a zobel network intended to improve speaker operation, again they're not involved with amplification directly.
Bearing those things in mind:
The input circuit is R1, R2, R3, and C1.
The amplification circuit is the LM1875, R4 and R5, with C2 added to prevent DC offset.
R6 and C7 are a zobel network.
Now to cases:
Lookee, I don't mean to be smarty mouth, but there are only two reasons for your circuit to not work.
1. The power supply is out of whack.
2. You soldered somthing up wrong--this is the problem in 99.9% of cases. Hey don't get your feelings hurt, we all do it. Well OK, so I do it, I don't know who else does or doesn't.
To fix all this, check power to the LM1875 at pins 3 and 5. Check them to each other, should be about 32 volts. Check each to circuit ground, should be about 16 volts. Good? Put away your meter.
All power off. Start at pin 1 of the LM1875. Check what's connected against what the schematic says should be connected.
Same thing at pin 2. Then at pin 3...you're gettng the picture?
This checking the circuit seems like a daunting task, but that's only because you haven't done it before. There are only a few components, so how long can it take? Answer: not all that long. Writing things down helps.
By the way, it's customary to refer to components by their designation on the schematic. For instance, don't say "the 1K resistor," say R1. This is because there might be fifty 1K resistors in a circuit--not this circuit, of course.
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I realize it doesn't seem so to a newbie, but this is a ridiculously simple circuit. Please note FYI:
C1 and C2 are both intended to prevent DC offset at the output. That is, with the input (left-hand side of R1) grounded there should be no output. Are these capacitors present? Never mind measuring anything, just are C1 and Cs present.
C3, C4, and C5, C6, are all associated with the power supply, not with amplification directly.
R6 and C7 are a zobel network intended to improve speaker operation, again they're not involved with amplification directly.
Bearing those things in mind:
The input circuit is R1, R2, R3, and C1.
The amplification circuit is the LM1875, R4 and R5, with C2 added to prevent DC offset.
R6 and C7 are a zobel network.
Now to cases:
Lookee, I don't mean to be smarty mouth, but there are only two reasons for your circuit to not work.
1. The power supply is out of whack.
2. You soldered somthing up wrong--this is the problem in 99.9% of cases. Hey don't get your feelings hurt, we all do it. Well OK, so I do it, I don't know who else does or doesn't.
To fix all this, check power to the LM1875 at pins 3 and 5. Check them to each other, should be about 32 volts. Check each to circuit ground, should be about 16 volts. Good? Put away your meter.
All power off. Start at pin 1 of the LM1875. Check what's connected against what the schematic says should be connected.
Same thing at pin 2. Then at pin 3...you're gettng the picture?
This checking the circuit seems like a daunting task, but that's only because you haven't done it before. There are only a few components, so how long can it take? Answer: not all that long. Writing things down helps.
By the way, it's customary to refer to components by their designation on the schematic. For instance, don't say "the 1K resistor," say R1. This is because there might be fifty 1K resistors in a circuit--not this circuit, of course.
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(Bentsnake)
i am sure that i hvnt done anything wrong with that schematic...i soldered nothing,i mean i mounted everything on a projectboard...now i m trying this circuit.... http://www.ti.com/lit/ds/symlink/lm1875.pdf (second one).....its pretty cool...but it has also a distortion problem...but this circuit supplies clear sound even at midhigh volume...as im using 3w speaker ,do you think it does matter?
i am sure that i hvnt done anything wrong with that schematic...i soldered nothing,i mean i mounted everything on a projectboard...now i m trying this circuit.... http://www.ti.com/lit/ds/symlink/lm1875.pdf (second one).....its pretty cool...but it has also a distortion problem...but this circuit supplies clear sound even at midhigh volume...as im using 3w speaker ,do you think it does matter?
I'm always sure too. But that's another story.
Before anything else, the circuit you're using must be known. The second circuit you reference is a single-supply circuit, but before you said you're using a dual/split power supply. The question of the moment is what's going on?
Note: Sure you could be overloading 3watt speakers, and that would cause distortion. Lots.
Note: The 100nF capacitors are "bypass" capacitors. Their purpose is to remove high (radio) frequency noise from the power supply by shorting it to ground. They're to be located as close as possible to the power pins of the LM1875, not in the power supply. But you could just as well omit them for now, for trouble shooting purposes.
Before anything else, the circuit you're using must be known. The second circuit you reference is a single-supply circuit, but before you said you're using a dual/split power supply. The question of the moment is what's going on?
Note: Sure you could be overloading 3watt speakers, and that would cause distortion. Lots.
Note: The 100nF capacitors are "bypass" capacitors. Their purpose is to remove high (radio) frequency noise from the power supply by shorting it to ground. They're to be located as close as possible to the power pins of the LM1875, not in the power supply. But you could just as well omit them for now, for trouble shooting purposes.
If you are using that, then where did you connect the trafo lines?
Then you don't have +, 0 and - lines, only 0 and + and you should have 24V, not 12. You have to connect the 12-0-12 trafo center lines and connect it nowhere else.
So only the originally - side is the 0 and the + side remains the +.
Also it was mentioned that R6/R5 has to be higher than 10, or the chip will oscillate and generate lot more heat.
Can you make a picture of your setup, so we can see what goes where?
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Hi Flame boy, I would discard your original schematic, the -ve supply capacitor wiring is wrong! It does not help casual hobbyists when people post such nonsense but not your fault, but appears to be the source of much of your confusion.....
Take a look at the TI application note, p.2:
www.ti.com/lit/ds/symlink/lm1875.pdf
It is pretty much the same circuit
In the above note input capacitor C1 can also be 2.2uF film or foil type, this is normally preferred. C2 should ideally be a non-polarised electrolytic but you can get away with polarised as specified.
Take a look at the TI application note, p.2:
www.ti.com/lit/ds/symlink/lm1875.pdf
It is pretty much the same circuit
In the above note input capacitor C1 can also be 2.2uF film or foil type, this is normally preferred. C2 should ideally be a non-polarised electrolytic but you can get away with polarised as specified.
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I have built two workhorse "monoblock" units using this chip on old Maplin app note circuit PCBs, the small Hammond enclosures and rearranged the input/feedback circuit to bootstrap the inputs.
This was to be able to test the outputs of valve preamps with their inherent higher impedances, without measureable loading. They do however fart quite loudly when input is touched! Bootstrapped input impedance is very high of the order of 10s of Mega-ohms, so they are very sensitive!
I used one 30VA transformer 18-0-18VAC per unit, smallish supply rail caps, 2 off 2200uF 35V per rail.
I have also alternate power connection for them to be used with external regulated PSU but have yet to complete this part of the project....
They were built for general audio/speaker testing, back in 2001 and they're still sounding great and going strong!
I will upload pics if you are interested...
This was to be able to test the outputs of valve preamps with their inherent higher impedances, without measureable loading. They do however fart quite loudly when input is touched! Bootstrapped input impedance is very high of the order of 10s of Mega-ohms, so they are very sensitive!
I used one 30VA transformer 18-0-18VAC per unit, smallish supply rail caps, 2 off 2200uF 35V per rail.
I have also alternate power connection for them to be used with external regulated PSU but have yet to complete this part of the project....
They were built for general audio/speaker testing, back in 2001 and they're still sounding great and going strong!
I will upload pics if you are interested...
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See third post down:
http://www.diyaudio.com/forums/chip-amps/227052-lm1875-fizzing-away-probelm-6.html
http://www.diyaudio.com/forums/chip-amps/227052-lm1875-fizzing-away-probelm-6.html
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I mean the secondaries.
Does it have 4 lines or 3?
If 4, then it is 0-12 and also 0-12. Here you have to connect one 12 and the others 0 together, so you get a center and it will act as -12 - 0 - +12 But if you don't use the middle 0, then you have the 0- 24 V and that is what you need.
A full drawing would be good as we don't know where did you connect what.
There may be more misconnected lines and kill other items.
We didn't see anything from before the amp stage.
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