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LM1875 Amplifier Watts

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cut off frequency will be around 100-107Hz
Thats the start of the cut off frequency, there is still a slope before its fully cut off.
What will be the lower end?
No its the high end of the low end.
Is this frequency range is suitable for small subwoofer system
It depends on whether your mid ranges can go that low can go that low.
 
Ok I mean.Subwoofer filters tuned like 30Hz to 90Hhz,60Hz to 160Hz etc.......Like that what will be my range?
 
Very nice to hear :) Most people say TL072 has more bass than uc4558.
No.
They have exactly the same amount of bass if the input coupling capacitor value is high enough for the 4558 since its input resistance is very high but is much lower than the TL072.

In my pcb I have two of 4558 IC's. I'll replace them with TL072.
If they are both made by American manufacturers then You will hear no difference.
Your input opamp circuit does nothing and can be replaced with a piece of wire.

The values of your coupling capacitors are WAY too high.

Off topic: I have never bought cheap opamps. Do they continuously produce the sounds of CHEEP, CHEEP, cluck cluck, CHEEP, CHEEP ... like a little bird??:D
 
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Once agin it all depends on your setup :confused:
How low do your mids go?
How low can your sub go?
 
How low can your sub go?
It is NOT a sub-woofer. Its spec's say it goes down to 40Hz (maybe at -10dB).
A REAL sub-woofer is at least 10" and goes down to 15Hz or less at -10dB or down to 20 to 30Hz at -3dB.

There are no "mids". Just little satellite tweeters. Hiss, boom boom. Hiss, boom boom.
 
It is NOT a sub-woofer. Its spec's say it goes down to 40Hz (maybe at -10dB).
A REAL sub-woofer is at least 10" and goes down to 15Hz or less at -10dB or down to 20 to 30Hz at -3dB.

There are no "mids". Just little satellite tweeters. Hiss, boom boom. Hiss, boom boom.
Yes at some point the OP may get the point.
 
I have never been to Australia (South Mald Isld is at the North-East). Maybe there are no deep bass sounds there, MATE!
 
Brilliant audioguru I'll change the coupling capacitors to 150nF (0.15uF).

The problem is I cannot remove the "Not needed section" that you marked because it is already in the pcb its very difficult to cut traces etc.....

Is it ok if change that C3 cap to 150nF (0.15uF)?so it will pass 30Hz overall!!!
 
Brilliant audioguru I'll change the coupling capacitors to 150nF (0.15uF).
Good. It is too bad that you did not use grade 6 arithmatic to calculate the values.

The problem is I cannot remove the "Not needed section" that you marked because it is already in the pcb its very difficult to cut traces etc.....
You do not need to remove the useless parts. it is easy to replace them with a piece of wire. Don't you have a desoldering sucker tool? I have desoldered thousands of parts with my desoldering sucker tool.
 
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I have never been to Australia (South Mald Isld is at the North-East). Maybe there are no deep bass sounds there, MATE!

I am not sure what sort of a map you are using there AG, but the Maldive Islands are about 5000km north east of Australia.
You could just about fit Canada into that gap.

JimB
 
I keyed, "South Mald Isld" into Google and it showed near Queensland, Australia.
But actually Maldive Islands are near the southern tip of INDIA!
 
Hi audioguru.

Ok now I'm going to bypass that not needed section using a wire.Thats easy.But I noticed I'll miss that R6, 4.7K.Without this resistor it will pass some highs as well :(
 
I keyed, "South Mald Isld" into Google and it showed near Queensland, Australia.
But actually Maldive Islands are near the southern tip of INDIA!

Good point AG, when I put "South Mald Isld" into google, the best it gives me is South Molle Island which is on the Great Barrier Reef.

So Suraj, what is it?
Maldives or Barrier Reef?
Enquiring minds need to know!

JimB
 
Ok now I'm going to bypass that not needed section using a wire. Thats easy.
But I noticed I'll miss that R6, 4.7K. Without this resistor it will pass some highs as well :(
No.
R6 in your circuit or in my circuit does almost nothing. It does not affect the frequency response. Since it forms a voltage divider with R5 it reduces the input level slightly.

I notice that your input volume control is connected backwards. Instead of reducing the input level, it shorts it.
Why do you have two volume controls??
 
Hi audioguru.

Here is my design, now you can easily understand my system.

Today I changed my transformer to 22 AC-0-22 AC. When it converts to DC it shows 28V.When the system operating & with some bass punches it will drop down to 25-26V.

Now I can notice a big sound level comparing with the earlier low voltage supply. This is a big sound my friend :) you must have this amp.

I have 3 LM1875 s, two for satellites & one for subwoofer. But all three amps are same wattage.

The problem is when I volume the two satellites sounds more than the subwoofer amp. So I cannot hear the bass. You know in every 2.1 system the satellites wattage is lower than the subamps volume.

I need to reduce the watts in my two satellite amps. They sound too much. Note that I cannot insert any volume controllers to the circuit. Because it is on a PCB. Only thing I can do is to change some resister values.
 
you still have the input controls wired backwards. the top of the control goes to the input, the wiper goes to the op amp. hypothetically, the sub amp should be twice the power of the front channels, since it has to move a larger air mass.

btw your filter is still drawn incorrectly. it should be as shown below:
 
Simply increase the value of R4 for more gain for the sub-woofer amplifier.

R30 does nothing and can be replaced with a piece of wire.
The value of C4 is far too high and it should not be a polarized electrolytic type. It should be a 100nF film type.

R19 and R29 are supposed to be 1 ohm, not 33 ohms.

The MINIMUM allowed gain for an LM1875 is 10 and the amplifiers in the datasheet have a gain of 20 for good stability. But your gain is only 6.7. So decrease the values of R17 and R27 to 2k or 2.2k ohms.

Why do you have a 4.7 ohm resistor in series with each satellite speaker? It destroys damping provided by the extremely low output impedance of the amplifier and might make them sound boomy at their resonant frequency.
 
Hi audioguru

I corrected the mistakes that you pointed out.

Changing the R17 and R27 will make my satellite outputs so stronger.My goodness :(

I need to reduce the wattage on satellites.
 
You do not reduce the power to a speaker by connecting a resistor in series. Instead you simply turn down the input level.
Then the satellites will operate at reduced power.

If you increase the gain of the first opamp in the subwoofer circuit (like i mentioned in my last post) then it will be louder which is what you want.

Did you notice that your subwoofer is fed from only the left channel instead of from both channels?
Add a simple mixer circuit madse with two resistors.
 
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