NE5532 based low pass filter not working

[raresserban]

Hey guys, hope it's the right subforum.
I have this low pass filter based on NE5532 that is not working:
CIRMECH Low Pass Filter Bass Subwoofer Pre AMP Amplifier Board Single DC Power NE5532 low pass filter bass preamplifier|amplifier board|bass preamplifierlow pass - AliExpress

It is brand new, the chip is fine since I have a known working spare, and the led lights up so it gets power, but no output. Measure the voltage at the output, it's like -0.06V to -0.11V, something like that. Tried switching polarities but again no sound.

Don't have an oscilloscope to debug further. Is maybe something simple I can check, maybe a cap/resistor is broken?

 

[Mooly]

moved to Analogue Line Level

 

[Mooly]

This looks like a single rail design. You should have zero volts on pin 4 and supply voltage on pin 8. I would expect all other pins of the opamp to be at around one half the supply voltage.

The output will be AC coupled and so you should see essentially zero volts there.

 

[jan.didden]

At what signal frequency and level do you test it?

Jan

 

[raresserban]

I tested with a song, coming from a 3.5mm jack on a laptop. I also have this 2.1 channel subwoofer preamp that works ok:
CIRMECH 2.1 channel subwoofer preamp board Low Pass Filter Pre AMP Amplifier Board NE5532 low pass filter bass preamplifier|Amplifier| - AliExpress

This looks like a single rail design. You should have zero volts on pin 4 and supply voltage on pin 8. I would expect all other pins of the opamp to be at around one half the supply voltage.

The output will be AC coupled and so you should see essentially zero volts there.

What does the "output is AC coupled" mean? So I can't use that directly to go to the amp (using a tda7498e in BTL mode)?Should I be doing something else at the output and then to the amp?

 

[jan.didden]

The reason I asked, if you try with music or a test tone you won't hear a lot because all the tones above a few 100Hz are filtered out.

AC coupled means there is a capacitor at the output that blocks DC going into the rest of your system. This is a Good Thing.

Jan

 

[raresserban]

Well that's what I want, to filter and only allow low end to pass. I have been using this with a subwoofer, and the other 2.1 board works perfectly. I thought this was is similar to that but just .1 but I guess there is more to it. Will try and measure capacitors/resistors, maybe I can find the issue.

 

[jan.didden]

If you say it the other works, what do you mean? Did you get output into the sub and not into the mid/high?
Maybe I am dense but I don't quite understand what the problem is.
No output at all, no output on the sub but output in the mid/highs, only sub output and no mid/highs?
It is important to know what the problem is for fixing it.

Jan

 

[JMFahey]

Will try and measure capacitors/resistors, maybe I can find the issue.

Sorry but it does not work that way, very very much doubt there´s "bad parts" there, think wiring above all.
Including a properly connected power supply.

What supply is powering it?

In principle,measure voltage to ground at both ICs; I expect +V (whatever it is) at pin 8; 0V at pin 4, and 1/2 +V at all others.

You also use 0.1" pitch connectors for Audio IN/OUT; another possibility for miswiring.

Did you assemble a kit or bought it preassembled?

If the first, yet another error possibility.

 

[Mooly]

The output will be AC coupled and so you should see essentially zero volts there.

What does the "output is AC coupled" mean? So I can't use that directly to go to the amp (using a tda7498e in BTL mode)?Should I be doing something else at the output and then to the amp?

It is as Jan says. All single rail circuits like this use capacitors to block DC voltages.

Have you measured the voltage on ALL the pins of the chip?