0
\$\begingroup\$

I am trying to build a pink noise machine to use at work. See schematic below. If I connect the output from the MM5837N (noise generator), directly to the amp circuit. It works fine, and is nice and loud. However, when I include the passive LPF as shown from the example, no sound comes out. Using a scope, Fig. 1 shows the output from the MM5837 w/o the LPF. Voltage is around 4V. Figure 2 shows the output after the LPF. The signal is around 2V. At this point, the output from the LPF is not connected to the amp input. When I do connect the output to the amp input and probe at the same point, the signal drops to around .2V, and there is no output from the amp. Scope shows a flat-line on the amp output. I am not an EE, so don't understand what is going on here. Do I need some kind of a buffer op-amp between the two? Any help is appreciated! Also the LPF cap is just a ceramic type, if it matters. Link to the amp data sheet.

\$\endgroup\$
1
\$\begingroup\$

You show a range of values for your LPF. If R=10k and C=0.2 uF, then the cutoff frequency of your filter is about 80 Hz. Most of the energy generated by your noise source is well above that frequency. If you set R=1k and C=0.02 Uf, then the cutoff frequency rises to about 16 kHz and you should see a considerably larger signal. Also your 10k pot will load the output of the LPF and also reduce the available signal.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.