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8 votes
Accepted

Why am I measuring such high THD+N on my active high-pass filter?

The number one suspects are the ceramic capacitors. Here is a SE link that shows the severe voltage dependence that ceramics have. The X5Rs are some of the worst, especially in the small SMD sizes. ...
  • 3,489
7 votes
Accepted

Op-amp - audio starts only after a few seconds

Try adding a 100nF capacitor in series with the input. There may be a large value capacitor in the source that has to charge in order to allow your op-amp to reach bias, since your amplifier is DC-...
6 votes

How to calculate gain (op-amp)?

You compute the gain of that circuit by scraping away bits of it until it looks like a basic OP-amp circuit; then you look at the textbook gain for that circuit. R27 and R29 are there to provide a ...
  • 38.8k
5 votes
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What wire runs between two speakers on a headphone, and how do I replace it?

The short answer is you can use pretty much any thin two core stranded wire. The fluffy stuff is just cheapness; manufacturers have been experimenting for years as to how much copper they can replace ...
  • 2,499
4 votes

How to calculate gain (op-amp)?

In addition, C34 acts as a higher resistance at low freqencies (below 1/(2.pi.R.C) = 1/(2 * 3.14 * 680 * 100n) = 2.3 kHz. Thus gain rolls off towards 1 at frequencies below 2 kHz (the 100 nF likely ...
  • 16.5k
4 votes

HDMI audio pin-out

There are no pins that you can simply combine. The audio in an HDMI interface is embedded in the same high speed data lines as the video data signalling (within the blanking periods of the video data)....
3 votes
Accepted

Is the cut-off frequency of a 4th-order filter at -12 dB or -6 dB?

Linkwitz-Riley filters are designed with 4 poles but each 2 pole stage should be designed to be 3dB down at the cross-over frequency so that each 4 pole stage is 6dB down at the cross-over frequency. ...
  • 6,924
2 votes
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Measuring the power output of an amplifier with floating outputs

Your caution is wise. I would recommend that you measure the peak-to-peak voltage of one output relative to ground. The load will see double that voltage as the two outputs will be in anti-phase. So ...
  • 163k
2 votes

Is the cut-off frequency of a 4th-order filter at -12 dB or -6 dB?

Cascading filters will never preserve the type of response, if the filters are designed so that they are distinct. E.g. if you cascade two Butterworth filters then the result will no longer be a ...
2 votes
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Linear vs Switching Supply for Class D Audio Amplifier

Like any regulated power supply, it is mainly there to provide low power supply impedance from DC up to perhaps ~1..10 kHz. This low impedance is provided by the error feedback of the PSU and has ...
  • 12.3k
1 vote
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Use of LM386 with simple regen receiver

Reading the data sheet definitely indicates that an \$8 \Omega \$ is within its specification. Follow the guidelines in the data sheet. The input resistance for the LM386 is 50K. This in parallel with ...
  • 3,489
1 vote

Where to put audio isolation transformer?

The microphone output is not balanced to ground. The receiver input is balanced to ground. Is that correct? A cable that is balanced to ground will pick up less noise than one that is not balanced. If ...
  • 3,489
1 vote

Building an attenuator

It sounds like you need to use a taper pad attenuator if you need to maintain those impedances: - Image from my basic website. Is it as simple as a resistor across the hi and lo (in parallel) to ...
  • 396k
1 vote
Accepted

Linear phase with audio amplifier

On one hand, I learned that linear phase is important to minimize distortions due to the different group delay Yes, important for applications where signal-shape needs to be maintained such as high-...
  • 396k
1 vote

Make a doorbell louder? Bypassing in-built amplifier

The audio signal is available at the bypass capacitor to the inverting input of the amplifier - the node circled in red below. This node is also pointed to by the arrow on the application schematic ...

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