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All power supplies that are isolated from the power line will have some form of transformer. There will be capacitance between primary and secondary of that transformer. There will be "displacement current" coupled across that transformer. That current will explore all possible paths, to return to the source of the charge. Switching power supplies ...


0

However, I don't understand how the audio device knows when to drive the serial data line with it's data. How is contention avoided? You need to design the device so that it skips as many slots as necessary, while someone else drives the serial clock. There's no bidirectional communication in I2S. There's no contention, only pre-defined slotting. However, ...


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https://datasheetspdf.com/pdf/570328/Motorola/MC1314P/1. For the quad VCA obsolete chip. Your schematic on the surface looks ok. Did it overheat immediately? Polarity correct on Vcc, Gnd https://4donline.ihs.com/images/VipMasterIC/IC/MOTO/MOTOS12755/MOTOS12755-1.pdf?hkey=D9A213CC6FEE7D103EF6B88F2AEB20B8 enter link description here Beware the pins are shown ...


1

There is ONE and only one compelling reason for an output capacitor. If the signal is to be switched further down the signal path, any DC offset will generate a 'click' when selected/deselected. That's it ! The value of the resistor to ground after the output coupling capacitor has no effect on noise whatever. The impedance here is dominated by the capacitor ...


1

I'm using uA741 op amps. There's your problem then. That thing was obsolete in the 1980's. The data sheet that I have for an LM741 lists an output voltage swing of \$\pm16\mathrm{V}\$ with input power rails of \$\pm20\mathrm{V}\$ -- and that's with a \$10\mathrm{k}\Omega\$ load resistor, so about a 15mA load current. That means you need four volts of ...


1

I've seen this amp operating with positive and negative rail supply I've seen this amp operating with positive and negative rail supply https://www.youtube.com/watch?v=1zRamh9HMQc which should be no surprise really. Then you don't need the output capacitor.


2

I know I'm responding to an old thread, but there were a lot of unanswered points that I can address, for any future readers. The circuit is an instrumentation amp as seen in the Art of Electronics (figure 5.88 C). The NPN transistors boost the signal to reduce the op amp noise, as well converting the voltage input to a current on the inverting input, which ...


2

I wonder if that's really a balun or just a straight-through connection? Anyway, the output impedance of "line out" is apparently in the 100-600 ohm range. So if you want to try a passive solution I would start with a 1k resistor across each line. This will attenuate the output somewhat along with attenuating the noise. If it's too much, add 1k ...


1

What can I do to reduce or eliminate the unwanted sound, ideally with a passive solution? I think your analysis sounds reasonable so... Your best bet might be to use an audio coupling transformer at the input to your amplifier. There's a good chance that your amplifier doesn't have a fully differential input stage but, if it did, the noise that you are ...


1

I can confirm the real world occurrence of microphonic effect from ceramic capacitors. I built an AM radio which had the same sort of effect. I saw Ambiorix's comment about ceramic capacitors acting as microphones (as described in the link he provided), and it turned out to be what was happening in my case.


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DC bias currents must flow into the opamp terminals for it to function since the transistors at the inputs inside the amp need to be biased. It's a tiny current, but it is there. From LM358 Datasheet But your 88nF capacitor is a DC-blocking capacitor. As the bias current flows through the input in the same direction (it is DC after all), the cap slowly ...


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people. I used the PAM8403 with phones using this circuit: Regards Sergio


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So here is a picture of the schematic that seems to work with it and there didn't seem to be any deterioration in the sound quality. Thank all of you for answering my texts.


2

Headphone drivers (Class D or otherwise) for portables are limited in swing by the power supply. They do however use a few tricks to achieve greater loudness: (more expensive ones) full H-bridge drive (cheaper ones) common-mode bass drive To answer your voltage-conversion question, Class-D drivers use a kind of PWM-to-analog conversion that basically ...


0

A Diodes Inc Class D is rated for 8R to about 1.5W @ 5.5V max so with 32R it may be about 1/4 of this. If you have a larger supply then it must be reduced It also operates down to 2.8V @ 0.5W @ 0.5% THD. Or 0.1W @ 0.1% PAM8302A. $5.71 for the PCB Adafruit Another example which shows power vs THD vs load R https://cdn-shop.adafruit.com/product-files/3006/...


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The microphone has an electret capsule and needs supply voltage (sometimes called bias voltage) of about 2 to 5 volts to work. Actual microphone inputs on equipment such as mobile phones, PCs, cameras and audio recorders can provide this bias voltage, and sometimes 3.5mm line inputs can be configured to provide mic bias, but XLR ports on equipment like the ...


1

This is a magnetic buzzer, so the real concern is current, not voltage (you're nowhere near insulation breakdown). The current is specified as no more than 100 mA, and the coil resistance is 12 +/- 3 ohms. Applying ohms law, you can calculate that 5 volts divided by 100 mA gives a minimum resistance of 50 ohms. At minimum coil resistance, you'd need 50-9 = ...


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I have used this chip n working fine. Only thing is that we have to connect 3.7volt supply. I used lithium ion battery. On vcc we have to connect +ve 3.7volt thats it. Rest of the point I.e. gnd, l out, r out n gnd for the speaker.


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There is no one true value, and unfortunately, all three output cases of line level, headphone level, and speaker level have different voltage levels and driving requirements. The volume level should of course be adjustable, as it depends a lot if you are playing a single audio channel quietly or loud, or playing multiple audio channels at the same time, ...


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Your computer's soundcard is unlikely to have an output impedance of greater than 100 ohms. More likely 30 ohms or less. Loading it with 64 ohms will only introduce a few dB of attenuation. Unless you have some really rubbish cables, I doubt you have any problem there either. It's likely that the high acoustic sensitivity of the amplifier is responsible. ...


0

when I tested that with my headphones it was really loud You're asking about the levels that an audio amplifier needs to receive at its input, which are different from what headphones need. Headphones are extremely efficient, like 95dB at 1 milliwatt. On 600 ohms headphones, 1 volt is already over 1mW, so more than 95dB which is really loud. And on lower ...


0

If your circuit has to drive a speaker then it'll need to deliver substantial current. More than an op-amp can deliver. A dedicated audio amplifier chip is the simplest answer. Texas Instruments (for one) have loads of possibilities. You'll need to offer more detail if you want more info but speakers are usually 8 ohms impedance and the current standard for ...


3

Audio gear is genearally designed to have nominal levels of “-10dBV” (consumer) or “+4dBu” (professional). -10dBV corresponds to 0.3Vrms and +4dBu to 1.2Vrms. But these are merely “nominal” levels. A certain amount of headroom, generally 12dB or more, is added to allow for the loudest signals to not clip. But these are for the synthesizer outputs that go ...


1

Get 4 of the 6v lantern batteries. Wire as +_12v. Retest. Regarding stability, your only gain_stage is Q9. Install 100pF or 1,000pF from base to collector.


2

is there any solid-state circuit which would be "normally closed" when power is not in there? Depletion mode FETs. All JFETs are depletion mode... Maybe not so convenient to use; you need something like -10V on the gate (Vgs) to open the switch, 0V to close (or pull it to +V via several megohms). But if you have +/-12V, go for it. If you have +/-...


3

Red is system +5 V supply rail, and yellow is my device's 3.3 V buck converter powered from the system's 5 V. You can see the power surge when switch is being turned on, and 3.3 V power supply also false-starts. Sanity check: +5V and +3V3 show very similar damped ~500kHz oscillation on scope display. In fact, almost exactly the same signal considering one ...


9

Congratulations, you've rediscovered the surprising electrical properties of a loose connection, which have historically played a major role in radio engineering. In the 1900s, this phenomenon was used to make the first RF detectors, known as a coherer, and numerous variants have been made. The most basic coherer has a loose metal connection, and when an RF ...


1

It could be a 2-core shielded cable, with the shield wired only at the PCB end to avoid hum loops. Here's one such example of 'Line in' RCA jacks, on a metal chassis, wired to a preamplifier PCB.


4

An 8-bit audio signal has a theoretical maximum SNR of 48.16 dB On the face of it, an 8-bit digitization process would increase "noise" by 3 dB (as per Brian Drummond's comment). However, when you take into account the natural "crest factor" for audio, the "noise" problem is worse: - Image from here. would an analogue audio (...


7

To answer your two questions: ADSL modems were usually >2Msps, often a multiple of 1.1Msps to simplify the signal processing later. E.g. the MTC20174 ADSL analog frontend had a 8.8Msps ADC/DAC. The reason for the higher than necessary sampling rate was the use the higher sampling rate to get more effective bits at signal frequency. This is a quite common ...


3

I recall taking a look at the spectrum of SHDSL modems once, those were capable of 15 Mbps over a single twisted pair. The spectrum had a steep roll-off above say 1.5 MHz if memory serves. So that's roughly 3 MBaud... times 5 bits per symbol? The modulation was called TC-PAM I guess... note that modern VDSL systems use very different modulation schemes, ...


8

They have a much faster ADCs. Also, ADSL2+ has its downlink up to maybe 2.2 MHz, so you'd need at least 4.4 MS/s to do that. In reality, single-digit MHz ADCs are "old tech" and relatively cheap. Together with it being desirable to oversample the signal to apply digital filtering to increase your SNR, I'd presume that modern (as in: of the last 20 ...


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