18

If it is a grounding issue, touching it could change the amount of hum, buzz or interference. However you say "It only works if you keep your hand on the volume knob" which I interpret as "there is sound only when the hand is on the volume knob, otherwise there is no sound." If this is the case, then I'd suspect a bad contact perhaps at the pot wiper, or a ...


11

Repair questions are off-topic on this site so let's make it an education question. Figure 1. Potentiometer terminals 1, 2 and 3. simulate this circuit – Schematic created using CircuitLab Figure 2. A schematic showing the potentiometer arrangement. As the wiper (2) is adjusted from (1) to (3) the volume goes from zero to maximum. If pressing on ...


6

You might want to consider these things: - Without the input resistor the 220 nF has an impedance of 723 ohms and this means that your mid band gain (1 kHz) is 150,000/723 = 207. At 10 kHz the gain will be 2070 and you will hear a lot of noise. Try a 10 kohm resistor in series.


4

The First Photo "looks" like it's broken... But assuming it's not, this behaviour looks like the potentiometer (variable resistor) is broken. The pressure of the finger pushes the wiper contact on to the track completing the circuit. It's also possible the solder joints are "dry" and need to be reflowed Otherwise replace the potentiometer or the whole ...


4

Long answer short: that circuit will badly work, and in general, youtube is (on average) a really bad source for electronics. So, the idea is relatively simple: Phantom power is a constant voltage thing. So for that, wherever there's a capacitor, replace it with an "open". The circuit simplifies to: simulate this circuit – Schematic created ...


4

EMI Ingress and suppression is far from trivial, and once understood where all your sources are from your geometry of conductors, the solution might appear simple. There are a few common noise sources. Line hum (often modulated SMPS PWM carrier noise from chargers or PSU) cell phone pings to server Microwave Oven line hum (modulated carrier) SMPS modulation ...


4

I guess you have an electret mic which works like this: I guess you built the preamp because you either tried the mic as is (some audio inputs allow it, they have the needed DC circuit) or you inserted a resistor, capacitor and DC voltage as shown in the datasheet, but the sensitivity was so low that to get acceptably high recording level one must shout if ...


3

You can safely bias the mic to 12v/2 by using TWO resistors in series as a voltage divider; the lower resistor ties to Ground. The microphone ties to the mid-point of the voltage divider.


3

This may be most easily understood by looking at an old-fashioned transformer balanced configuration. simulate this circuit – Schematic created using CircuitLab Figure 1. A phantom-powered microphone circuit using balanced / unbalanced transformers and a mute switch. How it works: The 48 V supply is fed in the centre-tap of XFMR2. Current splits ...


3

You have not linked to any relevant datasheets. One of the boards has part number SSM2167 so we can easily find its datasheet : where Page 3 reveals(!) voltage noise of 20nV/sqrt(Hz) ... fairly noisy, considering SSM made their name as specialists in high quality audio. I guess it's adequate for some specific purpose, probably in a noisy environment since it ...


3

I remember publishing in 2004 a column in the PCIM magazine (US) where I described how to emulate variable resistors, capacitors and inductors. The capacitor was done in a very simple way and could also work in ac if I remember well. Below is the simple architecture I used and you can probably duplicate it in LTspice: And if you compare the waveforms ...


3

I cut a 2 cm square out of a mylar 'space blanket', and placed my digital multimeter probes flat on either side to measure resistance from one side to the other. The reading (on the 200 Ω scale) was 1.8 Ω. The sheet thickness was ~0.01 mm (ten layers measured 0.11 mm on my digital calipers). It is only metallized on one side.


3

OK, from comments: That's not noise, that's either instability or interference, perhaps on the PSU. (The regularity of the waveform shows this. Start by arranging a perfectly clean 4.5V supply for the mic amp, and see how it goes. Having seen that a separate battery supply improves performance, I'd suggest improving the quality of power fed to the mic amp. ...


3

The problem is likely not with your preamp itself (the circuit is basically OK), but with the power supply and gain setting. Using the internal 5V from your PC (or USB port) for a mic pre is pretty much a no-no. There is almost certainly switching noise in that power rail which will be very audible. (The mic output is typically a few mV, perhaps 10-20mV or a ...


2

Perhaps a peak detector would help. The output of a peak detector rises when the input rises. But when the input falls again, the output stays where it is. When you have sampled, you can close the MOSFET switch to bring down the output back down again. However, there's a risk that a peak suddenly happens between your ADC sample, and the closing of the ...


2

You need faster sampling. I would say in the order of 10,000 samples per second if you want a well defined peek. How do you do that? Get rid of floating points. Integers only. Good luck.


2

The main point here is that the microphone will pick up all sounds at any distance. The problem, as has been already discussed, is that ambient noise plus electronic noise will limit your ability to distinguish them. Our ears (ears is important since we have two which helps the process), coupled with our brains, have significant signal processing capability ...


2

A microphone can pick up sounds of any level. However, it also generates noise, as does the amplifier following it. Very quiet sounds will be indistinguishable able the noise. You therefore need to concentrate on the Signal to Noise ratio (SNR) of your microphone + amplifier system. I emphasise system, as there are many sources of noise, and you need to ...


2

If all you want is to find the peak value, one can potentially connect a diode and capacitor at the output of the tape recorder, and measure the DC voltage (something like a sample and hold). simulate this circuit – Schematic created using CircuitLab Also, an arduino can be set up to repeatedly sample the voltage and display the maximum. Also, you can ...


2

If the answer by "csabahu" does not work, then lets clean up the VDD to the microphone. In that VDD, insert a series R and a shunting C. [NOTE: this is a LOW PASS FILTER; connect as external_VDD, series R, then the shunting C, then the existing R1.] Make the new R_VDD be 1/10 of R1. Make the capacitor be 1uF or 10uF or 100uF. Ground the cap to the ...


2

I find the frequency characteristics of the LM386 very unstable. There is likely to be a high frequency oscillation in the system. This can make a special noise. The problem is caused by 100nF at the output. If this is really the problem, it can be fixed with a serial RC circuit: Update: The circuit is theoretically stable, failures are likely due to the ...


2

100 ohms is probably a good starting point for the volume controls. R1,R2 is harder to pick. 1K perhaps.


2

Use the microphone as it is now. At 12 Volts with a Zener you can make a 5V power supply for the microphone. The current consumption of the microphone is 0.5mA. It is independent of voltage, a JFET output is actually. @analogsystemsrf suggests the simplest way to safely maintain the current state at 12V:


2

No problem. The R terminates the drain inside electret to provide voltage gain and bias near V+/2 near <1 mA . If you want more range, and also increase voltage gain the sameR may be increased proportionally to get V/2 drop.


2

Since you've provided a few more details, I'll tell you how to go about it. Install Raspbian (Debian Linux for the Raspberry Pi.) Find and purchase a USB sound card and a separate microphone, or an integrated "USB microphone." Plug it in and make sure your Pi recognizes it. Install GNU Radio on your Raspberry Pi. Here are instructions for ...


2

Markus, let's walk through the circuit, then talk about whether it "will work" to safely jam a microphone. Answering your questions: The 555 output at pin 3 is a square wave. It won't be perfectly symmetric because the capacitor C1 charges through R1+R2+R4 (178k ohms) and discharges through R4 (100k ohms), but close enough. The Scope and ...


2

Connect clean +5V DC supply between "+5V" and the GND. Connect "Out" to the hot wire of the audio input. Connect GND to the ground side of the audio input. "Clean" means "taken from a separate battery" or a carefully filtered voltage. C1 can do the filtering if you have say 500 Ohm resistor in series with the +5V wire. Some common elementary precautions: ...


2

Your problem is related to "integrator windup"*. It's what happens when a linear system goes non-linear (in this case by clipping) and stuff like phase and impulse response are out the window. At this point the integrating components in the feedback loop (ie, caps) will integrate an error signal which is garbage and it takes a while to get rid of. ...


2

No. Pad the line level signal down by 40 to 60dB, and amplify it after the cable in a decent professional mic amp (which you have previously tested) set to the same gain as your pad, not the "mic in" on your soundcard. The pad should present low (maybe 20 or 100 ohm) and 600 ohm impedance to the cable. In addition to your prescribed test: Repeat ...


2

You might be picking up environmental noise; basically all aspects of your implementation make that likely: Breadboard is exceptionally great at coupling in signals you don't want So are long, loops of wire You're using an amplifier IC with known-to-be-bad output noise, without appropriate filtering Your schematic has no decoupling capacitor on VCC of the ...


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