Contact mic preamp

Contact mics can be used to sense unusual sounds when attached to various surfaces. It also Produce sound when voltage is applied to it.

With the help of a basic Pre-amp circuit it can also be used to Electrify an Acoustic Guitar, where amplification is a must. A piezoelectric disk generates a voltage when deformed. Piezo elements come in handy when you need to detect vibration or a knock. You can use these for tap or knock sensors pretty easily by reading the voltage on the output. They can also be used for a very small audio transducer such as a Buzzer. This voltage is connected to the source through source resistor 1. One terminal of this amplifier is common to both the input and output signals.

This terminal is the JFET drain terminal. The Drain resistor k is connected to the source to the battery's ground terminal. Under no-signal conditions, bias voltage causes the JFET source to draw a very small current. This current sets the source voltage at a point halfway between the Supply and ground.

contact mic preamp

This is the recommended bias setting for most small-signal or analog audio amplifiers. It allows the maximum signal before distortion. The signal enters the amplifier through gate resistor 3.

contact mic preamp

The voltage drop across 3. This signal is an AC voltage. The signal enters JFET,which is a amplifying device. The bias voltage is a DC voltage. The varying gate signal causes the JFET's to vary. For this reason, more or less current passes through the JFET. The source resistor 1.

Since the input signal controls the channel width. That is, a small signal controls a large signal. The output signal appears between the Source and ground. Capacitor 4. The gate is more negative than the ground terminal. Now the output comes out across the Source and ground. But we've connected the Source to Supply. Then the Source is more positive than the ground terminal. With the gate negative and the Source positive, This output signal exits the amplifier through capacitor 4.

This Capacitor blocks DC and passes only. If you have any circuit related query, you may interact through comments, I'll be most happy to help! Your email:.Audio Samples. Your source for high-quality contact mics, suction cup mics, electronic stethoscopes, hydrophones, and other unusual microphones. Free worldwide shipping on all microphones! Click on any image below to enlarge. The unit runs on a single 9 volt battery included and is designed to switch off when the output is unplugged.

Extremely low-noise and wide bandwidth 8 - 2 Hz make it ideal for recording body sounds such as the heart, blood and lungs. Can also used as a bone conducted pickup or a regular contact microphone or vibration sensor. For most applications you will require the use of a hi-fi or guitar amplifier. Attach sensor with medical tape or stretchy gauze. This item ships worldwide for FREE! Please click here for the PDF datasheet.

Tiny and tough, this active mono condenser hydrophone is great for all kinds of underwater listening and recording. Made with shielded, waterproof cable, a high quality metal output plug and weighted copper head. Recommended for capturing even the quietest ambient water sounds including those in the ultrasonic range. This hydrophone is low noise and high sensitivity with a frequency response range of approx. Requires standard 2 - 9 volt plug in power.

Standard model comes with a mono mini male output. Binaural Condenser Microphone Set Each omnidirectional mic capsule is fitted with a strong metal alligator clip which can be attached to a baseball cap brim, headphone arms, glasses, headbands, earmuffs, etc. You don't have to use these mics on your head, they can be configured any way you see fit to obtain unique stereo recordings. Frequency response range of 20 - 20 Hz with a useable response up to around kHz.

Mic capsule backs are filled with clear silicone and protected with clear shrinktube.Marshmallow is available in a few different gain variaions. The standard model has red heat-shrink on the audio connector.

This mic is good for most things and corresponds to the discontinued burnt marshmallow. There is additionally a low-gain variant with white heat-shrink that is better for recording loud sounds, like percussion, and this corresponds to the discontinued original marshmallow.

Finally, there is a black heat-shrink model with high gain, that is good for recording very, very quiet sounds. If you watch closely, in the video above, you can see which variant I have used to record different things, which should give you a general idea of how they behave, although in many cases any of the mics would work just fine for a moderate sound source.

Hi, I'm Michael Krzyzaniakcreator of Marshmallow. While I was getting my PhD, I was building robots that played music. I needed the robots to listen to themselves while blocking out other sounds, so I thought I'd use a contact mic. Unfortunatly, due to questionable engineering, electromagenetic radiation spewed out of the robots' out of every pore. Needless to say I had considerable difficulty getting a clean signal through a contact mic; it was mostly hum.

Multi-Channel Preamps

I ordered every single comercially available mic and built every DIY one I could find on the internet. None of them could withstand the hum, and furthermore, most had very poor bass response, making them unsuitable for the spectral analysis I was doing in my research.

So I went on a quest to design a contact mic that could withstand massive hum and had good bass response, so I could complete my dissertation. The result is Marshmallow. It is the best contact Mic I have heard, so I decided to share it! Log In Sign Up. About Marshmallow is a piezo disc contact microphone with a nice high-impedance preamplifier. It is used to pick up sound waves traveling through solid objects, without also picking up sounds travelling through the air.

Make unusual recordings: You can stick Marshmallow to walls, tables, metal sheets, ceramic teacups, eggplants, etc Use as a sensor for scientific and research applications: You can stick Marshmallow to the ground to detect footfalls, you can use it to tell how an object was struck, or, using three, you can triangulate the position of tapping on a wall. These examples would require additional software which is not included. Archival information about the discontinued Original and Burnt models is herealong with a product comparison.

Features Built-in mic preamp: Other high-end contact mics require you to buy a separate preamp, often for an exorbitant price. Marshmallow has a builtin preamp that was specifically designed for this purpose. It boosts the signal and solves impedance-matching issues associated with homemade contact mics. Excellent bass response: Other contact mics in the same price range are just piezo discs solderred onto guitar cables. As a consequence, they have very poor bass-response, giving them a tinny sound.

Marshmallow's built-in preamp that solves this, giving it a full, rich sound. Flat frequency response: Flat across the entire audible range. A Bode plot of this is shown below. Plug it in to anything: Unlike traditional mics, Marshmallow has internal circuitry that makes it compatible with any audio equipment. You can plug it into a high end mixer or audio device, or using the appropriate adapter you can plug it directly into the audio input on your laptop.A contact microphone is a type of microphone that picks up vibrations from contact with objects, as opposed the the more common type of microphone that picks up pressure waves in air.

Here's a demo of a contact mic attached to an alarm clock, along with finger tapping on the table about a foot away from the clock:. In this Instructable, we show you how to construct a professional quality contact mic that is very rugged and sounds good. This particular version of a contact microphone was designed for the premier of The Immortal Fluxa composition for drum kit and prepared drumhead orchestra written by Glenn Kotchedrummer for the band Wilcoat the Solid Sound Music Festivalsponsored by D'Addario.

To learn more about about the common ground between technology and percussion music, including tips on composing your own works from ensemble Third Coast Percussionsee this Instructable on the WAVES project. Did you use this instructable in your classroom?

Make a Contact Microphone

Add a Teacher Note to share how you incorporated it into your lesson. A piezo element is a metal disk with a circle of piezoelectric crystals in the middle. When the crystals are made to vibrate, they produce an oscillating voltage.

Conversely, if you apply an oscillating voltage to a piezo element, it vibrates--that's why they also work as buzzer elements. A piezo element has 2 terminals: the inner circle which is the signal terminal and the metal disk which is ground. A good discussion of piezo elements and how they work can be found at Open Music Labs. Since a piezo has 2 terminals, we need a cable with 2 conductors to connect to it. You might think that simple speaker wire would do, but there's another consideration--cables can act as antennas that pick up stray electrical signals in the environment that can cause audible hum when plugged into an amp.

To counteract this, you need to use shielded cables that have a sheath of wire surrounding the conductors. Shields are typically made of thin copper wire that is either wound in a spiral or braided around the conductors. Foil shields are also used for cables that a part of permanent installations, but are not appropriate for this project.

Audio technicians typically agree that the highest quality and most expensive mic cables use braided shields, but spiral wound shields are perfectly fine for this project, and are somewhat easier to work with. In addition to the 2 conductors and the shield, mic cables may also have "filler" that helps the cable maintain its round shape. This filler may be plastic lines or bundles of thread, as pictured above.In a prior Instructable, we showed how to construct a contact microphone from a piezo element that could be pick up sounds from any vibrating object and play them through a guitar amplifier.

A well-known issue with piezo contact microphones is that they have poor bass response when connected directly to a typical amplifier. This is especially noticeable if the contact mic is used as a pickup for an acoustic instruments such as a guitar, which results in a "thin" sound. In this Instructable, we show how to build a very simple preamplifier for a contact mic that restores a fuller, richer tone with more bass. The design has only a handful of electronic components and fits neatly inside a candy tin such as Altoids or Sucrets.

The following sound clip demonstrates the preamp on an acoustic guitar first strumming without and then with the preamp, followed by fingerpicking without and then with the preamp. Did you use this instructable in your classroom? Add a Teacher Note to share how you incorporated it into your lesson.

Breadboard for soldering circuit together. I use this Proto Breadboard from Adafruit that has the holes wired in strips exactly like a protoboard which is very easy for transferring your prototype to a finished product and simple to use in general.

It is very well made and you can cut it to size with tin snips. The schematic above is the complete design of the preamp circuit. To understand how it works, we'll first take a look at the problem we're trying to solve, and then build up a solution in steps. A piezo element operates like a voltage source in series with a capacitor--when the piezo crystals vibrate, they produce a voltage.

This voltage may be high, but the current is very small. Because of the series capacitance Cpiezovirtually no DC current flows through the piezo. The input of an amplifier acts like a resistor to ground Rampknown as its input impedance. Together, Cpiezo and Ramp form a high-pass filter that cuts out low frequencies. For typical values of Cpiezo and Ramp, the cutoff frequency is well into the audible playing range of a guitar.

In order to reduce the cutoff frequency so that more bass tones get through, we need to increase the input impedance that the piezo is driving. This is where a preamp comes in. The role of the piezo contact mic preamp isn't really to amplify the signal the output voltage of the piezo is plenty highrather the goal is to provide a buffer with a very high input impedance of 10M ohms or so, which is more than 10 times or so greater than the input impedance of a typical guitar amp, so that more of the bass gets through.

It also provides more current to drive signals on the cable to the amp, which can also improve the highs. Amplifiers use transistors or tubes to amplify or buffer a signal. Bipolar transistors don't have a high enough input impedance. MOSFETs have an extremely high input impedance, but tend to be fragile static electricity can destroy them and also can be noisy in audio applications. The vast majority of contact mic preamp designs found on the web also use JFETs.

As a starting point to understanding the complete preamp, let's consider a simpler version shown below:. A JFET has 3 terminals called the gate gdrain dand source s.

In general, increasing the voltage Vin on the gate of the JFET causes an increase in current flowing through the device from the drain to the source. One of the unusual things about a JFET is that if the input voltage is 0, meaning that the input is grounded, there is still a current that will flow from drain to source, and you actually need to apply a negative voltage to the gate to turn the device off.

Vout goes to 0V when Vin is around In fact, for every increase of 1V of Vin, Vout also increases by 1V. The ratio of the change in Vout over the change in Vin the slope of the line is the gain of the amplifier, which in this case is just equal to 1. This configuration of an amplifier, where there is a resistor connected to the source of the JFET and the output voltage "follows" the input voltage, is called a source-follower.This is the purist approach solution to the tinny contact mic sound problem if you want the lowest electrical noise, or the lowest distortion at higher levels.

However, they are remarkably low noise. The calculation in the introduction showed a load of k was enough, so 1 meg is plenty for a contact mic. The first thing that sprang to mind was a TL — the overall schematic is shown below.

Diodes D1,D2 stop you destroying the opamp with large signals from the piezo device if you drop it. You can leave C1 and R4 out if you need less gain, though there is much to be said for the cheap version if you have lots of signal. The results were good. A satisfying drop in noise was obtained. However, substituting the TL for the usual audio workhorse opamp, the bipolar NE brought the lowest noise of all.

Noise comparison of 2n single fet with opamp version using a NE left and right channels respectively.

contact mic preamp

At the start of the recording you can faintly hear woodpigeons calling above the surface propagating through the water, and aircraft noise, before the chomping sound. Matching levels of the 1kHz test tone to correct for the slight difference in gain shows the NE offers a noise floor dB lower than the 2N, in return for extra complexity.

At the back of my mind was the wonder whether a piezo mic would not have more self-noise anyway, so I removed the test tone and put in the mic. This is a reasonably quiet location.

The hum is because this circuit is on a breadboard with the mic laid on the shelf, and some of the hum is mechanical, from the transformer of the power supply powering the unit, which is on the same shelf unit.

However, the piezo mic has not raised the noise level significantly. This goes to show that the piezo contact mic, for all its uneven frequency response faults, is capable of an excellent noise performance when used correctly.

A more practical stereo version of this was constructed in a box, measurements and test results are available. Using Piezo Contact mics right. See its datasheet. They give input resistance min 30k and typical kohms. You are trying to reach an input impedance of kohms by the schematic. However that IC makes it somewhere less than kohms.

That lowers the output of the piezo significantly. Especially on lower frequencies. Depending on frequency of interest. Thanks for your comment. Only then did I look at what was going on. I disagree with the hypothesis that the open-loop input resistance you indicate k, TI seems to indicate k determines the input resistance of this circuit, because of the action of negative feedback.

The circuit is pitched at a noninverting gain of For laziness I used 27k instead of 56k for R2, R3 and 47u all round because this came to hand. I omitted D1 and D2, because they are there to protect against overload. C2 bypasses R2,3 at signal frequencies so in an ideal world the input impedance would be 1M. I used a 12V power supply.

Piezo Transducer - the 5$ five minute DIY acoustic pickup

I am using a 10x scope probe so levels are measured a factor of 10 low. Theoretically the mid-point of a potential divider of two 1M resistors would give 7.

Your hypothesis of the impedance being defined by a k open loop input resistance would suggest a reading of 7.You bought the best microphone you could get your hands on and now it's time to pair it with best mic preamp possible.

A microphone preamplifier is the key to achieving the highest quality recordings your mic has to offer. So many people keep buying better mic's and aren't satisfied because they don't know the secret This buying guide is going to change your life Just how good can any of those components be? Check this out. It doesn't matter if you're in your studio tracking vocals or instruments with the world's most sensitive and expensive microphone in a perfect acoustic environment.

You haven't heard nothing yet until you run that signal through a proper preamp.

contact mic preamp

It's akin to listening to and analyzing a world class mix on tiny speakers with a kbps MP3 file If you're here then you're ready to score a dedicated preamp for your vocals or whatever's running through your signal path. You've identified the weak link in your recording chain, and you're right. In my opinion, preamplifiers are the most important yet also the most underrated piece of gear found in a studio.

Probably because it doesn't feel sexy, but that's also because newbies aren't quite sure what they do. Let's clear the confusion and take a look at the best of the best in every price range and even drool over the ones where price is no object We'll cover some of the frequently asked questions and talk about some of the physical form factor options before we start talking about the actual pre's, just in case anyone new is reading or something slipped past you in your research.

We'll keep it quick. We're going to discuss what a preamp is, what it does, why you must have one, and the types available. If you already know what's up, please feel free to scroll down past this short section to get to the buyer's guide! This post assumes you understand how to set up a studio and how the signal path flows mic then preamp then I cry every time I see someone recording a microphone without a preamp, mainly because I did it too.

Unlike electronic instruments like a keyboard or guitar that produces it's own line-level or instrument-level signal, a microphone produces a mic-level signal by converting acoustic energy into a very low-voltage output. The catch is that mic-level is anywhere from 50dB to 80dB quieter than line-level.

If you attempt to record a mic-level signal, you're going to find it's extremely quiet and the volume will have to be boosted significantly, with horrible results.

You're going to expose all of the noise in the environment, the hum of electricity, and any unwanted transients of the mic itself. What a preamp does is boost the mic signal without boosting the rest of the trash you don't want.

Of course, some preamps do that much better than others, which is where price comes in. Someone's gotta pay for that research and development! Yes, but they all affect your recording quality in good ways. What you'll want to decide is what flavor you like. This is why many studios have several preamps on tap that they like to pair with various microphones for certain instruments or styles of vocal recording. Let me explain while keeping it simple Transparent preamps are invisible to the ears.

What they do is boost the signal while maintaining the original flavor of the microphone, which might be dark, bright, or neutral. Colored preamps will add coloration, which is to say that it imparts its own signature sound to your recording.

Generally this is just different levels of "warmth" that is coming from harmonic distortion. This harmonic distortion is a type of saturation that can be very desirable, especially for vocals but it can always be added in the mixing stage too, so a transparent preamp might be what you want if you're only going to buy one. This keeps your options open. The saturation is the color and a lack of it is the transparency. Preamplifiers with tubes are going to impart a flavor of color to your signal.

Vacuum tubes pictured on the right above have gas inside them isolated by a space with nothing inside of it, not even air here's a great indepth explanation.


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