Metal Marshmallow Piezo Disc Contact Mic And Preamp

Metal Marshmallow Piezo Disc Contact Mic And Preamp




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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 traveling through the air.

'Electrify' acoustic instruments: Just stick Marshmallow to a guitar, cajon, or whatever, and it will pick up only the sound of the instrument while blocking out external sound traveling through the air. (Note -- the internal preamp clips when recording loud sounds, for instance when placing the mic directly on the soundboard of a piano or acoustic guitar. I am currently designing a new model for this, please message me if you are interested.)

Make unusual recordings: You can stick Marshmallow to walls, tables, metal sheets, ceramic teacups, eggplants, etc..., and record scraping, scratching, tearing, plucking and other strange sounds.

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).


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: across the entire audible range. (Plot in images above). There is a post about how I made that plot on my blog (no links allowed here).

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. You can even plug headphones right into Marshmallow and use it like a stethoscope.

Impervious to hum: Contact mics and amplifiers act as small antennas that pick up tons of electromagnetic radiation which can be heard as loud humming, buzzing, and clicking in the audio signal. Metal Marshmallow was carefully constructed with a shielded aluminum housing housing, so the signal is hum-free at all times. Metal Marshmallow is the quietest contact mic on the market.

Small physical size: Metal Marshmallow is 39 mm in diameter and 30 mm tall. The entire length, including the audio calble and connector is about 21 cm.

Long battery life: Metal Marshmallow will last for at least 10 days of continuous use. After that, it can be recharged via the USB connector. It takes about 1 hour to charge.

Tech Specs

Metal Marshmallow
Gain: 14dB (white), 24dB (red), 34dB(black)
Housing Color: Silver
Housing Material: Milled Aluminum
Housing Diameter: 39mm
Housing Height: 32mm
Battery Type: Rechargeable
Battery Life: 10 days
Recharge Time: ~1 Hour
Charge Indicator: White LED (on while charging, off when done)
Hum Protection: Built-In
USB Connector: For Charging Only
Audio Connector: 1/4" Female Unbalanced TS


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 on my website, 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.

WHITE 4.7x +14 dB
RED 15x +24 dB
BLACK 47x +34 dB


Sensor: The actual audio sensor (piezo disc) is inside of the metal housing, on the flat side that is closest to where the audio calbe enters the housing. This side should normally be mounted to whatever you are trying to record.

USB Charging Receptacle: Metal Marshmallow has a builtin preamp, which is powered by a builtin rechargable battery. USB is used to charge the internal battery. The recptacle accepts a starndard micro-USB charge cable (not included), such as is used to charge many cell-phones. The charge time is one-hour, and the battery will last at leat 10 days, whether or not you are using the microphone. Note that Marshmallow does not use USB for audio, only for charging.

Charge Status Light: This light will come on while Marhsmallow is charging, and will turn off once the battery is full.

Audio Cable: This is standard shielded instrument cable.

Audio Connector: This is a standard 1/4 inch mono (TS) female receptacle, which accepts a standard instrument cable. Marshmallow can then be plugged into any regular audio interface or mixer. Note that instrument cables and adapters are not included.


Metal Marshmallow has a built-in rechargeable battery that powers its awesome preamp. It will ship with the battery drained. Prior to use you must charge it via a standard micro-usb charging cable (not included). The charge-status light will come on when it starts to charge, and turn off when it is done charging. It takes about 1 hour to charge, and will last for at least 10 days of continuous operation. To reduce noise, Metal Marshmallow does not have a power switch; It is on all of the time until the battery drains. While it is technically possible to use the microphone while it is charging, this is not recommended because the internal charging circuit is a strong source of electromagnetic noise that will cause a loud humming or buzzing sound in the audio signal.

Origin Story

Hi, I'm Michael Krzyzaniak, creator 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. In retrospect, I was probably violating FCC regulations every time I turned it on, and people driving by probalby just heard "KSSSSHHHHHHH" on their radios. Needless to say I had considerable difficulty getting a clean signal through a contact mic; it was mostly hum. 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!

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15 reviews 5 out of 5 stars


J Ray May 16, 2020

5 out of 5 stars
This is a wonderful mic for exploring all sorts of sonic realms! It can be used in a more "traditional" sense, to mic an acoustic guitar for example. Or for exploring and recording wacky sounds for crafting psychedelic soundscapes! Well constructed/quality components and craft. Be sure to inquire about the gain if you have questions. I'm going to order another "regular" gain mic as the high gain is very hot. You will not be disappointed with your purchase!

Purchased item:

Kent McDonald May 13, 2020

5 out of 5 stars
Great product and super fast shipping. Thanks!

Purchased item:

Galileo Seven Apr 30, 2020

5 out of 5 stars
I've used this mic for over a week now. Hands down, the absolute best contact mic I've ever heard. Fantastic! A+++

Purchased item:

Will Thornton Jan 25, 2020

5 out of 5 stars
I was under the impression that I’d need the high gain model for what I was going to be doing.
That wasn’t the case. Regular gain (Red shrink tube) is fine. Didn’t dial the gain knob of my recorder past like 2.5 to get good sound!
The build quality is wonderful, and the sound? Unlike any other contact mic I have used!
Highly recommend this for anyone who need a crystal clear contact mic with high sensitivity.

Purchased item: