How to Mod an Art MP to Simulate Power Amp Distortion
Applied Research & Technology (ART) is a manufacturer of signal processing equipment, including digital interfaces, compressors and microphone preamps. The ART MP range contains three different mic preamps: The ART Tube MP Studio V3, the Tube MP Original and the Tube MP Project Series. Each unit in the range features a vacuum tube that adds warmth and character to the line-level microphone signal. You can perform modifications to any of these devices to simulate the sound of power amp distortion.
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Instructions
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Acquire a lower gain tube. The stock tube in the ART Tube MP Studio V3 is a 12AX7 type. This is not a brand, it is a tube classification. Various companies make these tubes, including Sovtek, Tung Sol and Electro Harmonix. By using a lower gain tube, you reduce the amount of power produced by the preamp. The 12AX7 has a gain factor of 100. By using a 12AU7 type tube, you reduce the gain factor of the preamp to 70. While this reduces the output of the preamp, it forces the connected to power amp to work harder to drive the speakers. If driven hard enough, the power amplifier will distort. The lower the gain factor of the new tube, the harder the power amp has to work.
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Unplug the preamp. Leave it to cool for 10 minutes so that the tube isn't hot when you handle it. Moving hot tubes can cause them to shatter.
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Dismantle the ART MP. Place it face down and use a small cross-head screwdriver to remove the chassis enclosure. This allows access to the tube socket. Place the preamp face up on your work bench. Stick the screws to a piece of electrical tape to prevent them from rolling away. Place them in the order you removed them so that you can put each one back in the original hole.
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Remove the stock 12AX7 tube. The tube socket is mounted flat inside the ART MP preamp. Typically, tubes are mounted vertically, requiring vertical removal. In the case of flat mounted sockets, pull the tube out horizontally.
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Install the new tube. Both the 12AX7 and the 12AU7 have nine connector pins, so you do not need to modify the tube base to install the new tube. Line up the pins so that they are level with the pin sockets on the tube base. Gently push the new tube into the socket until you hear a click.
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Reassemble the preamp. Fit the chassis enclosure back on and tighten the screws firmly. Plug in the power supply and test.
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Tips & Warnings
Wear latex gloves when handling vacuum tubes. This protects the glass from oils on your skin.
Performing any mod to your preamp might void the warranty.
References
Resources
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