
Vacuum Tube Microphony.
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Microphony in Vacuum Tubes: What to Know and How to Manage It.
At Vacuum Tubes Treasures, we are as passionate about vacuum tubes as you are, and we understand how important it is to grasp every aspect of their characteristics. Microphony is one of them: it is not a defect but a natural phenomenon that, when understood, can help you fully harness the potential of vacuum tubes in your audio system.
What is Microphony?
Microphony is an intrinsic characteristic of many electronic components, including vacuum tubes. It occurs when a tube converts mechanical vibrations into electrical signals, affecting the sound output from amplifiers.
A common example is audio or instrument amplifiers, where vibrations from speakers or the surrounding environment can be perceived as unwanted noise or signal interference.
How Does It Manifest?
Microphony can present itself in various ways:
- Muddled Sound: When the system volume increases, the sound may become less clear.
- Acoustic "Bump": Lightly tapping the glass of the tube can result in a noise or "bump" heard through the speakers.
- Feedback or Resonance: In high-sensitivity applications, such as guitar or bass amplifiers, feedback phenomena may occur.
Why Does It Happen?
The main causes of microphony include:
- Mechanical vibrations affecting internal components of the tube, such as grids or anodes.
- Vibrations transmitted through the amplifier’s chassis or the surrounding environment.
- Operating conditions, such as low signal levels, which make microphony more apparent.
For more technical details, please consult:
- Mullard's original studies published in Mullard Technical Communications, November 1962 , available at the following links:
- The article "Microphony of Thermionic Valves" by AudioValvole, which provides further insights and practical solutions, is available here.
Are New Production Tubes Immune?
Some customers ask if new production tubes are completely free of microphony. The answer is that, although many modern manufacturers implement measures to reduce microphony, no tube is entirely immune to this phenomenon.
Microphony depends not only on design and materials but also on the usage context, such as the type of circuit and operating conditions. In high-sensitivity applications, microphony can manifest regardless of the tube’s age.
If you have concerns or require technical support, we are here to assist you.
Is It a Defect?
Microphony is not necessarily a defect but an intrinsic characteristic of tubes, especially those designed to handle very low signal levels. However, there are acceptable levels of microphony, and every tube is tested to ensure compliance with these limits.
How Do We Test Tubes?
In our store, every tube undergoes rigorous testing using high-precision equipment such as the Amplitrex AT-1000. To ensure maximum accuracy, we use a computer-based system comprising a Mac Studio
and the professional-grade Audient iD4 audio interface.
Each signal is analyzed and documented, ensuring that the tubes meet our strict quality standards.
The tests include:
- Microphony Verification: Lightly tapping the glass of the tube and monitoring the signal with advanced tools.
- Performance Testing: Measuring parameters like Gm and Ia to ensure compliance with quality standards.
If you have specific requirements for microphony beyond standard levels, we recommend making a prior request or opting for products specifically designed to minimize this phenomenon.
How to Mitigate Microphony?
If you encounter microphony issues, there are several practical solutions:
- Using Dampers (Tube Dampers): Silicone rings that reduce mechanical vibrations. These simple accessories effectively reduce mechanical vibrations and are easy to apply to the tube.
- Amplifier Isolation: Position the amplifier on a stable surface, away from vibration sources. Ensure that your amplifier is placed on a stable surface, away from vibration sources such as subwoofers or powerful speakers.
- Positional Adjustment: Move the microphonic tube to a circuit position less sensitive to the signal. If you have concerns about the positioning of the tubes, we can provide specific guidance to optimize your system.
Frequently Asked Questions About Microphony
- What is microphony?
- Do all tubes have microphony?
- Can I reduce microphony in my amplifier?
Return Policy
We wish to remind you that returns for reasons related to microphony are not accepted, as this characteristic is intrinsic to the design of vacuum tubes and does not represent a defect. Each tube is individually tested to ensure that microphony falls within acceptable limits. Returns are only accepted for unused products with intact safety seals, as specified in our Return Policy.
We understand how important it is for our customers to receive high-quality tubes. This is why we test each product individually to ensure it meets our standards. Microphony is a natural characteristic of vacuum tubes and does not compromise their performance when it falls within acceptable limits. If you have any questions or need assistance, our team is always available to help you.
Our Commitment
At Vacuum Tubes Treasures, we are dedicated to providing high-quality tubes, individually tested to ensure excellent performance. We are here to answer your questions and help you choose the product that best suits your needs.
For more information, please feel free to contact us via our support page !