12AY7 Mic Pre Instructions

Back to Product Page / Instructions (PDF)

High Headroom Class ‘A’ Dual Vacuum Tube Mic Pre-Amp

Congratulations on your acquisition of the Electro-Harmonix 12AY7 Mic Pre-Amp. This high-voltage, pure class ‘A’ tube path has an 80kHz bandwidth, making it ideal for use with your favorite 96-192kHz A/D converter, high-end analog or digital console, or recording system. This dedicated microphone preamplifier has a single XLR input with an infinitely variable attenuator offering up to 50dB of gain.

Two premium Electro-Harmonix vacuum tubes, a 12AU7 and a 12AY7, operate at 200V, providing incredibly low distortion and high dynamic range. A discreet, matched, FET-based current balancing circuit allows for a low-cost, transformer-less design, offering more than 80dB of CMRR. The 12AY7 Mic Pre is small, portable and lightweight, allowing studios to place it near the mic and run it line-level to recorders and monitor mixers. Separate XLR and 1/4” balanced outputs can be used to split the signal for recording and monitoring in live performance applications. 

A host of standard features allow the 12AY7 to interface with most microphones and line-level input. Engaging the 48-volt phantom supply produces a “pop”-free ramp up. the 48 volt phantom supply supplies 10mA. Some modern direct-coupled condenser mics require more than this… you will need to test for best results. nearly all older condenser mics and all dynamic mics will be easily employed. The 12AY7’s Low-Cut filter is useful for controlling proximity effect and reducing rumble from wind or vibration. Also included is a Phase Reverse switch, which allows alignment at 0 or 180 degrees. Placement of multiple mics on common sources can affect overall sound. Toggling this switch inverts the phase of 12AY7.

POWER LED - This blue LED should glow brightly when the correct 12-volt /1 Amp AC power is applied, signaling that all operational voltages are satisfactory.

INPUT GAIN/OVERLOAD LED - The input gain knob controls the pad before the first tube gain stage, providing a range of 50dB. This range will work for dynamic, condenser and ribbon microphone types in most applications. We have provided enough gain to allow the large orange overload indicator to glow regularly if desired. This overload characteristic is musical in nature, with soft, warm, natural tube clipping that is great for blues harmonica. The OVERLOAD LED will begin to light at 0dBm and light solid at +4dBm or about +6dBu and +10dBu respectively

PHANTOM PWR/LED - Engages/disengages +48Volts on pin 2 and 3 of the input XLR. Turn on/Turn off transients, which could harm mics or monitor speakers, are eliminated by a slow ramp on/off power circuit. The Phantom LED should glow bright green when the phantom is active. Some condenser mics require more than the 10mA available for optimum use.

LOW CUT - Engages a simple, single-pole high-pass filter at 80Hz. This can be used to change the character of the mic, modify proximity effect or reduce rumble.

PHASE REV- This switch enables the user to invert their phase at the microphone input. Phase problems can occur when multiple similar mics are used in close proximity of the same sound source. Changing the phase typically can be heard as going between a thick or thin-sounding recording. This is dependant on the phase of the additional sound sources. This feature is also useful for accommodating XLR cables that have pin 2 and pin 3 swapped.

1/4” OUTPUT LEVEL - This separate, buffered output with a dedicated level control is “balanced out,” which can provide +18dBu. Shorting the ring to the sleeve allows for use of single-ended unbalance cables in some equipment. Test for best results.

WARNING Your unit comes equipped with a 12 Volt/1 Amp AC external power adapter. Use only the power adapter supplied, and make sure it is appropriate to your location (USA, Europe, Japan, Australia). Use of the wrong adapter can cause damage to the unit or to you, and will void the warranty.


Please register online at https://www.ehx.com/product-registration or complete and return the enclosed warranty card within 10 days of purchase. Electro-Harmonix will repair or replace, at its discretion, a product that fails to operate due to defects in materials or workmanship for a period of one year from date of purchase. This applies only to original purchasers who have bought their product from an authorized Electro-Harmonix retailer. Repaired or replaced units will then be warranted for the unexpired portion of the original warranty term.

If you should need to return your unit for service within the warranty period, please contact the appropriate office listed below. Customers outside the regions listed below, please contact EHX Customer Service for information on warranty repairs at info@ehx.com or +1-718-937-8300. USA and Canadian customers: please obtain a Return Authorization Number (RA#) from EHX Customer Service before returning your product. Include with your returned unit:  a written description of the problem as well as your name, address, telephone number, e-mail address, and RA#; and a copy of your receipt clearly showing the purchase date.

United States & Canada
55-01 2ND STREET
Tel: 718-937-8300
Email: info@ehx.com

Tel: +44 179 247 3258
Email: electroharmonixuk@virginmedia.com

This warranty gives a purchaser specific legal rights.  A purchaser may have even greater rights depending upon the laws of the jurisdiction within which the product was purchased.

To hear demos on all EHX pedals visit us on the web at www.ehx.com
Email us at info@ehx.com


Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmful interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:

• Reorient or relocate the receiving antenna.
• Increase the separation between the equipment and receiver.
• Connect the equipment into an outlet on a circuit different from that to which the receiver is connected.
• Consult the dealer or an experienced radio/TV technician for help.

Modifications not expressly approved by the manufacturer could void the user’s authority to operate the equipment under FCC rules.

mouse over image to zoom
Mailing List
Sign up to receive all the latest EHX news
To withdraw from this service, e-mail us and action will be taken within 2 weeks.
The EHX Community
Here are a few easy ways to stay informed on the latest news from Electro-Harmonix...
Forums (Discussion & Support)
Have a question, comment, suggestion? Come join the EHX Forums! You'll meet EHX staff and knowledgeable users from around the world.

Show your colors with genuine EHX tee shirts and authentic Electro-Harmonix accessories!
Get this limited-edition Day-Glo poster of the original 1968 art that inspired the Electro-Harmonix logo!

Mike Matthews stated: “The image on our Flashback Poster is of the original artwork that inspired the famous Electro-Harmonix logo. I think players who dig our pedals will also enjoy the chance to own a piece of EHX memorabilia.”
Did you know that Electro-Harmonix makes many of the world's greatest vacuum tubes? The next time you need to re-tube your guitar, bass, or hi-fi amp, be sure to insist on getting authentic Electro-Harmonix tubes.
Our new EH Strings allow you to capture every nuance of your playing style with lightning fast playability. Made of a pure nickel wrap with a specially-selected stainless steel, these sweet-sounding round wounds are truly like no other strings you've played. Not only do they last longer and stay in tune longer, but we think they're the best sounding strings ever made. Available in 9s, 10s and 11s.
Dig it, now you can rock EHX in our new heavy-duty black hoodie! It’s emblazoned with the iconic Electro-Harmonix Flashback logo in white on the left chest and back.