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Regular price $299.00 USD
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  • Optical Envelope Filter ala’ vintage Mu-Tron III
  • Funky, liquid, vowel-like Wah effects
  • Low Pass, Band Pass and High Pass filters
  • Low and High operation ranges
  • Threshold and Peak sliders
  • Up/Down Drive switch
  • True Bypass Switching

New look - Same great sound.

You may have noticed that the Maxon AF-9 Auto Filter has undergone a facelift. 

Specifically, the Sensitivity & Peak faders have been replaced by rotary pots and the slider switches are now toggles.

This change was made out of necessity due to the discontinuation of the fader pots that had been used on this model for nearly 40 years (original release date was 1981).

While these changes may have been necessary, Maxon saw no reason to update the AF-9’s classic, watery, 3-dimensional filtering that so many players have to come to count on over the years.  So, you can expect the latest version of this classic quacker to stand up to the original.

While change may be inevitable, if it ain’t broke, then don’t fix it.

The Maxon AF9 Auto Filter takes the most desirable auto-wah and swept filter effects and offers them up in a compact, user-friendly package. Opto-coupler circuitry produces the shimmering, watery filtering of legendary vintage units. Threshold and Peak sliders control the degree of effect; while Range and Drive switches determine range and direction of the filter sweep. Three selectable filter types (Low Pass, Band Pass, and Hi Pass) and a frequency range of 100 Hz – 4 kHz allow the AF9 to function with virtually any instrument or input signal.

Marty Friedman and the Maxon AF-9 Auto Filter

"The Maxon Auto Filter is one of my favorite "go-to" pedals. This really helps you give your playing a human voice without sounding like you just stepped on an effects pedal. It is really special and you can hear it on tons of my recordings." - Marty Friedman (Solo Artist, ex-Megadeth, Cacophany)


The AF-9 is Maxon’s version of the venerable Mu-Tron III envelope filter circuit (original version, not HAZ reissue).  The biggest difference between the two circuits is that the AF-9 runs on a single 9V supply while the Mu-Tron ran at 18V.

In addition, the III had a Gain pot which controlled the output level of the pedal as well as the Threshold of the Filter – this was an awkward design, as it prevented increasing the filter sensitivity without raising the output volume of the pedal.

These items aside, the basic structures of the two circuits are very similar. The AF9 starts with a unity gain buffer Op Amp and then splits the signal into control and effected circuits. The control circuit is shaped by the Sensitivity pot and amplified by an Op Amp.  This control signal then travels to a series of two photocouplers.

The effected portion of the circuit split goes into a three Op Amp filter network that is almost identical to the Mu-Tron’s, right down to the Low Pass, Band Pass, and High Pass switch that selects which portion of the filter network is used.  These filters are triggered by the CdS cell side of the previously mentioned photocouplers.

The AF-9’s Range is selected by changing the gain structure of the filters.  After the filter network the signal is run through a unity gain buffer to provide a low impedance output.

The AF-9 features Mechanical True Bypass switching via a Fujisoku 4PDT switch.

Input Impedance: 500K Ohms

Input Jack: 1/4 inch standard phone jack

Output Impedance: 10K Ohms

Output Jack: 1/4 inch standard phone jack

Output: 1

Residual Noise: -95 dB or less (input shorted IHF-A weighted)

Filter Frequency: 100 Hz 2 KHz (Low) / 200 Hz 4 KHz (High)

Controls: Sensitivity, Peak

Switch: Normal/Effect (true bypass configuration), Filter LP/BP/HP, Drive Up/Down, Range High/Low

Power Supply: 9V Manganese dry cell battery (6F22) or special AC adaptor

Power Voltage: DC9 V (Battery) / DC10 V (AC-adaptor)

Current Consumption: 17 mA (9 V) / 19 mA (10 V)

AC Adaptor: AC210N (option) Input: AC120V Output: DC9V/200 mA Center - / Sleeve +)

Dimensions (whole): 74 mm (W) x 124 mm (D) x 54 mm (H)

Weight: 580 g

Accessories: 9V Manganese dry cell battery (S-006P) x 1

Warranty Card: x 1

User's Manual: x 1

* All specifications are subject to change for improvement without notice or obligation.All brand names and product names are trademarks or registered trademarks of their respective companies.





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