Maxon AD-9 Pro Analog Delay

When Panasonic closed down their BBD production line in the mid 2000’s, Maxon had a tall task ahead of them to redesign their legendary AD-9 Analog Delay around a different IC chip. The resultant AD-9 Pro trumps the original version, offering several new features and a decidedly superior tone.
The AD-9 Pro provides 450 milliseconds of fat, warm analog delay tone thanks to 4 x custom-made Maxon MC4107D Bucket Brigade IC’s. The delay repeats of the AD-9 Pro are filtered using Maxon’s proprietary noise reduction circuitry which reduces the aliasing, clock noise and distortion common to analogs. The result is a rounder, smoother delay repeat that doesn’t overpower the original note.
With a wider dynamic range and max input level of +12 dB, the AD-9 Pro can accept signal from any source. This improved response offers a better balance between low and high frequency ranges, creating a delay tone that is clear and firm while still retaining that characteristic analog warmth. It also allows the Pro to be used in line level effects loops on amplifiers.
The AD-9 Pro features a Multi-Head mode controlled by a top-mounted mini switch. This switch activates a midstream delay feedback loop, creating polyrhythmic repeats against the main delay repeat. The Multi-Head mode can create a striking Tape Echo simulation, or it can be used to create ambient reverb effects at shorter delay time settings.
Topping off the AD-9 Pro are dual outputs that allow routing of the dry and delayed signals to two separate amps or mixer channels. Both outputs feature Mechanical True Bypass via a 4PDT switch.

Tech Talk
The AD-9 Pro starts with a string of low gain, low voltage op amps designed to boost the signal and shape the sound without adding distortion. Signal then passes to a THAT4315s Compander – a precision low voltage, low noise Compander IC designed to boost signal while killing any noise. This IC brings the input signal up to an ideal level and keeps it there as notes decay. This is good for signal-to- noise ratio and also gives the delay chips a clean, strong signal to work with.
The 4 x Maxon MC4107D BBD delay IC’s are controlled by two clock driver IC’s. The driver is running the BBDs at a very low clock rate to achieve maximum delay time. This rolls off a fair amount of high frequencies, giving the AD-9 a big, warm delay sound.
The delay circuit has a switchable tap that grabs midstream delayed signal and adds it back in with the main delay signal. This setup is very reminiscent of the multi-head feature on vintage tape echoes (Roland Space Echo, etc.).
Both the tapped and untapped signals are sent through their own sets of filtering op amps (3 apiece) which help get rid of clock noise and hiss. Then the signal is sent through another THAT4315s Compander chip and into a mixing Op Amp (where the clean signal is mixed with the delay) and out.
The AD-9 Pro features Mechanical True Bypass switching on both outputs via a Fujisoku 4PDT switch.
NOTE ON POWERING THE AD-9 Pro – this pedal’s voltage regulator IC requires a high inrush current of approximately 2000 mA upon startup. When using with a Power Brick such as the Voodoo Labs Pedal Power 2+, this pedal should be connected to a high current power jack when possible.
If it is not possible to connect to a high current jack, you can power the AD-9 Pro by leaving a battery in the pedal. Upon initial start-up, unplug the external DC power input cable, engage the pedal, and then plug the DC power input cable back in – the pedal will now power up normally off the external power supply until you power down your pedalboard.