Ibanez CS9 Stereo Chorus with upgrades (vintage 80s MIJ Maxon model)

This is a heavily mod'ed CS9. Cosmetic condition is vintage good, as you can see, but it really does sound better than other CS9's I've played.

From the Reverb'er I bought it from, who did the mods. I cannot verify the accuracy below but it does sounds special:

"This is a pretty special CS9 that started life as a vintage 80s unit with the Maxon battery compartment cover and Maxon-branded circuit board. It has been carefully and selectively modified to address design flaws that make stock CS9s somewhat noisy and a little dark-sounding. Visually and physically, it's in well-used condition with extensive paint scrapes, dings, and bumps. Electrically, it's flawless and works perfectly. Mechanically, it's perfect: the pots are smooth and quiet; the stomp switch is quiet and reliable.

The internal upgrades addressed two goals: remove tone suck and reduce background noise by taking two approaches:

Power Supply Upgrades

• Apply appropriate power supply decoupling (2x 10uF solid tantalum) at the power jack.
• Add 100nF X5R op-amp decoupling capacitors right on each of the op-amp pins.

Component Upgrades

• Upgrade the cheap stock op-amps to modern, high-performance Burr-Brown OPA2134 SoundPlus op-amps.
• Replace the 20-odd year old electrolytic capacitors with modern audio capacitors: Elna Silmic II, Panasonic FC, and Panasonic FM.
• Replace the decades old cheap signal coupling capacitors with very high quality Wima MKS2 film capacitors.

The component upgrades use high quality parts to replace cheap old parts. In particular, the Burr-Brown OPA2134 op-amps are designed specifically for high-end audio equipment and dramatically improve tone by making the chorus effect sound wider and more expansive. They also reduce background noise, making the pedal quieter than standard CS-9s. The capacitor upgrades replace the cheap old electrolytic caps used by Maxon in the 80s with Elna and Panasonic capacitors common in high-end audio systems. No film caps have been replaced (no need), however the electrolytic signal coupling caps (one on the pedal's input and one on its output) have been replaced with 10uF Wima MKS2 film (PET) capacitors.

The power supply upgrades were designed to address serious shortcomings in the CS-9's power arrangements, namely: there is no power supply decoupling in a stock CS-9. None. This is important in a chorus pedal because input signals can modulate power supply voltages enough to cause audible effects. For example, if you listen to a stock CS-9 plugged into an amp with the guitar's volume down, there's a quiet-but-noticable swirling sound in the background. While the swirling noise is somewhat inevitable in the chorus' design, it's exacerbated by the lack of power supply decoupling, particularly of the op-amps, which aren't decoupled and therefore inject more noise than necessary into the signal path.

The power mods applied to this CS-9 add decoupling (with a decent touch of ESR to keep upstream power supplied happy and to help prevent oscillation of the OPA2134s) right at the input of the pedal. Further to that, the OPA2134's datasheet explicitly specifies that "Power supply pins should be bypassed with 10-nF ceramic
capacitors or larger to minimize power supply noise". This CS-9 uses 100nF X5R ceramic capacitors fitted directly across each op-amp's power supply pins. This mod alone reduced the background noise and improved the sound of the pedal more than any of the other modifications.

You can run this CS-9 at voltage ranges of 9 - 15V. Lower voltages have the quietest background noise, whereas higher voltages have greater headroom but slightly increased noise. 12V is fantastic.

I think you'll love this pedal. It retains all the character of a stock CS-9; nothing has been done to modify the sound - there are no "leslie" mods or any other changes to the audio circuit. It's still sounds like a CS-9... it's just a better CS-9."