MXR Commande Flanger Clock Noise

[Dan-O Twelve]

Howdy! I've been away a looong time and it's good to see that the world does, indeed, turn without me. ;-) I just bought one of those black plastic MXR Commande pedals, the 2-knob Flanger. (I have several Commande pedals, and actually gig with some of them: cheezy build quality but great sound, esp. the compressor and delay!) I fired it up, and true to form, it sounded sweeeet, but there is this awful "geiger counter" noise whose sweep speed responds to changes in the Speed knob. I'm guessing clock noise, but I'm far from an expert in BBD technology. I paid $38 and the seller is willing to trust me for a no-return refund of $25, which would mean I'd be paying $13 for a hopefully fixable pedal. Is this thing fixable? It sounds great in spite of its obvious malfunction. I'm a complete naif when it comes to fixing this kind of stuff and I'd be very grateful for any and all suggestions.

[Mark Hammer]

I have one, and it's actually a pretty decent flanger, and fairly crisp and quiet (especially when you consider it is an unshielded chassis), though obviously NOTHING about it corresponds to the "Stereo" emblazoned on its chassis.

The audibility of the clock noise can be a function of two things, either in combination, or individually. Typically, the lowpass filtering selected for any BBD-based pedal is selected in order to both maximize usable bandwidth but minimize audible noise. So....

1) Something could be amiss with the clock circuit such that it is clocking at a slightly slower rate that is not eliminated by the filtering (i.e., filter is set too high for the clock), or...

2) Something is amiss with the filter such that the clock is spot on but the filter is set too high for it.

The clock portion is located in the 4069 chip over in the corner to the left of the stompswitch (when the board is out of the chassis and placed copper-side down).
I posted a schematic for the Micro-Flanger, which is very very close to the Commande circuit. Unfortunately, I'm not allowed to see photobucket pictures (or accounts) from work, so I can't give you the link. If you want to send me a PM, and a valid e-mail address, I can send you the schematic.

There are 6 poles of lowpass filtering for the unit. This is provided by four 820pf caps and two 82pf caps. These are likely all very small ceramic units, which can be fragile. Verify that none of them is cracked or otherwise compromised. Damage to any of those caps would reduce the amount of overall filtering and render the clock more audible.

There should be a 50pf ceramic cap beside the 4069 chip which would also need to be in tip-top shape to assure the clock frequency corrsponds to what the filtering anticipates.

[Dan-O Twelve]

THANKS!

I appreciate your time and your thoroughness. Thanks to you, I may actually have a chance of making this thing work. I will now try to PM you with my e-mail address...here goes!