Maxon AD999 - doesn't oscillate anymore?

dirk_benedict

Silver Supporting Member
Messages
6,465
Weird issue here gang...two nights ago at practice I used my AD999 with the band. As has always been the case since I've owned this pedal, it would self-oscillate with the repeats at 2-3oclock.

Last night, at the gig, with the exact same set up, down to the cables and all, I couldn't get it to oscillate even with the repeats maxed out.

Anybody have any tips/troubleshooting ideas on this one? Could a cable have gone wonky and affecte this somehow? Very curious.
 
Last edited:

soulsonic

Member
Messages
980
There should be a trimmer inside that can adjust the maximum feedback it gets when the Repeats knob is at maximum. This is the case with the AD-900 anyway...
It could be possible that the trimmer has moved out of place and isn't giving enough feedback signal to oscillate. But, since I've never been inside an AD-999 (only ever worked on the AD-900), I can't tell you for sure which trimmer to look at. Though, it may be labeled on the actual board which one it is. I can say for sure that there will be a bunch of trimmers all near to each other that will be for adjusting the BBD chips - don't mess with those - the feedback trimmer will likely be located by itself, away from those, probably near the compandor chip (which is probably an SA571, or something like that).

But first, try the pedal again by itself at home, and see if it will oscillate now. Just to make sure it's totally the fault of the pedal and not some other random crazy thing that made it misbehave.
 

soulsonic

Member
Messages
980


Welcome to the trimpot hell!!! :knitting
Upper right corner of this photo, under the small bundle of white wires connecting to the board... looks like there is a trimmer there, and that is probably the one I'm talking about. Looks like it is right next to the compandor chip, just as I had predicted.
 

dirk_benedict

Silver Supporting Member
Messages
6,465
Thanks guys! I usually power it off an isolated power supply. Sometimes it's own tap, sometimes daisy chained. The issue presented itself no matter how I powered it...I even used a 1-spot direct (not daisy chained with anything else).

Anyway, I think I've gotten it back to semi-normal now...after inspecting the outside of the pedal, I had noticed that the housing for the power jack had gotten very slightly out of alignment, so I popped it back to flush and it seems to have solved it. I guess it was just enough to throw off the amount of power it was getting.

Those trimmers: YIKES!
 

chilln

Member
Messages
258
Thanks guys! I usually power it off an isolated power supply. Sometimes it's own tap, sometimes daisy chained. The issue presented itself no matter how I powered it...I even used a 1-spot direct (not daisy chained with anything else).

Anyway, I think I've gotten it back to semi-normal now...after inspecting the outside of the pedal, I had noticed that the housing for the power jack had gotten very slightly out of alignment, so I popped it back to flush and it seems to have solved it. I guess it was just enough to throw off the amount of power it was getting.

Those trimmers: YIKES!
On the Maxon AD999 Pro webpage, they list this under Tech Talk, although it's not on the AD999 webpage, it might be useful info.

http://www.maxonfx.com/vintage-series-effects-pedals/ad-999-pro-analog-delay

"NOTE ON POWERING THE AD999 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 AD999 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."
 






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