Author Topic: VOX AD50 problems and mods!  (Read 3830 times)


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VOX AD50 problems and mods!
« on: February 23, 2010, 11:15:51 PM »
Hi! I want to fix a problem in a friend's Vox AD 50, it seems that oscillates with distorted amplifier emulations at max gain, master volume and PA gain pot... also sound gets noisy after a few minutes of hard playing. Can I do anything to solve this? Maybe changing output IC? A power amp schematic would help me a lot!

MODS? Pretty easy... just replace 12AX7 for a high quality NOS 12AU7 and 2200 uF caps for 4700... tone improvement! Really awesome!

J M Fahey

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Re: VOX AD50 problems and mods!
« Reply #1 on: February 25, 2010, 11:28:37 PM »
Hi slideman.
From what you say, maxing *everything* and using highest gain emulations, I'd be surprised by it *not* oscillating.
Even real Marshalls do.
It's hardly a power chip problem, rather an excessive gain preamp, used full tilt.
Going from "X" to "U" will certainly lower the gain a lot, and tame the beast.
Duplicating power supply filtering, specially if skimpy to begin with, is always a good improvement.


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Re: VOX AD50 problems and mods!
« Reply #2 on: February 26, 2010, 11:21:21 AM »
Thanks, anyway! I'll improve filtering. and probably add other cooler. Heatsink it's not quite big, and maybe I'll change it later...

This amp is what I call  a "toy amp". It has some noise gate effect that't can't be switched off, and this removes some of the amp's dynamics (not too much sustain).

I'll see what I can do, I already have a AD30 schematic, it's the same but with dual 30V DC supply instead of 40.


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