American Audio QD5 MK2 decay mod

Posted this to skratchlounge but I was told you guys might wanna know too.

The American Audio QD5 MK2 is actually an ok mixer for the price, but the "decay" on the fader is far too long for crabs and double click flares etc (it's somewhere around 40ms). I spent the last couple days trying to see if that could be fixed. Turns out the answer is as simple as removing two capacitors.

1. Remove the 9 screws along the top edge of the sides of the unit
2. Lift the whole top assembly out, faceplate and all (unplugging any ribbon cables you need to)
3. On the underside of the main PCB there is a smaller (EQ) PCB attached with plastic standoffs, detach that (again unplugging any cables you need)
4. De-solder and remove capacitors C588 and C589 from the EQ board. They're both 2.2uF 50v.
5. Re-attach the EQ board to the main PCB, plug all the ribbon cables back in, and reassemble the unit.
6. That's it - the decay should be reduced to approximately 15ms. There don't seem to be any nasty popping or clicking noises when cutting and I haven't noticed any other problems (yet) so I think it's going to work.

This turns the QD5 from a crappy little budget mixer into a very nice scratch mixer, and very worth considering if you're broke (like I am). I'll let you know if anything breaks long term.

Very cool. I had read that the crossfader on that mixer was already an optical crossfader with a quick cut-in but I guess not? Kudos to you for figuring out how to do this!

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Originally Posted by djproben

Very cool. I had read that the crossfader on that mixer was already an optical crossfader with a quick cut-in but I guess not?

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It is an optical crossfader, and the curve is very sharp - these are two of the things which make it a potentially great scratch mixer. The problem lies with the VCA circuit - the control voltage is "filtered" far too much, meaning that it takes around 40ms for the signal to cut out after the crossfader has been moved. This has the effect of making cuts sound off-time and completely smoothing over things like fast crabs. It's also very noticeable with drum scratching, as it tends to cut off the start of the transient.

Removing the caps doesn't completely remove the filtering as there is another .22uF cap in parallel with the 2.2uF one, which handily seems to reduce it to 15ms (which is pretty much exactly what the rane scratch mixers' decay is). Any quicker and it would probably start clicking/popping while cutting.

hey, ive been thinking of doing your mod to my mixer, how have you been getting on with it? any problems?

I've taken it to dozens of gigs and had no problems at all.

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Originally Posted by rasteri

I've taken it to dozens of gigs and had no problems at all.

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Is it just as simple as taking those caps out and thats it? Is there anything I should know before doing it? Thanks a lot for your help

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Originally Posted by pich

Is there anything I should know before doing it?

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Well, you'll need to know how to use a soldering iron and screwdriver...