Question about amp and cabling

I'm in the process of saving up for a used GK MB115 combo, which I will be using along with the MB115 I already have. I wanted to make a custom built cable to connect them from the active output jack of the top amp to the passive of the bottom amp. So I ordered the parts to make the cable from Small Bear Electronics. Here's what I ordered:

http://www.smallbearelec.com/servlet/Detail?no=131

A 1/4 in. Mono, Flat, Right-Angle jack. Stacking one amp on top of the other doesn't give me much room for a standard sized jack, so I figured a small, flat jack would work better. I got two of these. I also got 4 ft. of this:

http://www.smallbearelec.com/servlet/Detail?no=998

Proco 120SX instrument cabling. Standard instrument cabling.

So this afternoon I soldered everything up, then I plugged it in to the active side of my GK combo, and plugged in the other end into my Yorkville combo. I was disappointed to find out that while the signal was getting through I had to crank up the Yorkville to the max to get any sound out of it. Yet when I plugged in a regular instrument cable the Yorkie was nice and loud.

Is there something about those small flat jacks I'm not aware of? Why is the regular instrument cable so much louder?

 

I'm pretty sure I wired them correctly. I soldered the hot wire to the tip, and the shielding wire to the plug body. They are working fine, but it's almost as if not enough of the signal is going from the GK to the Yorkie. Yet with a regular instrument cable there's plenty of signal going through, and both amps are loud as hell!

Maybe I got some bad instrument cable!