I have a Juicedlink CX231 minimixer which is great to use attached to my Sony PCM-D50. One drawback with the Canon 7D and Panasonic GH1 is their AGC for audio.
It sounds crappy with lots of hiss and noise. Juicedlink made the DN101 to address several issues. One, defeat AGC, two add headphones monitoring and three to have a visual meter.
The way they solved this (rather than releasing a new mixer with this function built in) is the DN101 which bolts outside of the mixer and uses the same battery.
You simply take out the battery drawer, remove the spring.
Cut away some plastic from the drawer and attached the battery connector which then goes into the battery tray.
Problem is it doesn't fit! Bad design from the start and it doesn't work as advertised in the instruction video.
(A user on dvxuser.com got an email from Robert at Juicedlink and he said that the tray should be forced into position.
But I think this is a bad excuse for a bad design)
I am beginning to regret this purchase... But as usual I don't just sit and cry. I opened the lid on the CX231 and figured out a better solution.
A small hole was drilled with my Dremel to the right of the battery compartment.
I cut the wire from the DN101's battery connector so I got two wires going through the hole and soldered these inside the mixer directly on the other side of the battery compartment.
I used a bit of tape to get the cable away from the tripod screw inside and put everything together.

Now I don't believe this will affect anything inside the CX231.
Only difference is that the DN101 has a better connecting and that the wires inside goes a few millimetres to the side of the battery tray.
After this modification the battery tray now can be closed firmly in position and as you can see the DN101 is powered up as it should!
Now when I had a decent function I found another thing that is extremely irritating. If you try to put a GH1 on top of this it doesn't work.
The DN101 extrudes above the mixer and either the lens can't be fitted or the swivel display can't be opened.
I think this product was rushed and Juicedlink should introduce a mixer with this functionality built in. Not this tacky add-on!
How does it work then? If the camera (Canon 7D) isn't powered and you enable the AGC disable function all that noíse goes into the headphones.
Even if the camera is on but not recording you get noise.
Only when you start recording the noise goes away and you only hear the left channel without noise.
Again bad design. If the 7D is somehow looping audio from right left and back to the DN101 there should be a feedback filter inside the DN101.
It seams this is not the case. The headphone amplifier is also noisy in it self so it's hard to judge if the recorded audio is of pristine quality.
Compared when I monitor using the Sony D50 I have a very clean monitoring via headphones. Bad design all around.
If I use a GH1 it does work without noise when the camera is off or don't record, but when unplugging/plugging I get a short burst of noise in my ears.
Also, why is the supplied cable so long? The connector for the CX231 output and the DN101 input is next to each other.
And when you connect the output cable it is hard to pull out the battery tray to swap battery... think again JL.

But if you don't mind all these shortcomings the recorded left channel is free from AGC and no noise from the right channel is apparent.
How useful is the headphone output? I can't be sure to get a noise free recording and really the only thing I'm sure of is that audio is inside the DN101.
The meter on the side seams to be just bling since it tells me nothing more than there's some sort of signal inside the DN101.
So to conclude. One of three issues was solved. But to be sure I still have to use my Sony PCM-D50 for dual sound recording...