Topic: putting line transformers inside a batt box -- please help (DPA4061 related)

[jamonyorke]

Hi !!!

I love the sound of my DPA4061s and i love to keep things small (just a PCM-M1, batt box and the mics) but i have huge problems when the sound is not very loud (and i mean **VERY** loud)
- If i go through line-in the levels are tiny.
- If i go through the built-in mic preamp the sound is crappy...and there is risk of brickwalling

So i have thought about using line transformers to boost the signal and allow me to go line-in in these cases.

I have tried a pair of hosas and they give me a much appreciated gain boost (about 12-14db) when going line in.
The problem is, adding these transformers and the XLR adaptors makes the setup much less stealthable, and it's harder to get into shows.


My idea now is to cut out the transformer cores, put them **inside** a battery box, and get rid of the XLRs.

Anybody tried something like this?

Ideally, the battery box would be as small as possible and include:
- two hosa transformer cores
- two small capacitors to provide a fixed rolloff at about 70hz (much needed when using the DPAs)
- two resistors
- a 9V cell
- a mini-XLR to act as the interface with the mics (like the core sound box)

And that's it

Is it possible to cram all this inside a standard core-sound HEB battery box?
Anybody would be willing to help?
I'd really appreciate it !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[fozzy]

I dunno how much real estate is available in the battery boxed but you could always move everything into a slighly larger box.

FWIW the internals of one HOSA's takes up about $2 worth or quarts stacked up.   

[leegeddy]

iirc, there's very little room to manuver inside of those HEB batt boxes.

marc

[jamonyorke]

iirc, there's very little room to manuver inside of those HEB batt boxes.

marc

that's really true, specially in the case of the switchable box, and the no-rolloff box.

but if you take out the large capacitors and substitute them with some smaller ones, maybe it's possible?

just trying to figure out the SMALLEST possible box.

other alternative I have in mind would be to cram it all inside a fake metal cigarette box...also quite easy to stealth

[jamonyorke]

well, i have just been doing some testing to see if the hosa's would fit inside the HEB box.
the pics speak for themselves !!!!

it will certainly take quite some skill to wire things up there, but looks like it is possible indeed!!!

(note, both boxes are of the "fixed response" type.
big caps for no rolloff, small caps for rolloff)

[larrysellers]

well, i have just been doing some testing to see if the hosa's would fit inside the HEB box.
the pics speak for themselves !!!!

it will certainly take quite some skill to wire things up there, but looks like it is possible indeed!!!

(note, both boxes are of the "fixed response" type.
big caps for no rolloff, small caps for rolloff)

Whats the wiring diagram for that transformer look like?

[leegeddy]

iirc, there's very little room to manuver inside of those HEB batt boxes.

marc

that's really true, specially in the case of the switchable box, and the no-rolloff box.

but if you take out the large capacitors and substitute them with some smaller ones, maybe it's possible?

just trying to figure out the SMALLEST possible box.

other alternative I have in mind would be to cram it all inside a fake metal cigarette box...also quite easy to stealth

javi;

i thought i recognized my old Hosas!

+t for good luck, man.

marc

[Sanjay]

call me crazy but why don't you just buy a Sound professionals battery box with bass rolloff and the adjustable levels to turn it down, and have your DPA's reqired with a miniplug?  Save you a shitload of trouble.

-Sanjay

[jamonyorke]

call me crazy but why don't you just buy a Sound professionals battery box with bass rolloff and the adjustable levels to turn it down, and have your DPA's reqired with a miniplug? Save you a shitload of trouble.

-Sanjay

thanks for the suggestion!
unfortunately i don't think the SP box would make a difference, because AFAIK it does not provide any gain.
i'm trying to use the transformers because they provide the gain i need, and they are small and clean sounding
if i can cram them inside my current, small batt box that would be superb !!!!
it's like having an invisible high end preamp!!!! 

ok i've been inspecting the stuff and heres a quick and dirt schematic (for 1 channel)


          BATT BOX   CABLE OUT         HOSA LINE TRANSFORMER
          ________  _________        _________________________
         /        \/         \      /                         \
            9V
            |
            R
            |  C        XLR OUT  XLR IN  white      yellow   
mic -----o--x--||--o--------o 2    2 o --------&  &----------o DAT
                                               &  &
                                               &  &
    -----o---------o---x----o 3    3 o --------&  &--x-------o
          (chassis)    |                red          | green
                       -----o 1    1 o ---------------

 
so as you can see what i have after plugging in the XLR is this

              9V
               |
               R
               |
 mic ----------x---------||----------&  &---------   DAT
                                     &  &
                                     &  & 
     --------------------------------&--&---------

now i have some questions

is the capacitor strictly needed now i have a transformer?
in case it is required, may i move it to the other side of the transformer?
(so as to be able to make it smaller)

i hope these questions make sense...i don't remember much about electronics
(although i'm somewhat good at drawing ASCII transformers)

btw, thanks marc for the hosas!!!!
one channel works fine and provides loadsa gain !!!
the other seems to have a lousy contact, but i think they will work fine after they have been rewired
still have not used them in the field but i'm eager to do so when all works fine (and everything is small enough!)

[Sanjay]

sorry i misread, i thought you had said it was overloading because it was too loud.  Doh.

back to your regularly scheduled smart person talk. 

[Lil Kim Jong-Il]

You need the capacitor to block DC.  If you remove that capacitor, you'll have a short across your battery via the transformer windings. (if I'm reading your schematic properly)

[Steelcorner27]

I had Doug Oade modify my dat preamp awhile back so I never have problems geting levels or distorting mic in with my 4061's now I admit its at a price tag of $125 but if your looking at staying the same size with your rig I can't imagine a beter solution.

Brad

[shaggy]

I also run an Oade mic-pre mod on my modSBM with 4061 and it is real clean sounding.  Will Doug mod a M1 that wasn't bought from the Oade Bros?  The other thing you can do is get 4060s and definitely run them line-in and get a nice signal. 

Nice pics!  Methinks your are nearly there!  +T the sheer will power and effort to make your dreams come true. Keep us posted with how the project turns out!

ANDY

[macdaddy]

+t for the effort...

The other thing you can do is get 4060s and definitely run them line-in and get a nice signal.

[pfife]

JKLabs is talking about building a box that provides +20db gain for just this situation... I get the same thing w/ my 4061's - but I sometimes think its a blessing, becuase I just turn up the SBM-1 all the way, and don't worry about it.  Its a stealth rig, and most people run levels low for stealth anyways, as to not peak it, so I sacrifice a bit of dynamic range - but most stealthers have to do that anyways.

It sounds like you are getting way lower levels than I am though,.  It also sounds like you might have a hosed BB, becuase I know some people (ellaguru on TS) that runs HEB -> BB -> Dat, and makes great tapes with no gain issues.