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.

[dklein]

Just curious - what's the cap value on the small one?  And how about the resistor?
It'd be nice to file away a powering scheme for the 4061s.

[Nick's Picks]

I'll slap on another +T for your ideas and efforts.
4061s...I dont know.
far to "un sensitive" w/o some sort of gain that you can add.

imo, the one to get is the 4070.  built in roll off and more sensitive.

but, that doesnt' help, does it.

I think maybe gutting the BB and building it in a different sized project box might do the trick.  But then again, the Oade mod M1 would solve everything, wouldn't it.

[pfife]

even the 4060.  As macdaddy has.

[jamonyorke]

Just curious - what's the cap value on the small one?  And how about the resistor?
It'd be nice to file away a powering scheme for the 4061s.

Here are the values:

R= 10K
C (small) = 2.2uF
C (big) = 0.15uF

(thanks JK for deciphering the caps values for me a while ago)

The bass rolloff filter (small C) is suposedly designed for mic-in impedance (4,7K), but applying the formula gives me a cutoff freq. of 226Hz.
This somewhat contradicts what's written on Coresound's Page (120Hz).
Maybe he considered the mic-in impedance as 10K?

[dklein]

Here are the values:

R= 10K
C (small) = 2.2uF
C (big) = 0.15uF

(thanks JK for deciphering the caps values for me a while ago)

The bass rolloff filter (small C) is suposedly designed for mic-in impedance (4,7K), but applying the formula gives me a cutoff freq. of 226Hz.
This somewhat contradicts what's written on Coresound's Page (120Hz).
Maybe he considered the mic-in impedance as 10K?

Interesting...exactly the same as the standard CSB box - same powering as the Panasonic capsules

Remember that when you use that formula you get the -3dB point (on a 6dB/octave slope).  CS says it's down 6dB at 120 Hz - I would think the -6dB point is somewhere near 167 Hz.

[relaxing]

Did this actually work?  I'm considering doing the same thing, all homebrew.

It'd be better to not kill a pair of hosa's - do you know the specs of the transformer?

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

[zhianosatch]

the 4060s would be the much easier solution here, but good job for doing what you're doing!

[relaxing]

the 4060s would be the much easier solution here, but good job for doing what you're doing!

The 4060s really put out enough signal to get a good recording on the jb3?   

In any case, the 4061s are cheaper and easier to find, so I really want a solution like this.

[pfife]

yeah, the 4060's are higher sensitivity.

[SparkE!]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

[relaxing]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

Excellent!  I'll try to put something together tonight.

Thanks SparkE!  I'd +T you if I could!

[relaxing]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

ok... so what do I do with all these wires? 

one side, labeled "8 ohms",  has red and white wires.  the other, labeled "CT" (center-tapped?), has blue, black and green.
by sides I mean the diagram goes    =3||C=

I found combinations that didn't work, and some that did, but none gave me a huge boost in sound.  I'm using a pair of transformers after the battery box, with just a plain signal/shield stereo pair to a 1/8 mini plug.

hope that makes sense.

[SparkE!]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

ok... so what do I do with all these wires? 

one side, labeled "8 ohms",  has red and white wires.  the other, labeled "CT" (center-tapped?), has blue, black and green.
by sides I mean the diagram goes    =3||C=

I found combinations that didn't work, and some that did, but none gave me a huge boost in sound.  I'm using a pair of transformers after the battery box, with just a plain signal/shield stereo pair to a 1/8 mini plug.

hope that makes sense.

So, you'd go mic signal between the red and white wires and the coupled signal would come out between the blue and green wires.

[relaxing]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

ok... so what do I do with all these wires? 

one side, labeled "8 ohms",  has red and white wires.  the other, labeled "CT" (center-tapped?), has blue, black and green.
by sides I mean the diagram goes    =3||C=

I found combinations that didn't work, and some that did, but none gave me a huge boost in sound.  I'm using a pair of transformers after the battery box, with just a plain signal/shield stereo pair to a 1/8 mini plug.

hope that makes sense.

So, you'd go mic signal between the red and white wires and the coupled signal would come out between the blue and green wires.

Between the wires???  Sorry, what gets connected to what?

(This must be what it feels like when I'm explaining computer things to the computer illiterate...  It's all so unintuitive to me!  I've googled and no one explains how this stuff works on the level I need.) 

[SparkE!]

Would something like radshack #273-1380 work? ("Audio Output Transformer 1,000-ohm center-tapped primary, 8-ohm secondary. Many uses including audio output and low-level impedance matching.")

The voltage gain is going to be the square root of the impedance ratio.  You're talking about an impedance ratio of 125, so the voltage gain will be 125 ^ .5 = 11.18.  If you express that in dB, you'll have 20 log 11.18 = 20.97 dB gain.  You'd run you mic signal into the 8 ohm side and get your boosted line level signal on the 1000 ohm side.

ok... so what do I do with all these wires? 

one side, labeled "8 ohms",  has red and white wires.  the other, labeled "CT" (center-tapped?), has blue, black and green.
by sides I mean the diagram goes    =3||C=

I found combinations that didn't work, and some that did, but none gave me a huge boost in sound.  I'm using a pair of transformers after the battery box, with just a plain signal/shield stereo pair to a 1/8 mini plug.

hope that makes sense.

So, you'd go mic signal between the red and white wires and the coupled signal would come out between the blue and green wires.

Between the wires???  Sorry, what gets connected to what?

(This must be what it feels like when I'm explaining computer things to the computer illiterate...  It's all so unintuitive to me!  I've googled and no one explains how this stuff works on the level I need.) 

Your mic signal wires will connect to the red and white wires (one to each).  Then your blue and green wires will connect to the output connector.  I don't know enough about the connectors you are using to tell you exactly how to wire the connectors.  I also don't know if you are balanced or single ended.  Both are shown below:


                         Red      Blue
       Mic +  o--------------. ,-------------o  Line Out +
                             )|(  Black
                             )|(-------------o    GND
                       White )|(  Green
       Mic -  o--------------' '-------------o  Line Out -
                                                                     +
                           Balanced



                         Red      Blue
       Mic +  o--------------. ,-------------o  Line Out +
                             )|(  Black
                             )|(-------------o   Unused
                       White )|(  Green
        GND   o--------------' '-------------o    GND

                         Single Ended

created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

[relaxing]

Muchas Gracias!

I'll be taping band practice tonight, so I'll let you know how this works out.  I noticed the specs for the transformers was something like 300Hz - 10kHz so we'll see just how nonlinear it gets outside of that range.

[Lil Kim Jong-Il]

Muchas Gracias!

I'll be taping band practice tonight, so I'll let you know how this works out.  I noticed the specs for the transformers was something like 300Hz - 10kHz so we'll see just how nonlinear it gets outside of that range.

+T for DIY.

Once you get the circuit working, you can always substitute better components later - upgraded transformer and some auricaps for the signal path. 

[relaxing]

well, the good news is:
1. my homemade battery box seems to be working well.
2. the transformers did provide +5 dB gain

the bad news?
1. The transformers suck.  They completely trash the signal with what I would call a comb filtering effect, leaving the recording sounding hollow. (I can provide frequency graphs if anyone's curious.) 
2. 5 dB gain is not enough.

Granted, these are ratshack parts, so suckage is to be expected.  If anyone can help me find higher quality components from someplace like Mouser, I'd try it again.  But I believe I need an active preamp for the 4061s.

[Evil Taper]

What's the big deal with boosting the signal during post work?

[shaggy]

If you don't put enough signal onto the tape, you are effectively making a 12 or 14bit recording.

ANDY

[Evil Taper]

This true with the JB3 also?

[relaxing]

This true with the JB3 also?

It's true with any A/D conversion.  "16 bits" of CD quality refers to 2^16 possible volume levels for each sample.  If you only supply it with volume levels up to, say, bit 12, then you're  wasting the upper 4 bits and making a lower-quality recording.

[Lil Kim Jong-Il]

If anyone can help me find higher quality components from someplace like Mouser, I'd try it again.  But I believe I need an active preamp for the 4061s.

Jensen www.jensen-transformers.com
Reichenbach  http://www.cinemag.biz/line_input/line_input.html

Digikey has a long list of broadcast quality audio transformers last time I looked.

[Evil Taper]

When someone gets this problem fixed I'd be very interested in a step by step how to.  What is up with JK Labs though...he's awol.

[relaxing]

If anyone can help me find higher quality components from someplace like Mouser, I'd try it again.  But I believe I need an active preamp for the 4061s.

Jensen www.jensen-transformers.com
Reichenbach  http://www.cinemag.biz/line_input/line_input.html

Digikey has a long list of broadcast quality audio transformers last time I looked.

Yeah but I have no idea what specs I'm looking for.