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Gear / Technical Help => Recording Gear => Topic started by: goofy23 on May 16, 2008, 08:20:07 PM
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I want to adapt the prof. balanced XLR line out of my battery driven Mystere field mixe, please see here http://ourworld.compuserve.com/homepages/billdrucklieb/specs.htm
to the H2 line -in.
I know i need a att pad.
I tried to connect the H2 to the RCA line-outs which should be at 0dB (please see link above), but this was too much for the H2.
RCA connection was only for testing, i want to use XLR which have Nominal: +6 dBu (1,55V)
Maximum: +25 dBu (13,6V) (cause i want to use the cable on different mixers), but what resistor values will be perfect for XLR to 3,5mm
-15dB should be ok, someone said.
I have a description for a +4 to -10 pad, please see attachment (which is very usefull! i hope it is allowed to post, dont know).
Will this be perfect for my purpose?
Or do i need a other values?
This what i also found
http://www.williamson-labs.com/attenuator.htm
Anyone had this problem before?
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Maximum LINE input is -2.8 dBu at minimum REC level setting of #100, so design your attenuation network to handle the output level expected from what ever preamplifier is being used.
Link to a java driven design page for calculations of virtually anything can be found by searching linked graphics at:http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html (http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html)
However, if wanting to push +6dBu or higher preamp output levels into -2.8dBu limited H2 line input, at least 15 dB attenuation is required (~5.6-to-1 reduction) that can be approximated using a simple 2-resistor voltage divider on each channel as shown in the image below using the Hyperphysics calculator.
(http://www.sonicstudios.com/15dbatten.gif)
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acording to the pads from my attachment above.
Last night i did some trial and error testings.
So far resistors are the right way to go, seems to be the most elegant solution without addidng a balun.
I tried to build a pad with this way
R1 R1
XLR Pin2 out-----200Ohm---------200Ohm------ + H2 Line-in
(.......................................) I
(.....................)R2 750OHm or 590Ohm
(....................................... )I
XLR Pin1 out-------------------------------------- - H2 Line-in
And it seems to work quite good first bulid it with 750Ohm and it was almost ok but alittle to high at 100gain on H2.
With 590Ohm almost perfect, had to push the limiter hard to overload the H2 in.
Today i will try 250 or 300 Ohm for R1 and R2 750Ohm.
Maybe R1 200Ohm and R2 470Ohm is also good, dont know will try.
I will also try your voltage diver today, i have 2.2k and 470/590ohm here, maybe good enough.
I wonder a bit cause in my "build your own tap" how to, they use two R1 resistors (see above, sorry for the bad shematics) instead of only one in you example?
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I tried your way.
thanks, almost perfect, i found some 2k resistors, instead of 500 i took 620ohm, i tried also 590 ohm and 750 ohm, but 620 ohm seems to be perfect, almost imposible to overdrive now, have to push him very hard to get above -6, my normal peaks will be around -9dB.
With 750Ohm also very save, but if i push the the limiter to his limit, it over on H2, but should be ok, there is enough headroom if you have Levels at the usual levels.
I like a little bit more headroom so i decided to go with 620ohm.
590 Ohm is save i any way, i can not overdrive input of H2, even without limiter, a little too save but not bad.
My reference tone which is at -9dB on the mixer, on H2 (on #100) is
(if i remember corectly)
590Ohm -24dB on H2
620Ohm -23dB (relative exact)
750Ohm -20dB (ca.! dont remember axactly)
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Your mixer has two outputs: high level balanced and low level unbalanced.
The output level of the unbalanced output is 0 dBu. We will assume an impedance of 10k ohms.
The line input level of the Zoom H2 is -10 dbm at 10k ohms:
http://www.samsontech.com/products/relatedDocs/H2_user_manual.pdf
You need 10 dB of attenuation in an unbalanced circuit.
A T pad looks like so:
Input hot------------R1------------R2----------Output
|
|
|
R3
|
|
|
Ground-----------------------------------------------
Where
R1 and R2 = 5195 ohms
R3 = 7027 ohms
If you want to use the balanced (XLR) outputs you will need 16 dB of attenuation. Connect XLR pin 3 to ground -- this will unbalance the output. The resistor values then become:
R1 and R2 = 7264 ohms
R3 = 3251 ohms
You will want to round the resistances to standard resistor values.
You can do the calculations yourself here:
http://www.daycounter.com/Calculators/PI-T-Pad-Attenuator-Calculator2.phtml
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thanks a lot, will try it but dont have these values here, have to order first.
But what is the difference betwenn your pad with 3 resistors and the one guysonic posted with just 2?
I allready have a working one with 2 resistors, one 2k and one 620Ohm, working good.
I did not connect Pin 3 to ground, my mixer got an electronically balanced output.
I tested the cable today with a other mixer, a SQN 4 Series II (the reason i want to use XLR, no RCA here), also a portable field mixer, which should have transformer balanced outs, but it worked also (with just two resistors and without pin 3 to ground?).
???
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A T-pad presents equal impedances (10,000 ohms in this case) to both the input and output. It is a standard audio circuit.
Why are you trying to make a one-size-fits-all attenuator for both of these mixers? Resistors cost but pennies.
In the case of the SQN mixer, try to find out the line output level and impedance. You may need to ground pin 3 of the XLR connector in order to get full output level.
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Ok so maybe a t-Pad is better, but there seems to be no problems with the impedance.
The level with the SQN is ok, i want to build only one cable cause i dont want to carry so many cables arround with me, so a one size fits all cable will be perfect.
till now i did not connect pin 3 to ground, i may try when the resistors arrived.
But you think to the unbalanced outs from my mystere will be the best?
i can not open the daycounter link, what will you recomend when i need a maybe 3dB more headroom?
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Primary benefit for impedance matching T-Pad is MOOT for this application where 2-resister divider that just slightly loads preamp output, and provides low attenuated output impedance to help ignore effects of cable capacitance is most important.
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Holy crud, this thread makes my head spin! This makes me really feel ignorant about the guts of the gear. :-[
Personally, I needed a pad to lower the outputs of my Neumann KM140 > Beyer MV100 > unbalanced outputs in order to go into the line-in of the H2 without distortion. I purchased the -11dB pad cable from coresound, and have had very good results with it. Seen some REALLY loud shows and not clipped except maybe one hot peak in months with the pad cable.
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Maximum LINE input is -2.8 dBu at minimum REC level setting of #100
I'm curious where you got this specification. The published spec for the line input on a Zoom H2 is -10 dBV into 10,000 ohms or 0 dBv:
http://www.samsontech.com/products/relatedDocs/H2_user_manual.pdf
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Maximum LINE input is -2.8 dBu at minimum REC level setting of #100
I'm curious where you got this specification. The published spec for the line input on a Zoom H2 is -10 dBV into 10,000 ohms or 0 dBv:
http://www.samsontech.com/products/relatedDocs/H2_user_manual.pdf
Measured with REC @#100 (the minimum operating adjustment level)