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Old 5th April 2003, 08:55 AM   #1
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Question Hello all this is my first post and I have an XLR Question.

Greetings all,

As the topic implies this is my first post here though I have been
passively reading for a while and completely mesmorized at the
amount of knowledge most users have here absolutely astounding!


Okay here's my question and yep it's tube related!

I ordered a pair of Antique Sound Labs Wave AV-20DT's these
are the newly released much upgraded version of the original
Wave's they are 20 watt monoblocks that run a 12AX7 Input
Stage and dual 6L6's on the output stage.

I don't have them in my possesion yet (they are currently held up
in Canadian/US customs ) so I am not 100% positive of
the input options but I am fairly certain there is no Ballanced XLR
Input only unballanced phono.

I would like to add a set of Neutrix Ballanced XLR Inputs to the
back of each Mono and I am not sure if this is possible?

I know that I could install them and just tie pin 1 and 3 (I belive
that's VE- and Earth without looking at the Neutrix documentation)
but that wouldn't be true ballanced would it?

The Earth (sheild) line on a true ballanced component does it
ever tie in with the VE- anywhere in the design or are they always
completely seperated?

I want to use Ballanced since I am going with a Parasound Halo
P3 Preamp and I also have a Behringer Tube Ultra-Q Parametric
Linestage Tube unit that I want to chain together and both the
P3 and the Ultra-Q have ballanced XLR. The Ultra-Q only has
1/4 TRS (Ballanced and Unballanced) and XLR (Ballanced and Unballanced)
In's and outs where as the P3 has Ballanced XLR In's and outs
and Unballanced Phono In's and outs.

Any help would be greatly appreciated.

Thanks a mill!
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Old 5th April 2003, 04:53 PM   #2
PassFan is offline PassFan  United States
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Yes, you are correct in thinking there is more to balanced than a connector. Jensen sells input transformers for this conversion, or some sort of circuit could be utilized as well. The BOSOZ located in the pass labs forumn is an excellent circuit which can be used for this purpose with a 1:1 gain setup. I'm not sure how much you want to spend or go through. Perhaps someone else has an easier solution.
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Old 5th April 2003, 06:05 PM   #3
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PassFan,

Thank you for the reply and the information. I figured there was
some sort of differntial circuitry involved. Sure I could just install
a set of female XLR's into the chassis and bridge pin 1 and 3 but
all you wind up with is a non ballanced XLR and that sort of defeats
the purpose

I read the online manual for the Halo today and it cleared up
something I was worried about.. I can come out of the P3 into
my Behringer as ballanced and come out of the Behringer as
Phono into the amps that's not a problem so I guess I may just
go that route "for now" but I would like to squeeze in the fully
ballanced connections into the Wave20DT's later on.

Again many thanks!
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Old 5th April 2003, 09:49 PM   #4
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You'll have to check the output level of your processors and the input sensitivity of your amplifiers. A lot of the XLR equipped equipment out there is set up to operate at +4 dBm and some is still being made (Sony Broadcast products) at +8 dBm. Our ubiquitous friend the RCA jack most commonly has a -10 dBm reference level.

Because these reference levels are often defined as the point 24 dB or so before the equipment goes into distortion, it is important to get the interface levels correct in order to optimize the Signal to noise ratio.

It is often possible to lower the output of on piece of equipment and decrease the input level of another to make up the difference in the levels, this method however will likely throw away a significant and audible portion of the dynamic range. What Iím getting at here is that I think you will need 14 dB of attenuation at the input of your amplifier. This is achievable with an H or a T pad between the XLR connector and the RCA input, but that does not address the issues of common mode noise rejection (the big reason to use a balanced circuit) or differences in impedances.

Jenson transformers are great and will solve all these issues.

The first thing to be done is to figure out how much attenuation will be needed at the input. Then check out the output impedance of your other equipment (likely 50 to 150 ohms) and the input impedance of your unmodified amplifiers (likely between 600 an 10 Kohms). Then check out the Jensen transformer site, they have some great circuits that showcase their products and should do exactly what you need.

Clear as mud?

-Dave

I found his ckt that looks close to what you need:
http://www.jensen-transformers.com/as/as012.pdf

Ive also found the people at Jesen to be friendly an dhelpful to talk to about aplications.
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Old 6th April 2003, 09:14 AM   #5
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Dave,

Mud couldn't get any clearer! Makes perfect sense to me!

I have to check the documentation to see what the output level
of the Halo is, the ASL's are 10Kohm if memory servers me right.

But at the very least thanks to you and Pass I have the info right
here for when I am ready to do the changeover.
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