The schematic is in the Design Documentation (appendix A-3 if I recall correctly).
A differential input has three connections:
IN+ : Signal + (or "hot")
IN- : Signal - (on "return")
GND/SHIELD : Shield ground
Wikipedia explains it well: http://en.wikipedia.org/wiki/Differential_signaling
Perspective Andrew... My Modulus-86 and recommendations for how to wire it up follow AES48-2005. As builders report, there is no Pin 1 problem.
~Tom
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The connections I recommend are equivalent to AES48-2005 Figure 3.
AES48-2005 recommends taking Pin 1 of the XLR directly to ground due to concerns about the shield acting as an antenna for RF injection into the enclosure. That's fine. However, unless the shield continues from Pin 1 of the XLR to Pin 1 of J2 on the MOD86 board, the RF filtering on the board will see a rather high inductance return path back to Pin 1 of the XLR via the chassis. This will render the RF filtering ineffective.
If you insist on connecting Pin 1 to ground directly at the connector, at least continue the Pin 1 connection to the board via a cable shield so the RF filter can have a fighting chance. This will leave you with something equivalent to AES48-2005 Figure 1.
Last I checked, AES48-2005 allowed the designers to exercise sound engineering judgement... I'm pretty sure the AES Police won't come after me here...
~Tom
AES48-2005 recommends taking Pin 1 of the XLR directly to ground due to concerns about the shield acting as an antenna for RF injection into the enclosure. That's fine. However, unless the shield continues from Pin 1 of the XLR to Pin 1 of J2 on the MOD86 board, the RF filtering on the board will see a rather high inductance return path back to Pin 1 of the XLR via the chassis. This will render the RF filtering ineffective.
If you insist on connecting Pin 1 to ground directly at the connector, at least continue the Pin 1 connection to the board via a cable shield so the RF filter can have a fighting chance. This will leave you with something equivalent to AES48-2005 Figure 1.
Last I checked, AES48-2005 allowed the designers to exercise sound engineering judgement... I'm pretty sure the AES Police won't come after me here...
~Tom
This is getting remarkably like the discussion that was had on Tom's thread in the vendors area. I really appreciate your crusade to help people understand good wiring practice and how to avoid hums, buzzes ground loops and the infamous GSM 217Hz pickup Andrew, but in this case and given the RF filtering on board as per the THAT data sheet is there a reason to push this point or a different way to do this that could offer better performance? I don't want people to get confused and make things worse.
the "hummer" is one method to test for pin1 problem.
Pin 1 Problem
and section3.3 on p23 (3.9MB pdf)
http://www.google.co.uk/url?sa=t&rc...7HWrcWrJJVZlGgA&bvm=bv.85464276,d.d24&cad=rja
Pin 1 Problem
and section3.3 on p23 (3.9MB pdf)
http://www.google.co.uk/url?sa=t&rc...7HWrcWrJJVZlGgA&bvm=bv.85464276,d.d24&cad=rja
In respect of the lack of clearance between the PCB and the heatsink !!!!!!
one Member found and reported the problem.
How many more would not have noticed?
No.
The Pin1 problem happened because builders assembled their equipment without the Screen connecting to Chassis.
The Screen does not carry wanted signal. It carries the unwanted interference signal.
The screen goes to chassis via pin1, if the XLR is that type.
Better is where the screen connects to chassis via the plug on the exterior of the chassis.
But most important is that the internal connection of Audio Ground to Chassis does NOT replace the direct screen to chassis connection.
The audio signal does not require the cable screen connection of the balanced interconnect.
The Pin1 problem happened because builders assembled their equipment without the Screen connecting to Chassis.
The Screen does not carry wanted signal. It carries the unwanted interference signal.
The screen goes to chassis via pin1, if the XLR is that type.
Better is where the screen connects to chassis via the plug on the exterior of the chassis.
But most important is that the internal connection of Audio Ground to Chassis does NOT replace the direct screen to chassis connection.
The audio signal does not require the cable screen connection of the balanced interconnect.
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That is derogatory.
Is a Troll someone who has no intended useful input?
I am not a Troll and hope I never get seen as such.
From Wikipedia:
"In Internet slang, a troll (/ˈtroʊl/, /ˈtrɒl/) is a person who sows discord on the Internet by starting arguments or upsetting people,[1] by posting inflammatory,[2] extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the deliberate intent of provoking readers into an emotional response[3] or of otherwise disrupting normal on-topic discussion.[4]
jb74
"In Internet slang, a troll (/ˈtroʊl/, /ˈtrɒl/) is a person who sows discord on the Internet by starting arguments or upsetting people,[1] by posting inflammatory,[2] extraneous, or off-topic messages in an online community (such as a newsgroup, forum, chat room, or blog) with the deliberate intent of provoking readers into an emotional response[3] or of otherwise disrupting normal on-topic discussion.[4]
jb74
The line between a useful post given in haste and trolling is thin, very thin. You have not crossed the line and I hope you don't as you have useful information to share. I've been guilty myself of posting one line where I should have waited until I had time to write a fully reasoned response. And I respect how strongly you feel about pin one going directly to chassis, do not pass go, do not collect £200. I don't know if there is a real problem here until I test one of my boards, but looking at the THAT1200 datasheet, unless I have misread, it has been implemented according to that.
When I get mine running I will test and report back.
When I get mine running I will test and report back.
No. I sat down and thought through the problem and designed a circuit around the limitations of physics. This is a process know as engineering and circuit design.
As I've mentioned before, I suggest that you tweak your communication style to include more of the thought process behind your statements. It should be pretty clear now that merely throwing out a dogmatic decree, "IT'S THE LAW" or "IT'S THE STANDARD", without any reflection or insight doesn't get you the results that you want. In fact, it probably gets you exactly what you don't want. You can choose to take this personally or you can choose to grow as a mentor and a DIY resource. The choice is yours my friend...
Way off topic (sorry Bill) but on the topic of trolls, I do find the Flame Warriors Guide rather amusing: Flame Warriors Home
~Tom
Just to be clear, you reported the lack of a clearance gap. I found that to be not a problem but a feature to aid soldering the chip.
The amp has an integral RF filter so I use it. If there was no filter I would earth the shield as Rane guide suggests. I don't want to connect earth to signal ground because I believe the earth in residential outlets is not very quiet.
My own experience is that I connect my signal shield directly to the PCB as instructed in the design doc and it is dead silent with my ear to the tweeter. I have no metal box chassis and I am using 12 foot length of inexpensive foil shielded "install grade" cable, not braided copper shield. There are FM and TV broadcasting towers all around me, one is 26kW, 2 miles away which screws up my Sansui radio reception.
I like Rane's treatment of the subject (linked by Richidoo above). Connecting two pieces of audio gear is a surprisingly complex affair. Then think about how much gear is connected at a live concert or during studio recording and you quickly realize that it's only thanks to good engineering that anything works at all. You also suddenly realize that optical connections really are pretty neat...
~Tom
~Tom