Ok I finally found Owen's pdfs here:
http://www.diyaudio.com/forums/vend...e-here-bal-bal-se-se-lpuhp-3.html#post3684804
For those of us who don't use 8.5x11 old-fashioned paper sizes and who don't want to screw up 4 holes in their chassis, is it really the case that the grid for the 4 mounting holes is 35mm x 53mm? This what I measured with the pdf displayed on my computer screen (which seemed to match a 60x42.5mm outline).
Owen it would be good if you can confirm as this is the sole remaining item for my chassis design.
http://www.diyaudio.com/forums/vend...e-here-bal-bal-se-se-lpuhp-3.html#post3684804
For those of us who don't use 8.5x11 old-fashioned paper sizes and who don't want to screw up 4 holes in their chassis, is it really the case that the grid for the 4 mounting holes is 35mm x 53mm? This what I measured with the pdf displayed on my computer screen (which seemed to match a 60x42.5mm outline).
Owen it would be good if you can confirm as this is the sole remaining item for my chassis design.
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Ah ok - thanks a lot. I was unnerved by the odd mm dimension. 
Parts ordered. Enclosure design done. Just waiting for a PM to complete the board purchase. Note the LME49610 are disappearing fast. RS Online's stock in the UK went in the last two days. Mouser got a new bunch in and they're already down to just 56 left.
Parts ordered. Enclosure design done. Just waiting for a PM to complete the board purchase. Note the LME49610 are disappearing fast. RS Online's stock in the UK went in the last two days. Mouser got a new bunch in and they're already down to just 56 left.
Can I ask for guidance on terminating the inbound balanced connection?
I was reading TI's application note SLOA054D on Fully-Differential Amplifiers. Section 11 regarding terminating the input source was particularly interesting. I haven't seen anyone discussing "double termination" of balanced inputs into this "Wire BAL-BAL" amplifier - perhaps I missed it. The discussion in the TI document including Fig 17 and the example provided (Fig 20) suggest input termination should match the output impedance of the source (in my case, 100 Ohms) with 3 resistors used and, of course, if done so then the values of the two resistors at the input to the amplifier (the TI doc designates these R1 and R3 - they are R22+R23 and R26+27 on the BAL-BAL board) need to change to maintain overall unity gain.
Can I get people's thoughts on this?
I was reading TI's application note SLOA054D on Fully-Differential Amplifiers. Section 11 regarding terminating the input source was particularly interesting. I haven't seen anyone discussing "double termination" of balanced inputs into this "Wire BAL-BAL" amplifier - perhaps I missed it. The discussion in the TI document including Fig 17 and the example provided (Fig 20) suggest input termination should match the output impedance of the source (in my case, 100 Ohms) with 3 resistors used and, of course, if done so then the values of the two resistors at the input to the amplifier (the TI doc designates these R1 and R3 - they are R22+R23 and R26+27 on the BAL-BAL board) need to change to maintain overall unity gain.
Can I get people's thoughts on this?
That section is about high speed transmission.
That's like 10MHz and above. Probably aimed at digital transmission but can apply to high speed analogue signals just as appropriately.
Double termination in that high speed application means terminating the transmission line at the source end and at the receive end.
In a video application where 75ohms cable is used, the output of the source has an output resistor added so that the cable sees 75ohms looking back into the Source.
At the receive end the cable has a 75ohms load attached so that the cable sees 75ohms looking into the receiver. This is to stop reflections passing back and forth along the cable.
This does NOT apply to normal audio bandwidth cables. They are not feeding into transmission lines.
That's like 10MHz and above. Probably aimed at digital transmission but can apply to high speed analogue signals just as appropriately.
Double termination in that high speed application means terminating the transmission line at the source end and at the receive end.
In a video application where 75ohms cable is used, the output of the source has an output resistor added so that the cable sees 75ohms looking back into the Source.
At the receive end the cable has a 75ohms load attached so that the cable sees 75ohms looking into the receiver. This is to stop reflections passing back and forth along the cable.
This does NOT apply to normal audio bandwidth cables. They are not feeding into transmission lines.
Hello,
Probably a noob question but how do I connect the outputs from a BAL-BAL to a 3-pin XLR on both channel ? Where do I connect gnd on the board ? Or maybe there is no need to connect it ?
I've seen a lot of implementations with a 4-pin XLR but couldn't find much info regarding my issue here.
Cheers
Probably a noob question but how do I connect the outputs from a BAL-BAL to a 3-pin XLR on both channel ? Where do I connect gnd on the board ? Or maybe there is no need to connect it ?
I've seen a lot of implementations with a 4-pin XLR but couldn't find much info regarding my issue here.
Cheers
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You don't connect ground to the loads.
There isn't an earth referenced ground return from the load. So nothing for the two channels balanced outputs to share.
The balanced output is two amplifiers with the load connected between them. Same for the other channel.
I used two three pin XLR, using only two pins in each, because I had them. Eventually I may buy a 4 pin, or two fancy copper 3 pins. Or hard wire to the output chips.
There isn't an earth referenced ground return from the load. So nothing for the two channels balanced outputs to share.
The balanced output is two amplifiers with the load connected between them. Same for the other channel.
I used two three pin XLR, using only two pins in each, because I had them. Eventually I may buy a 4 pin, or two fancy copper 3 pins. Or hard wire to the output chips.
A balanced impedance connection uses two wires for signal and usually has a screen/shield.
The screen/shield is connected to Pin1 at both ends.
Pin1 is connected to Chassis at both ends. AND should not use a long pigtail. These MUST be very short low impedance connection to the Chassis AT the XLR socket.
Neo is asking about the output, not the input
Same would apply at the output. Not sure there's much value in adding a shield on the output wires, but it might be worth it anyhow.
The key there is that Pin 1 should be bonded directly to the chassis at the connector, even on the output.
Regards,
Owen
Seems that to certify for the CE mark in 1997 we had to connect the incoming RCA grounds to chassis only via a capacitor, 0.01uF in that case. Is it different for XLR?
What would be the point in chassis'ing pin 1 if you're only using pins 2 and 3 for (headphone) speakers leads? Especially if they are, like most after market high quality leads, un-screened. Or you used a 4 pin connector? Maybe if you want to make your home built headphone amp compatible with industry standards for dual 3 pin XLR headphone leads?
I only presume that balanced headphone amps use, for speakers leads, pins 2 and 3 for the two hot wires and don't bother with pin 1.
I've just checked a few bits of very old Hi-Fi laying around here and none have pin 1 grounded at the chassis, for input nor speakers leads; input done on the PCB and speaker leads direct back to earth star, though that power amp, for speakers leads, still does use pin 1 for earth and 3 for hot wire, but it's not a balanced output. Perhaps things have moved on in that regard since the '80's and '90's?
What would be the point in chassis'ing pin 1 if you're only using pins 2 and 3 for (headphone) speakers leads? Especially if they are, like most after market high quality leads, un-screened. Or you used a 4 pin connector?
Maybe if you want to make your home built headphone amp compatible with industry standards for dual 3 pin XLR headphone leads?I only presume that balanced headphone amps use, for speakers leads, pins 2 and 3 for the two hot wires and don't bother with pin 1.
I've just checked a few bits of very old Hi-Fi laying around here and none have pin 1 grounded at the chassis, for input nor speakers leads; input done on the PCB and speaker leads direct back to earth star, though that power amp, for speakers leads, still does use pin 1 for earth and 3 for hot wire, but it's not a balanced output. Perhaps things have moved on in that regard since the '80's and '90's?
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Pin1 has been wired many ways and the "professionals" were just as bad as the amateurs in getting Pin1 wrong.
Around about 1995, after decades of seeing it being done wrong, by so many, there was an article telling everyone how to wire Pin1 properly. I think it was by Neil Muncy.
But since then there are still many that get it wrong. Even equipment manufacturers are still wiring Pin1 incorrectly.
The audio standards authority in the USA (AES) has even changed the test so that measurement can prove that Pin1 is wired incorrectly.
There are dozens of articles and AES guidance to show how to do Pin1 correctly.
There is no excuse for any informed builder to wiring Pin1 incorrectly. It would be simple incompetance.
On the face of it, I consider the information to be incorrect, but there may be some operational circumstance where it would be mandatory to add an RF attenuating capacitor at the input RCA.
As far as I know the RF attenuating capacitor is optional.
This capacitor is one I have been recommending for years. And on the speaker cables and on the mains cables. Every cable entry to the enclosure can have an RF attenuating capacitor to the enclosure.
Are any of them mandatory?
Around about 1995, after decades of seeing it being done wrong, by so many, there was an article telling everyone how to wire Pin1 properly. I think it was by Neil Muncy.
But since then there are still many that get it wrong. Even equipment manufacturers are still wiring Pin1 incorrectly.
The audio standards authority in the USA (AES) has even changed the test so that measurement can prove that Pin1 is wired incorrectly.
There are dozens of articles and AES guidance to show how to do Pin1 correctly.
There is no excuse for any informed builder to wiring Pin1 incorrectly. It would be simple incompetance.
We need the context of this.
On the face of it, I consider the information to be incorrect, but there may be some operational circumstance where it would be mandatory to add an RF attenuating capacitor at the input RCA.
As far as I know the RF attenuating capacitor is optional.
This capacitor is one I have been recommending for years. And on the speaker cables and on the mains cables. Every cable entry to the enclosure can have an RF attenuating capacitor to the enclosure.
Are any of them mandatory?
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