DIY balanced interconnects

Oldears, I don't think I've seen any cable wherein the barrel of the XLR was tied to anything. I would ignore that connection. The only ground you need to be concerned about is pin 1, which is always the shield at **both** ends of the cable.

Tvad, its not really a VHS/Beta thing- the point is that if you want to get off the cable merry go round, using the low impedance standard is the ticket. Otherwise feel free to pay whatever you have to to get an unterminated cable to do the same thing :) the way I see it, you either pay for the technology to make it happen, or you pay for the cable to make it happen. Seems to me using the technology to advantage is cheaper.

Tvad, its not really a VHS/Beta thing- the point is that
if you want to get off the cable merry go round, using the low impedance
standard is the ticket.
Atmasphere (Threads | Answers)

Thus far, unless I have missed something in the discussion, Atma-Sphere is
the only high end audio company that has been identified as adhering to the
600 ohm standard. Rowland, Modwright, and Wadia have been eliminated as
having non-standard output impedances.

So, unless there are other as yet unidentified companies the adhere to the
600 ohm standard, to get off the cable merry-go-round one has only one
option: Atma-Sphere. Additionally, Atma-Sphere doesn't produce source
components, so strict adherence to the 600 ohm standard appears to be an
impossibility.

In this scenario, the Beta/VHS analogy seems to be appropriate.

I'm honestly not trying to be argumentative here.

What am I missing?

The components I want to connect are a BAT VK30 preamp,Pass Labs aleph amp, Cary CD, and theta gen V DAC. I feel pretty confident they all meet fully balanced criteria and probably 600 ohms (if not let me know please).
Oldears (Answers)

BAT VK30 output impedance = 300 ohms.

Cary 303/200 output impedance = 99 ohms unbalanced and 198 ohms balanced. You don't mention which Cary CD player you are using.

I couldn't find any info on the Theta Gen V DAC, but the Theta Gen VIII DAC has output impedance specs of 11.5 ohms for the unbalanced RCA jacks, 23 ohms for the balanced XLRs.

I'm a little curious. Let's go with Ralph's theory for a bit. If I own an MP-3 preamp and M-60 amps, then logically, the cable between these should not be an issue with regard to cable artifacts since the MP-3 conforms to the 600 ohm standard. However, let's assume I put my DAC into the equation which in balanced mode via it's XLR outputs has an output impedance of 100 ohms. In this case cable artifacts could be an issue running from the DAC to MP-3. Do I have this correct?

From my perspective I thought the key aspect of a balanced design was that it is differential with the circuit balanced throughout. BAT and Rowland meet this criteria, but not the 600 ohm standard. If I read Kirkus' post correctly, the 600 ohm standard should not be relevant.

I'm more confused than ever.

Clio09, there are two common meanings of the term "balanced" in high-end audio these days.

First, there's "balanced" as it applies to interconnects, where the idea is that there are two signal-carrying conductors, each with equal impedance (though not necessarily voltage) to ground, the signal being defined as the voltage between the two conductors. Both the driving source and the receiving equipment are responsible for maintaining this impedance balance, and the receiving stage is responsible for separating the signal voltage that appears between the two conductors (the "differential mode" voltage) from any noise voltage that happens to develop equally between both conductors and ground (the "common mode" voltage). The performance of the receiving equipment in performing this task is usually expressed as "common-mode rejection ratio", which is the difference in sensitivity between the same voltage, applied common-mode vs. differential-mode.

"Balanced" or "differential" as it applies to circuitry inside the equipment usually refers to the fact that there are actually two equal (voltage and/or impedance) and opposite-polarity signal paths inside. It is possible to have an unbalanced input feeding a differential circuit, or vice-versa . . . and ditto on the output side.

It does seem that a huge percentage of high-end audio manufacturers are unaware of the distinction between these points, as it's common to build a "balanced" preamplifier by simply building two non-differntial circuits, and connecting one each to pins 2 and 3 of the input and output XLRs. Equipment designed this basically takes all the incoming noise, sometimes amplifying it, adding some noise of its own, and "passes the buck" to the next piece of equipment in hopes that it may have some common-mode rejection capability. Frequently, that next piece of equipment ends up being the speaker.

From past threads, I think that Atmasphere and I are both in agreement about the need for equipment to have good common-mode rejection. We're also in agreement about the need for balanced line output stages to have a low output impedance, and excellent performance into low-impedance loads. Where we differ is in the specifics of how to design a balanced input stage.

My main problem with the 600 ohm terminating resistor is that it places a very high current demands on the preceeding electronics, which in all likelihood will have degraded performance into a 600 ohm load. It is relatively ineffective at reducing the effects of cable reactance - this is determined mainly by the source impedance.

The 600 ohm resistor may show a slight improvement on the common-mode rejection ratio, but the same or better results can be obtained by raising the common-mode impedance instead of lowering the differential-mode impedance . . . without affecting the performance of the preceeding equipment. And the only argument left is that of transmission-line effects . . . which is irrelevant for typical (<100 feet) lengths in a voltage-transfer system.