Balanced vs RCA between amp/preamp

Use caution if driving an unbalanced amplifier. Best results will probably result from using Pin 3 & Gnd ONLY.

Hi Ian,

Not sure where you are quoting this from, or if you are quoting it, but to be clear I assume this statement is intended to apply to the unusual situation in which XLR cables are used to connect the balanced outputs of a preamp to an amp which receives the signals provided to its XLR inputs in a single-ended manner, and would short one of those signals to ground if the signals on pins 2 and 3 were both routed to the amp by the cable. In most cases, of course, at least when it comes to consumer-oriented gear, unbalanced amplifier inputs would be driven by the preamp’s unbalanced outputs via RCA cables, and the statement would not apply.

And in most cases involving consumer-oriented amplifiers which provide XLR inputs but are not "fully balanced" I would nevertheless expect signals provided to their XLR inputs to be received differentially, not single-ended. As is the case with the OP’s amp.

In any event, thanks for providing the additional insight in your post.

Regards,
-- Al

As promised, I have downloaded and examined schematics for the OP’s preamp and amp, which as I had mentioned in my previous post can be obtained at hifiengine.com if one is registered there.

The amp is not fully balanced. However, while the circuit configurations used to receive balanced and unbalanced inputs are of course somewhat different, both inputs are processed through circuitry described as follows:

HDAM SA3

Marantz developed its own discrete circuit boards to replace standard IC's. These HDAM's consists of discrete surface mount components with short mirror image L/R signal paths. Those devices are doing exactly the same thing as the Op-Amps, but outperform the regular IC Op-amps dramatically in terms of the Slew Rate and reduced noise level, resulting in a much more dynamic, accurate and detailed sound. Over the years Marantz developed different types of the HDAM to improve quality and to fit to the special requirements of a product category like CD or amplifier.

Two HDAM SA3's are in the path through which each balanced input is processed; one of those two is in the path through which each unbalanced input is processed.

The preamp is also not fully balanced. However, a good deal of the circuitry which precedes its balanced outputs is symmetrical and is therefore balanced, although not differentially (i.e., it does not utilize differential stages). That circuitry also utilizes the HDAM SA3, followed by a number of stages utilizing discrete transistors.

Given all of that, my guess in this specific case is that it is more likely than not that a balanced interconnection will be preferable to an unbalanced one.

Luisma31 8-4-2019

Reading the initial post again I missed something, the input source is single ended, this is a question for the others answering in this thread as I'm not sure of the answer. When the source is single ended shouldn't be the output single ended as well even when using the XLR output?

While I suppose there may be a few exceptions, usually a preamp which provides balanced outputs when it is provided with balanced inputs will also provide balanced outputs when it is provided with unbalanced inputs. And examination of the schematic for the OP’s preamp confirms that is the case here.

Best regards,

--Al

 

Thanks for your input, Peter (Pbnaudio). Yes, depending on the specific designs what could be connected first and disconnected last when XLR cables are connected and disconnected may be either chassis ground or circuit ground. As you are doing in your designs and as explained in this Rane application note, connection of pin 1 to chassis ground in both components is proper practice (although unfortunately far from universal practice), with connection of chassis to the shell being optional.

On another note, regarding whether or not the OP’s specific components are fully balanced and whether or not they use inexpensive op amps to generate or receive one or both signals in the balanced signal pairs, I see that service manuals for these components, presumably including schematics, can be downloaded at hifiengine.com if one is registered there. I’ll try to take a look at them tomorrow, as that site imposes a limit of three downloads per day and I’ve already reached that limit today.

Best regards,
-- Al

Engineears 8-2-2019

Horse puckey! I just got up, walked over to my handmade true-balanced end-to-end differential headphone amp, disconnected my Mogami XLR interconnect from my R-2r resistor ladder DAC and measured the pins on its standard Neutrik-branded male connector. ShOcKeR! All pins are the same length.

So I thought, well there’s *no*way* anyone would mansplain so authoritatively if they weren’t actually knowledgeable. Better give them the benefit of the doubt and find another cable with a non-Neutrik XLR connector on it. It took some digging, but I eventually found another cable with Amphenol XLR connectors. Nope. All the same length....

... Today, unless you can link to a whitepaper or standards doc that specifies a longer ground pin, I say we can safely assume the pins are the same length.

@engineears

Apparently you didn’t read my post on this subject very carefully. I clearly said that the pin lengths on the male connectors of my XLR cables appear to be the same for all of the pins. It is the female connector for which I described a difference, which when mated with a male connector having equal length pins would result in the ground connection being made first, upon insertion, and removed last, upon removal.

Regards,
-- Al

Ricevs 8-1-2019
All balanced cables sound different from each other and that includes on Atmasphere gear.

Ric, I don’t doubt your experience. But see Ralph’s post dated 3-22-2013 near the beginning of the following thread for what I consider to be compelling proof of his contention regarding immunity to differences between balanced cables, **if** the components being connected meet the criteria he states in that post (which are not met by most high end components, as he indicates). Also see one of my follow-up questions later in that thread, and Ralph’s response, which it seems to me might account for your findings. The question I am referring to is in the last paragraph of my first post dated 3-27-2013, beginning with "Also, to eliminate interconnect cable differences is it necessary ..."

https://forum.audiogon.com/discussions/what-tube-pre-amp-match-up-with-a-solid-state-amp

Regards,
-- Al

@atmasphere

Ralph, I agree with your comments 200% (or I would if >100% were theoretically possible), except that like Millercarbon my understanding has been that XLR connectors make the ground connection prior to the making the signal connections, upon insertion, and break the ground connection after breaking the signal connections, upon removal.

And upon close examination of some XLR cables I have, which are terminated with Neutrik connectors, it does appear that on the female end the metal contact within pin 1 extends slightly closer to the front surface of the connector than the contacts within the signal pins. And likewise for female (input) connectors I looked at on the rear panel of a component. And although the pins on the male end all appear to be the same length as far as I can tell, it seems to me that the make & break sequences I described would occur regardless of which end of the cable is inserted or removed, as a result of the configuration of the female connectors.

Best regards,
-- Al