XLR to RCA to XLR

Assuming that the KUBE is connected between the processor and the amp, and if it has a 3-prong AC power plug, chances are that the noise is being caused by a ground loop between the KUBE and one or both of the other two components.

To verify that, temporarily isolate the AC safety ground pin on the KUBE's power plug by connecting it via a 3-prong to 2-prong adapter (a "cheater" plug), with the adapter's ground lug or ground wire left unconnected.

That will break any ground loops between the KUBE and the components it is connected to. If that eliminates the noise, remove the adapter from the KUBE's plug and use it on the plugs of each of the other two components, one at a time. That will enable you to determine which interconnection is causing the problematic ground loop (although the answer might be both).

Post back your results, and also see the following references:

http://www.jensen-transformers.com/an/an003.pdf.

http://www.jensen-transformers.com/an/an004.pdf.

Also, if you are connecting the KUBE to the power amp by means of an unbalanced RCA cable followed by an RCA-female to XLR-male adapter at the amp's input, you may be able to improve the noise by instead using an RCA-male to XLR-male adapter at the KUBE's output followed by a balanced XLR cable. That would be electrically equivalent to the approach shown in Figure 2.1 of the first reference. Although as indicated in the reference that approach is less ideal than a well implemented transformer-based approach.

Regards,
-- Al

01-21-13: Rdeckard
Will these work if mixing consumer audio (-10dBV) and pro audio (+4dBu) gear? In other words, do they provide any level-matching?

The PI models will function in that situation, but they will only provide a very slight amount of attenuation (corresponding to their "insertion loss," which under the test conditions shown in the datasheet is 1.6 db typical, 2.0 db max).

Assuming that what you want to do is to reduce the signal level, what you would probably want is their model PC2-XR, which provides about 14 db of attenuation. A phone call to them would be a good idea, though, to confirm its suitability to your specific application.

Also, at a considerably higher price point Steve McCormack of SMc Audio offers a transformer-based product called Flex-Connect, which provides 12 db of attenuation, together with various other features. I have no specific knowledge of it, but I know that his VRE-1 preamplifier, which utilizes coupling transformers, has an exceptionally good reputation.

Regards,
-- Al

Jedinite, thanks very much. Regarding ferrites, they will not help a hum problem, as they are only effective at radio frequencies (and higher).

05-29-12: Dbphd
I used a female XLR to male RCA adapter into the KUBE from the XLR line out of a Cary 11a and a male RCA to male XLR adapter to the line into a Proceed Amp 3.

Most adapters of either type short the signal on XLR pin 3 to ground (pin 1). That is what should happen when adapting to an XLR input. However, IMO it makes absolutely no sense for XLR-female adapters, that would be used on outputs, to be designed that way. As I understand it, Cardas adapters are one of the few types that (correctly) do not short pin 3 to pin 1 on XLR female adapters.

This is just a speculative guess, for which I can't formulate a precise explanation, but if you are not using Cardas adapters I'm wondering if the noise may be somehow resulting from an inability by the Cary 11a to handle having its output on pin 3 shorted to ground. Many components can handle that ok, but some cannot, this being one example. I note that you referred to "a sizzle, a kind of HF hum," while the poster in that thread referred to "buzzing," those being descriptions that are not all that dissimilar. And I suspect that the fact that the short to ground is at the far end of the cable, at the input to the KUBE, may not be helping matters.

Does the noise still occur if the Cary is turned off or disconnected? Is it sensitive to the volume control setting?

Regards,
-- Al

Kudos to Tvad!!

DB, just out of curiosity do you know if the adapter you were using at the INPUT to the KUBE (the XLR-female to RCA-male adapter) is one of those that shorts XLR pin 3 to XLR pin 1?

If you happen to have a multimeter that can be easily determined, of course.

Regards,
-- Al

Rdeckard, see the part number table at the bottom of this page. Information shown in the PI-2XX datasheet is applicable to the versions that provide either RCA or XLR inputs and/or outputs, as well as either 1 or 2 channels. The various configurations are differentiated in accordance with the part number definitions shown in the table.

Regards,
-- Al

Hi Jedinite,

Regarding the Rane BB44X, which I see sells at B&H for $279, based on a quick Google search I didn't find much that would shed light on the sound quality it would provide in a high-end home audio system.

Looking at the datasheet, though, a concern would be that while a statement is made that the unit provides "wide bandwidth," the only spec that is provided is that frequency response is 20 Hz to 20 kHz +/- 2 db. The 2 db tolerance is very uncomfortable, IMO, and the fact that no margin is indicated relative to the audible frequency range is as well. Without a margin of 5 times or more (i.e. 4 Hz to 100 kHz), and preferably even approaching a factor of 10, I would not feel comfortable that audibly significant phase shifts wouldn't occur within the 20 Hz to 20 kHz range.

In contrast, Steve McCormack's unit is specified as having a 3 db bandwidth of 0.5 Hz to 150 kHz, and the frequency response graph shown in the datasheet for the Jensen PC2XR shows it as being in a similar ballpark.

Also, some cautions that would apply if any of these level converters were used to step UP "consumer level" to "pro level":

First, using one of these devices in that direction will increase the impedance seen "looking back" from the destination device toward the signal source by a factor of about 16 (corresponding to the square of the nominally 4:1 turns ratio), and will decrease the load impedance seen by the signal source by that same factor of 16. That will result in impedance incompatibilities in many cases.

Second, at 20 Hz the unbalanced input of the Rane device will reach its overload point at only 1.68 volts, with the Jensen PC2XR being only slightly better in that respect. So, as might be expected, one would not want to use one of these transformers to step UP the outputs of unbalanced signal sources which provide the 2 volt kinds of levels that are typical these days, especially with digital sources. And chances are that other components in the signal path would overload as well, if that were done.

These two cautions do NOT apply to 1:1 transformers, such as the Jensen PI models, and do NOT apply to the 4:1 level converter devices when used as step-DOWN transformers, i.e., going FROM "pro levels" TO "consumer levels."

Regards,
-- Al

01-23-13: Rdeckard
What's confusing is, it seems balanced doesn't always mean "pro" or +4 and unbalanced doesn't always mean "consumer" or -10. What does most high-end balanced home audio (not pro) gear operate at, +4 or -10?

The reference to unbalanced signal levels on consumer equipment being around -10 dbV lost whatever meaningfulness it may have once had when the CD medium was introduced, which was standardized with a full scale (maximum) level of 2 volts, for unbalanced outputs. 2 volts is +6 dbV, or +8.2 dbu. Some digitally based equipment will exceed even those numbers significantly, while phono stage outputs will usually be considerably less.

Each situation needs to be analyzed individually, although it is more common these days to have too much signal and too much gain, rather than too little, regardless of whether the connections are balanced or unbalanced.

Grant (Tvad), thanks for your always knowledgeable inputs.

Regards,
-- Al

Rdeckard, I took a look at the manual for the Kube 200, and I see that its level control provides a maximum boost of 5 db for its variable output, relative to the level of the fixed output. Your findings seem consistent with that.

The approach you are considering would work, except that it may be that a PI-2RX should be used between the Kube and the power amp, rather a PI-2XR connected "backwards".

HOWEVER, in the light of Grant's (Tvad's) comment above that ...

Jensen makes 1:1, 1:2, 1:4, 2:1, 4:1 transformers, and I suspect any of these could be built into their XLR>RCA or RCA>XLR converter boxes at a customer's request.

... a call to Jensen would seem to be in order, to explore additional possibilities.

Those possibilities would include stepping up the signal level by 1:2 (6 db) between the Kube and the power amp; or stepping down the mid/hi frequencies by inserting into the XLR connection between preamp and power amp a PI-2XX (XLR ins and outs) specially configured with a 2:1 stepdown transformer (with no transformers being used in the low frequency part of the signal path, unless one is needed to eliminate groundloop hum).

Looking at all of the numbers that are involved I don't see anything that would necessarily rule out any of those alternatives. But my instinct, assuming that you are not presently using your volume control near the upper end of its range, would be that it is generally better to step down than to step up, given the cautions I expressed yesterday in my post about the Rane unit. And also given the very high degree of transparency Tvad and others have reported the Jensen transformers as providing.

Hope that helps. Regards,
-- Al