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Introducing the Khadas Balanced RCA

Gouwa

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A 3-pin RCA jack:

1601116245410.png


Why balanced RCA?

Pictured below, you can see the huge size differences between the balanced jacks and single-end jacks. Balanced audio usually comes with a compromise; the XLR jacks and plugs are more than double the size of regular single-end equipment:

1601116295862.png


Some audio enthusiasts would mention that there exists the diminutive “3.5 Pro” and “Mini XLR-5” jacks. However, we did not favour those solutions because they are uncommon and unpopular. The “3.5 Pro” jack also has crosstalk issues. Within the Hi-Fi audio industry, both RCA and XLR-3 jacks continue to be the most popular and widely used standards.

Therefore Khadas believed that we must design our Tone2 DAC with the end-user in mind, and building-in small but unpopular audio jacks just wouldn’t do. So we decided to continue on with the popular RCA standard that we would update to incorporate balanced audio.

Differences between Single-End & Balanced-Audio:

1601116341571.png


How did we design it?

After consulting with up to seven different suppliers and manufacturers, we finally found one who was up to the challenge of both designing and manufacturing a new kind of RCA jack and plug. Depicted below is our balanced RCA jack and plug design. The structure of each signal line is shown in yellow, blue and pink:

1601116360381.png


Our patented “balanced-RCA design” is also compatible with standard RCA cables, so you won’t have to buy a special RCA cable just to use the Tone2 DAC; it is backwards-compatible with existing RCA cables and will function in single-end mode.

The “protective-patent” covers both the balanced RCA jack and plug, and will ensure that our design remains free and open source for the community. We did this to prevent predatory entities from co-opting and patenting this new design to corner the market.

If you are curious about the technical details, such as how we solved the crosstalk issue, you may refer to the original patent document.

3rd Party Usage:
  • RCA connector vendors, feel free to use our patents to design new balanced-RCA jacks. However, please register with Khadas via ‘[email protected]’. We want to ensure that all balanced-RCA jacks are made with good design and user experience. Note: you must follow the “two holes” design.
  • For DAC / amp vendors, same as above, however you need to “label” your product as incorporating ‘Khadas Balanced-RCA’.
  • In addition, we would be grateful if all vendors mentioned above would add a link to khadas.com/balanced-rca in their relevant product descriptions.

Applications:

A smaller balanced-RCA jack enabled us to design a thinner and lighter Tone2 DAC. As you can see, it is 4.4mm thinner than a prototype aluminum case designed for Tone1, and at least 8.3mm thinner than an XLR-3 jack:

1601116405500.png


This also enables Tone2 to be used in more situations, such as with smartphones:

1601116440357.png


We have also designed a “Balanced-RCA Plug to XLR-3” converter cable, so you can use your Tone2 DAC with popular industry-standard XLR-3 pre-amplifiers, amplifiers and speakers:

1601116552212.png


Links & References:
  • Further information and updates: https://khadas.com/balanced-rca
  • Pre-Order: Khadas Balanced-RCA Jack (RJ-B01)
  • Pre-Order: Khadas Balanced-RCA Plug (RP-B01)

 

JohnYang1997

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Brilliant, especially the compatibility with SE RCA jacks.
Yeah that's the main advantage over 6.35mm TRS and 4.4mm. But for many designs the HOT in balanced output is independent to the SE signal. So then I think it's not really that attractive.
 

gvl

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Yeah that's the main advantage over 6.35mm TRS and 4.4mm. But for many designs the HOT in balanced output is independent to the SE signal. So then I think it's not really that attractive.

I would call it a reasonable compromise for space-constrained applications.
 
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Berwhale

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Is it possible that the momentary shorting of the hot and cold lines during plug insertion will cause an issue?

*edit* On closer inspection, it appears that the cold ring has a larger diameter than the hot tip, maybe this avoids the issue?
 

gvl

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So one of these could be used for SE stereo. Imagine the real estate that could free up on AVR's.

I was thinking along the same lines, this is probably a good solution as an input jack for amps that feature both balanced and SE inputs as there is really no need for 2 sets of connectors as only one can only be used at a time.
 

TimW

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Many of the 1/4" TRS jacks on my pro equipment can be single ended or balanced. This new RCA connector probably requires less internal depth though. Kinda cool.
 
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Gouwa

Gouwa

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I've seen it in Guangzhou Hifi show. But is it any better than either 6.35mm TRS solution or 4.4mm solution?
Both 6.35 or 4.4 are kind of phone connectors main for headphones, and the Balanced RCA & XLR-3 are designed for LINE OUT with Pre-amp/Amp or active speakers as the next stage.

Good day!
 

andymok

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It’d be even more attractive if can incorporate a locking/latching mechanism, which I reckon is the biggest drawback of the original design making unreliable connection for installation
 

JohnYang1997

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Both 6.35 or 4.4 are kind of phone connectors main for headphones, and the Balanced RCA & XLR-3 are designed for LINE OUT with Pre-amp/Amp or active speakers as the next stage.

Good day!
6.35mm TRS have been used in studio equipments for very long time. And 4.4mm is starting to get more use, the ifi zen dac combo uses 4.4mm for bal out. In size constraint applications, there's little merit for the balanced rca. 4.4mm to XLR cable is certainly more easily to obtain than balanced rca cable isn't it?
 
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Gouwa

Gouwa

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It’d be even more attractive if can incorporate a locking/latching mechanism, which I reckon is the biggest drawback of the original design making unreliable connection for installation

Yep, that’s great idea!

And actually if you check the Balanced RCA Jack, you can find two holes on top & bottom sides, and we designed these two holes for:
1) UI: Distinguish from the Standard SE RCA in appearance
2) Lock: Potential lock with two bump points the Balanced RCA Plug.

But our team also with a worry that the two bump points on RCA Plug will cause a some scratches on the RCA Plug after long term usage.

We are still working on the RCA Plug mold design and haven't confirmed the final solution at this time.

Anyway, thanks for your good suggestion!

And, we trust in deep that a small step can make the audio world difference.

Have fun!

1601178935193.png
 

restorer-john

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Interesting, but really just a solution looking for a problem. If you want RCAs for balanced, why not just put two on the device, one for +, one for - ? Make your twin RCA to XLR cable and call it done. No need to make a socket and plug nobody asked for.

The balanced RCA connector still has the same issue with the shield/gnd being connected last.

Adapt an already existing triaxial BNC and all the problems are solved. Earth connected first. Locking connector that can rotate. Very strong and difficult to damage. Proven over decades as ultra reliable. Low cost.
1601183146747.png


And when you want SE RCA, use these 50c adaptors:
1601183411094.png
 

JohnYang1997

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Interesting, but really just a solution looking for a problem. If you want RCAs for balanced, why not just put two on the device, one for +, one for - ? Make your twin RCA to XLR cable and call it done. No need to make a socket and plug nobody asked for.

The balanced RCA connector still has the same issue with the shield/gnd being connected last.

Adapt an already existing triaxial BNC and all the problems are solved. Earth connected first. Locking connector that can rotate. Very strong and difficult to damage. Proven over decades as ultra reliable. Low cost.
View attachment 84997
First solution is not very good because of the room it takes. Thus making it pretty much useless comparing to TRS and XLR even.
BNC triaxial tho, it's doable but it's incompatible with the current triaxial convention. If the middle connector is V- then the capacitance between the two becomes an issue where originally the middle connector should be a signal shield. Let alone none audio equipment has triaxial connectors to begin with. RCA on the other hand is still the most supported line signal connector. Compatibility is one of the key points here.
 

restorer-john

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First solution is not very good because of the room it takes. Thus making it pretty much useless comparing to TRS and XLR even.

Two horizontal or vertical RCAs are still smaller than a single XLR socket and you don't have the depth of a 1/4" socket to worry about.

I just don't get this miniature HiFi obsession. We've got stuff so small and light the weight of the connecting cables can pull it off the bench. I mean look at the concept rendering of this Khadas thing above. It's a joke and looks like a busted hand controller from a 1980s TV game, not a piece of serious HiFi.

At least when the Japanese made miniature HiFi, they did it properly. Why not draw inspiration from those kings of miniaturization, form and function? And to your credit, Topping has made some serious improvements to their aesthetic.
 

JohnYang1997

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Two horizontal or vertical RCAs are still smaller than a single XLR socket and you don't have the depth of a 1/4" socket to worry about.

I just don't get this miniature HiFi obsession. We've got stuff so small and light the weight of the connecting cables can pull it off the bench. I mean look at the concept rendering of this Khadas thing above. It's a joke and looks like a busted hand controller from a 1980s TV game, not a piece of serious HiFi.

At least when the Japanese made miniature HiFi, they did it properly. Why not draw inspiration from those kings of miniaturization, form and function? And to your credit, Topping has made some serious improvements to their aesthetic.
The depth is a good point. It is barely making it for the current developing A30pro. Now IMO it's another win for the balanced RCA.
 
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