Why do DAC manufacturers use the wrong USB A connection? Oppo replacement needed
Jun 8, 2020 at 12:12 AM Thread Starter Post #1 of 8

Isaacc7

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My Oppo portable Dac/amp has died and I need to replace it. I use an iPhone 11 Pro Max with 320 ohm Beyerdynamic DT-880 Pro headphones. Looking around it looks like I would need to use the camera connection kit to connect to the DAC instead of the regular charging cable. Why are manufacturers doing that? The camera connection kit is much less flexible and I think just a little too short to carry The DAC/iphone combo around. Oppo did it right, I used the Regular .5M charging cable.

Are there any portable DACs that use a more standard connector? What is the advantage of using the male USB connector instead of the female one? What are some good models these days? I mostly listen to streaming audio but have a handful of high res tracks and it would be nice to be able to listen to them at their native resolution. Thanks!
 
Jun 8, 2020 at 11:54 AM Post #2 of 8

fastfwd

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I use an iPhone 11 Pro Max with 320 ohm Beyerdynamic DT-880 Pro headphones. Looking around it looks like I would need to use the camera connection kit to connect to the DAC instead of the regular charging cable. Why are manufacturers doing that? The camera connection kit is much less flexible and I think just a little too short to carry The DAC/iphone combo around. Oppo did it right, I used the Regular .5M charging cable.

The short answer is that every DAC manufacturer who uses a male "A" or female "B" connector IS doing it right -- USB is a host/device protocol, and those are the correct connectors for the device side.

In standard USB, devices can't connect directly to each other. The iPhone has a device-side connector, so it requires some intermediate hardware -- the Camera Connection Kit -- to connect to a DAC that also has a device-side connector.

Oppo's DACs have device-side connectors like everyone else's, but they also have a host connector that makes them more convenient for iPhone users. But this costs extra and makes them non-compliant with the intent of the USB spec, so it's not something that a lot of other manufacturers will do.

Note that this is only a problem for Apple phones. Android phones don't need that intermediate hardware because they support USB On-The-Go, which lets one device negotiate with another to act like a host. So an Android phone can attach to a DAC (or flash drive, or camera, or any other device with a device-side connector) with just a cable.
 
Jun 8, 2020 at 1:26 PM Post #3 of 8

Isaacc7

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Ah, so what you’re saying is I didn’t know how good I had it with the Oppo lol. Sigh. Would USB C change the equation? I keep hoping beyond hope that Apple will finally move to USB C for their iPhones...
 
Jun 8, 2020 at 2:33 PM Post #4 of 8

fastfwd

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Ah, so what you’re saying is I didn’t know how good I had it with the Oppo lol.

Yeah, sorry.

Sigh. Would USB C change the equation? I keep hoping beyond hope that Apple will finally move to USB C for their iPhones...
Yes. With luck, everyone will eventually converge on USB4, which uses only USB-C connectors and is compatible with Thunderbolt 3. USB-C ports can be configured as dual-role host/device -- similar to the old-style USB OTG -- so if future iPhones had those ports they could do what Android phones do now.
 
Jun 8, 2020 at 2:47 PM Post #5 of 8

rkw

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The USB standard specifies that a USB-A connector is only allowed (and required) if the device supplies power to connecting devices. In that regard, the Oppo is unique for an amp/DAC because it is also designed as a battery power bank. Fundamentally your issue is not the type of connector but the factors @fastfwd mentioned regarding USB host/device.
Ah, so what you’re saying is I didn’t know how good I had it with the Oppo lol. Sigh. Would USB C change the equation? I keep hoping beyond hope that Apple will finally move to USB C for their iPhones...
USB C should work. Apple already put USB C on the iPad Pro since 2018 and someone can verify whether it works with an OTG cable.
 
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Jun 8, 2020 at 2:49 PM Post #6 of 8

gimmeheadroom

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I thought another connector was dumb but USB-C is kind of amazing. With one cable I can charge my laptop and handle full HD video and network over one USB C cable to the dock. Finally somebody got something right. And I think you can't screw up the orientation when plugging it in but I can't remember.
 
Jun 8, 2020 at 4:12 PM Post #7 of 8

fastfwd

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I thought another connector was dumb but USB-C is kind of amazing. .... Finally somebody got something right. And I think you can't screw up the orientation when plugging it in but I can't remember.

You can't screw it up -- the connector is physically symmetrical and the ports can figure out which way the plug is inserted.

It's not so much that they finally got it right, but that the requirements changed. When USB was first developed 20+ years ago, the existing serial-communication standard was called RS-232. It was used everywhere because it was cheap and easy -- one low-cost chip on each side, and possibly as few as three wires in the cable -- but its specification was very loose, so everyone's implementation was a little different.

As a result, "RS-232 compatible" came to mean only that two RS-232 devices could be connected without starting a fire. To actually communicate from one device to another, everyone had a box of cables, switchboxes, gender-changers, null-modem adapters, and 9- to 25-pin converters for handling the physical connection, and it was just accepted that once you got the two sides wired together, you'd then spend time figuring out baud rate, parity, and flow-control settings for the connection before you could actually use it.

To replace all the existing RS-232 interfaces, USB had to be capable of reaching all the way across the room to devices like printers or modems, and it also had to be cheap enough for a low-cost device like a keyboard or mouse. Those requirements drove the design, so we got a cable with only 4 wires plus shield, a generous 5 meters max cable length, and very low-cost connectors that were physically incapable of being mixed up rather than electrically self-orienting. But the price we paid was a strict host/device distinction (with the host almost always a consumer PC), and low speed across the wire, with only a few standard predefined interface classes.

But now we have Wi-Fi for medium-speed across-the-room communication, and Bluetooth for closer low-speed communication, and silicon costs have dropped significantly, and people are willing to pay $1000 for a phone anyway... So the latest USB standard prioritizes speed and convenience over cost and distance. USB-C requires at least 9 wires in the cable, and the expensive connectors have 24 tiny contacts, and the silicon at each port has to be a lot more sophisticated, and the maximum cable length is only 1 or 2 meters.

But it exactly fits our present requirements: PC-to-phone syncing of gigabytes at a time, very high bitrate uncompressed audio to a nearby DAC and/or from an ADC, high-speed charging, high-speed access to flash drives and other storage devices, etc. -- with the convenience of a cable that can be connected 8 different ways, all of which will just work.
 
Jun 8, 2020 at 10:08 PM Post #8 of 8

Isaacc7

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Huh. Looks like my Oppo isn’t dead, I was just stupid. Grabbed it The other night and it was completely dead Despite having just charged it the other day and not having used it. Turns out I had left it on the entire time I had it disconnected to the charger. Doh! So hopefully it will continue working until the iPhone goes to USB C!
 

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