SDS100/SDS200: SDS100 - Headphone Jack is Wired Out Of Phase - Uniden Support Notified and Temp Fix Made

[KevinC]

One is new firmware, one is not. Two threads in seven years is still not indicative of a problem.

Whether it affects you or not I think the big news is Uniden is actually responding.

 

[Ubbe]

My SDS100E are from 2018 and one audio channel from the earphone jack have full frequency range but the other channel lacks low frequencies, maybe below 250Hz. If I listen to its audio difference between left and right channel, instead of either left or right in relation to ground, there's about half of the audio level but the lowest frequencies are gone. I connected tip of my earphone to the scanners left channel and ground from my earphone to the scanners right channel. If it was a true mono signal I would have heard no sound at all.

The earphone audio are not taken from a mono amplifier and then split up thru two resistors to left and right channels, they are two individual signals that are amplified and have different phase anomalies.

To me it is like one channel are full range audio, like when listening to the audio from a digital system, and the other are run thru a high pass filter to get rid of low frequencies where subtones can be found, like in an analog system, and at the same time the filter processing change the phase of the whole audio signal.

/Ubbe

 

[crippledchicken]

There are plenty of online descriptions (by speaker manufacturers etc.) regarding what it sounds like when stereo speakers are wired out phase. There's also a thread on diyaudio.com called "If headphones are out of phase, can you hear it?"
But these assume a wideband high fidelity stereo audio signal with plenty of bass and treble. There is loss of bass, a "hollow" sound and poor stereo localization.

With the scanner, we are dealing instead with a narrowband mono voice audio signal so it is harder to describe the effect. It sounded hollow and poorly focused to me as soon as I put the headphones on for the first time. But YMMV. Plus I found that the signal is not 100% out of phase in that the line on the scope was (dynamically) not a straight line. I can see where some folks may not be bothered by this.

In any case, Uniden have acknowledged the problem.
They may or may not provde a fix. I suspect there is more likelyhood of a fix if the problem is fixable in the software.
Even if they don't, I'm OK using the adapter cable I made.
If it doesn't bother you, thats OK. If it does, you can make the adapter cable like I did.

diyaudio.com is a very informative forum which I have been a member of for years.

 

[jim2733]

The SDS100 headphone jack left and right channels are indeed out of phase.

Here's the output of the two channels when summed together.

This is not what I would have expected from a company selling their scanner for $699 now.

 

[Ubbe]

Here's the output of the two channels when summed together.

The upper channel have a lot more noise between the audio bursts while the lower have silence and the result from the addition shows almost 180 degree difference between channels resulting in minimal audio and the noise from the upper channel are dominating. Maybe this anomaly also produce too much noise and a tinny sound from the internal speaker.

I have difficulties understanding this from a hardware perspective and it has to be a DSP producing 2 channels with this phase shift and different background noise levels. So hopefully Uniden can do a firmware change to correct this.

/Ubbe

 

[garys]

Or at least pretending to.

Whether it affects you or not I think the big news is Uniden is actually responding.

 

[jim2733]

I just received my new SDS100 and noticed the first time I plugged in a pair of stereo headphones that the headphone jack (which is a stereo 3.5mm TRS jack) has the 2 channels wired out of phase. There's an older thread about this from 2019 but is closed.
The same headphones receive a normal in-phase signal from my BCD160DN.

This is interesting because since 3.5mm stereo headphone jacks use a common ground for both channels, and the SDS100 is really a mono device, the headphone amp chip in there must have separate grounds for each channel. Like a quasi-balanced output.

I have emailed Uniden Customer Support asking them to forward it to their engineering team.
We'll see what they have to say. I have copied the email I sent to them below.

For now, I have constructed an adapter cable which connects the tip of the 3.5mm plug to both the tip and ring of the 3.5mm jack. This routes the output of one channel from the SDS100 to both headphone channels. It is working perfectly and sounds just fine. No straining or overload detected with multiple headphones. Here's a photo of the adapter cable:

View attachment 180620

And here's the email I have sent to Uniden Support:

Hi,

Let me preface this by saying that I’m an audio and broadcast engineer in my professional life.

I just purchased a new SDS100 and it is a fantastic scanner! With a lot of help from YouTube videos and the Radio Reference forums, I had programming setup in Sentinel even before it arrived!

And it is working great so far. Except for one issue…
Today I tried plugging in a stereo headset (tried several to be sure and an external headphone amplifier) and find the 2 channels of the stereo headphone jack on the SDS100 are wired out of phase.

Yes, the shaft of the 1/8” stereo plugs are fully seated in the jack and the shells of the connectors are not being blocked from fully seating by the way the jack is recessed from the top surface of the unit for the rubber flap.

Also, when plugged into my BCD160DN, all of these headphones receive a normal, in phase signal.

There’s an old RR forum thread about this that concluded the same but I’m not sure anyone has notified you guys about this.

In any case, this is really disappointing for such an expensive device.
Might there be a chance this can be fixed in software?
Or is it a physical design or production issue with the actual wiring to the jack or the headphone amp reversed?
If it is physical, I’ll have to build a short phase reversal cord when I want to use headphones with the SDS100. But I really shouldn’t have to 😊

Thank you in advance for routing this to the appropriate engineering team.

Best regards,

--Mark--

I ran the stereo output of the SDS100 into Audacity on my Mac and you can clearly see that the right channel is clearly an inverted image of the left. Your solution on how to wire up stereo headphones to the SDS100 is spot on. If all you got is a passive mono speaker like I do and need to get more volume out of it then wire up your external speaker as a bridged external speaker where the tip wire coming from the SDS100 is connected to the + terminal of your external speaker and the ring wire s connected to the - terminal. You should get about twice the volume output out of your SDS100 now as you did before.

 

[TeeJayZee]

I have constructed an adapter cable which connects the tip of the 3.5mm plug to both the tip and ring of the 3.5mm jack. This routes the output of one channel from the SDS100 to both headphone channels. It is working perfectly and sounds just fine. No straining or overload detected with multiple headphones.

Just wanted to thank you directly for sharing your oscilloscope findings and adapter instructions. I followed your guidance on routing the tip signal to both the tip and ring of a 3.5mm TRS plug and built a short male-to-female adapter using parts I ordered specifically for this test.

Before the mod, with my SDS100 connected to powered stereo speakers, I noticed a strange spatial pull toward one side—thin on the other. It wasn’t a volume issue, but clearly phase-related. In fact, the more I raised the volume, the thinner and more fatiguing the sound became. It reached a point where comprehension was difficult, and extended listening caused noticeable ear strain. After bypassing the ring and feeding only the tip signal to both channels, the sound snapped into place: rich, centered, and full-bodied. Now when I listen to broadcasts, it feels like the speaker is right in front of me—anchored perfectly between both monitors. It’s almost conversational.

Your post helped me validate what I’d suspected all along. I appreciate your clarity and the time you took to share the fix. You didn’t just solve a problem—you gave the community a repeatable solution. Respect.

If Uniden ever acknowledges this design flaw, they should consider bulk-producing these adapters and sending them to every SDS100 owner. It’s a simple fix with a massive impact on audio fidelity—and it’s long overdue.

 

[jim2733]

Thank you for the kind words but MarkyM at the start of this thread should get all of the credit for the design of the adapter you built. I was just able to visualize what he and others were saying about the sound coming out of the TRS headphone jack of the SDS100 using the adapter he described. BTW, I sent a copy of what I posted to Uniden. They say they opened a ticket.

I got into this to see if there's is any way of increasing the volume coming out of a Uniden BC7 passive monaural speaker. Although it comes with a TRS jack only the left channel is wired up to the speaker. I got bits and pieces coming in from Amazon so that I can wire up the BC7 speaker in bridged mode to see if I can get more sound out of it. If the idea works then all I need to do is to replace the two wire cable that came with the BC7 with a standard TRS stereo cable and wire the T and S of the new cable across the posts of the 7 watt speaker. Don't need to do anything with the ground wire. The electrons will know what to do.

 

[Ubbe]

I informed about the increased performance when connecting both channels together a year ago. I have used that connection daily so no ill effects from doing so. I use this kind of cable that give me access to different kinds of configurations, as I use a Motorola speaker without any connector at the end of its cable.

https://www.amazon.com/zdyCGTime-Terminal-Headphone-Adapter-Cable/dp/B07QPL3S7C/

"when I connect left and right together I get noticeable increase in speaker sound level."

SDS100/SDS200: - SDS100 External Speaker/Audio options

A passive speaker is one that does not have it's own, powered,amplifier built in to it. It can be plugged directly into the earphone jack and does not require being connected to a 12 volt power source. Think of it this way, it is no different than having the speaker in the radio. Instead, it...

forums.radioreference.com

/Ubbe

 

[jim2733]

What you have posted Ubbe about the left and right channesl of the headphone jack being out of phase was absolutely right. I sent the same JPG that I posted above off to Uniden. They acknowledged what I sent to them and opened a ticket. I have not heard back from them yet.

I got into this to see if I could get more sound out of my SDS100 when wired up to Uniden's BC07 passive monaural speaker. I ran across a graphic on Google suggesting that I could get more sound out of it if I wired it up in bridged mode. I tried that tonight and it seems to have worked.

Ubbe, that phase shift cable you were talking about last year that you could plug a pair of stereo headphones into, could I get there by rewiring a TRS ground loop isolator by crossing the wires to one of the inductors connected to one of the jacks?

EE is not my thing. I'm more into chemistry. BS CM '72 RHIT.

 

[hexagon_keyhole]

If you haven't heard, there is a firmware update for the SDS100: 1.23.20 Main (10/17/2025) and 1.03.15 Sub (10/17/2025).

This new update seems to fix this issue:
• A new menu for switching headphone audio output phase has been added. (SDS100 only)

I just updated my SDS100, and there is a new menu option under Menu > Settings > Headphone L/R output. There are now two options for "In Phase" and "Invert Phase," with "Invert Phase" seeming to be the default option.

 

[TeeJayZee]

Hey, good job there Uniden! Glad this was figured out, did hate having to always use a modded pigtail audio cable for this.

 

[Ubbe]

I guess that the audio channel with the reduced frequency range are the one that needs to be used for the internal speaker as the bass frequencies would otherwise overload it. So they cannot fix that but they added a phase shift for that channel. I have the E model so cannot test how an external speaker sounds with either left or right channel connected to it and when both channels are connected together to drive one single speaker and if switching the phase when left channel goes to one speaker terminal and right channel to the other, without using ground. It's pretty loud using the original phase shift so don't know if it gets any different when activating phase shift when using a low impedance speaker.

/Ubbe