BCD536HP: Headphone jack has distorted audio

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dhoffman83

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Yet another "my BCD536HP has audio issues" thread, but I don't believe this is related to other issues...

Scanner was purchased new back in July and everything was fine for about 2 months, until one day things went horribly wrong. Nothing was changed on that day or for at least a week prior. I have a sample of the bad audio and a diagram of the entire setup available at these URLs:

http://hoff.mn/scanner/files/BCD536HP-audio-problems.mp3
http://hoff.mn/scanner/files/diagram.png

Equipment list:

DPD OmniX
Alpha delta GBWM/ATT3G50N
PAR notch filters (152.5/162.5)
4-port Keyspan RS-232 interface
USBpre2 audio interface
Mac mini (latest generation)
APC SU1000

Audio interface was connected to the headphone jack using a 3.5mm mono to RCA adapter. I tried connecting only tip, but that just made the problem worse (and increased the noise floor by about 60dB). I also restarted the scanner, restarted the computer, swapped out the USBpre2, and connected audio to internal sound interface instead, all with no improvement.

I later decided to give the external speaker jack a try, connecting 3.5mm tip to RCA tip and chassis ground to RCA shield. Much better - the distortion is gone, but the noise floor is 30-40dB higher than the headphone jack (up to -72dB). Volume level with the headphone jack was at max, down to 18 for the ext speaker jack (both set to peak around -10dBV, which is RCA line level). Also, it seems the problem isn't present with the internal speaker or when headphones are connected to the headphone jack.

Some other observations...

-Headphone sleeve is bonded to the chassis only when squelch is closed
-With squelch open, headphone sleeve has the inverse signal of the tip present on it, about 12-14dB lower (connecting the RCA cable to left channel results in the right channel having the inverse signal, which didn't happen originally)

You can listen to my feed on RR to hear how the external speaker output sounds, for a comparison.

Any thoughts? I'm leaning towards component failure within the scanner at this point.
 

Ensnared

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Stereo

Yet another "my BCD536HP has audio issues" thread, but I don't believe this is related to other issues...

Scanner was purchased new back in July and everything was fine for about 2 months, until one day things went horribly wrong. Nothing was changed on that day or for at least a week prior. I have a sample of the bad audio and a diagram of the entire setup available at these URLs:

http://hoff.mn/scanner/files/BCD536HP-audio-problems.mp3
http://hoff.mn/scanner/files/diagram.png

Equipment list:

DPD OmniX
Alpha delta GBWM/ATT3G50N
PAR notch filters (152.5/162.5)
4-port Keyspan RS-232 interface
USBpre2 audio interface
Mac mini (latest generation)
APC SU1000

Audio interface was connected to the headphone jack using a 3.5mm mono to RCA adapter. I tried connecting only tip, but that just made the problem worse (and increased the noise floor by about 60dB). I also restarted the scanner, restarted the computer, swapped out the USBpre2, and connected audio to internal sound interface instead, all with no improvement.

I later decided to give the external speaker jack a try, connecting 3.5mm tip to RCA tip and chassis ground to RCA shield. Much better - the distortion is gone, but the noise floor is 30-40dB higher than the headphone jack (up to -72dB). Volume level with the headphone jack was at max, down to 18 for the ext speaker jack (both set to peak around -10dBV, which is RCA line level). Also, it seems the problem isn't present with the internal speaker or when headphones are connected to the headphone jack.

Some other observations...

-Headphone sleeve is bonded to the chassis only when squelch is closed
-With squelch open, headphone sleeve has the inverse signal of the tip present on it, about 12-14dB lower (connecting the RCA cable to left channel results in the right channel having the inverse signal, which didn't happen originally)

You can listen to my feed on RR to hear how the external speaker output sounds, for a comparison.

Any thoughts? I'm leaning towards component failure within the scanner at this point.
I experienced audio problems with my 436 until I learned that it was a stereo setup. I used a mono-stereo 3.5 mm adapter along with the Uniden stereo external speaker. The Uniden Speaker, 23A works very well with my unit.
 

fxdscon

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A mono plug inserted into the stereo headphone jack will short out 1/2 of the audio output.

.
 

dhoffman83

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Has the headphone jack been confirmed to be stereo by Uniden? The only reference I can find is on page 10 (or 2, if you go by the footer) of the manual:

Earphone Warning

You can use an optional 32Ω stereo headset or earphone with your scanner. Use of an incorrect
earphone or headset might be potentially hazardous to your hearing. The output of the phone jack is monaural, but you will hear it in both headphones of a stereo headset.
That's not at all clear whether it's tip and sleeve or tip, ring, and sleeve.
 

dhoffman83

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That still doesn't seem to clearly state this model (or any other) has a stereo jack... only that Uniden's speakers have stereo plugs so they don't short stereo jacks.

If the jack is stereo, that would explain the inverted signal I'm seeing on the opposite channel, though. It doesn't explain why everything was working fine for 2 months, and then just wasn't. It also doesn't explain why the inverted signal wasn't there to begin with. Maybe initially defective, then decided one day it wanted to be a 2-channel output...
 

jonwienke

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Yes, UPMan (the Uniden factory rep who posts here) has confirmed that all newer Uniden scanners have stereo headphone jacks. It's pretty easy to check for yourself--plug in a set of stereo headphones, and note that you hear sound in both ears.
 

ko6jw_2

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Uniden scanners have had "stereo" headphone jacks for a long time. My 396T has one. Of course, it's not stereo, but I guess they figure most consumer headphones are stereo. Obviously, the tip and ring carry the same signal, but a mono plug will short the ring to ground. When connecting my scanner to a computer I always use a stereo patch cord.

As to why your radio worked and then stopped working, I don't have an answer.
 

dhoffman83

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Thanks all for pointing me in the right direction. Perhaps UPMan can make sure future documentation always specifies what type of connector is used, so there is zero confusion (hint hint). RR's wiki needs lots of updating too, because it references mono (TS) headphone jacks as the norm all over (which, when combined with the lack of proper documentation, is the reason I ended up in this situation).

Using a 3.5mm TRS -> 2xRCA adapter fixed the distortion. Overall audio quality is still a lot worse than it originally was - lots of hiss, continuously. It's actually better if I only connect tip and no sleeve... or use a single side of the BTL output with chassis ground. Maybe it's time to order an audio isolation transformer.
 

fxdscon

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Overall audio quality is still a lot worse than it originally was - lots of hiss, continuously.
Perhaps the mono plug - shorting half of the audio amp - eventually caused some damage to the audio amp circuit after a period of time ??

.
 

dhoffman83

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Perhaps the mono plug - shorting half of the audio amp - eventually caused some damage to the audio amp circuit after a period of time ??
I was hoping nobody was going to suggest what I was already thinking. That would also explain why everything was fine for 2 months, then wasn't suddenly.
 

jonwienke

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Thanks all for pointing me in the right direction. Perhaps UPMan can make sure future documentation always specifies what type of connector is used
Actually page 2 of the manual says:

"You can use an optional 32Ω stereo headset or earphone with your scanner. Use of an incorrect earphone or headset might be potentially hazardous to your hearing. The output of the phone jack is monaural, but you will hear it in both headphones of a stereo headset."

Seems pretty unambiguous if you actually RTFM.
 

dhoffman83

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Yup, quoted that exact text above. The part about "output of the phone jack is monaural" doesn't exactly agree with headphone jack = stereo.
 

ko6jw_2

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I expect people would complain if they plugged in their stereo headphones and only heard sound out of one earpiece. They did it that way because it's very hard to find a mono headset these days at a reasonable price whereas everyone has a stereo headset. By the way, my Yaesu FT-897D and 817D both have "stereo" headphone jacks. Of course, they also have speaker jacks. The 817 is switchable between headphone and speaker so you can plug in a mono speaker.
 

dhoffman83

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That could be the reason it's stated as "You can use an optional 32Ω stereo headset", as if it weren't going to be ideal (such as only a single channel of output). I'm just saying, it wouldn't be expensive to print "Headphone jack: 3.5mm TRS" in the specifications (the first place I looked, and found nothing) and avoid any confusion. There is definitely no shortage of headphone jack threads on the forums, specific to this model or others.
 
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ko6jw_2

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The real question is: Why not design the audio output to detect that the ring is at ground potential and switch all the output to the tip. That would eliminate all the problems and prevent damage to the radio. You could also have a menu choice for stereo or mono output.
 

jonwienke

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Yup, quoted that exact text above. The part about "output of the phone jack is monaural" doesn't exactly agree with headphone jack = stereo.
Actually it does. Mono signals are sent to stereo devices all the time without compromising their stereoness. The key phrase is "you will hear it in both headphones of a stereo headset". That isn't possible unless the jack is stereo, with audio output being sent to both L and R. Whether the L and R outputs happen to be identical or not is irrelevant.
 

jim202

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Has anyone even bothered to check to see if there is a DC voltage on the audio output connection? If there is, a simple series coupling capacitor will probably solve everyone's problem. Many computer audio inputs don't like to see a DC bias voltage on their input.

You can try using something like a 1.0 uf cap to block any DC bias voltage.

Like most Motorola radios that have DC voltage on their speaker outputs, it wouldn't surprise me that the scanner engineers took the same approach with the scanner. Adding a capacitor to block any DC voltages at the earphone jack would cost them another $0.80 per scanner.
 
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