Hooking up 996P2 or 536HP to an audio amplifier

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marvin547

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Im trying to replace a uniden bdc996XT with a 996P2. I hooked everything up as it was before but when I plug the scanner into the Amp through the external speaker jack, the audio is extremely muted. The same result with a 536HP. The old 996XT works fine on the same wire. Any thoughts?
 

scottyhetzel

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Im trying to replace a uniden bdc996XT with a 996P2. I hooked everything up as it was before but when I plug the scanner into the Amp through the external speaker jack, the audio is extremely muted. The same result with a 536HP. The old 996XT works fine on the same wire. Any thoughts?
Try a different amp... use a speaker to listen and bypass amp... the 996 is high level out for 8 ohm speaker.... you need line level out which is millivolt level.. calrad sells a high level to low level adapter.
 

jonwienke

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You have a ground loop problem. You cannot plug the scanner into an amp where the ring connector of the 3.5mm plug is grounded. Also, you must use a stereo plug or the output will be shorted.
 

iMONITOR

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Try the REC jack on the back, or the Earphone jack on the front. The Speaker output impedance, and output level is too high for the input of an amplifier.
 

Mike_G_D

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BTL amp

The 536 uses a BTL audio amp output. The "sleeve" (outermost contact of phone plug/jack) is NOT ground as in most common amplifier outputs including that of the 996. Also, unlike the older Uniden models, the 536 lacks a "record output" (line output) so you are forced to use the speaker output with BTL amp considerations.

Connecting a passive speaker to such an output is usually not a problem as the speaker is essentially a coil (usually) not connected to ground in and of itself.

But connecting a BTL output into a single ended input such as a PC soundcard or an audio amplifier input wherein the sleeve is grounded will essentially short the amplifier (well, at least one half of the total amp circuit which is essentially two amps).

A VERY simple way to avoid this is to modify a cable such that the ground wire (usually the outer shield in most cables of the coaxial variety) is left "floating" (not connected to anything) or is connected to the case ground of the radio (like a convenient case screw), which would be best, and leave the tip connected to the radio speaker output normally. You then safely pass one half the total audio output of the amp (which is fine as it is still plenty for driving a line input as in an audio amp input or a sound card of a PC, etc.) without shorting anything.

I am attaching a zip file which includes a picture of what I am talking about for clarity. The file with the name of "536_extspkrbasic.png" illustrates this approach. The rest of the files I will explain shortly.

A very common second option that most people will advise you to use (and works with some limitations) is to use a "ground loop isolator" which is essentially a transformer which isolates the DC connections between the source and load (no DC connection so no DC short - only passes the audio AC). These work but are really not designed for speaker outputs with high level low impedance drivers. Theoretically, they can yield issues wherein the transformer primary is "overdriven" (simplified, not a fully accurate description) which can cause some distortion (again, theoretically). But, from a practical standpoint, they seem to work fine and, I'd say, the vast majority of folks on here who want to connect their 536's speaker output to an active line level input of another device use this method and have no issues. If you want "plug and play" and are not comfortable modifying cables or employing any form do-it-yourself electrical work then this is likely the way to go for you. Just ask on here for recommendations for "ground loop isolators" and you will get many results.

Technically, this is not a true "ground loop" problem as defined by most audio engineering circles. That's another issue concerning some line and mic level audio interconnections which usually results in undesired "hum" in the audio. Those isolators are designed for these types of issues. But they will also work for the BTL-to-single ended line connections if you pay careful attention to the speaker output level.

If you or someone you know is reasonably proficient with soldering and general electronic assembly then you could build a circuit which is essentially like a "ground loop isolator" with additional components to better match the levels between the speaker output and the line input. The attached zip file also includes circuits like this. They include fixed and variable transformer and transformer-less versions which you can experiment with. These circuits also allow you to simultaneously connect a speaker to the adapter for use when you are driving a sound card input or other recorder device and do not or cannot use the device's speaker (or it lacks audio pass through). Texts are included in the zip file for explanations of design approach and suggestions for use. I have no current way to actually build or test these circuits so they have not been tested by me. Still, they offer suggestions and none of the component values are very critical to begin with; also, they will prevent any harm to the BTL audio output of the radio.

-Mike
 

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Ubbe

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slylingus

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Thanks for the effort

The 536 uses a BTL audio amp output.
I am attaching a zip file which includes a picture of what I am talking about for clarity. The file with the name of "536_extspkrbasic.png" illustrates this approach. The rest of the files I will explain shortly.


-Mike
A quick thank you for your effort
I have just purchased a 536 and I am trying to add audio to my stream from it
Im assuming this was my issue
Many thanks Cheers
 

jonwienke

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The 536 has direct digital output via WiFi. Use that instead. You'll have better quality audio and not have to worry about isolators.
 

slylingus

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Have resistors cant read the Cap values?

Thanks I have set this up now
The (Scanner) stream drops out with the wifi.
feed was only up for a day and dropped out.
All updated firmware more than likely my router kicking the wifi.
(Ive been reading threads and the wiki for a couple of days now)
Would much rather cable connection Im just working through this now.
Just cant read the cap values is there a better image?

This is the new network here in Victoria that is the RMR P25 P2 so would be nice to get it up and running b four the encryption starts could be a couple of months.
Currently streaming analog comms
Cheers (Still reading)
Edit Just connected WiFi stream see how this works
Cheers noob to the 536
 
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