4 scanners > audio mixer > L & R channels on wireless headphones

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Ubbe

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Fortunately, I was able to activate the mixer's "instrument" mode on two of the inputs. My guess is that this feature acts like a Direct Injection (DI) box, which in this case is transforming impedances. Audio experts, correct me if I'm wrong.

Normal input is balanced (+signal and -signal and ground) but you can make it unbalanced (+signal and ground) with the instrument mode. See explanation earlier in the thread.

/Ubbe
 

Anderegg

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I used to use a powered Behringer MX400 mini mixer, pretty affordable, to mix 4 PRO197 scanners into my remote Win500 server. I have since switched to an unpowered passive 4 port mixer, as it provides full audio levels for my PC input. The MX400 can really amp up the levels, so would be more useful for headphone use.

One big thing I would recommend, would be a small mixer with an EQ...the 536's on P25 can get VERY BASSY, so you might want a way to low cut them or turn up the treble to hear more clearly if P25 will be monitored alot.

Paul
 

N0BDW

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Items arrived today.

The headphone port on the 536 units does NOT work into the mixer. I tried both mono and stereo and in both cases there is a significant hum/hiss.

The ext speaker works but requires a ground loop isolator.

I ended up going with the Mackie Mix8.
 

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SquierStrat

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Great choice on the mackie! I have that exact mixer, and a mackie subwoofer for my in home PA (home stereo wasnt cutting it) and they've both continued to perform great!
 

dsalomon

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You really don't need a ground loop isolator. Just hook up ONLY the positive (i.e. center pin) of the speaker out and leave the negative disconnected. That will allow you to hook it up to anything without ground issues.

To the guy who posted about hum coming from his at the firestation - this will fix your problem as well. Just disconnect the negative (shell or ring) and the hum will go away. The output will still work just fine.

That's what I did with mine and I have no issues.

Also, re: the post about getting line out from inside the unit - that's actually the discriminator out connection. This will not only work great, but if you want to do any digital decoding, you will get much better results using a discriminator out than any speaker or line out connection. This is because the discriminator out connection comes before any audio filtering. Usually, when the audio is filtered there is enough spectrum cut off at the top and bottom that needed signal goes away and digital signals won't decode properly. Getting audio from the discriminator point fixes this.

Finally, be VERY CAREFUL with the speaker out connection on the 536. If you do connect the negative side and connect it to any equipment that has the negative side grounded to earth, which BTW is probably over 99% of all equipment, you run a high risk of blowing the audio amp that powers that speaker out connection. There is really no protection for that port. That's why this warning is in the manual. I don't know why Uniden chose to use that design. I imagine there are many people out there that have had issues with the speaker out because they hooked up first and didn't bother reading the manual (which I'm guilty of most of the time as well :)).
 

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N0BDW

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You really don't need a ground loop isolator. Just hook up ONLY the positive (i.e. center pin) of the speaker out and leave the negative disconnected. That will allow you to hook it up to anything without ground issues.

Is it possible to buy cables already wired that way? I'm not really looking to build my own cables.

I guess it is a bit of a moot point now as I've already invested $40+ in ground loop isolators and it seems to be working, but if I ever add another to the fleet it might be worth knowing.

To the guy who posted about hum coming from his at the firestation - this will fix your problem as well. Just disconnect the negative (shell or ring) and the hum will go away. The output will still work just fine.

Yeah, that was also me...

I have one 536 at the fire hall and three in my home setup.

Also, re: the post about getting line out from inside the unit - that's actually the discriminator out connection. This will not only work great, but if you want to do any digital decoding, you will get much better results using a discriminator out than any speaker or line out connection. This is because the discriminator out connection comes before any audio filtering. Usually, when the audio is filtered there is enough spectrum cut off at the top and bottom that needed signal goes away and digital signals won't decode properly. Getting audio from the discriminator point fixes this.

If you tap from the discriminator you also need to do your own digital decoding, correct? Not really an option here. Might be handy for Unitrunker or something, but not for general listening.

Finally, be VERY CAREFUL with the speaker out connection on the 536. If you do connect the negative side and connect it to any equipment that has the negative side grounded to earth, which BTW is probably over 99% of all equipment, you run a high risk of blowing the audio amp that powers that speaker out connection. There is really no protection for that port. That's why this warning is in the manual. I don't know why Uniden chose to use that design. I imagine there are many people out there that have had issues with the speaker out because they hooked up first and didn't bother reading the manual (which I'm guilty of most of the time as well :)).

Seems like a poor design choice. At a minimum it would've been nice if they'd included some sort of ground fault in the circuit. I am not an electrical engineer and don't pretend to be, but from a layman's perspective.... ugh.
 

AA6IO

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Tell me about it, I stupidly hooked up the speaker on one of my 536HPs directly to my audio input on a PC and forgot about the warning (about a year ago). Result was a blown speaker. Live and learn.
 

Ubbe

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I would have thought that modern IC amplifiers are shortcircuit protected, current limited and God knows what, so it would be impossible to blow the amplifier. Maybe Uniden saved 50cent and opted for an unprotected version.

/Ubbe
 

Anderegg

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Maybe Uniden did it on purpose, knowing that 99.999% of the existing scanner speakers being sold have a MONO tip that will destroy the scanner audio amp, resulting in a $69.95 repair by their service department. :)

What would be the advantage to the end user in designing their audio output this way...at least Apple has an excuse when changing connectors...

Paul
 
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