Audio amplifier

[MarkEagleUSA]

I'd like to find a small audio amplifier for in-vehicle use with my 246 and 396. However, they both have warnings in the manual:

WARNING!
Never connect any part of the headphone jack to
the antenna jack or connect the radio to an
installation where the antenna and audio
connection are grounded. This might damage the
scanner.

Both the 246 and 396 have the antenna ground attached to power ground. Every cheap stand-alone amp I've seen all seem to have the audio ground attached to the power ground. I think this means that use of these amps does essentially what Uniden is warning us about in the manual, since audio ground and antenna ground end up connected.

I think the amplified speaker that RadioShack sells suffers from this as well (though I have not verified it).

Can anyone recommend a solution? I'd even be willing to build my own if someone could provide a schematic and parts list.

 

[CQ20m]

I use the RS amplified speaker with my RS PRO 96 in the car. It works great in my situation, and they recommend using it in the owners manual. I, of course, don't know how it would work with your Bearcat equipment.

 

[MarkEagleUSA]

I use the RS amplified speaker

Do you by any chance have a multimeter that you can check the ground with? All you need to do is check for continuity between the audio input ground and the -12v line on the speaker itself.

 

[LarrySC]

FYI: A sub-woofer from a defunct computer speaker system is the best thing in the world for a portable. Put one on my 96 - WOW

 

[pro92b]

The Radio Shack amplified speaker has a transformer isolated input and is safe to use. Buy one and test it first to be sure things haven't changed since my rather old amplified speaker was made. Plug in an audio patch cable and do an Ohms check from tip and barrel of the audio plug to the red and black power leads. There should be no connection between them - very high resistance. If you do get a low resistance reading just return the speaker for a refund.

I think Uniden also sells an amplified speaker if the Radio Shack speaker doesn't work out.

 

[MarkEagleUSA]

Buy one and test it first

If I don't get a definitive answer here, I was just going to ask them to let me test it in the store before I buy.

I just don't know if/when I'll make it to a store in the next few days.

I think Uniden also sells an amplified speaker if the Radio Shack speaker doesn't work out.

If they do, I can't find it in their store.

 

[Julian1]

Amped speakers

I have used the Radio Shack amplified speaker and a General Electric amplified speaker on my Uniden 780 and 785. Great results. I do not know how their circuitry may or may not differ from your handhelds on grounding.

Please note *** The Radio Shack speaker has a nice feature that will be confusing if you aren't expecting it. At least I was. If no audio is present from the scanner, the speaker will "time out". I did not know of that feature and I kept thinking my dc power connection was not holding. Only to find out later of the "time out" feature. This is to save you car battery.

Good luck,
Julian

 

[Thayne]

I use a radio shack amplified speaker in my truck with a 780, it works great

 

[hiegtx]

I'd like to find a small audio amplifier for in-vehicle use with my 246 and 396. However, they both have warnings in the manual:


Both the 246 and 396 have the antenna ground attached to power ground. Every cheap stand-alone amp I've seen all seem to have the audio ground attached to the power ground. I think this means that use of these amps does essentially what Uniden is warning us about in the manual, since audio ground and antenna ground end up connected.

I think the amplified speaker that RadioShack sells suffers from this as well (though I have not verified it).

Can anyone recommend a solution? I'd even be willing to build my own if someone could provide a schematic and parts list.

Mark,

It's been a while since I've built kits. But you should be able to sovle this by inserting a capacitor in line (series) on the ground side of the patch cable from the 396 pr 246 to the amp. The capacitor would be transparent to the audio, which is an alternating current anyway. The dc-current of the ground circuit would see it as an open circuit, preventing a short and any damage. As far as capacitor value, I'd probably experiment with a couple of disc capacitors to see if one sounded any better than another.

Steve

 

[MacombMonitor]

Typically on Uniden hand-held scanners in the past, shorting out the outer (ground side) of the antenna, and the outer side of the earphone jack, would increase the volume to the earphone. Uniden put a resistor between ground, and the outer side of the earphone jack, to limit the audio level so people wouldn't damage their ear by turning up the volume too much. I used to deliberately put a small jumper wire across the two, to bring the level back to normal, so a hand-held could properly drive an external speaker.

Maybe UpMan could verify this? Possibly they've done something different on newer models?



I found this amplified speaker at Universal Radio, that you might want to check out! It's an MFJ-382, for $37.95.

http://www.universal-radio.com/catalog/speakers/1129.html

 

[MarkEagleUSA]

Maybe UpMan could verify this? Possibly they've done something different on newer models?

Here's a good explanation of the 246 audio circuit. I think the 396 is the same, but haven't been able to confirm it. Either way, both models definitely have the warning in the manual, so I'm not going to take any chances..

 

[Al42]

Radio Shack carries a small 600 ohm-600 ohm transformer. Since the input to the amp is bridging, just use the transformer to feed the amp.

 

[mn2deep]

I'm using a Motorola amplified speaker I bought on Ebay for $10 with my 246. It works great.

 

[MarkEagleUSA]

Radio Shack carries a small 600 ohm-600 ohm transformer.

Do you mean this 600 ohm-900 ohm 1:1 Isolation Transformer?

Since the input to the amp is bridging, just use the transformer to feed the amp.

Can you explain further? How would this be done?

 

[MarkEagleUSA]

But you should be able to sovle this by inserting a capacitor in line (series) on the ground side of the patch cable from the 396 pr 246 to the amp. The capacitor would be transparent to the audio, which is an alternating current anyway. The dc-current of the ground circuit would see it as an open circuit, preventing a short and any damage. As far as capacitor value, I'd probably experiment with a couple of disc capacitors to see if one sounded any better than another.

Can anyone explain this in more detail?

 

[hiegtx]

Mark,
sent you a pm

 

[Al42]

Do you mean this 600 ohm-900 ohm 1:1 Isolation Transformer?

That's the one.

Can you explain further? How would this be done?

Two wires - each with a 1/8" mono plug on one end and one winding of the transformer on the other end.

Plug one plug into the scanner and the other into the amp.

  <-----------) | (------------>
  p           ) | (            p
  l           ) | (            l
  u           ) | (            u
  g           ) | (            g
  <-----------) | (------------>

 

[MarkEagleUSA]

I broke down yesterday and got the RadioShack 21-541 Amplified Speaker. I'm very impressed. Though a bit pricey, it gives great sound... not tinny at all and even has a bit a bass to it. The 396 sounds awesome on it, and I haven't had to set the volume to more than 4 to be able to hear while driving with the windows open.

As pro92b pointed out to me, the input jack of the speaker is grounded UNTIL the cable is connected, so you need to plug into the speaker BEFORE plugging into the 246 or 396. That being the case, I also bought a 273-1374 1:1 Isolation Transformer and wired it inline to the speaker to prevent any connection mishaps.

I wish I could find or build a similar stand-alone amplifier to drive the Uniden ESP20 speakers I already have, but can't find a cross for the Korea Electric KIA6227H IC that's used in the RS speaker.

 

[pro92b]

This amplifier should work: http://cache.national.com/ds/LM/LM4950.pdf

 

[epbernstein]

I broke down yesterday and got the RadioShack 21-541 Amplified Speaker. I'm very impressed. Though a bit pricey, it gives great sound... not tinny at all and even has a bit a bass to it. The 396 sounds awesome on it, and I haven't had to set the volume to more than 4 to be able to hear while driving with the windows open.

As pro92b pointed out to me, the input jack of the speaker is grounded UNTIL the cable is connected, so you need to plug into the speaker BEFORE plugging into the 246 or 396. That being the case, I also bought a 273-1374 1:1 Isolation Transformer and wired it inline to the speaker to prevent any connection mishaps.

I wish I could find or build a similar stand-alone amplifier to drive the Uniden ESP20 speakers I already have, but can't find a cross for the Korea Electric KIA6227H IC that's used in the RS speaker.

I'm confused (not an unusual state for me), primarily because I know next to nothing about electronics.

Will the RS amplified speaker work out of the box on my 396? If so, does it need to be connected in the manner described above, and if it isn't, what can happen?

I haven't a clue what the aforementioned isolation transformer does, or how to "wire it inline to the speaker..."

Any clarifications appreciated...

Erik