P25RX Line Out Provision

[W0RS]

I have a amplified speaker with a digital filter that I am using. I have the speaker plugged into the line out jack on the P25. I have the line out volume set to the most drive I can get which is 1.0 but is just not quite enough. I can hear voice transmissions but just not really loud enough to overcome road noise while moving. I am sure the P25 has limitations on the hardware side preventing any more drive.

Anyone know of anyway to provide more drive from the line out provision on the P25 by any other devices?

 

[cmjonesinc]

You could try a preamp between the two. I noticed the volume thing as well. I have a small preamp laying around that I'm going to hook up and see how it works. I'll report back.

 

[ka3jjz]

Btt can comment but I think that jack is for connecting to a laptop or a recording device for recording audio. It's at a very low level for that very reason. Better to use a Bluetooth speaker...Mike

 

[btt]

It is a "line-level" output. It is not designed to drive anything except for a high-impedance input such as powered speakers, line-level input on a sound card, etc. A setting of 1.0 would be too high for almost any application. The default setting is now 0.5.

See here for information on line-level jacks:

Line level - Wikipedia

en.wikipedia.org

I think most of the Bluetooth speakers that you can buy have a line-level input that could be used for a direct connection.

Another thing to mention is that the line-out jack on the P25RX is a standard 3.5mm stereo jack.

 

[btt]

One more thing to mention.. You can set the line-out volume value higher than 1.0. In the console with a command:

$ vol 1.5 (set volume to 1.5)
$ save (save the value to flash)

-edit: Let me know if this works for you and I will make the max a higher value than 1.0 in the BTConfig software.

 

[W0RS]

One more thing to mention.. You can set the line-out volume value higher than 1.0. In the console with a command:

$ vol 1.5 (set volume to 1.5)
$ save (save the value to flash)

-edit: Let me know if this works for you and I will make the max a higher value than 1.0 in the BTConfig software.

Will give that a try....Thanks

 

[W0RS]

So, I think I entered correctly. The $ was already there so I just entered vol 1.5 then I hit enter. Entered save then hit enter. Then I checked Enable logging when I was done. Is there a command that will bring everything up so that I can see it took?

 

[W0RS]

So, I think I entered correctly. The $ was already there so I just entered vol 1.5 then I hit enter. Entered save then hit enter. Then I checked Enable logging when I was done. Is there a command that will bring everything up so that I can see it took?

Never mind....I see where it made the change

 

[kruser]

Never mind....I see where it made the change

Just curious if that raised the line out level enough to overcome your road noise or do you still need more line out audio?

 

[W0RS]

Just curious if that raised the line out level enough to overcome your road noise or do you still need more line out audio?

No, it was not enough so I pushed it to 2.5 but did not help....

 

[btt]

You might need a higher-power speaker in order to overcome the road noise?

 

[kruser]

You might need a higher-power speaker in order to overcome the road noise?

Or possibly an intermediate preamp to get more gain into the speaker. This was mentioned earlier in this thread.
I agree though that a higher power amplified speaker is probably the better solution. It would also be less components to hookup in a vehicle.

 

[btt]

@kruser, are you having an issue with this as well?

@W0RS, what model of speaker are you using?

-edit: I connected a scope and checked voltages here. It looks like a line-level output should.

 

[kruser]

@kruser, are you having an issue with this as well?

-edit: I connected a scope and checked voltages here. It looks like a line-level output should.

No, the line out level is just fine for me. I'm in a quiet environment though unlike the OP that has bad road noise the way I understood the post.

I've been working on taming the outputs down from my P25RX! Our fire department sends an alert tone over the P25 Phase I system when a new fire call is dispatched. It's an attention getting tone sent before the voice. That tone definitely gets your attention. It overdrives the cheap amplifier chip into distortion. The same basic amplifier circuit seems to be used in many cheap computer speakers. I've been trying different settings with the sound card and basically notching the tones frequency down (using the sound cards equalizer) so it's about the same level or less than the average speech level. There's an electrolytic cap in the cheap amp circuits. That cap has blown in more than one set of amplified speakers on me. I'm pretty sure when the amp is driven into distortion, the voltage across that cap rises well above it's voltage rating and it eventually vents out the top. When the cap blows, the speakers go into a clipping mode even at low volume levels and sound like the speakers are blown but it's really just the cap causing the clipping.
The next time I replace that cap to repair a spare set of speakers, I'm going to record the voltage across the cap when the tone is broadcast and see just how high the voltage goes.

 

[goldmyne99]

Interesting that the cap blew, wow! Perhaps trying passive notch filter for the tone's freq? There are notch filter calcs on line showing circuit values for a handfull of resistors and caps.

 

[btt]

No, the line out level is just fine for me. I'm in a quiet environment though unlike the OP that has bad road noise the way I understood the post.

I've been working on taming the outputs down from my P25RX! Our fire department sends an alert tone over the P25 Phase I system when a new fire call is dispatched. It's an attention getting tone sent before the voice. That tone definitely gets your attention. It overdrives the cheap amplifier chip into distortion. The same basic amplifier circuit seems to be used in many cheap computer speakers. I've been trying different settings with the sound card and basically notching the tones frequency down (using the sound cards equalizer) so it's about the same level or less than the average speech level. There's an electrolytic cap in the cheap amp circuits. That cap has blown in more than one set of amplified speakers on me. I'm pretty sure when the amp is driven into distortion, the voltage across that cap rises well above it's voltage rating and it eventually vents out the top. When the cap blows, the speakers go into a clipping mode even at low volume levels and sound like the speakers are blown but it's really just the cap causing the clipping.
The next time I replace that cap to repair a spare set of speakers, I'm going to record the voltage across the cap when the tone is broadcast and see just how high the voltage goes.

That is strange. The P25 Phase 1 fire tone levels are good here. Just heard one a few minutes ago. You might try reducing the volume to 0.25 (-12 dB)? All the speakers I have tested with are fine. They also all have volume controls on them. I'll keep looking into it. Is anyone else having these kind of issues with the line-out?

 

[kruser]

That is strange. The P25 Phase 1 fire tone levels are good here. Just heard one a few minutes ago. You might try reducing the volume to 0.25 (-12 dB)? All the speakers I have tested with are fine. They also all have volume controls on them. I'll keep looking into it. Is anyone else having these kind of issues with the line-out?

It's not a P25RX issue Todd. It's just the way they broadcast the attention tone here for one of the fire dispatch talkgroups.
I'd never had issues with any of my cheap amplified computer speakers until I started monitoring this fire talkgroup. I immediately noticed how blastingly loud their attention tone was compared with other traffic. It took me a long time to realize that loud tone may have damaged the speakers when it drove the speakers amp into clipping levels. That's probably why the caps blew on three sets of cheap computer speakers. All different makes but all from China with very similar amp circuits in them. Mine also have volume controls on the speakers. I always keep that set around 50 to 60% max but when they broadcast that tone, you'd think the speakers volume was set at 300%!
That same tone is also overdriven and distorted sounding on a scanners speaker. I'd imagine they inject the tone into an audio stage in the transmit radio and its gain was never set correctly. Of course the fact it's an analog tone coming over a P25 digital signal also makes it sound bad.
When I finally opened up one of the bad speaker sets, I immediately saw the blown cap. The cap is in the audio output stage and not a power supply filter cap. I forget the typical value but they are not very big and have a 25 VDC rating.
When I replaced a bad one, the speakers worked just fine again. I also forget but I think they may be non-polarized electrolytic caps commonly used in the audio output stage of audio amp circuits.

The tone I'm talking about is not a part of the tone-out tones used for station alerting. The departments that send those tones over the P25 system sound fine with good audio levels but those tones are not stable because of being converted to digital. Most departments here mute the analog tone-out tones on the P25 side of things. Then some departments send this loud single frequency tone as an attention getting tone.

 

[Mike_G_D]

Something to remember here, at least for the OP: ramping up the input level to a line driven audio PA once you hit the maximum voltage level before saturation will gain you nothing except distortion depending on the design of the input line level small signal amp and/or the input of the PA.

There are very well defined maximum voltage levels for both consumer and professional audio line levels and the link that btt posted explains this well. If the OP raised the voltage to the input stage of his powered speakers with little to no change to the output level then we are already in the non-linear stage of "goes-inna" vs. "goes-outta"! PA inputs will have a set level range to drive them after which you control the output with the PA's volume control.

So it sounds to me like his powered speaker system simply does not have the "oomph" to overcome the car noise. You need a heftier PA - more watts and a compatible speaker. No amount of ramping up the voltage output of the line driver in the P25RX will help past this point, rather, you may end up just overdriving the preamp/amp input of the PA causing it, depending on the design, to start adding distortion and/or clipping and/or reducing its input gain to compensate.

Find out what is the power output of the powered speaker and the maximum input level voltage of the line input. If you've already hit that maximum input voltage level on the peaks of the audio you pretty much are at the mercy of the PA's maximum output power. You just may need more.

Something else - you (the OP) mentioned a "amplified speaker with a digital filter" - exactly what are you using, make, model? Are these two seperate devices placed in line with each other, i.e. P25RX -> digital filter ->amplified speaker or is the "amplified speaker" a model that includes a built-in "digital filter"?

That "digital filter" adds another layer of complexity to the audio chain that has its own maximum drive levels - and you REALLY don't want to overdrive a digital filter! Digital audio filters are usually pretty picky about their drive levels and you generally have to maintain things within a well defined window at least as far as the raw levels into the A/D converter otherwise you get lots of wierd artifacts you really don't want.

If possible, try either removing or bypassing that "digital filter" and see what kind of results you get. Otherwise, I would recommend getting a higher powered amplified speaker - there are many out there.

But trying to ramp up the input line level past the normal maximum at this stage will likely gain you nothing (no pun originally intended).

-Mike

 

[W0RS]

@kruser, are you having an issue with this as well?

@W0RS, what model of speaker are you using?

-edit: I connected a scope and checked voltages here. It looks like a line-level output should.

It's a BHI product NES10-2 MK4 and I paid $169.00 for it from DX Engineering. It's an amplified speaker with a digital filter if desired...

 

[goldmyne99]

I have this same speaker. I have not tried it on the p25rx. The user manual page 16 does talk about low audio when connected to line out. Basically, advises the unit may not work.