Bcd536hp external speaker connection considerations and precautions

[Mike_G_D]

I've noticed degrading volume on Uniden scanners since the 15x came out. Will the Ground Isolation Transformer - 3.5mm M/F work on all scanners? I'd like to put them on all my audio lines but want to make sure I won't blow anything up as I have some ground loop issues that have been bugging me for a long time.

If you're referring to the transformer from the linked to company that JamesO mentioned, I see no obvious reason why it wouldn't work on any audio line with 1/8 inch audio jacks/plugs... BUT...and here's the, pardon the unintended "pun", big "BUT" -

I have looked and cannot find an internal schematic of that particular model on-line. Therefore, I cannot be absolutely sure how that thing will perform in all conditions. Now, the posted specs are pretty sparse also, so, again, not much to go on here. Also, I read a comment by one user (don't remember which reseller site - maybe it was the linked one, not sure) who did say that he found that it did not truly isolate the ground. But he didn't elaborate so I can't be certain what he was really looking at and how he tested it. Most every other commenter said good things about it.

Now, I will hazard a GUESS that it is designed such that the internal 1:1 transformer may have a ground shield that is at least isolated from one side but may be connected to the shield of the cable on the other side. Since, as far as I can tell, we are dealing with only two conductors on either side I am guessing that it is pretty simple and just uses the two transformer terminals on each side for the tip and sleeve of the 1/8 inch jack and plug respectively. Again, I don't know if the internal transformer has a metal shield around it that is grounded to one of those connections' shield. Obviously, if both sides have their cable shield (sleeve of the jack/plug) grounded it wouldn't be a "ground isolation transformer".

So, if it does have that transformer shield grounded to one side's cable shield would that matter and how could you tell? Well, it might matter but I don't think so and it would be difficult to tell without an ohmmeter and maybe opening up the transformer housing if it is surrounded by insulating plastic (which it looks like it is from the picture). If you could ohm out the shield of the cables with a meter I would first make sure that there is no ground commonality between the two sides - the main thing you want with this device. Then I would try and find a metal outer shield contact of the transformer housing if there is one (maybe a convenient housing screw?) and ohm that out with the shields/sleeves of the cables on both sides. If one of those sides has the shield/sleeve common with the transformer shield, I would be inclined to use that side to connect to the PC and the fully isolated side would go to the radio external speaker jack. But again, as long as there is no common connection between the shields of the two sides then it should likely work either way. Do understand, though, that without any attenuation a connection to the external speaker jack of any radio will way overdrive a PC mic input and you may not be able to compensate enough with just the software mixer controls. If you have a line input that would be better but it will still need to be turned way down. That's a major advantage of the designs I submitted above as they all have fixed or variable attenuation built in (plus I KNOW how they are constructed and how they work!).

I'm curious, when you say that you've "...noticed degrading volume on Uniden scanners since the 15x came out..." what exactly do you mean? That seems odd. I wonder what it is in your setup that makes this such an issue?

-Mike

 

[Ben96cal]

re: 536

What I mean by is that comparing to a 780 or 895 I have to set the volume WAY higher on the knob on the 15x and even higher on the 996 or 536 to get the same amount of volume out of the radio. Where on the 780 I'd set the knob around 10 o'clock on the 15x and 996 I'd have to set it to noon or 1 pm and on the 536 I'd have to to set it to 3 or 4 pm. I run feeds so it's very noticible.

 

[Mike_G_D]

What I mean by is that comparing to a 780 or 895 I have to set the volume WAY higher on the knob on the 15x and even higher on the 996 or 536 to get the same amount of volume out of the radio. Where on the 780 I'd set the knob around 10 o'clock on the 15x and 996 I'd have to set it to noon or 1 pm and on the 536 I'd have to to set it to 3 or 4 pm. I run feeds so it's very noticible.

Ok, I thought maybe you meant that the radios degraded badly over time, age-wise in terms of audio. But you mean, if I'm understanding correctly, that the radio models that have come out since the 15X have seemed to need a higher volume setting to provide your feed than you were needing to set it at in the older models, is that correct?

Now - if I got that right then I have to ask, why did you not use the record out jack with a fixed line level on the newer scanners (except the newest 536 which doesn't have one any longer) rather than the external speaker jack? Seriously, that is what it is there for and is now a problem for the latest scanners as they have omitted it. It isn't just for recording, it is a true line level audio tap that is perfect for using to feed a PC line input or even, with some extra attenuation, a mic input. Now, yes, unfortunately, Uniden has abandoned that feature on their latest scanners so we have to go back to using the speaker output (or headphone output) unless or until they get digital audio output via WiFi or USB available in a future firmware update. Anyway, if you haven't tried the record out jacks on the older stuff yet you really should as that is the best way to go!

Also, what makes you think that you have serious ground loop issues on the older scanners (the models newer than the 780 and 895 but older than the newest 536) other than the low volume? Do you hear hum and buzz noises? Now, I actually wonder if those models also use a BTL driver in the speaker output - I assumed they did not but since I don't actually have any (I do have an old 15 non-X version) I just guessed they had the standard single ended grounded cold lead speaker output. I'll have to look at my 15 and see what it has - I have a scope to test it. I use the record out jack for any recording and the speaker jack just connects to a speaker so I never noticed a problem. Hmm...need to check this out...

Maybe the later model Unidens all used a BTL driver in the external speaker jack and it was never an issue before because the record out line level jack was available so the speaker jack was only ever used strictly for a speaker except in special cases such as your setup, apparently.

-Mike

 

[Ben96cal]

536

I've also noticed degrading audio somewhat over time.. 6-7 years but I can definitely tell an out of the box audio issue..

Sorry I did mean that I use the port in the back, not the mic in the front. As far as the ground loop issue.. I've had crosstalk on different feeds, buzzing and little bursts of audio....

 

[JamesO]

I did get a few of the mono audio ground loop isolators.

They seem to have a resistance of 132 Ohms, no DC coupling between the input and output for either the tip or sleeve.

I tried the unit on my 996XT as my 536HP was not readily available and all I can say is using this device as a external speaker isolator, it is NOT very efficient. I did not run the unit long to see if it heated up at all, but I had to turn the volume up considerably on my 996XT to match what I was typically running, I think it was about 2 times the set point I usually listen to the scanner at with the current external speaker.

I did not play around with a line card or audio input to a recording or streaming device.

I am starting to realize why not having an external line level output is BAD.

I plan on stacking a number of scanners, running audio though a mixer and possibly running a single or 2 speakers. So now I have the issue is if I want to listen to the scanners via the mixer and external speaker, but if something interesting starts to happen, I cannot just easily increase the volume on the scanner with the action and listen via the scanners internal speaker. I can raise the volume on the scanner with action, but it may over drive the mixer and I will need to know where the "set point" for the specific audio level is when I am finished listening to the action. Same holds if I want to stream with a scanner, it I have to use the external speaker output, then I have to be very careful on how I adjust and deal with the volume level as it will impact the streaming levels.

Guess someone will have to guinea pig their scanner to find a way to get a fixed line level output?

Seems like such a simple and useful thing that Uniden kicked to the curb and assumed people would not need? Big loss in my opinion.

 

[Ben96cal]

536

I dove in and ordered 12 of these and are coming tomorrow so we'll see what happens...

 

[JamesO]

They at least work for the output to drive an external speaker.

Not sure if they will last driving a speaker and I was not able to determine if they would resolve any of the ground loop issue, but they should.

I hope they work out as there are not many mono 1/8" stand alone devices out there for a decent price.

Let up know if they work for your application.

 

[Mike_G_D]

I've also noticed degrading audio somewhat over time.. 6-7 years but I can definitely tell an out of the box audio issue..

Sorry I did mean that I use the port in the back, not the mic in the front. As far as the ground loop issue.. I've had crosstalk on different feeds, buzzing and little bursts of audio....

That still doesn't make it clear to me - the record out and the external speaker out are two different jacks on the back of the scanner. The record out has a green ring (on the BCT15 anyway) while the speaker jack is black. You want to use the record out for connection to a PC audio input and not the speaker jack. The record out will output a line level audio signal that is completely unaffected by the volume control. It is perfect for the use of feeding any external active audio device such as a PC audio soundcard input. You don't want to use the external speaker jack for this primarily because the level is so high (in order to drive an external speaker - a "power dependent load") and also because the volume control will affect it. The line level of the record output is a low consistent level for feeding voltage "information" to line level devices (including mixers, preamplifiers, etc.) and the volume control will have no affect on it - you adjust using only the software mixer controls in the PC.

I think, as it has been a while since I last used my BCT15, that you have to activate the record out individually for each channel or talk group that you want to send to the record out jack so if you haven't used this and you do try it then you should make sure it is activated for what you want to monitor or else you may not get a signal on that jack. Anyway, it is well worth the effort to use it for your purposes if you haven't tried it yet. Again, unfortunately, this feature was omitted in the two new scanners from Uniden but at least you could use it in your older stuff.

As to the use of the transformer isolator, understand that it is intended for low line level signals and not for power outputs like an external speaker driver. I am nor surprised that it will not drive a speaker well; in fact if you want to drive a speaker anyway then you should just plug the speaker into the jack directly as intended! Now an amplified speaker is a special case. It is usually (but not always - depends on the design and intended operation) intended to be plugged into an external speaker jack so that it expects a high level power signal which it will buffer and/or attenuate and then amplify itself with its own internal amplifier. It is usually intended for use with low power audio devices that deliver a watt or less output for those who need more audio power from their speaker (usually an amplified speaker for communications use has probably between 4 watts and 10 watts of power, some may have more or less for special cases). The 536 already has about 5 watts of output audio power which should be plenty for most uses. To get a major boost from that you shouldn't bother with anything less than 7 watts in an external amplified speaker.

If I were to use the 536 and wanted to plug the external speaker jack into a speaker and wanted more than what the radio could deliver in audio power I would use an amplified speaker with probably 10 watts minimum and one capable of isolating the ground for a BTL driver. If it did not have that feature (BTL ground isolation) I would simply wire my input such that only the tip of my connection was plugged into the radio's external speaker jack and the sleeve was left floating (unconnected). Then I would wire the shield of the cable at the radio end to a chassis ground point on the radio (like a case screw, etc.). This should yield plenty of level for the external amplified speaker to use while completely isolating the BTL negative lead from ground. No transformer needed. In fact, for this use, an isolating transformer, unless intended for an audio power output, would probably not be a good idea. Again, most audio isolation transformers are for low line level signals and not high level power signals.

If you have one of those isolating transformers and are trying to use it to drive a speaker then you likely will run into problems. It is entirely likely that the transformer is being saturated by the high power level of the external speaker output which may mean we have to be more selective in choosing a transformer capable of handling that output (and I may have to reflect that in my designs - may have to use a differential audio attenuating pad in front of the transformer to lower the level before it gets to the transformer rather than relying on the transformer to take the full load). Now this may not be a problem when the transformer is connected to a high impedance load like a line or even mic input but may be a real issue when connected to a low impedance power element like a speaker. However, with an inline amplifier as in the case of an amplified speaker, then it is the input impedance of that amplifier that is the factor to consider. If it is well higher than the 8 ohms nominal of a typical speaker (like closer to a nominal line input impedance of 1500 ohms) then I would think it should be ok provided that that impedance is well reflected back into the primary of the transformer (side attached to the radio). But still, really, if I were using an amplified speaker in this case I would simply omit the transformer entirely and just use a single connection to the tip of the external speaker jack and ground the shield of the cable to the case of the radio and be done with it. That should work fine.

-Mike

 

[Mike_G_D]

Aaaaannnd.....here are my latest updated versions of my pugnaciously penultimate passive external speaker interface adapters...yippeee!...yaahooo..?!....hey there crickets, keep it down! Can't here the applause! ...??!...umm...

Yeah, LOTS of coffee and been up quite a while so forgive me...

Aaaaanyway, for anybody interested, I've attached my latest schematics.

Basically, fixed one mildly big error on my part (stupid tired mistake - the second jumper header for non-BTL operation on the transformer coupled versions was not only unnecessary but would likely have resulted in very low or no audio due to shunting out the signal through the coils of the transformer...OOOPS!...so it's gone, don't need it anyway) and put a large part of the attenuation before the transformer rather than after it so as to prevent the huge level from the external speaker output from possibly saturating the transformer. Now there is a differential 10:1 attenuation prior to the transformer input. After the transformer, there is another divider formed by the series resistor and the input impedance of the preamp being fed. However, it will really only come into play with a mic preamp input as that will typically yield another 5:1 attenuation (assuming a 1500 ohm typical mic preamp input impedance). If driving a line input it will have little to no effect as a typical line input impedance is around 10K ohms or greater but you wouldn't need as much level drop for a line input anyway so the 10:1 before the transformer should be enough. The values are not critical and can be changed as needed - so if you want greater attenuation than 10:1, say, then you can change the series resistance to a higher value like 15K (15:1) or 20K (20:1); just be sure that if you are doing this for the transformer version that you halve the series resistance values for each leg of the differential input (so if you wanted a series 20K, for example, you would use one 10K resistor in series in both the + ("hot") and - ("cold") lines whereas on the non-transformer versions you would only use one series 20K as it only uses the + ("hot") line (but since you are only using "half" the BTL output anyway, in this case, you may not really need as much). The variable versions add a pot that, if the values are as I've shown them, will, when the pot is set at about the mid-level yield approximately what the fixed attenuation versions yield, so you get to have some extra play either way. Again, the values can be changed, if desired, for greater or lesser attenuation levels.

-Mike

 

[cupman]

BCD536HP external speakers

So I tried to connect external speakers to my 536hp and they cut out the internal speaker. Also, only one of the external speakers would work. I tried this with two different sets of speakers. The two sets of speakers I tried are computer type speakers the plug into the wall. The concerns I hope you can help me with are- 1) Is the internal speaker supposed to cut out like this? And 2) After reading your post I am now wondering- Am I doing anything to damage my scanner when I hook up these speakers and the internal one cuts out? Thanks for your help with this.

BTW- Would you know what size the external speaker jack is? I cannot find this info anywhere. Thanks again.

John

 

[KC9NEG]

Hey, guys, I just put a BCD536HP on my feed and I want to stream tags, so I'm interested in using the external speaker port since I'll have the USB cable connected. Although headphones sound great connected to the headphone jack, I can't get good feed audio from it (I'm using RadioFeed). How would this setup work?

External Speaker port (mono) > 3.5mm mono male to 3.5mm stereo female adapter > 3.5mm stereo cable (male-to-male) > this isolation transformer (I paid half at amazon vs. this listing): 3.5mm Stereo Audio Isolation Transformer > 3.5mm stereo cable (male-to-male) > 3.5mm female Line In on soundcard

Thanks for any help you can offer!

Todd Bettenhausen
KC9NEG

 

[KC9NEG]

Hey, guys, sorry to bump my own here but if anyone with specific knowledge could have a look at this I'd really appreciate it. I want to hook this stuff up and start streaming tags on my feed via serial USB, but I don't want to take any chances with my 536.

Thanks!

 

[KC9NEG]

Bump again for assistance, please.

 

[KC9NEG]

Since only the sound of crickets on this issue, I'll close it out by saying that the setup I posted in #51 works perfectly. No loss in audio output with the USB cable connected and my feed is now streaming tags again.

 

[Triangulum]

I've noticed many threads and posts about the topic. Just looking for a quick clarification.

Can I use a pair of external speakers with the 536hp that plug into an electrical outlet? They are old dell speakers I have around. I don't want to somehow blow up my device.

Here are two images of them that I found online:
http://i1129.photobucket.com/albums/m507/digitalquicks/Dell_Speakers/IMG-20120115-00801.jpg
http://i.ebayimg.com/00/s/OTAwWDE2MDA=/z/MKgAAOSw-dBTuIse/$_35.JPG

 

[Voyager]

Yes, you can if you're talking about plain amplified computer speakers.

 

[Triangulum]

Yes, you can if you're talking about plain amplified computer speakers.

They are very old and have a humming sound when I plug them into my laptop. But yes, they are dell computer speakers that plug into the electrical outlet for power.

Are these kind of speakers irrelevant to the discussion in this thread? Or am I putting my device in danger with these speakers.

Thanks by the way.

 

[Voyager]

Sounds like they may have either a ground loop issue or perhaps the power supply is going bad. Might be best to resolve that issue before using them for anything.

 

[Triangulum]

In regards to the 536:

Will any of the Uniden speakers (BC7, 15, 20) work inside the home without any modification? I've been reading some reviews that seem to indicate that at least a couple are designed mainly for the car and get their power that way

 

[UPMan]

Those speakers are all unpowered. They are appropriate to connect to EXT. SP. outputs, but not headphone outputs.