BCD536HP: Speaker hissing noise again

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pepsima1

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So I have been biting my tongue again for the past couple of months and have noticed more issues with the internal speaker on the bottom of the scanner and the external rear audio jack to the radio when hooking up the Uniden BC-7 speaker.

I have two BCD536HP radios. One which was the original radio that was sent back for the headphone jack issue which was fixed and now has a 3 year warranty. The other one was bought two months ago from the HAM station which was new stock.

Attached is a recording file from the radios internal speaker on low and volume adjust turned all the way down. It is a hissing and a weird noise that is generated when the speaker opens up for conversation on either a trunked system or a conventional system. This also happens on the external rear jack with a BC-7 speaker plugged into the radio too on both units.

It does not happen on the headphone jack at all on either models but does happen all the time on both units. I also, have a Uniden BCD436HP and do not have any of those issues at all on the internal speaker or the headphone jack at all.

Keep in mind I have a Uniden BCD996XT and have never experienced these issues with the headphone jack nor the external or internal speakers.

3 year warranty replacement from Uniden is 375Z38001888

New stock radio from HAM station is 375Z48000120

link to the file

https://www.dropbox.com/s/bi9qgk8prrlxdkp/Uniden BCD536 Noise Again.zip
 

Mike_G_D

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Sounds a bit like an old fax data transmission with a little RTTY mixed in;-)

Anyway, a few questions:

1) Have you ever connected anything else to the speaker out of either radio besides just the speaker (like a PC line in, etc.)?

2) Have you always heard this noise on these 536 radios (since you first started using them)?

3) Do you have any other devices connected to the radios (USB, serial, etc. for PC control, logging, etc.)?

If you answered yes to #3 then try disconnecting everything else except the external speaker and see if the noise is still there.

Also, if you are using the recording feature maybe try turning that off and see if the noise remains.

-Mike
 

Boatanchor

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cpu crosstalk noise

I had an early production 396xt that suffered from terrible cpu noise crosstalk every time the mute opened. The noise sounded like pops, whines & clicks. I could (just) put up with this noise when using the speaker and with the volume turned up as the received audio masked the noise. It was virtually impossible to use the noisy 396xt with earbuds though as the noise nearly drove me insane. (Actually, come to think of it, I haven't been the same since.. Hmmm)

Anyway, I thought it was endemic to the model until I purchased another 396xt with a much later serial number a couple of years later. The crosstalk problem was virtually eliminated in the second unit.

The problem of cpu noise crosstalk(ing) into the audio stages can be a tricky one to sort out. It usually involves installing additional filtering on the cpu and audio power supply rails and sometimes re-routing of pcb tracks. It's not usually something that can be fixed with a firmware update.
 

JamesO

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I believe it is CPU crosstalk into the audio circuits.

I raised this issue when the headphone problem was going on. If you plug a pair of earbuds into the external speaker jack and make sure the volume is turned way down or all the way.

You will hear all the R2D2 digital crosstalk.

So I WONDER??? if when the headphone problem was created in the assembly plant, someone actually mixed up the surface mount resistor tubes in 2 locations on the component placement machine and there was a wrong component BOTH in the headphone circuit and the external speaker circuit??

Did Uniden only find the problem with the headphone circuit??

Anyway, the overall sensitivity of the speaker/amplifier can really impact how much of the R2D2 that is heard. The less sensitive the speaker/amplifier the less crosstalk you are likely to hear.
 

pepsima1

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I believe it is CPU crosstalk into the audio circuits.

I raised this issue when the headphone problem was going on. If you plug a pair of earbuds into the external speaker jack and make sure the volume is turned way down or all the way.

You will hear all the R2D2 digital crosstalk.

So I WONDER??? if when the headphone problem was created in the assembly plant, someone actually mixed up the surface mount resistor tubes in 2 locations on the component placement machine and there was a wrong component BOTH in the headphone circuit and the external speaker circuit??

Did Uniden only find the problem with the headphone circuit??

Anyway, the overall sensitivity of the speaker/amplifier can really impact how much of the R2D2 that is heard. The less sensitive the speaker/amplifier the less crosstalk you are likely to hear.
I just plugged a pair of ear buds into the external jack to both radios and hear all of the R2D2 digital crosstalk.

I really have been debating on how to address this issues since I raised the issue right from the beginning about the headphone jack issue. I honestly thought that we were all buying a great radio and it comes to find out that these issues are all hardware related issues with the radio which any firmware update is not going to fix these issues.

I really think at this point that Uniden needs to figure out on how they are going to deal with these major issues. Its very un-acceptable at this point and when these radios were made there must have been no quality control on these radios. I was really excited that Uniden came out with this great radio and there are a lot of great features but the hardware related issues is such a huge dis-appointment on such a very high priced scanner.

The BCD436HP radio does not have these hardware related issues at all. Somebody in Asia that was building these radios one evening went to sleep on the job and these is a huge factory problem on their hands. The BCD996XT does not have any of these issues at all.

I really think Paul from (Uniden) needs to relay these issues back to his team. I guarantee I am not the only one with these issues. It looks like other people having just been putting up with these problems.
 

JamesO

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As with anything, did Uniden knee jerk on the wrong component replacement for the headphone circuit and maybe miss the bigger picture??? Who knows.

But this is what I do understand, with surface mount components you usually have long tubes or reels of 500-1000 pieces that get mounted/inserted into a component placement machine.

Common sense tells me if you mix up the tube or reel, for one position, then there is a mix up for another position. You can bet the proper components were likely ordered and shipped, and hopefully someone in QC made sure the proper components were received.

So if the proper components were received and some were mixed up, likely 2 or more were mixed up and it could have affected other locations on the circuit boards unless this was a clear case or programming the component placement machine wrong, but in this case, there would have been a clear shortage of one or more components and the red lights and flags should have been raised LONG before the scanners were ever shipped.

So the REAL question is the R2D2 problem with the 536HP a DESIGN problem or a BUILD problem. A DESIGN problem is much harder to rectify then a BUILD problem.

See my comments on R2D2 that pretty much went ignored!!

http://forums.radioreference.com/uniden-owner-tech-support/287338-bcd536hp-strange-noise.html

http://forums.radioreference.com/un...-headphone-related-issues-12.html#post2136711

http://forums.radioreference.com/uniden-bug-reports/282877-bcd536hp-headphone-related-issues-13.html

Paul was all over the Headphone thread and there was NO acknowledgement of the cross talk problem via the external speaker on the 536HP that I posted!

It is apparent on my scanner, I only have the one 526HP, not sure it is inherent on all 536HP or just the early units.

My unit falls in Headphone Campaign window, but I have never sent it in as I wanted all the dust to settle on the issue, glad I do not sent it in due to the all the shipping damage from the sloppy packing of the units when returned from service.
 

FeedForward

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Audio output - hissing

Lately I've been reading so many bug reports on the 536 I can't keep them all straight. Here's some extra information on audio output hiss that so many have commented on. I refer to this complaint:

a continuous low level hiss in muted audio which is NOT affected by the volume control position, and a continuous higher level hiss which is present during normal audio output.

Reading through the 536 o.m it states on page 10 that all audio is class D amplified. For those who are familiar with this mode, no further comments are necessary. But here are a few ideas as to why you all are hearing hiss noise. Class D audio amplifiers, the type used in the 536, are a kind of digital / PWM switching amplifier. You will find them used almost exclusively in the fancy home audio control centers that provide audio to various home areas. The advantages are that the amplifier is very efficient (around 90%) and that many individual amplifiers can be squeezed into a small enclosure.

Now, the disadvantages. The line-level audio signal (that arrives at the volume control) is turned into a digitized PWM signal that is "sampled" at a rate higher than normal hearing. That rate might be 30 KHz, 50KHz or 100KHz or higher - it doesn't really matter. The power devices switch on and off at the higher rate producing larger pulses of the high frequency samples. Then, an LC filter does its best to smooth out the switching pulses and deliver nice low distortion audio to the speaker. Not. Every class D power amp I have ever had the pleasure to work on emits a constant relatively low hissing noise even with the amplifier inputs shorted (no signal going into the amplifier).

I did not notice this feature of Class D myself until I looked at the output on a scope. Even then I couldn't believe this was a characteristic problem until after looking at dozens of Class D units I finally had to admit that these amplifiers just inherently hiss. Its part of the design. You are hearing artifacts of the power switching pulses as the harmonics add, subtract, multiply and divide just like they do in any non-linear mixing environment.

So, can the hissing noise be eliminated? Probably not, unless you simply get rid of the class D amp and substitute an analog audio output IC. That's what I'd do. Can it be improved? Yup, but it is not a software issue. More filtering on each class D stage would be necessary, and filters usually require large, heavy and relatively expensive parts. Probably not a great fix once a unit has been sent out.

Class D output stages do have their place in the audio world and of course don't forget we have even more exotic types like class E, F and G. Headphones have always been the most sensitive - if not the most convenient way - to reproduce audio. For a unit that features a HEADPHONE jack, the use of a class D switching amplifier is an obvious goof. I shake my head in amazement. But there you are, some extra food for thought.

-FF
 

pepsima1

Completely Banned for the Greater Good
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Lately I've been reading so many bug reports on the 536 I can't keep them all straight. Here's some extra information on audio output hiss that so many have commented on. I refer to this complaint:

a continuous low level hiss in muted audio which is NOT affected by the volume control position, and a continuous higher level hiss which is present during normal audio output.

Reading through the 536 o.m it states on page 10 that all audio is class D amplified. For those who are familiar with this mode, no further comments are necessary. But here are a few ideas as to why you all are hearing hiss noise. Class D audio amplifiers, the type used in the 536, are a kind of digital / PWM switching amplifier. You will find them used almost exclusively in the fancy home audio control centers that provide audio to various home areas. The advantages are that the amplifier is very efficient (around 90%) and that many individual amplifiers can be squeezed into a small enclosure.

Now, the disadvantages. The line-level audio signal (that arrives at the volume control) is turned into a digitized PWM signal that is "sampled" at a rate higher than normal hearing. That rate might be 30 KHz, 50KHz or 100KHz or higher - it doesn't really matter. The power devices switch on and off at the higher rate producing larger pulses of the high frequency samples. Then, an LC filter does its best to smooth out the switching pulses and deliver nice low distortion audio to the speaker. Not. Every class D power amp I have ever had the pleasure to work on emits a constant relatively low hissing noise even with the amplifier inputs shorted (no signal going into the amplifier).

I did not notice this feature of Class D myself until I looked at the output on a scope. Even then I couldn't believe this was a characteristic problem until after looking at dozens of Class D units I finally had to admit that these amplifiers just inherently hiss. Its part of the design. You are hearing artifacts of the power switching pulses as the harmonics add, subtract, multiply and divide just like they do in any non-linear mixing environment.

So, can the hissing noise be eliminated? Probably not, unless you simply get rid of the class D amp and substitute an analog audio output IC. That's what I'd do. Can it be improved? Yup, but it is not a software issue. More filtering on each class D stage would be necessary, and filters usually require large, heavy and relatively expensive parts. Probably not a great fix once a unit has been sent out.

Class D output stages do have their place in the audio world and of course don't forget we have even more exotic types like class E, F and G. Headphones have always been the most sensitive - if not the most convenient way - to reproduce audio. For a unit that features a HEADPHONE jack, the use of a class D switching amplifier is an obvious goof. I shake my head in amazement. But there you are, some extra food for thought.

-FF
Awesome findings. Thanks. I always knew that this fix would not be with a software firmware upgrade. That hissing pulse noise is very annoying and that is why I sold both of my BCD536HP radios because of these bad design flaws. Also, because of the headphone jack issue too. I just did not want to deal with it and be un-happy with the radio. Just went back to the 996XT radio which is bullet proof.

Uniden I hope you are looking at this issue and hopefully fixing these radios for the future.
 
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