What means this exact in case of the TDA-7492 (SML-SA-50) ?? - go to
http://www.diyaudio.com/forums/class-d/286090-noise-smsl-sa-50-tda7492-low-level.html
A friend of me uses follow speakers with digital controller and three SML-SA-50 without potentiometer at the input
Bass: Klipsch horn
Klipsch Khorn V-Trac Upgrades - Restoration - "M" Khorns - Volti Audio
Midrange/hights: Jabo KH72B/BMS4590
http://gwhmm.de/eckhorn/pictures/800_pixel/eckhron_14_800.JPG
Overview
http://www.eckhorn.com/images/phoca...thumbs/phoca_thumb_l_eckhorn sota spiegel.jpg
First step is the introduce of an alps 6-ch attenuator at the inputs.
What is possible additional?
Try connect signal gnd to power gnd (at the PSU capacitors) with a thick wire. In one occasion I managed to get hizz down to subjectively half the level.
I heard a interview on the amp hour with a guy from TI who was saying some customers would do exactly this. Apparently turning on and off the amp for any click or pops (almost as a dare)
There are some other amusing stories.
An Interview With Dafydd Roche | The Amp Hour Electronics Podcast
Pretty good interview.
And did you do this actually? 7492 is already bridged, but does your module have balanced input? Knowing the topology may help identify the problem.
Anyway: try to short inputs directly! If noise appears, then the source is not the amp itself, but interference. 2 MHz on rail is weird, and can also be one of the source of the interference.
I use a tpa3116 module with max gain, and im satisfied, but I use 83 dB sensitivity speakers...
ClassD is capable to produce almost as good noise figure as best ClassA, but definitely sensitive to interference. You can do many things to ease the problem, but can never say you did everything to avoid interference unless you only have 1 clock in the whole system (including environment). But you also can be lucky and you can get noise free signal even in the presence of high disturbing signal if frequencies are locked at a lucky ratio.
Also there is a source of real white noise: fast comparators have higher noise due to high bandwidth. In my designs I intentionally use medium speed comparators and preamplified signal levels at comparator input.
Good advice - thank you therefore.
I will ask for additional advices at the manufacturer of the IC, STMicroelectronics
The most interesting question for me in the moment is follow:
The lowest possible noise floor of background noise in µV/mV at the output from TDA7492 without audio signal at the input and the associated necessary steps therefore (like e.g. emitter/source follower stage at the input).
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Hi Everyone,
Thanks for the feedback (ho ho), I may jump ship to Class-A/B chip amps.; this project is not about ultimate fidelity, or as my colleague refers to it "damped miniature leaf-springs widening the sound stage". It's merely an attempt to re-use some speakers intelligently.
I'll order up a selection of ready-made Chinese boards, compare them, double check my PSUs, decoupling, mute etc.. and report back. The hissssss must be defeated !
Cheers,
ET.
@ET,
Very sensible approach. Looking forward to your findings.
There could be many possible causes of the hisses that you mentioned. It could be design, implementation, components related, nobody knows before a thorough trouble shooting is done (one has to invest a lot of time and effort to do that). All the suggestions put forth may solve the symptom. But then again, it may not.
Regards,
Hiss
ET102.5
I am by no means an expert. But your hiss could be something inherent in the boards.
Don't be discouraged.
I look mainly at the 3116 thread. I have several of these amps and none of them ever hissed except one. (And by the way no turn on/turn off pops either). The one amp I had hiss with was a dual chip 3116.
Fortunately, a smart friend of mine suggested I replace the stock volume pot on that one with a lower value one. He thinks the stock volume was a 50K linear, and I replaced that with a 10K stereo audio. So glad I did that because, although a bit difficult to pull off the board........that totally killed all the hiss.
If you are not an electronics wizard capable of doing complicated calulations and modification (like me), well, you just have to hit on the right amp.
If you find a good amp, post a photo and tell us where to purchase.
Regards,
Mark
ET102.5
I am by no means an expert. But your hiss could be something inherent in the boards.
Don't be discouraged.
I look mainly at the 3116 thread. I have several of these amps and none of them ever hissed except one. (And by the way no turn on/turn off pops either). The one amp I had hiss with was a dual chip 3116.
Fortunately, a smart friend of mine suggested I replace the stock volume pot on that one with a lower value one. He thinks the stock volume was a 50K linear, and I replaced that with a 10K stereo audio. So glad I did that because, although a bit difficult to pull off the board........that totally killed all the hiss.
If you are not an electronics wizard capable of doing complicated calulations and modification (like me), well, you just have to hit on the right amp.
If you find a good amp, post a photo and tell us where to purchase.
Regards,
Mark
Just implemented ICEPower 250 ASP's. All noise I can tell is from the preamp and before. When preamp is muted amps are dead silent.
ET102.5
Did you do the most trivial test: shorting all inputs?
What you did with unshielded CAT5 cable is a perfect way to insert hugh common mode noise, and CMRR of the amp is unspecified, so it can do anything.
Did you do anything to discover some quantifiable noise figure?
Truely interesting, but what is the relevance of this?
Did you do the most trivial test: shorting all inputs?
What you did with unshielded CAT5 cable is a perfect way to insert hugh common mode noise, and CMRR of the amp is unspecified, so it can do anything.
Did you do anything to discover some quantifiable noise figure?
Truely interesting, but what is the relevance of this?
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Errr... bows head in shame
Hi Everyone,
Thanks for the many helpful responses over the last months !
I confess. I simply put the class D/G etc. to one side; life intervened, you know what it's like.
I must say, I feel a natural nervousness towards PWM, it feels unnatural somehow, all that switching, transients, harmonics. I do have some time opening up now, but audio is down the priority list.
All is not entirely lost, I did purchase some genuine PPM meters the other day, you remember them, analogue, black, white numbers, high impedance loop through interestingly, so there is a dim light on the horizon.
Once again, many thanks everyone. ...(exits stage left to chorus of boos and airborne fruit).. for now...http://files.diyaudio.com/forums/images/smilies/grumpy.gif
ET.
Hi Everyone,
Thanks for the many helpful responses over the last months !
I confess. I simply put the class D/G etc. to one side; life intervened, you know what it's like.
I must say, I feel a natural nervousness towards PWM, it feels unnatural somehow, all that switching, transients, harmonics. I do have some time opening up now, but audio is down the priority list.
All is not entirely lost, I did purchase some genuine PPM meters the other day, you remember them, analogue, black, white numbers, high impedance loop through interestingly, so there is a dim light on the horizon.
Once again, many thanks everyone. ...(exits stage left to chorus of boos and airborne fruit).. for now...http://files.diyaudio.com/forums/images/smilies/grumpy.gif
ET.
hiss is nearly always due to a ground loop in the system.. and in some rare cases bad amp design.. test it without being connected to any other equipment, then with a portable audio source
There are lots of EMC issues involved in the design of switcher amps, ground loops being just one, there is a thread with some good guidelines from Keith Armstrong. Having a good layout is often paramount with high speed switching, return loops are critical, ground planes can help, silly spiders legs star grounds are a killer....
check out post #266 and the associated postings under
http://www.diyaudio.com/forums/class-d/275505-tda7492-amp-27.html
http://www.diyaudio.com/forums/class-d/275505-tda7492-amp-27.html
Agree very much. The good news is there are good reference designs available for the more popular ICs and these will usually come with expert layouts as a starting point.
There are data sheets and designs for class D amps and SMPS's as you have said, you would be surprised at how many people DON'T follow the recommended design and design practices, just relaying a board now because its failed EMC, been done by a professional bureau, and the SMPS's are a disgrace to PCB design, I would be looking to sack the designer myself its that bad...
So I agree USE the recommended layout, ignore audiophile deign ideas such as spiders legs style star grounds... Yuk.
So I agree USE the recommended layout, ignore audiophile deign ideas such as spiders legs style star grounds... Yuk.
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