Noise from my TPA3122D2 amp

[Lo_Tse]

I bought the kit from Sure Electroninc on EBay. I think this kit is the same as the one on sale at Parts-Express. Soldered everthing and the amp worked with no issue. The power supply that I use is an old lab top brick (+-19V). The sound was much better than I expected. Quite enjoyable.

However, as I listened more carefully, I heard some low level hissing noise . I confirmed that by putting my ears right in front of the speaker drivers (tweeter). It did not sound like some kind of background noise because the noise seemed to be modulated by the signal i.e. when the sound level is higher, the noise got higher. Also, the noise seemed to follow the music's rythym too!! I suspect the noise is associated with the power supply. Those lap-top switching PSU are known to be noisy. Does anyone has similar experience?

Regards,

 

[DUG]

Hi Lo_Tse

Perhaps a mixing of the two switching frequencies.

Try an L - C - L - C filter to really clean up the supply lines?

 

[Lo_Tse]

Hi Lo_Tse

Perhaps a mixing of the two switching frequencies.

Try an L - C - L - C filter to really clean up the supply lines?

Hi, DUG

Thank you for the suggestion. I am thinking along similar line - may be I should rig up a linear psu with a CRCRC (I have no inductors in my bin) filter bank and try it out.

Regards,

 

[DUG]

If that is the issue...I have some...when is the next Toronto meet?

 

[Lo_Tse]

If that is the issue...I have some...when is the next Toronto meet?

DUG,

Thank you in advance. I am not sure. Missed you last time. I guess it depends on how interested people are in getting together and whether someone is willing to host. Soon, I hope!

Regards,

 

[xrk971]

Tpa fans! I wish I was in Toronto area to drop by your meets. I have had more noise on bricks that are not grounded (2 prong wall plug) vs grounded (3 prong).

Dug, I am still enjoying my tpa3116d2 very much thanks to you. I need to design a pcb and order boards and make more. They are so useful to have. Being so small it makes sense to put them inside speaker cabinets for powered monitors.

 

[Lo_Tse]

Hey, xrk971

I was thinking about that too. The cable that connect my "brick" to the wall is three pronged. However, between the "brick" and the amp board, only two => + and -. So my interpretation is that there is no ground. I do not know whether it is good or bad. I guess the amp does not need a "ground" per say, as long as there is a signal return.

Apart from the noise, my 3122 amp sound pretty decent. A TPA3116D2 amp is definitely in my near future .

Regards,

 

[xrk971]

The ground is internally connected to the ground or non positive 19 v line. Your power supply is not the problem, switching power supplies are actually pretty quiet at audio frequencies. The 3122d2 uses electrolytic caps on the output side, make sure those aren't damaged or in backwards, or maybe not rated for 38 volts? I think output voltage can swing double the input rail? If it is 35 volt rated cap, you may be getting some leakage. Try 50 volt caps.

 

[Lo_Tse]

The ground is internally connected to the ground or non positive 19 v line. Your power supply is not the problem, switching power supplies are actually pretty quiet at audio frequencies. The 3122d2 uses electrolytic caps on the output side, make sure those aren't damaged or in backwards, or maybe not rated for 38 volts? I think output voltage can swing double the input rail? If it is 35 volt rated cap, you may be getting some leakage. Try 50 volt caps.

Thanks for the tip. I'll check again.

Regards,

 

[DUG]

Update on my TPA3116 that I had at the show.

Put it in a box with some other stuff and I have some "noises" similar to what you may have heard with your amp / SMPS combination.

I had a piece of one sided pcb and some very low ESR caps and chokes laying around (inductors from computer PS...output filters, the common mode choke from computer ps)

put some cuts in it and drilled some holes (most in the right place)

Threw in some 0.1uF 0805 caps as well

built a filter and installed it...no more SMPS noise.

 

[xrk971]

Nice work Dug. Did you scavenge those chokes from an old AT style PC power supply box? I have thrown so many of those away. Should have scavenged them... How did you come up with the circuit?
Glad it worked.

 

[Lo_Tse]

Update on my TPA3116 that I had at the show.

Put it in a box with some other stuff and I have some "noises" similar to what you may have heard with your amp / SMPS combination.

I had a piece of one sided pcb and some very low ESR caps and chokes laying around (inductors from computer PS...output filters, the common mode choke from computer ps)

put some cuts in it and drilled some holes (most in the right place)

Threw in some 0.1uF 0805 caps as well

built a filter and installed it...no more SMPS noise.

DUG,

Hey, I think I still have one of those sitting in my basement waiting to go to the "computer heaven". May be I should salvage the PS unit, just for parts.

By the way, I found a way to deal with the noise - just cut the gain . The gain was set at high (36 dB). I recalled that typical commercially produced amps are ususally come with a gain of around 26 dB. So I reduced the gain (using the sliding switches) to 32 dB, the noise is essentially gone!! The 10$ amp sounds great!

Definitely, this TPA3122D2 amp tend to tilt towards the high frequency a little more. However, this property renders the amp more lively and quite airy sounded. I would not call the amp bright at all, just more sparkle at the high. Did not get a chance to check out its low end yet. I have to find an occassion when my wife and kid are not in the house, then I can pull out all my special CD collection to test thebase perfomance at "realistic" level. One thing I noticed too is that the amp does not provide as "dark" a background as my Bryston.

Overall, I am happy with this 10$ amp (the speaker binding posts cost me extra $5). I have ordered a tiny preamp from EBay and I am going to pair it with this class d amp. Really curious how would this combo compare to an entrylevel receiver!!

Regards,

 

[DUG]

I don't trust the caps in dead computer supplies but the inductors are great.

On another note

My 3116 in a box:

http://www.diyaudio.com/forums/class-d/87913-class-d-amp-photo-gallery-69.html#post3480239

 

[xrk971]

DUG,

Hey, I think I still have one of those sitting in my basement waiting to go to the "computer heaven". May be I should salvage the PS unit, just for parts.

By the way, I found a way to deal with the noise - just cut the gain . The gain was set at high (36 dB). I recalled that typical commercially produced amps are ususally come with a gain of around 26 dB. So I reduced the gain (using the sliding switches) to 32 dB, the noise is essentially gone!! The 10$ amp sounds great!

Definitely, this TPA3122D2 amp tend to tilt towards the high frequency a little more. However, this property renders the amp more lively and quite airy sounded. I would not call the amp bright at all, just more sparkle at the high. Did not get a chance to check out its low end yet. I have to find an occassion when my wife and kid are not in the house, then I can pull out all my special CD collection to test thebase perfomance at "realistic" level. One thing I noticed too is that the amp does not provide as "dark" a background as my Bryston.

Overall, I am happy with this 10$ amp (the speaker binding posts cost me extra $5). I have ordered a tiny preamp from EBay and I am going to pair it with this class d amp. Really curious how would this combo compare to an entrylevel receiver!!

Regards,

That was the cheapest solution I have ever heard I think I have my 3116D2 set at the lowest setting which is 26 dB - still plenty of gain when driven by line level. When driven by an iPod, it could use more but the noise performance and "dark" level are outstanding. If you can live with less gain, try the 26 dB setting to reduce your noise floor.

 

[Lo_Tse]

@xrk971

I am going to set it to the low gain setting (26 dB) and see (hear). Actually, the lowest setting available is 20 dB. I have my preamp (which can provide 20 dB gain if needed) connecting to the amp, so there are plenty already. I wish all the amps would come with selectable gain settings.

Regards,