• State
  • Locked Locked
  • Replies 5 replies
  • Subscribers 30 subscribers
  • Views 996 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Whistling noises with TAS5630DKD

Mattijs de Vries
Prodigy 40 points
Other Parts Discussed in Thread: PCM1795, TAS5630

Hello,

I designed an active stereo organ amplifier (with build in DAC) using the TAS5630DKD fully balanced. One half of the IC does the bass and the other half tweeter. Amplifier is used in AD and BTL configuration, with 43V dc and 12V from a seperated 7812 power supply. We coursly used the TI application digramm, only little differences and off course a different layout, since it had to build inside the organ.I can provide PCB layout and pictures for reference. We use Coiltronics HC1-5R1-R chokes in the filter section and 680nF MMK capacitors. Chokes do not get really warm (40 degrees C) and also residual carrier is about 600mV, seems ok? Design is symmetrical right from the DAC outputs (PCM1795 mono mode).

Amplifier works fine, also sounds really good, but we have constant very audible whistling noises from both bass and tweeter amplifier halves, and also both channels the same. Also a little hum and quite a lot of hiss noise from the tweeter. But these also can be caused by the zero feedback and very compact design. Biggest problem is the quite loud whistling noises.

Can there be any cause for this, probably it is because of the PCB design or Hf filtering/decoupling somewhere, but as far as i can see I did everything the datasheets asked for and still have the problem. Any help would be greatly appreciated! Thanks!

Mattijs

  • 0
    TI__Guru**** 189401 points
    Hi, Mattijs,

    Welcome to e2e, and thanks for your interest in our products.

    I'm not sure what you mean by a "whistle" in the output. Do you have a scope shot?

    -d2
  • 0 in reply to Don Dapkus
    Prodigy 40 points
    Hello,

    thanks for your quick response! It is hard to measure since it is falling inside the residual carrier wave 400kHz sine. Sound is something like wie-oe-wi-oeoeoeh-wiieeewiie, irregular. It comes from both speakers channels alike, and also is present in both bass and tweeter halve, so both chips we use do it alike and also both BTL channels inside the TAS5630. It very probably is from an instability/sensitivity from the power supply, either the PVDD (43Vdc) (30Vac, schottky bridge, 10.000uf, 2.2mH common mode choke, 30000uF, and then splits to both chips with 4x1000uF for each PVDD (8 total), all bypassed with 2u2 X7R caps) or the VDD (12v) (7812 regulated and each pin locally buffered with 47uF X5R, for each pin and the VDDA and B pins with 1R5 and 220nF extra, right on the pin), maybe you can give some hint where it could originate? I designed many amplifiers also with the IRS2052, but did not have this before.

    Thanks! Mattijs
  • 0 in reply to Don Dapkus
    Prodigy 40 points
    Hallo Don,

    I experimented a little further and it indeed seems to come from power supplies. When I supply both with a single PVDD (external) supply they are quiet. Two chips on one supply seems to be the problem. I have added ferrites in the 12V line and three ferrites parallel in the PVDD line, from the star output of the +43V supply to both of the stages. The whistling noises reduced a lot, but still is present, but at a lower level. Input also was shorted at the input capacitors and this also did not make a difference. I also tried different filter chokes, but this did not make any difference, so it seems to be in the supply indeed.

    Does anybody have any idea what to do next, any tips could be very helpfull!

    Thanks!

    Bye,
    Mattijs
  • 0 in reply to Don Dapkus
    Prodigy 40 points
    Hello,

    found it! It is the same carrier wave in both channels (of course, when you found it it is logical, maybe good to mention in the datasheets!). When I put left channel amplfier in AM1 mode and the other channel in AM2 mode (I use AM1 and AM2 because they are close in frequency, but the difference is just outside the audible range) the problem is solved. Both in the same mode gives interference though the PVDD power supply.

    Bye,
    Mattijs
  • 0 in reply to Mattijs de Vries
    TI__Guru**** 189401 points
    Hi, Mattijs,

    Great! Thanks for letting us know! We usually refer to this as beat noise where the difference in switching frequency between two parts can cause noise on the power supply which can feed back.

    You can also fix this by using the SYNC pin.

    -d2