Announcement

Collapse
No announcement yet.

Interesting Power Supply Issue...

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Interesting Power Supply Issue...

    I've been working on the internals for a table radio project outlined here: http://techtalk.parts-express.com/fo...o-build-thread

    Started messing around with the components again and was thinking of just using a 12V power supply to make my life easier with wiring, possible noise issues, etc. I have used that amp previously with 12 V at 3 or 4 amps and it powered the little ND65's nicely.

    The amp is this one: https://www.parts-express.com/tda749...2x50w--320-606
    The faceplate unit is this one: https://www.parts-express.com/12-vdc...remot--320-348
    The PE power supply is this one: https://www.parts-express.com/12-vdc...-plug--120-056

    The faceplate has a plug that actually fits right into the socket on the amp board, making things a bit easier. I tried to power it with the PE 12V, 5 amp unit and I got all kinds of noise on the amp. I disconnected the faceplate, still lots of noise. Not high freq. hiss, but just noise... way too much to tolerate. I took the faceplate off of the common PS so it was not connected to the amp at all thinking maybe that was it, but the noise was still there. Touching the heat sink on the amp quieted down the noise a lot. I also removed it from the MDF mounting panel to which it was secured with those little brass standoff's for mounting circuit boards... thinking maybe it was causing interference somehow with that, or that the brass pieces were touching something on the board that it shouldn't, but nope.

    Thinking it was the amp, I tried another of the same type... same noise exactly. So I changed out the PS for another 15V one.... the noise was there, a bit different, but mostly the same, and still way too loud to tolerate. Then I tried the 16V PS I had originally intended to use with it and it got quiet, good enough to use no problem. The wire runs were real short, I was just testing this on the bench... I moved things around with no changes in sound/noise. It was the PS that was the issue. I've used this amp board a few times before with no issues, it always seemed pretty quiet to me, so when it started making so much noise, it surprised me. The 16V PS was a fairly cheap one not from PE, can't even remember where I got it, MPJA or Amazon... but it was nothing special, and I'm sure I didn't pay much for it.

    I'm not bashing PE's 12v PS either, it puts out the right voltage and I have no reason to believe it won't get close to it's 5 amp rating, just strange that I had so many noise issues. Makes me wonder if some of my other previous noise issues with small amp boards may not have been at least partially caused by incompatible power supply bricks.

    So is this a switching issue with the PS, since the amp and PS both using digital technology at various frequencies to operate? The non-noisy 16V PS had a ground plug on the AC side where the other two did not BTW.

    I have a solution... just use the 16V PS I intended to use in the first place, but I'm just curious as to what may be the cause of the noise and if any of you have experienced this before.

    TomZ




    *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
    *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

    *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

  • #2
    Hi Tom:

    Given that the noise is diminished by touching the heat sink, take a pair of clip leads and a non-polarized capacitor and connect the heat sink to ground on the amp. If it makes a big difference, you have your solution. Be prepared to disconnect quickly if there is any suspicion of letting out the magic blue smoke.

    Comment


    • #3
      Originally posted by Roger Hill View Post
      Hi Tom:

      Given that the noise is diminished by touching the heat sink, take a pair of clip leads and a non-polarized capacitor and connect the heat sink to ground on the amp. If it makes a big difference, you have your solution. Be prepared to disconnect quickly if there is any suspicion of letting out the magic blue smoke.
      +1. The sink may be acting as an antenna. The TDA7492 datasheet implies the heat sink is supposed to be grounded by the implementation. That the chip's pad is not grounded within the chip but it should be grounded.

      Comment


      • #4
        Tom, sounds like a ground loop or missing ground you fixed by adding the earth ground back to the power supply.

        I recently debugged a similar problem (but opposite "fix" to yours) with a new dac/pre connected to my laptop through USB. In my case to get rid of bad noise, I had to break a ground loop by using a double insulated 2 prong supply to replace the laptop's 3 prong supply. Word of safety caution: if you're ever replacing a 3 prong supply with 2 prong, consider using a double insulated 2 prong supply. A single insulated supply could send a shock to case (if gounded) if there's a failure. Double insulated is denoted by a symbol on the supply label, box within a box.

        Comment


        • #5
          Thanks for the insights guys.

          So if I were to try and ground the heatsink to the board to cut down on the noise... I would drill/tap a machine screw into the heat sink for a short wire, then connect the other end of that line to (I'm guessing) the negative power input phoenix terminal? Sounds easy enough to try.

          TomZ

          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

          Comment


          • #6
            Originally posted by tomzarbo View Post
            Thanks for the insights guys.

            So if I were to try and ground the heatsink to the board to cut down on the noise... I would drill/tap a machine screw into the heat sink for a short wire, then connect the other end of that line to (I'm guessing) the negative power input phoenix terminal? Sounds easy enough to try.

            TomZ
            Alligator clip to test ..

            No disrespect to DDF, but the PS is 2-prong and the only thing connected to house power - no ground loop. This is likely HF switching noise from the PS unit (and/or from it's wires). You could also try some small caps (1uf, and below) across the amps PS input terminals to further reduce PS noise.

            Comment


            • #7
              Originally posted by Millstonemike View Post
              Alligator clip to test ..

              No disrespect to DDF, but the PS is 2-prong and the only thing connected to house power - no ground loop. This is likely HF switching noise from the PS unit (and/or from it's wires). You could also try some small caps (1uf, and below) across the amps PS input terminals to further reduce PS noise.
              I tried to ground the heat sink to the negative and it had no effect.
              Do you mean by "Across the PS input terminals" to place that tiny cap connected to the (-) and (+) terminals?

              TomZ
              *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
              *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

              *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

              Comment


              • #8
                Hi Mike, Tom mentioned the noise was fixed by switching to a 3 prong supply. Sounds like that provides a return path to ground for the noise Sent from my SM-P600 using Tapatalk

                Comment


                • #9
                  I put a small .01 cap from the (-) to (+) terminals and it had no apparent effect. I'll just go with the 16v and use the voltage reducer to get 12v for the faceplate.
                  Just had a funny strange experience.... earlier today I tested this setup with my iPod on bluetooth. Turned it off and took it downstairs.

                  Just a few minutes ago I fired the amp/faceplate up to give the Mike's suggestion a try and it started playing music and it wasn't on the radio. The faceplate goes into BT mode first I guess and it sent out a wake-up message to the iPod and it started playing. Freaked me out a little bit. Also, using the remote control for the faceplate volume up/down changes the volume on the iPod and vice/verse. Going up/down on the iPod volume changes the volume on the faceplate unit. Maybe that's always been, but other BT devices I have didn't work that way. Cool though. I think this faceplate pre-amp thing might end up working out. FM is marginal, but BT seems to work well enough.

                  Oh, I clipped an extra long lead to the antenna to see if it helped with reception and it did not. So, I'll scrap the extra antenna idea I guess.

                  TomZ
                  *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                  *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                  *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                  Comment


                  • #10
                    Originally posted by DDF View Post
                    Hi Mike, Tom mentioned the noise was fixed by switching to a 3 prong supply. Sounds like that provides a return path to ground for the noise Sent from my SM-P600 using Tapatalk
                    Yes, but I still wouldn't call it ground loop. How could it be? There's only one device plugged in. When true ground loop issues arise, it is between devices (at least my definition).

                    I'm more inclined to think it's the the 3-Prong PS output exhibiting lowered emissions / noise. Many 3-prong supplies tie their minus DC output to the third prong. That may provide some stability to the particular PS design.

                    That's what I read you saying. And I would agree.

                    Comment


                    • #11
                      Hi again, Tom's post didnt describe the source (maybe I missed it). The source could create a ground loop. I've put a lot of products through gr-1089 emissions/ susceptibility testing in rf chambers, it would a really bad design to suffer so much susceptibility to rf/emi especially if the smps brick is feet away. Of course you could be right though Sent from my SM-P600 using Tapatalk

                      Comment


                      • #13
                        Originally posted by DDF View Post
                        Hi again, Tom's post didnt describe the source (maybe I missed it). The source could create a ground loop. I've put a lot of products through gr-1089 emissions/ susceptibility testing in rf chambers, it would a really bad design to suffer so much susceptibility to rf/emi especially if the smps brick is feet away. Of course you could be right though Sent from my SM-P600 using Tapatalk
                        It's the "Toni Radio Table" build thread. All self contained with the amp and BT / Aux / FM PE control panel powered off the incoming DC (with some step down for the max 12 V ctrl panel). They both only have DC gnd and DC+ inputs, DC isolation in the signal between the two is handled by the amp's input coupling caps.

                        Comment


                        • #14
                          So this project is 'complete' in a sense for now.

                          Toni Table Radio thread: http://techtalk.parts-express.com/fo...o-build-thread

                          Regarding power supply issues..... I ordered 3 different 12v power supplies for this radio from MPJA in hopes one will eliminate most of the noise. Reason I didn't order from PE is that two of them had a third ground plug on the AC side, so I'm hoping that will help me out with an easy solution. PE doesn't sell any with the ground plug that I saw.

                          Also, noted above, the 16v PS that was fairly quiet powering this amp had a ground plug, but upon further inspection, it only connected to the brick with the usual 2-prong connector, so..... The ones I ordered from MPJA have three prongs (mickey-mouse type) on the brick, so maybe that makes a difference. Just for fun, I put the three-prong AC cord on the 12v power brick and it was still noisy.

                          Also, I've ordered this 12v T-amp from PE as another option if the PS issue can't be resolved. This one: https://www.parts-express.com/t-amp-...board--320-600 Hopefully, this one will be quieter.

                          I'll need to do a slight rework for that to fit, but it shouldn't be too hard to accomplish. I'm hoping that a decent 8-10 watts or so should be enough for these speakers to sing.

                          Either way, I'm having the usual issues that many seem to have with electronics and power supplies, but maybe with a bit of help from the braintrust here, I'll get this figured out soon enough.

                          I'll report back here and on the other thread how it works out in a few days when the parts come in and I get a chance to try the different options out.
                          Thanks guys for all your help and suggestions. It's appreciated and needed.

                          BTW, once the volume goes up and bit to drown out the noise, it's a REALLY nice sounding little radio, I'm surprised at how bassy and clear the sound is.

                          TomZ
                          *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                          *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                          *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                          Comment


                          • #15
                            Well, a picture is worth a thousand words...

                            here's a video that may help describe what's happening on this 50 watt amp board: https://www.parts-express.com/tda749...2x50w--320-606

                            VIDEO -----------> https://youtu.be/Ct5gfyyjWm8

                            TomZ
                            *Veneering curves, seams, using heat-lock iron on method *Trimming veneer & tips *Curved Sides glue-up video
                            *Part 2 *Gluing multiple curved laminations of HDF *Cello's Speaker Project Page

                            *Building the "Micro-B 2.1 Plate Amplifier -- Part 1 * Part 2 * Part 3 * Part 4 * * Part 5 'Review' * -- Assembly Instructions PDF

                            Comment

                            Working...
                            X