Improving audio output from an HD radio receiver

[Phil] picked up an HD radio receiver when Radio Shack was clearing them out at a 60% discount. But to his disappointment, when he hooked it up the sound left a lot to be desired with limited mid-range and flat bass. After some forum mining he discovered that the optical output didn’t have this problem, and came to the conclusion that the op-amp driving the analog audio-out jack needed some tweaking. He didn’t get his hands on a schematic for the board, but took the advice from some vintage equipment gurus and swapped the stock IC for a Burr-Brown OPA2604AP chip.

This fixed the problem without any other adjustments to the hardware. But while he was in there, he also secured the external antenna connector jack to the chassis for good measure.

If you’re wondering about the particulars of the equipment, [Phil] was hacking an Auvio HD Radio tuner. But he also mentions that Best Buy sells an Insignia NS-HDTUNE which may benefit from the same modification.

Comments

  1. The Timmy says:

    nice. this project has me thinking… what electronics of mine are lacking in their potential due to poor/cheap component selection.

  2. echodelta says:

    Interesting how the makers of this NPR aided scam can’t even do audio as good as an old walkman.
    Can anyone hack an FM tuner to restore the severe multiband maximum compression that seems to be coupled with the use this very low definition digital mode. Perhaps by using the crap on the Hybrid Digital a reference for restoration of the FM service can be done. Or is it just as smashed as what is done to the FM? I have lost the listenable FM service of several public radio stations, even the hifi service of WBAA AM. Only one station, WBAA FM Purdue still leaves the audio alone. Gone are Chicago, Elkhart, 2 Indy, Normal, Chambana. It may be time kill radio and TV and just saturate the EM spectrum with digital internet conectivity. Many AM stations are stoping using HD at night because of the interferance it makes to other stations!
    Hack away please, this killing radio.

    • Chris says:

      As odd as that rant reads, I understand and sympathize.

      Let me give a little background on that.

      Analog FM audio is compressed, always boosting the loudest sounds to 100% volume/modulation, and making quieter sounds disproportionately louder.

      The original reason this was done was to help hide the noise floor (the low, constant hiss heard if you crank up the volume). And that was OK, even though it constituted a change in the way the music sounded.

      Eventually transmitters and receivers improved, and the noise floor dropped enough that compression wasn’t needed anymore. Some stations dropped the compression, to play the music the way it was meant to be played; only to find their listeners dropped off precipitously.

      Research was done. And it was found that when someone was flipping through channels, they were significantly more likely to stop on stations with the loudest, fullest sound. Furthermore, if someone is listening to a station with less volume (but better fidelity and dynamics), they tend to increase the volume. And when they eventually switch to another, artificially louder station, they get blasted; so they get irritated with the softer station.

      And that’s where it all went wrong. Because then it became a pissing contest to have the loudest, fullest sound, rather than the best fidelity. Stations cranked their compressors to the max, trying get as close as possible to 100% volume, all the time. Multiband compressors were added, to individually boost bass, midrange, and treble to 100% for an even louder and fuller sound, regardless of the original frequency balance of the music.

      Unfortunately, we’re stuck in this mess for good. No one, save for maybe a few college radio stations, dares reduces the compression to improve fidelity. Because that means less listeners, which in turn also means less income from commercials. Volume is money!

      I have a high-fidelity, low-power FM transmitter to distribute music throughout my home. I compress lightly, and music sounds very good. I must remember, however, to reduce the volume before I switch to a commercial FM station. :)

      • Panikos says:

        Chris,

        I am not even interested in FM and I loved reading your comment. Somehow the rant before didnt make sense without the context you provided. I ended up re-reading echodelta’s comment again and it made more sense after your input.

        Regarding the home FM transmitter you mentioned is this a homebrew or commercial product? Any legal implications to running it at home that you know of?

        Thanks

      • Jay says:

        One of the college stations in the Northwest I’ve volunteered at only uses compression on their stream; http://www.kmhd2.org

      • cutandpaste says:

        Ramsey Electronics sells FM radio transmitters in kit form, or prebuilt, with complexity output power ranging from “tiny” to “quite a fair bit.”

        Fidelity is whatever it is, but the kits don’t seem to change much (if any) so anything suboptimal about them has surely been hacked around and documented by now.

    • N0LKK says:

      Good to know if I where ever to purchase a low end HD receiver, and not be satisfied with the audio performance.

  3. John W says:

    Is it just me, or does the construction of that board look ancient. I mean, through-hole components? Really?

  4. flux says:

    Do people still listening to the fm/am radio? Really?

    • cutandpaste says:

      For those of us who like original and/or live programming, or just don’t feel like being a DJ today: Radio works fine, especially when mobile.

      When I still had a good FM antenna (and before podcasts and live streaming became common), I had a FreeBSD box which recorded (and encoded) NPR shows automatically with a few simple cron entries. The results sounded wonderful, and it was very reliable and punctual (thanks to ntp)

      I can do much the same thing with wget and/or pre-packaged podcasts nowadays, but I digress.

      My Droid is perfectly capable of playing everything I have at home via subsonic, wherever there is Verizon coverage. But if I’m taking a trip in the car on a Saturday afternoon, or spending half my workday driving around for service calls, I like radio.

      But, you know: That’s just me.

  5. strider_mt2k says:

    HD Radio remains one of the worst marketed things…like…ever.

  6. John says:

    No wonder that HD radios are so lacking. I envisioned one in which you bought it, took it home, allowed it to connect wirelessly to your router, and it would give you ‘unlimited’ HD content with the abilty to record it, and without the range constraints of regular am/fm. Sadly there is not a single device I know of which actually does all that.
    As for the question as to whether am/fm is still listened to, are you daft? Just because you can now stream hundreds of radio stations from all over the world does not mean you will get quality sound whatsoever, much less that the server and or connection will actually work 24/7 as do ‘normal’ radio station broadcasts. My favorite radio station is in HI and I am forced to listen to it via the net, but the sound has degraded to pretty much unlistenable. It stated out at 64kbps stereo and is now at 32kbps mono. Believe me, the actual fm broadcast is heaven compared to that.
    Too bad about hd. Most stations won’t be able to afford it anyways.

  7. Strider_mt2k says:

    The HD in HD Radio means hybrid digital, not high definition.
    There is no HD content, just existing content at a supposedly better resolution.

    • Min says:

      No supposed involved. HD Radio is awesome. I wouldn’t buy a radio without it now. It makes a slight but noticeable difference with FM but a staggering difference with AM. If you listen to AM regularly, you MUST get an HD radio. Who cares what the “HD” actually stands for? It works and it is a very significant difference for little cost.

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