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pre amplifier/ line in mixer chip

Discussion in 'General Electronics Discussion' started by swagguy8, Feb 25, 2015.

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  1. swagguy8

    swagguy8

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    Dec 10, 2014
    hey guys, so i'm building a super hifi power amplifier from a chip amp, the harmonic distortion is 0.0003%, and i need a line in mixer. but all the line in mixers they sell in stores are => .01 harmonic distortion. i'm curious if anyone knows a weak hifi chip amp that'll do the job.

    thanks!
     
  2. BobK

    BobK

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    Jan 5, 2010
    If you think you can hear the difference between 0.0003% distortion and 0.01% distortion, you are wrong.

    Bob
     
    KrisBlueNZ likes this.
  3. swagguy8

    swagguy8

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    6
    Dec 10, 2014
    its not like i can hear a difference, and i know that, i am an audiophile. But my power amp is .0003 % thd, and putting a inline mixer thats 0.01% will kill the purpose of the power amp being an overachiever in THD. but, once you crank up the power amplifier or the inline mixer, the distortion goes up, and i wouldn't like to hear it. the center frequencies ~5k-10k will still be low, but the high and low frequencies will be distorted.
     
  4. swagguy8

    swagguy8

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    6
    Dec 10, 2014
  5. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    After years of exposure to high-volume rock and roll, my ears are no longer "golden" (if they ever were). Still, I can appreciate (to a certain extent) the audiophile's desire to approach perfection. Fortunately you are in good company with the wizards at Texas Instruments, who absorbed the analog geniuses at Burr-Brown many years ago and continued their tradition of analog excellence. The OPA2134 looks like it will be ideal for your line-mixer application.

    Be sure to pay close attention to layout and grounding to prevent cross-talk. Make sure the signal levels are well below the maximum limits and that the power supply is well-regulated and by-passed at the OPA2134. Depending on the line impedances involved, you may be able to avoid buffering the inputs, but separate gain blocks for each input channel would be preferable, IMO.

    Can you provide any information (specifications, schematics, pictures) of your power amplifier? How do you even measure THD down to 0.0003% much less 0.00008%? Sounds to me like you need really expensive test equipment.to separate the fundamental frequencies from the harmonic frequencies. I bet you need a really low noise floor, too, for meaningful measurements. This is just to satisfy my curiosity; I haven't "played around" with audio circuits in more than forty years.

    73 de AC8NS
    Hop
     
    swagguy8, davenn and KrisBlueNZ like this.
  6. swagguy8

    swagguy8

    73
    6
    Dec 10, 2014
    heres what im doing:
    LME49811 for subwoofer amp, highs arent really good, but lows are siiiick, its basically a flat line thd across most frequencies lower than 10k.
    circuit: http://www.elisanet.fi/ch/gainx2.html (courtesy of chris)

    LM4702B (4702A if possible) for main amp, designing something according to datasheets, there arent any circuits available online, so ima gonna use the original circuit on the datasheet and application notes, and select the best config for it.
    http://www.ti.com/product/LM4702/technicaldocuments
    download all three documents, and you should be able to figure out the circuit.

    building amps are really fun, especially when you could build something that has better sound quality than a high end 5k dollar marantz, and possibly get better sound quality, especially when a marantz has 0.01% thd.

    thanks for your advice in grounding by the way.
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    I would love to design a pair of Bluetooth digitally programmed hearing aids with DSP to filter out background noise and perhaps enhance response to speech to match my ears. These are available commercially of course for several thousand dollars per ear. What a rip-off! The Bluetooth interface is both for programming the DSP as well as for connecting to external audio devices. Probably ain't gonna happen in what time I have left. Thanks for the links!

    P.S. I have considered "designing" tube-type audio equipment. The good circuits performed well back in the day, and some people with deep pockets and a penchant for nostalgia (and probably not-so-golden ears anymore) are willing to pay big bucks for a chromed chassis and glass tubes that glow softly in a dimly lit room. Hard to find tube components though, unless you go with "new old stock" or foreign manufacturers. You can purchase custom-wound transformers easily enough, but those are pricey. And if I were to do this, I would have to build one for me as well as one for them. <sigh>
     
  8. swagguy8

    swagguy8

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    Dec 10, 2014
    wait, hearing aids? whats the bluetooth for? listening to music? i wouldn't use bluetooth, as its sound quality is limited to like 48k hz bitrate i think. using another type of transmission would be better, but the problem is that stuff thats on the market isn't high quality enough, so you probably have to design and program your own.

    tube type audio equipment sucks sh*t (no offense). the thd is so high, there sooo inefficient. I'm paying a visit to china in the summer, so that'll probably be my "parts run". stuff is like 1/4 of the price in the USA, you just have to make sure its genuine parts from TI.
     
  9. hevans1944

    hevans1944 Hop - AC8NS

    4,560
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    Jun 21, 2012
    Bluetooth data rates are about 2.1 megabits per second. See this link. And, yes, I would like to have a Bluetooth link to listen to audio from other electronic sources, such as television or my cell phone, without assaulting the ears of people with "normal" hearing. No problemo designing my own stuff. Biggest problem is making something that will fit in my ear canal, although behind-the-ear would be okay for me. I am not style-concious.

    Good luck buying "genuine" parts in China. They are experts at counterfeiting electronics (as well as other consumer items). Part numbers and logos are no guarantee that a part is genuine. You have to decap the device and examine the actual die under a microscope. Even then you need to know what to look for because the Chinese decap genuine parts and "reverse engineer" them. That saves them tons of development costs, and sometimes it works very well and you won't notice any difference, but its always a crap-shoot buying parts in China. There is a whole industry devoted to exposing counterfeit electronic parts... and they are losing the battle. Best best to get "genuine" parts is to purchase them from an authorized distributor who guarantees authenticity. You can also purchase TI parts online directly from TI.

    I am well aware of the limitations of tube type audio equipment, but not all designs are poor. Most people don't have "golden ears" and would fail to recognize harmonic distortion or cross-over distortion if it bit them in the ass. Witness the popularity of "boom boxes," which are not high fidelity (just loud) sound producers. Rock music groups deliberately add distortion to create their own unique sound signature... which is then promptly copied. Some people actually like the sound produced by tube-based audio electronics. Just as some people prefer vinyl records over digital media, and some people will swear by OFHC copper cables and gold-plated connectors, there is a high-end market for tube-type audio equipment. You pays your money and you makes your choices, for better or worse. I am almost cynical enough to cash in on the vanity exhibited by many rich audiophiles. Maybe I will build some handmade vacuum tubes based on Philo T. Farnsworth's multipactor design... I could probably make all sorts of esoteric claims for these long-forgotten puppies. Heh.
     
    davenn likes this.
  10. swagguy8

    swagguy8

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    Dec 10, 2014
    well, i guess everyon has their own opinions. My dad knows how to buy genuine parts from china because he used to live there... so yeah
     
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