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Convert Speaker Level signal back to Audio Level?

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  • Convert Speaker Level signal back to Audio Level?

    If Craig is going to call this place Tweak City, I'm going to ask a Tweaking question: I’d like to buy or build a circuit to connect a speaker-level signal to an unbalanced audio-level in. Anyone got any leads? Or could you please give me criticism or other thoughts on the following?

    Cause I want to use this circuit to connect back to Room EQ Wizard (REW) (to use it as a speaker-level signal spectrum analyzer), I tried to ask on the REW forum, but I got defeated by those thinking I didn’t know I wanted and trying to help with the problem they thought I had instead. Since there’s nobody here but us chickens (and a few pimps :)), I’m not afraid to look like a total fool – give it to me straight!

    Is all I need a Voltage Divider circuit with the ability to handle enough power? To my poor lil’ mind, based on the 200 Watts into 8 ohms an amp would put out 40V; and if I do the calc with 4 ohms I get 28V. Anyway, what with normal audio levels vs. the power required, and a good margin of safety (e.g., not allowing a teenage boy - including my inner teenage boy - to take over any volume controls), my guess is that 1/25 Voltage Divider would give me a nice input range to the computer sound card for this analysis.

    I’d think I could use the following 10W resistors safely: http://www.radioshack.com/product/in...ductId=2062292

    They are 50 ohm, there’s also 10 and 1 ohm 10W models. Put two of the 50s in parallel with a 1W below the outputs. One of the 50s with two 1’s in series below would be half the current – Might that be better?

    Or is there a problem with that much resistance total, and I should try to mimic an actual speaker impedance? Both of these give me a 1/20 voltage division: a 10 ohm above and two 1’s in parallel below (10.5 ohm ckt), or even go to two 10s in parallel and four 1’s in parallel below (5.25 Ohm)?

    Thanks in advance!

    And for those who aren’t totally bored yet, this is a post with an Appendix! (it’s not important to the original question, but perhaps of interest or worthy of separate discussion): What I want to do is to look at the electrical signal to be able to measure and characterize the noise in my signal chain and try to diagnose if the majority of noise is coming from an amp, the preamp (or AVR, etc), earlier in the chain, or from power, or from cable interactions, RF interference, etc. And do this without having to account for the speaker, room (including ambient noise), or microphone (including repeatability of setup – location and orientation).
    Sent to my room. :smoke1:

  • #2
    Let me Google that for you
    Never Argue With An idiot. They'll Lower You To Their Level And Then Beat You With Experience!

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    • #3
      Dammit!

      You know, I really tried looking for those things earlier, but probably didn't use the right search terms. Then while formulating and posing my question, I get the terminology worked out and forget to go back and search again.

      I'm the guy on the right: :fryingpan:

      OK, since I asked, is my planned approach (a voltage divider circuit) all those things are? Any other notes of interest? Any more piling on to the doofus (said doofus being me)?

      P.S. Thanks
      Sent to my room. :smoke1:

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      • #4
        Originally posted by Eric D
        Dammit!

        You know, I really tried looking for those things earlier, but probably didn't use the right search terms. Then while formulating and posing my question, I get the terminology worked out and forget to go back and search again.

        I'm the guy on the right: :fryingpan:

        OK, since I asked, is my planned approach (a voltage divider circuit) all those things are? Any other notes of interest? Any more piling on to the doofus (said doofus being me)?

        P.S. Thanks
        Whilst you may be impressed with my search engine acumen...you will be less than impressed with my other knowledge.

        I just knew immediately what type of device you were talking about because they are commonly used in car audio when adding an amp to a factory stereo.

        As far as your plans....you'll have to rely on someone else for that....:toilet:
        Never Argue With An idiot. They'll Lower You To Their Level And Then Beat You With Experience!

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        • #5
          This looks nice ... looks like they're using an adjustable resistor to give a variable output level ... And the price sure is nice.. I think I'm going to pick one up just to have it...

          Pyramid Audio NS60

          ..dane
          Attached Files
          (The first to sport a signature on TCAforum..)
          "Be kind, for everyone you meet is carrying a great burden." - Philo of Alexandria
          "Love God and be nice to people." - Brooks Everett of CBC
          d&k's webpage

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          • #6
            My question is, "Will you measuring the quality of the speaker cable or the quality of the your circuit"? :D

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            • #7
              Loop-back tests should tell me the noise level of my equipment (or the capability to measure low). Then I'm curious about all kinds of things, and not having golden ears I prefer to conduct measurements. Some I'd like to try:
              • Try to tell if noise (hiss?) from amp is inherent, or if it is amplifying noise out of my cruddy ole AVR.
              • Continue that chain all the way back to the various sources - DVD, CD, cable, (hopefully streaming coming up) to fight those problems.
              • Troubleshooting the effects of the cable ground, other minor ground loops, RF interference from the TV, etc.
              • See if I can tell what is coming in through power supplies.
              • Noise rejection by twisted pair and/or shielded cables
              • Curious to compare the measurement with a measurement of the room. In particular, where are the largest problems to be found, and where can I get the largest benefit compared to the cost. If I can't distinguish where something is coming from, I keep taking steps that may not be the right ones. (For example but not to start an argument, I'm of the opinion that the really expensive cables are a waste of money compared to room treatments. Maybe I can find something that would either confirm - or change! - that opinion. I do have an open mind, but I like data instead of anecdotes)


              So yeah, measuring the quality of thmy circuit AND the cables.

              enjoy!
              Sent to my room. :smoke1:

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              • #8
                I gotcha, but I think on the speaker cables you need to be able to do the measurements without the conversion from high level back to line level because that is going to screw up your measurements. By how much I don't know... Or maybe I am just :crazy:

                PS - I think you idea is great, hard data is great.

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                • #9
                  Oh, agreed! Forgot to say that different speaker cables are also one of the things to investigate.

                  And I wonder about the speaker-level to line-level conversion. That's kind of one of the questions about whether a simple voltage divider is all that these things are (and whether doing it at the different total resistances, and therefore current, makes any diff).

                  For example, I'd think that a variable resistor and it's wiper would be noisier than a hard-wired resistor network. But at the cost, I'm probably going to get one of those Pyramid Audio boxes too. Even if I make my own, it will be fun to do a comparison.

                  It's all good!
                  Sent to my room. :smoke1:

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                  • #10
                    Generally speaking fixed elements are longer lasting than mechanical-variable elements... however "when new," mechanical-variable elements can be just as high quality.. In many cases the "higher cost = higher quality" statements are true.. (please, let's not bring Monster Cable discussions into this! I'm making a very generalized statement here! :) )

                    I think the Pyramid Audio box with variable output looks very useful since everyone's systems are different, it offers a level of customization to filling your needs.

                    I agree that you should measure your AVR's pre-outs also, however, and include them as a part of your measurement.. But to answer one of your questions-- yes, they are simple voltage dividers.. :) HOWEVER-- they may have a power load resistor in there also so that the amp is actually putting out some power. Your amp will be much higher quality when only spitting out 1W of power.. Hookup a 6-8ohm power resistor and crank up the volume, however, and your amp will be putting out 70-100W or more of power into that load resistor (careful, it WILL get hot) and you can see the "performance" of AVR output stages start to suffer..

                    And even that is only hooking up a purly resistive load to your AVR amplifier.. If you want a "real" load attached, then hook up a no-load resistor divider network (a divider network withOUT a 6-8ohm load resistor) in parallel with one of your actual speakers, and let the speaker be a true load to the AVR, and then take a measurement. Of course THAT type of measurement will only be valid with that speaker's particular crossover network, and itself again will not give a difinitive answer on the 'performance' of your AVR.. but it will give you one more datapoint that can be used in the "big picture" of understanding your AVR's output stage...

                    you can be as simple or as complicated as you'd like.. you just have to well-document your entire setup so that you're AWARE of any setup limitations..

                    look forward to reading more in this thread...
                    ..dane
                    (The first to sport a signature on TCAforum..)
                    "Be kind, for everyone you meet is carrying a great burden." - Philo of Alexandria
                    "Love God and be nice to people." - Brooks Everett of CBC
                    d&k's webpage

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