I can see all the Engineering students and techies getting out the books and researching on the net now... probably boring for some, but the techies in the hobby / business will walk away with a better understanding of audio. Kevin Custer wrote:
I think this discussion will end up being very interesting, but I think we need to quantify all of the parameters so we are playing with apples and apples. Discriminator audio is not always high impedance; many radios. . . I think he was asking because he got out the formulas which involve impedance in calculations. The prize / discussion is to prove that the resistor or even two series resistors, wherever you place them in series with the audio, change the output de-emphasis. Pick whatever impedance you want in and out, but the arrangement of the components is the discussion. Ken, will get $100 if he and his supporters can prove it makes a difference. If he can, I will send the "C note", and go build it myself in the shop. When I went to school, it's a time constant formula, with two variable values. The values are given, so it's now a discussion of circuit design. So, how about we use a source impedance of 100 ohms, and an audio range of 50 to 5000 cycles.. . . That sounds good to me. As you said, make it simple. Pick any impedance in or out, and that is a constant. The value of "C" is defined, and the value of the series resistance is defined. If Ken or his helpers can show me that arranging the series resistance of the circuit, either before, after, or (I added this opportunity) even split into two resistors, makes a difference in the EQ output like they say, Ken get's a crisp $100 bill. The slope of the De/Pre-Emphasis isn't what is important here, as that won't change in a 2 component circuit, what is important is where the circuit starts (or finishes) working; which will affect the equalization of the transferred audio. . . You're going to have to help me with this one Kevin. The "slope of the De/Pre-Emphasis" is "the equalization of the transferred audio." I missed something. We'll wait for the results after the soldering iron heats up. If I'm wrong, boy am I going to have to apologize for using all this bandwidth! Bill Hudson, W6CBS Kevin Custer Bill Hudson wrote: Discriminator is always high impedance so high impedance into the circuit. De-emphasized audio is typically used for microphone input, which would typically be low, but you can hang whatever impedance you want because in this case, "it's only audio". The output impedance isn't going to matter much for audio EQ, except really low impedance is going to "horse down" the level into the transmitter (circuit output). In this case, you can just about choose your "output" or "transmitter input" impedance. EQ wont change enough, to make a difference. From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Doug Zastrow Sent: Saturday, December 30, 2006 6:23 PM To: [email protected] Subject: Re: [Repeater-Builder] Re: audio equalizers for repeater audio-circuit correct?? Bill, What source and load impedance are you looking at for this test? Doug ----- Original Message ----- From: Bill Hudson <mailto:[EMAIL PROTECTED]> To: [email protected] Sent: Saturday, December 30, 2006 8:12 PM Subject: RE: [Repeater-Builder] Re: audio equalizers for repeater audio-circuit correct?? To: Ken Cc: Laryn Tell you what Ken. I'll make you a deal. You have the facilities to do it, and you have the test equipment to prove it. I'll let you do the work. The time constant equation is the same, if you put the capacitor in front or behind the resistor. In fact: You could put a 7.5K in front of, and a 7.5K behind the capacitor to ground, and you should get the same time constant, roll off, de-emphasis. I have never tried it. Here's the deal. You build it and test it, and if you can make the de-emphasis different by placing the resistor before, after, or splitting them with 7.5K resistors on both sides, I will send you a crisp one hundred dollar bill ($100) in the mail. I've never done it - but where I went to school, it shouldn't matter. Let us all know what you find. If you find a difference, I'll send you $100. Of course, I'm going to be out $100, but then I'm going to go build it myself and make sure you're not fibbing! :-) Bill Hudson W6CBS
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