wallyns10
44 posts
Oct 20, 2009
8:56 PM
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Could you explain the what the hell Hi-z and Lo-z means? I've got an EV664 which has a Hi and Lo-z function but I don't know what the difference is. One of them is shot, and I don't know which one. I have a spare mic (same model) that I got from the school my mom teaches at. Would this be a wiring issue or should I try swapping the elements or is it best just left alone since I am totally green at mic work. Also, do you have any good sources for someone who is very ignorant about but very eager to learn about circuitry and electronics and stuff like that? Thanks!
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isaacullah
406 posts
Oct 20, 2009
10:44 PM
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Hi wallyns10, yeah I'll do my best. The "Z" stands for impedance. Electrical impedance is a concept that is similar to, but not the same as electrical resistance. They are related, but not the same. Resistance is opposition to the flow of electrical current through a conductor. In DC circuits, resistance is all you get because the voltage stays steady. However, in AC circuits, the voltage is always swinging along its sine curve (amplitude) from positive to negative. Because of this, the actual resistance of a conductor in an AC circuit is variable, and is thus referred to as impedance. Because sound is a sine wave, when we use a mic element (a transducer) to transform this into electrical signals, these signals are best represented as AC signals. Therefore, we have to deal with impedance rather than resistance.
So there are TWO types of impedance we have to deal with. Input and output impedance. The impedance characteristics of a mic element are OUTPUT impedance. This refers to how strong the signal will be at the output of the circuit (ie. coming out of the mic), and details the amount of AC resistance the output signal will be able to handle. All audio circuits will also have an INPUT impedance. This refers to the amount of signal they are expecting to see, and details the amount of resistance they are going to put up to the flow of the AC signal.
So this leads to Impedance matching. Obviously the best situation is when the output impedance of one audio device matches the input impedance of the next. If this is true, then the output signal of the first device is JUST high enough to get through the second device and do what it needs to do there. Now in harp world, perfectly matched impedances is not always desirebale. In fact, you may want mic with a high output impedance (hi-Z mic) that will actually overdrive the input to the following circuit (usually a tube preamp). If your mic has too low of an output impedance, then the AC resistance it encounters in the next stage will be too much, and the signal will be very weak when it reaches the amplification stage. You won;t get that nice fat overdrive, or even a nice clean tone. It'll just sound weak.
A mic may have a switch so that it can be used with different devices. If you plug into a PA, you may need a lower output so as not overdrive the PA. If you plug into a guitar amp, you;ll need that hi-Z setting to even be heard well through it. This is done with a simple transformer inside the mic, and the switch just selects different output windings on the transformer.
As for learning this stuff. I can't say as I found any of it all in one place. I joined various forums and read posts and asked questions (just like you are doing), and then i did some googling. I did lot's and lot's and lot's of googling. And then ultimately, I just plunged in and started building stuff...
Good luck!
Isaac
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The magnificent YouTube channel of the internet user known as "isaacullah"
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Preston
536 posts
Oct 21, 2009
6:10 AM
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Hey Isaac, not that it amounts to a hill of beans on the actual topic, but I wanted to add a little more to your definition of impedence.
It's not refered to as impedence because the amplitude of the sign wave is always changing. Impedence is the total value of opposition to current when you add Resistance, Capacitance, and Induction all together. (It IS posible to have a purely resistive AC circuit)
Induction is caused when magnetic waves of flux circle a copper wire. They induce a voltage onto it. Inversly, voltage through a copper wire will creat magnetic waves of flux. If a wire is wound in coils and energized it will actually induct on itself. And it will happen when your mic cable is wound in a circle.
Capacitors store a charge, and then when the charge is full they resist the voltage. I haven't torn my amp apart yet. Do amps have capacitors?
Anyway, like I said the true def. of impedence isn't really pertinent to the great answer you gave, I just felt like sharing knowledge this morning.
Preston Moore,
Master Electrician
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tookatooka
671 posts
Oct 21, 2009
6:39 AM
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Hey guys, we need an electronics forum. I have some questions I want to raise on this topic as I have gaps in my knowledge.
Mic volume control. What does it do? Is it there so you can adjust the mic impedance so it is optimally matched to the amp?
Anyone tried putting a dynamic 600 ohm insert in parallel with a piezo element which is infinite resistance? Could get the best of both worlds, volume and grit.
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Last Edited by on Oct 21, 2009 6:46 AM
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isaacullah
407 posts
Oct 21, 2009
10:22 AM
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Preston: Thanks for filling that in more completely! See, this is what happens when someone (ie. me) learns about electronics over the interweb! Anyway, yes, amplifiers have plenty of capacitors in the signal chain. You need one between each stage (and at the input and output) to block any stray DC. This DC usually comes from the power supply to the transistors/tubes. If it's allowed to get out to the next or the preceding stage, it could do some damage. eg. if it gets out of the input into a dynamic mic, the mic will lock up (the DC will push the magnet out) and you won't get a signal. If it goes through to another amplification stage, you might blow a transistor or amplify the DC to dangerous voltages.
Amplifiers also use capacitors in the power supply and in the tone section. They basically using R/C networks to filter out frequencies that are unmusical (hum from the mains power in the power supply), or to shape the tone (R/C networks in tone controls). Also, the Caps in the power supply help to provide little bursts of extra power when the circuit needs it.
Amps may or may not have inductors. Sometimes, they use inductors right before going out to speakers to prevent oscillation due to hard-to-drive speaker loads. This is also done with another R/C network (Zobel network) that filters the high frequencies that cause this oscillation.
Tooka: the volume control forms a resistive divider that shunts part of the signal to ground. As you turn the pot, the resistance changes on either side of the divider sending more or less signal to ground. There is always *some* signal loss when using a VC, so this is why some folks prefer to not use them. IMO, the signal loss is very minimal, and the extra control you get is worth it. I have mics with and without VC's, and I prefer the control of the mics with the VC's.
And yes, the VC does change the output impedance of the mic as you turn it. That's basically how it works. You use the VC to more proberly match the mic to the input of the amp. The result is a quieter sound, but also less feedback, noise, etc.
Most amplifiers are meant to see signals from devices (mics, guitars, etc) with higher impedance than the amplifier's input impedance. Designers do this so that multiple types of instruments/mics can be attached without too much difference in the resulting sound. As long as the input is not too much higher than expected, the circuit will always sound pretty good. If the input is TOO hot, then the circuit will be way overdriven,a nd you'll get nasty squarewave distortion and howling feedback at all levels. Impedance mismatch the other way (signal lower than input impedance on amp), however, will always result in a weak sounding circuit, which is what happens when you plug your typical Low-z mic (output impedance 300-600 ohms) into a guitar amp that has an input impedance of 1 to 2 megaohms (that's 1,000,000 to 2,000,000 ohms!). Your typical high-z ceramic/crystal mic might have an output impedance of 3-5 megaohms. You need a step up transformer to ramp your low-z mic into these output levels. A PA amp or a mixer will have a much lower input impedance (perhaps 10 to 15 kilohms), and so you can plug your low-z mic right in. You might need a step-down transformer to plug your high-z mic in though!
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The magnificent YouTube channel of the internet user known as "isaacullah"
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jawbone
130 posts
Oct 21, 2009
11:17 AM
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Now might be a good time to ask my question - If I am using a dynamic cartridge and I wire it with a 2 wire 1/4" cable how much signal am I losing? Should I be using XLR? Should I be using some sort of transformer like they do on the shure 57 & 58's? OK - that's 3 questions but...I'm feeling frisky!!
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If it ain't got harp - it ain't really blues!!!!
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tookatooka
674 posts
Oct 21, 2009
1:03 PM
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Thanks issacullah, That's just what I was looking for.
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Tuckster
237 posts
Oct 21, 2009
1:30 PM
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I have to dust off the cobwebs. It's been 30+ years since school.
@jawbone If you use a low Z element,you will have to use an impedence xformer before you can go to 1/4". On my 57,I use an XLR cable from the mic to the x
former.Xformer has XLR on one end,1/4" on the other.
@Issac-I wish I knew as much about archeology as you do electronics. One small point: signal level does not equate to impedence. The rule of thumb I learned was that for small signals, input Z should be 10X output impedence. You can look at it as a voltage divider. If the output Z is say 100K,and the input Z is 50K,you'd be dropping 2/3 of the voltage before it got to the amp. Why won't a low Z element not work then? Because it's a balanced signal,where the amp input responds to the difference between hot and negative. With a 1/4" and no Xformer you're only getting 1/2 the signal.
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jawbone
131 posts
Oct 21, 2009
2:32 PM
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Thanx Tuckster - but how should I be wiring my low z element, should I be using the two wires on an xlr style cable with each wire going to the proper pins then into the transformer. I've never looked inside my 58 to see what all is in there. But I think there is more than just the cartridge.
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If it ain't got harp - it ain't really blues!!!!
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Tuckster
238 posts
Oct 21, 2009
3:30 PM
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jawbone--I not sure what you're trying to do.If you have a 58,the easiest way is to just use an XLR cable and connect the amp end of the cable to a xformer.But my Superlux is a low Z element with a 1/4" cable. In that case,they piggybacked the xformer onto the element inside the shell.
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jawbone
132 posts
Oct 21, 2009
7:08 PM
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Sorry Tuck - I wasn't clear - I'm using a dynamic cartridge (low z) in a home made mic. I have wired the cartridge with red wire to the centre of a 1/4" cable and the black to the shield of the cable. I have a feeling that there is more components that need to be used ie. the transformer and such that is in the 58. Would that boost the output. I find that my mic has about the same volume as my green bullet when the volume control is 1/2 way. I like the sound of my mic better than the bullet but I think I need more output to overdrive the tubes. I may not be able to achieve a suitable result with what I have. Also I'm afraid to pull my 58 apart to see what all is in there. I need it for vocals.
Now if I read your other post properly I need that transformer to boost the signal. Am I on the right track? I wish I had high speed so I could watch the youtube videos.
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If it ain't got harp - it ain't really blues!!!!
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Tuckster
239 posts
Oct 21, 2009
7:41 PM
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OK First off,don't tear the 58 apart! LOL I don't think there's much in there besides an element and maybe a cap.As for your home brew,as it is now,it's like running your 58 straight into the amps sans Xformer. You should be getting a pretty rolled off low end. Does it lack bass? XLR's are 3 conductor--a hot(+)usually red,a negative(-) usually black and a shield. (-) and the shield are not tied together. I.E. the negative is not grounded.You need a xformer between the element and that 1/4' cable. Here's a link so you know what I'm talking about:
http://www.jt30.com/jt30page/eacstore.html
One of those should get you in business.
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jawbone
135 posts
Oct 21, 2009
9:41 PM
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OK - Now I'm getting somewhere - I'm starting to feel like some mad scientist - can't wait to get out to the shop and let the lightning connect with the bolts on either side of my creations neck and bring my monster to life......muwahhhaaaa (as he wrings his hands in glee) Oh I need sleep....
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If it ain't got harp - it ain't really blues!!!!
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KeithE
36 posts
Oct 21, 2009
10:20 PM
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Issac - you can search for complex impedance to see a way to deal with this mathematically.
For example if you had an R, L, and C in series, the complex impedance would be:
Zin = R + sL + 1/sC
It's been a long time, but just substitute jw for s for sinusoids. So the resistor is the real part of the impedance, and the L and C are the imaginary part of the impedance.
Anyways you can see that in the ideal world:
R - impedance is independent of frequency
L - impedance increases with frequency
C - impedance decreases with frequency
By using this type of expression you can do things like figure out the resonant frequency by seeing when the L and C cancel each other out.
Last Edited by on Oct 21, 2009 10:21 PM
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isaacullah
412 posts
Oct 22, 2009
9:35 AM
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Wow, see this is why it's good to have some folks with REAL knowledge of electricity in this forum. I'm just an amateur hack who learned a bunch of disjointed facts off the net... Guy's like you who really went to school for this stuff are the real authorities! Thanks for posting that, it was VERY informative for me!
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The magnificent YouTube channel of the internet user known as "isaacullah"
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wallyns10
46 posts
Oct 22, 2009
9:40 AM
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Thanks Isaac, I need to get like a text book or something. I think I understood what you said but everything everyone else is talking about underneath is like way over my head. Its been years since I had a physics class and even then we didn't go too in depth on this stuff.
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isaacullah
413 posts
Oct 22, 2009
9:56 AM
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Sure thing! I actually never took physics... Not even once!
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The magnificent YouTube channel of the internet user known as "isaacullah"
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MrVerylongusername
576 posts
Oct 22, 2009
11:58 AM
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Talking of ultra high impedance into a guitar amp, you can easily make a device called a Unity Gain Amplifier, with just a few very cheap components - a couple of sockets, some battery clips and an op-amp. It'll basically act as a buffer between the mic and amp to ensure a perfect match.
The knowledge of electronics here puts me to shame. Basically I can solder reasonably well and follow a simple diagram, but I managed to make one of these. The circuit was published on Harp-L by Ironman Curtis. He called it the micmojo:
http://www.harpl.com/2002101611.html
It takes 2 9v batteries, and can fit into a small pedal sized project box (if you had a big mic like an Argonne bullet, you might fit it all in the mic itself). It makes a huge difference to the tone of a crystal mic and works pretty well with a CM too.
Last Edited by on Oct 22, 2009 11:59 AM
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isaacullah
415 posts
Oct 22, 2009
12:21 PM
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Also do a search for "basic buffers". It'll take to Jack Orman's page at AMZ (musique.com). Plenty of other buffer designs there including some nice JFET transistor buffers that'll work too. These will run off of one 9volt, so it's a bit more economical that way. Battery life will be very long...
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The magnificent YouTube channel of the internet user known as "isaacullah"
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jawbone
136 posts
Oct 23, 2009
5:57 AM
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So Isaac - what do these buffers do - balance the impedence levels? Would they take the harshness out of a crystal element? I'm not gonna be happy 'til I blow up an amp, a'm I???
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If it ain't got harp - it ain't really blues!!!!
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isaacullah
416 posts
Oct 23, 2009
1:10 PM
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Yeah, buffers are there to balance impedances, and to provide enough current to drive a long cable without signal loss. The general thought is to have one buffer in front of all your pedals, and one at the end of all your pedals. Most buffers are designed to give current gain without (too much) voltage gain. I'm pretty sure this is what is meant when they are called "unity" gain amplifiers.
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The magnificent YouTube channel of the internet user known as "isaacullah"
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jawbone
138 posts
Oct 23, 2009
1:36 PM
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I can see my education is just beginning...oh my aching head...
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If it ain't got harp - it ain't really blues!!!!
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