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Dirty-South Blues Harp forum: wail on! >
High Z or Low Z?
High Z or Low Z?
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Littoral
514 posts
Apr 26, 2012
4:43 AM
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I should understand this better than I do but I don't. I am ordering an ultimate 545 to use primarily with a brown concert. I've read some of you say use one or the other. Why?
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MrVerylongusername
2345 posts
Apr 26, 2012
4:53 AM
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To go straight in the input Hi-z.
Low-Z and an external transformer gives you more flexibility with other setups (like going straight into a PA desk).
It's about the signal level. A guitar amp is designed for... guitar! A low z mic will not match well; the voltages that can be transferred will be lower than is ideal.
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ridge
333 posts
Apr 26, 2012
4:59 AM
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So you should use Mid-Z
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Stevelegh
484 posts
Apr 26, 2012
5:38 AM
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I spoke with Greg on this when I ordered mine. I opted for Low-Z and bought an impedance transformer. In the UK they're about £10.
The reason I went this route because I was thinking of channeling out to both an amp for harp(Hi-Z)and the PA using an A/B switch for vocals(Low-Z).
If you're only ever intending to plug into an amp, go Hi-Z.
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5F6H
1165 posts
Apr 26, 2012
7:16 AM
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Basically a Hi-Z mic will kick out a volt or two, which your amp will like. Lo-Z will only kick out a 1/10th of that...fine for a Lo-Z circuit, lik a PA/mixer but no good for direct into a tube amp.
I wired my XLR fitted 545 lo-z for a while, to make it more flexible & figured I could put a IMT in line for Hi-Z. The difference between the 545 wired Hi-Z and wired lo-Z with a generic, in line, IMT was night and day! Promptly rewired the mic back to Hi-Z! :-)
Here's a post from a little while back...
@ Willspear "iirc the inline transformers for balanced xlr to 1/4 inch jump to 50k from 150-200"
OK, let's break down what all those numbers really mean, hopefully simplifying the issue. I'll use an AKG D19C as an example...just because I have one in my hand...
It's a "200ohm" lo-z mic. That is it's rated AC impedance & the impedance of the circuit that it should be used in.
The actual element has dc resistance (DCR) of 50ohms.
A Shure A95UF in line transformer takes that 50ohm DCR & "200ohm impedance" and converts it to 3Kohms DCR and "high" impedance (where the "50kohms" comes in in your example Will...that 50Kohms is more of a ideal/minimum target, you would typically plug into a guitar amp input or a hi-z instrument input on a PA/preamp that might actually be from 50kohms to a few megaohms). The in-line transformer may also be rated in terms of a gain boost which may be expressed as "+29db" for example.
Wired lo-z the mic puts out 0.04 volts AC (40 millivolts) @ 50ohms DCR/200ohms impedance. Now plug that into a tube amp's input and you bring down the overall impedance of a circuit that is expected to be 50,000 to 1,000,000 ohms, or to put it in perspective 1/250th of the lowest expected impedance. The signal level in that much reduced impedance circuit is also 1/26th of the signal level that you get with the transformer.
Wired hi-z, via the Shure in-line transformer, the same mic now makes 1 volt AC (1000 milivolts), a much bigger signal (x25), supported by an impedance of at least 250 times that you get in a low Z circuit and a DCR 60 times bigger.
Conversely, plug the hi-z mic (1 volt AC @ 3kohms DCR/50kohms impedance minimum) into a lo-z circuit (200ohms impedance load) and that 1 volt AC is now subject to the 200ohm circuit acting like a 16:1 resistive voltage divider reducing that 1 volt @ 3kohms DCR/50kohms hi-z to a "barely audible" 62 millivolts @ 200ohms.
All this is even without considering the factors of unbalanced vs balanced operation, where the balanced lo-Z mic has 2 signals (3 wires to the element) V+ & V- and exploits the difference in potential between them which an unbalanced circuit cannot do.
You can see that the magnitudes of signal level are quite extreme, but your amp might amplify a signal by several thousand times so you might get away with some mismatch...as long as your sound isn't too loose & lacking in dynamics. So if you are gigging a certain amp & mic, getting the job done & wondering whether your impedances are "right", then you probably don't need to wonder. On the other hand, if several mics work in a certain amp, some stronger than others, but all useable...then you try a known working mic that puts out no/very faint signal through that amp, then you may need to investigate impedance matching (after ensuring the connectors & cables have a matching "pin-out" - e.g. some XLR connector Astatics were wired "pin 2 hot" while others were "pin 3 hot", using a cord wired the wrong way turned the mic off!)
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www.myspace.com/markburness
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timeistight
550 posts
Apr 26, 2012
8:34 AM
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A couple of other issues:
Do you like a long cable? You can run as much cable as you can afford from a low-z mic. If you wire it for high impedance, you should use 15 feet or less.
Will you ever want to go wireless? There seem to be lots more low-z transmitter options than there are high-z.
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Littoral
515 posts
Apr 26, 2012
9:55 AM
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Thanks. High-Z it is.
Cable length: isn't 20 ft reasonable?
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FatJesus
8 posts
Apr 26, 2012
10:02 AM
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@Littoral: from what Greg told me when i inquired around the time of ordering my own Ultimate 545, 25 feet is the max length before you notice signal loss (and you would notice this more in recording/studio than live). but after 25 feet, you'll notice degradation by every foot.
two addendums to this rule of thumb:
1. it's 25 feet--from mic straight to amp... OR, from mic to a powered pedal (like a LoneWolf, for instance; i'm not sure this cover all pedals). so you could theoretically run 25 feet from mic to delay, and then 25 more feet from delay to amp. so you'd have 50 feet max (though that would be a lot of cable).
2. if you have any kind of pedal train, consider all the little patch cables when you do your calculations. they add up, quick.
(btw, i had Greg make me a 15-foot cable--and it's great, and plenty long for me.)
Last Edited by on Apr 26, 2012 10:06 AM
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orphan
131 posts
Apr 26, 2012
10:14 AM
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Along with Littoral, I have always heard 20' as reasonable. What happens if you go longer? Would this depend on how hot the mic is? Or is the signal too weak if you exceed 20'?
If you have a hot mic and an amp that feeds back even on a lower setting of the preamp gain knob would a longer mic cord give more gain before feedback?
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timeistight
551 posts
Apr 26, 2012
10:45 AM
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Until the experts show up with better info than mine, my understanding is that the longer the cable, the more capacitance it displays (all else being equal) and that this causes loss of high frequencies. There's also a greater chance of noise pickup as unbalanced cable length increases.
Of course, you may not care about or even notice these effects. Buddy Guy, Guitar Slim and Albert Collins all used to use extremely long guitar cords (like, walk-out-of-the-club-while-playing long) and no one complained about their tone. It's just something you don't need to worry about with a low-z, balanced cable.
Last Edited by on Apr 26, 2012 10:52 AM
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5F6H
1166 posts
Apr 26, 2012
11:17 AM
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About a decade ago I bought lengths of all the locally available cable stock, plus premade cables at 10'. Some of the best performers were indeed low capacitance (just over 20pf/ft)...but so was at least one of the worst! Cable & even plug construction & materials play a big part. Some at mid/late 30's pf/ft wise were still very good.
Some like the Klotz La Grange (my favourite) only showed nominal degredation at 20' or more, some cables were like wet string even when chopped back to 5'!
Price seems to have little bearing too, the very best cable might cost anywhere from $50 to $200, some low price cables perform very well indeed. Planet waves is a good performer, widely available. Sommer Session II (not "Spirit" guitar cable), Proel regular guitar cord was good cheapie, George L above average. Really suck & see, if you're happy with your cable & another doesn't appear to sound different then don't sweat it, but it's worth trying any you come accross just to see.
@ Fat Jesus - The signal from a typical guitar effect box is usually lower impedance & less susceptible to losses, it's the cable from mic to 1st device's input that really matters.
Taste comes into it, if you are looking to dull down a bright set up then a "bad" cable *might* help you. I think this why some cables regarded as good for guitar just don't cut it for harp, guitarists are often looking for something to soften the plucked string, make their "pling" more of a "bling". I prefer a cable that colours the sound the least. Signal lost at the cable simply cannot be made up anywhere later, you can only adjust what makes it to the amp.
Cables get overlooked a lot, people tend to see them as a single component with limited "states", but a cable is really some capacitors, a few resistors and inductors all at the same time.
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www.myspace.com/markburness
Last Edited by on Apr 26, 2012 12:28 PM
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5F6H
1167 posts
Apr 26, 2012
11:24 AM
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@ Time is tight "Of course, you may not care about or even notice these effects. Buddy Guy, Guitar Slim and Albert Collins all used to use extremely long guitar cords (like, walk-out-of-the-club-while-playing long) and no one complained about their tone. It's just something you don't need to worry about with a low-z, balanced cable."
But you cannot connect a hi-Z mic to a balanced mic cable, or get the same tone with a lo-z mic (unless you researched & made your own in line transformer set up at the amp connection end, off the shelf IMTs rarely give the same performance as a hi-z mic). In fact, you can use a balanced mic cable & "unbalance" it by connecting unused conductors to the shield, but proprietry "microphone" cable (those meant for lo-z PA & broadcast mics) ALWAYS have more capacitance than single conductor instrument/guitar/hi-z harp mic cables.
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www.myspace.com/markburness
Last Edited by on Apr 26, 2012 11:52 AM
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orphan
132 posts
Apr 26, 2012
11:41 AM
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Thanks 5F6H that was some great info and I appreciate all the tech help you give.
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5F6H
1168 posts
Apr 26, 2012
11:57 AM
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Cheers Orphan, I'd like to say it was down to my "generous & pragmatic nature"...well, that's what I'd *like* to say...it's more that obsessive behaviour has a lot to answer for! ;-)
Hopefully others may benefit from my & my neighbours sleepless nights. :-)
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www.myspace.com/markburness
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MrVerylongusername
2346 posts
Apr 26, 2012
12:19 PM
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A couple of things:
1). Most of the tone loss due to cable capacitance is the high frequencies. That's bad news for guitarists, but most harp players tend to dial down the highs anyway, so as 5F6H says it is somewhat subjective.
2). Re: pedals. If you are the sort of person who insists on true bypass pedals then, when the pedals are off, the whole length of your cabling comes into play. When you switch one on, it suddenly shortens the length of that critical signal path. Probably only an issue if you have a huge board full of boutique pedals. Personally I've never been too obsessive about the minutiae of tone to worry about true-bypass, one way or the other.
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timeistight
552 posts
Apr 26, 2012
3:04 PM
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@5F6H: I didn't mean to suggest using a low-z, balanced cable with I high-z mic. I guess I should have said "with a low-z, balanced mic and cable."
I don't really get why a good quality IMT at the amp end can't give as good performance as a transformer inside the mic shell, but I'll bow to your greater experience.
@Littoral: Maybe you should get two 545s, one low-z and one high. Then you'd be ready for anything.
Last Edited by on Apr 26, 2012 4:20 PM
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Greg Heumann
1592 posts
Apr 26, 2012
5:49 PM
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The difference between low and hi should NOT be night and day. It is a dB or 2 according to the Shure spec, and my experience. 5F6H - I suspect you had a cabling issue. If anything, the low-Z configuration has a little more output. But you can't use it without an IMT. My standard email response is this (referring to the configs on The Ultimate Series Web Page:
There is no advantage tone-wise to any one of these options.
Config A is like any standard modern vocal mic. Use a low impedance cable with XLR connectors at both ends and connect to a low impedance input like a PA, or add an impedance matching transformer at the far end of the cable and plug into a high impedance input like an amp or pedal. This configuration is compatible with the Samson AX1 wireless transmitter
Config B is the simplest, lightest, most compact and reliable for cabling to an amp. Use a cable with female screw-on connector at the mic end and 1/4" plug at the amp end to plug into an amp or pedal. To connect to a PA you need to go through a "DI" box.
Config C and D represent the two standards for high impedance wiring over XLR. They both use a cable that has an XLR connector at the mic end and 1/4" plug at the amp end, which plug into an amp or pedal. To connect to a PA you need to go through a "DI" box. B is compatible with the Samson AX1 wireless transmitter but C is not. Cables for C are more readily available in the U.S. while cables for B are more readily available in Europe and Asia.
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/Greg
Last Edited by on Apr 26, 2012 5:52 PM
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5F6H
1169 posts
Apr 27, 2012
1:59 AM
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@ Greg - "The difference between low and hi should NOT be night and day. It is a dB or 2 according to the Shure spec, and my experience. 5F6H - I suspect you had a cabling issue. If anything, the low-Z configuration has a little more output. But you can't use it without an IMT."
No, no cabling issue Greg. I think you are misunderstanding, I was saying that the difference in performance between 545 wired lo-z & a generic in-line IMT and the 545 wired hi-Z was night and day. Not all IMTs are the same. Shoot FJM at Harp-l an e-mail, he had exactly the same issue.
@ Timeistight - "I don't really get why a good quality IMT at the amp end can't give as good performance as a transformer inside the mic shell, but I'll bow to your greater experience." I didn't say that, an off the shelf IMT from your music store that you plug in the XLR cable may not be the same as using the mic's on board transformer.
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www.myspace.com/markburness
Last Edited by on Apr 27, 2012 2:30 AM
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