Tom Lauten
52 posts
Mar 16, 2019
10:08 AM
|
“Basic” question....
Is there such a thing as “too high” in terms of impedance going into a guitar style amp?
Thing is, I have a few CM elements that are apparently mid to high-ish impedance and they sound fine but getting them to really break up is kinda tough (for a newbie who’s cupping isn’t always super tight) but then when I put them on a 10:1 transformer they REALLY snarl and seem quite powerful. I mean I like the sound that gives them and on lower volume on the amp they can still be pretty clean. When I don’t cup much they also have a pretty clean sound. I know a lot of stuff is down to the ear and that may change for me as I actually practice a bit and actually play and learn what I like.
I have a Spher-o-dyne and my CM mics are now only a little hotter than that one and that’s as per Shure specs I would assume...am I doing myself a disservice here?
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 16, 2019 10:09 AM
|
Harpaholic
936 posts
Mar 19, 2019
12:16 PM
|
Since no one has responded, I will give it a shot.
What amp are you using? Hi Z input?
Mid Z you need a transformer in most cases. Hi Z you Don't. You can't go too high into a Hi Z input with a mic. Amp inputs usually start at 68K (Bassman) and go up to 5.6 Meg (Harp king) or maybe higher.
My amp knowledge on the technical side is closer to intermediate, so don't bet your paycheck on it.
Last Edited by Harpaholic on Mar 19, 2019 12:19 PM
|
Tom Lauten
57 posts
Mar 19, 2019
2:42 PM
|
I’m using a Fender Champ 600 modified for harp with an Alnicomods kit and an 8” Weber harp speaker.
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 19, 2019 2:43 PM
|
Bruce S
53 posts
Mar 20, 2019
6:43 AM
|
Harpaholic has it right with regards to average amp input impedances; the Low input on the classic Fender input is 68K, 1 meg on the high input. IIRC Some of the old Valco/Supro amps had 100k; fine with a CM but too low for the full dynamic range of a crystal. Crystals really benefit from very high input impedance, as far as I'm concerned. 1 meg is the minimum here, and preferably 4.7Meg or higher (or an old school grid leak input). I recall Mark Burness (5F6H) stating that he found the 520DX element doesn't really like anything over 1meg, and I'd agree from my experience. If you've got some mid z elements then a transformer will help. I had a Shaker dynamic mic years ago with the XLR lead and found that really was at it's best with an impedance matching transformer into a guitar amp, otherwise it was a bit lacking.
|
Tom Lauten
59 posts
Mar 25, 2019
2:20 PM
|
Thanks again.
Why doesn’t everybody put a transformer on every element if an element with only 1000 ohms is called a Hi-Z mic element and amps are often in the 1meg range? I just don’t get it. I mean 1000ohm is Hi-Z but I am also told that 10k is solid Hi-Z as well? Shure transformers go up to 50k...what gives? To my ears 1000ohms isn’t exactly SCREAMINGLY powerful compared to, say, a 300 ohm mic. I am soooooo lost ....
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
|
MindTheGap
2589 posts
Mar 26, 2019
11:29 AM
|
The reason it doesn't seem to make much sense from the numbers is that the terms Hi-Z and Lo-Z are just convenient terms for a lot of detail. Although impedance does come into it, it's really much more about signal strength, wiring schemes, plugs and sockets.
The end product is that you use a mic that's suitable for a particular kind of amplifier input, and you get the right amount of signal in with good fidelity. If you use the wrong one it tends not to work too well in one way or another. But for harp, 'wrong' might sound good.
Last Edited by MindTheGap on Mar 26, 2019 11:32 AM
|
Bruce S
54 posts
Mar 27, 2019
4:32 AM
|
Hi Tom, one of the confusing things is the DC resistance of the element is only part of the equation; A high Z sure CM might have a measured DC resistance of 1000 ohms, but that's *not* the impedance of the element, which is actually higher, although I don't have the time & test equipment to measure what it actually is at present :-(
Impedance is a reflection of AC resistance and reactance; it varies with the load. This is why a low Z vocal mic element of 300-600 ohm impedance might only measure 15-30 ohms -you're measuring the DC resistance of the winding. Similarly an 8 ohm speaker often has a DC resistance of 5 ohms. IIRC Greg Heumann has a good download available that discusses impedance in relation to harp mics that will do more justice than I can in a short post...
|
Tom Lauten
62 posts
Mar 27, 2019
5:52 AM
|
Hi Bruce,
That is great information but I’m afraid it is like the International Space Station....PROFOUNDLY over my head!!
I understand that you used “words” and did “sciencing” but “pearls before swine” in this case my friend... lol
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 27, 2019 5:52 AM
|
Bruce S
56 posts
Mar 27, 2019
6:34 AM
|
Hi Tom,
No problem! I had to do some bits about impedance for my full amateur radio licence, and I only remember parts of it myself!- But do take a look at Greg's piece, I think it's titled "all about harmonica microphones..and then some", which has some very useful stuff in layman's terms.
One byproduct of doing the amateur radio thing is I've picked up a couple of US made dual impedance Shure CM elements from desk mics, a nice Turner shell and a mix of NOS and used valves/tubes, and various other amp parts for pretty cheap from tabletop sales/rallies...
|
MindTheGap
2590 posts
Mar 27, 2019
8:02 AM
|
Tom, Bruce - although what you say about DC vs AC resistance is right (although just to say that the impedance can vary with frequency, rather than load) - it's not really the main thing here.
As I say, there's a lot of detail and often people confuse the impedance of source and load (mic and amp input, or amp input and speaker) thinking they always need to be the same. Sometimes they do, sometimes they don't - depends on what you are doing.
For instance, you can put a low-impedance mic into a high-impedance input and that is a good thing, just in terms of fidelity.
But the shorthand terms 'Hi-Z' and 'Lo-Z' mean a lot more than just the ohms (DC or AC) - it's about signal strength, cable wiring, type of amplifier etc. For instance, a 'Hi-Z' guitar amp input is set to expect a certain voltage, and 'Lo-Z' mic doesn't give enough volts. Which is why it sounds quiet and won't break up when used for harp. Its low impedance doesn't really matter though.
Is that any help?
Last Edited by MindTheGap on Mar 27, 2019 8:07 AM
|
Tom Lauten
66 posts
Mar 29, 2019
6:40 AM
|
Guys, this all sounds like wonderful information, thanks so much for sharing it...I just wish I was smart enough to translate it all into some conclusions / experiments I could work with in some nuts and bolts way. You see I’m tryin to get away with not practicing and just collecting the right gear for that perfect sound...wha?
So even though the impedance may not be exact there are other (measurable?) factors which effect things like break up and signal strength? Voltage? Is it that certain impedance ranges allow signal information to be carried along and made available (in the right amounts) to the right “recipient” of the signal to be exploited in the way we like?...or Am I over/under simplifing this?
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 29, 2019 6:46 AM
|
MindTheGap
2591 posts
Mar 29, 2019
7:35 AM
|
Tom, I know what you mean. There is a lot of rule of thumb out there which is valuable and based on understanding the basics, but also some misunderstandings which can lead you down frustrating paths.
Let's have a go...
Without going too much into the theory, yes it's voltage that gives you the break up you are looking for. The 'hot mic' gives more volts. But then you have to get that into the amp, and that's where impedance matters.
One useful rule of thumb for amps and mics is that the output impedance of the mic should be a lot lower, commonly at least 10 times lower than the input impedance of the amp. That way most of the volts created by the mic go into the amp. If the mic output impedance is too high, or amp input impedance is too low then it reduces the voltage and you get a weak sounding mic.
There are other effects than just sapping the voltage, to do with frequency response. That's important for hi-fi amplification but generally harp players aren't after that, so it doesn't matter so much. If anything it's the opposite, we like the colour that frequency distortion adds.
Once you get to this 10x ratio, it doesn't matter how high you go. Which is why you can have a range of mic impedance and they are all called Hi-Z.
One problem is that harp players like to use old crystal mics that have a very, very high output impedance and so it matters a great deal what kind of amp you plug them into - your hot crystal mic may work great with one and rubbish with another. That is why e.g. the Lone Wolf pedals have very, very high input impedance and very low output impedance. They 'buffer' your mic so it will perform the same into every amp, as well as doing whatever effect they do.
Your question about mic transformers is a good one, and yes if you wanted to make a mic more lively you could fit a different transformer if you can find one - it increases the voltage. That's not really the reason they are used, that's to transform between 'balanced' and 'unbalanced' audio but that's a whole other story...
So...
You could get yourself an oscilloscope and see what voltage you can get out of your mics by playing into them. Of course good cupping technique raises the signal significantly, but you know that. Then compare the mic impedance and amp impedance and if they are in a good ratio then you are in business!
BTW you're not supposed to use an ohm-meter on your mics as it can damage them. It won't give the right answer anyway, as Bruce pointed out.
OR
Get a Lone Wolf or some other buffer pedal and you don't have to worry about this stuff anyway!
Last Edited by MindTheGap on Mar 29, 2019 7:47 AM
|
Tom Lauten
67 posts
Mar 29, 2019
7:49 AM
|
Ooooooo...”A tiny little light like one on an old fashioned coffee pot goes on in Toms brain...”
Ok, that’s great info...I’m starting to grasp some of the broader thinking. So increasing the impedance with a tranny (c’mon, behave) isn’t a disastrous crime for a “natural” 1000 ohm mic element going straight into a Champ 600 (1M ohm input) even with a 10:1 ratio (I’m not convinced it’s actually as high as that) I n the transformer. The LW pedals should also help moderate that if using an amp with lower input impedance?
What would I likely notice if I were “over cooking” the element with a transformer? What would I lose? What would all those who know much more than me be rolling their eyes at as I type?
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
|
Tom Lauten
68 posts
Mar 29, 2019
7:53 AM
|
So THAT’S what the Terminator pedal is for!!!? I only half not get it now!
So that would go at the beginning of the chain then? With any mic, transformer or not? (Please say yes and let my OCD perfectionist mind rest easy...even though I’m a crap player).
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 29, 2019 7:54 AM
|
MindTheGap
2592 posts
Mar 29, 2019
8:02 AM
|
Tom
I think it is about 10:1. Be aware that a lot of mics have a transformer on them already. If you want to experiment, that's the easiest thing. I could imagine it working/working, depending on the particular transformer - that has an input impedance too so the same rules apply.
As for the Terminator Pedal, yes exactly. It's got a FET input stage which is super-high impedance so will work with anything, and you could plug it into the worst of worst amps (in terms of impedance anyway) and it will work. And yes it should be the first thing in the chain.
You shouldn't really need a Terminator though unless using a crystal mic. But the Terminator can drive more than one output so you can have two or three amps if you like - imagine the possibilities! You'd never have to practice again :)
Just to say their other pedals work as buffers too, so you wouldn't need a Teminator AND a Harp Break or whatever.
Also to add that some people think that a pedal or buffer weakens their sound, as it's not the pure signal. Not sure what to say about that - I can imagine a particular mic/amp combination does give a particular pleasing distortion, and cleaning it up may spoil it. Possible.
Last Edited by MindTheGap on Mar 29, 2019 8:08 AM
|
MindTheGap
2593 posts
Mar 29, 2019
8:10 AM
|
...I have to add I've often thought that selling bespoke mic transformers would be a nice business idea. You could wind them hot or cool, or have ones that colour the sound. Another thing to get round to.
|
Tom Lauten
69 posts
Mar 29, 2019
8:22 AM
|
Lol...yeah ANOTHER project! My list isn’t quite long enough yet either! ????
This is the transformer I tend to use...I don’t know much but I haven’t found anything I hate about it.
https://uk.farnell.com/neutrik/nte10-3/transformer-audio-1-3-10/dp/724610
Transformer link
----------
Tom "Bad Paw" Lauten
Loch Ness, Scotland
www.nimbacreations.com
Last Edited by Tom Lauten on Mar 29, 2019 8:26 AM
|
MindTheGap
2594 posts
Mar 29, 2019
8:53 AM
|
I don't think there's much choice, they are all designed to a similar spec I imagine.
My only note of caution is if you are thinking to daisy chain two transformers, say, with the idea of multiplying up the voltage. Given the spec, you are likely to run into the same 'voltage-sapping' problem I described earlier.
BTW you can get buffer pedals for guitar that have a variable gain > 1 which would make any mic as hot as you like. Not tried one though - people often say that guitar pedals don't always work well for harp.
Personally I prefer the idea of a 'hot' transformer though, as it's more elegant and doesn't need batteries.
Last Edited by MindTheGap on Mar 29, 2019 11:25 AM
|
