This is a good article in it's own context, but doesn't mention some concepts that are important to harp players. In that regard, Greg's practical guide is very much more relevant IMO. Where he explains when and where to use IMTs to convert between balanced and unbalanced signals, and the issues around very high impedance crystal and ceramic mics which no one else uses any more.
But there are some useful things that come from understanding that mics use Impedance Bridging (and not Impedance Matching). For instance, some people seems to think it's bad in some way to put a Lo-Z dynamic mic into a guitar amp without the IMT. It's certainly not what it was designed to do, and usually you do want an IMT. But if you have a nasty hi-gain amp, it's a simple way to reduce the input signal. Understanding Impedance Bridging explains why it won't affect the tone.
Last Edited by MindTheGap on Mar 29, 2016 4:15 AM
Thanks for the reference - I read Greg's guide, very helpful. I was about to go completely transformerless, and get a XLR-1/4 cable, but that would be a mistake with my Lo-Z signal. As you mentioned, understanding impedance "bridging" is important.
Yes that would be a mistake, in general. It may not be possible to overdrive the amp as you like, for instance.
The rule of thumb (as discussed in the article) is that the load should be at least 10x the source impedance. There's nothing much to be gained by going better than that.
A general rule of thumb ---regardless of low or hi----Any time u have to have one volume way up or way down---and another thing [attached to it] way up or way down ---impedance is not correct--
snowman I think that's a good rule of thumb for the normal audio world, but for harp world there's all these examples of tube amps with high gain preamp tubes which are all twitchy and feedback-y with their mics. And in that case the impedances are correct. Hence the need for the LW mojo pad.
I know electronic engineers discuss this stuff in terms of impedance, but it's important to understand it's about simple signal voltage levels too. The point about Impedance Bridging is that you are approximating the mic to a voltage source.
Last Edited by MindTheGap on Mar 29, 2016 8:11 AM
1847 I said 'no one ELSE uses any more'. No one else than harp players, who love them and bemoan that quality elements aren't made any more.
(yes, and I'm sure there's some counterexample so what I mean exactly is that they used to be a very common, conventional mic-type when valve circuity was the consumer norm, and now they aren't. Maybe they resist the EMP and are used in fighter jets or something. I've no idea).
Worth saying that crystal elements and tube amps are naturally nicely matched for impedance without fuss, but not so much with transistor-based amps when they came in. That's one of the things about the LW gear, they know that and have nice very hi-impedance inputs. Maybe modern SS amps have hi-Z inputs too, I don't know. I don't see why they should, as guitar pickups are fairly low impedance. Someone will know.
Last Edited by MindTheGap on Mar 29, 2016 8:50 AM
oh i see... my bad. it was a good excuse to post rusty and rick anyway, i love that song.
i have a transistor amp, a crystal mic works quite well with it. i have posted examples. i use it a fair amount i will have to record it next time. lately i have been using the lone wolf terminator pedal with 2 amps. it has a vey high impedance input.
Yes it is a great song, thanks. That's why I'm here really, to discover things like that song rather than discuss impedance :)
But yes, my crystal (or ceramic whatever it is) mic actually works with various guitar amps I tried so I expect they must have high impedance inputs. Maybe it's the norm now.
Last Edited by MindTheGap on Mar 29, 2016 11:20 AM
