beginner forum: for novice and developing blues harp players > Impedance converters
Impedance converters
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Ian
390 posts
Dec 07, 2016
6:55 AM
Can someone explain impedance converters to me please?
I don't have one, I am going to be playing through a solid state amp over Christmas... What do I need? Do I need one? What do they do?
Thanks
MindTheGap
1920 posts
Dec 07, 2016
7:18 AM
There are two common electrical patterns in current use for the kind of audio mics we use for harp and they are labelled Low or High impedance. There's a lot more detail to those labels, but that's not important here.

If you have a Low Impedance mic and want to plug that into a guitar amplifier you ought to use one. The low impedance mic will typically have an XLR connector, and the guitar amp will normally be expecting a 1/4 jack.

In this context, the IMT does two things:
1. Conveniently converts between the XLR and 1/4" jack.
2. Correctly raises the mic signal level to typically what the guitar amp is designed for.

However, harp players spend a lot of effort reducing the gain of their amps because a typical cupped-mic signal is much higher than a guitar signal, which leads to all that too-much-distortion-and-feedback. So in some circumstance you can actually be better off with the cheapo XLR-to-1/4" jack cable.

One of the complaints about SS amps is they tend to be high gain, and that's not good for harp. So you might get good results by not using an IMT.

Try it and see!

Last Edited by MindTheGap on Dec 07, 2016 7:33 AM
MindTheGap
1921 posts
Dec 07, 2016
7:24 AM
BTW there's a lot of misinformation on the MF about impedance matching - normally along the lines of 'the amp expects to see a certain impedance for the mic to sound right, and it will affect your tone'. It's not correct for a low impedance mic. In this context, it's all about signal levels.

For the record, what we call an IMT is actually something called a 'Balun' which converts between 'Balanced' and 'Unbalanced' audio-electrical schemes (which also includes a signal voltage conversion). These schemes are very important in audio generally in terms of rejecting interference in long cable runs and noisy environemnts. But not much to do with plugging a harp mic into a guitar amp that's six feet away from you!

Last Edited by MindTheGap on Dec 07, 2016 7:48 AM
MindTheGap
1922 posts
Dec 07, 2016
7:32 AM
Perhaps this is more use: if you have a low impedance mic like a SM57 with an XLR output, and it sounds too quiet when you plug it into your amp, so you can't get the overdrive you like, then an IMT will make it louder.

Fin.
Ian
391 posts
Dec 07, 2016
4:37 PM
Thanks man, that's v useful info.
So I currently have 3 mics, a superlux (which has a fitted cable and 1/4" jack), an akai adm8 (which also is fitted with cable and quarter jack) and a pyle pro sm57 ripoff. So of those I'm guessing the pyle is the most likely candidate for an IMT (check me using the lingo!)?

When buying one of these are they generic? Do they all do the same job or do I need to be searching for something specific?

Thanks again bud
Killa_Hertz
1979 posts
Dec 07, 2016
9:08 PM
Yes, the pyle needs a imt. Well it doesnt NEED it, but you can't get a good driven sound out if it without one.

I have a shure imt that was only like $20


Heres the one i have. Works great. And its on sale.


https://www.amazon.com/gp/aw/d/B0006NMUHW/ref=pd_aw_sim_267_2?ie=UTF8&psc=1&refRID=74JXDKQS88JDVBZ9VDK1
MindTheGap
1924 posts
Dec 07, 2016
11:16 PM
Yes indeed. Do you have the Akai ADM8 Killa? I remember you had one and liked it. Is it hi-impedance like the DM13?

Ian, for info, if you looked inside your superlux or the akai, you'd find a little transformer that does the same job as the external IMT we are on about.

Ian's in the UK though, that Shure A85F is £40 here. There's an Audix T50k for £24, and that's got the rat's tail design which some like, to protect your amp's socket from physical damage.

You'll need a conventional XLR-XLR mic cable too.

Other than the physical package they all do the same job. You'll see ones that have 1/4" in and 1/4" out - they are different (explanation on request!) DON'T get one of those.

I repeat though, try your pyle pro with the XLR-1/4" cable that it came with first, into the amp you are going to use. It may sound fine, in which case it IS fine and you'll save some money.

You'll read a load of tripe, from those who should know better, about that cable only giving you half the output, that's why it's quieter. No, it's because you've not got a 1:10 transformer in the circuit! It's stuff like this that makes me take all the info I read on MBH with a pinch of salt.
Killa_Hertz
1982 posts
Dec 08, 2016
5:21 AM
I honestly don't remeber if i have an 8 or not. The 13 i like best, but they all sound pretty decent. Im pretty sure they are all HiZ.

Well if the Shure is that much, dont get it. Ask greg about which he recommends. He always recommends this cheap one that i can remeber the name of. But he swears by it and it's well under $20, i think.


An imt is a great tool to have. I recommend getting one either way.

I think one of the best, cheap, new, mic combos you can get is the pyle pro pdmic 78 (57 copy) and an imt. It works very well. The lesser quality elements are actually better for harp usually, so this cheapo mic can actually sound better than a real shure.


Another low z mic i LOVE is the EV 627c. This mic is fantastic with my Vox ACTV4 Mini. It's a very clean mic, but it just sounds great cupped. People say it is very similar to the re10. But it's MUCH cheaper. I got mine for under $20. Excellent mic. But it too requires a imt to sound good.

Again i think every harp player should have a good imt on hand. It's a great piece of kit to have handy.

Could always grab an sm58 vocal mic and plug it into your amp in a pinch. If your mic craps out at a gig.
MindTheGap
1926 posts
Dec 08, 2016
7:02 AM
Last time I looked, Greg recommended one called 'Little Imp' but I can't find it in the UK. It's a standard pattern.

But how about this, last time it was discussed I looked and found one in a much better package than Little Imp format...

http://www.visiosound.co.uk/stage-studio-c50/stage-electronics-c51/di-boxes-c76/pulse-passive-di-box-p1143

...it's actually intended to go the other way i.e. guitar 1/4" jack hi-impedance -> XLR output -> PA XLR balanced input. But these are passive components and ought to work either way. If you get one and it doesn't work - don't shoot me! If I'd known about this one I'd got this first but I followed the standard advice and got the Little Imp style - complete with the risk of damaging my amp's input jack when someone blunders into 6" of lever sticking out the front :)

Whenever I see an IMT that's been used out of the home, it's bent!!! You'll see why when you get one and plug it in. The rat's tail one is best I suppose.

Last Edited by MindTheGap on Dec 08, 2016 7:08 AM
Ian
393 posts
Dec 08, 2016
3:53 PM
Thanks boys. Lots of good advice there. I'll probably grab one just incase regardless.
Seems like a drop in the ocean compared to all the other harp costs I've racked up over the last couple of years!
SuperBee
4325 posts
Dec 08, 2016
9:55 PM
I was sure I made a post in this thread. I certainly wrote one.
I'm just wondering about the op.
What's the deal with the solid state amp? Is it a guitar amp, 'acoustic' amp, PA?
MindTheGap
1927 posts
Dec 08, 2016
11:17 PM
Superbee - I looked and there was nothing in spam.
SuperBee
4328 posts
Dec 09, 2016
11:16 AM
I probably just forgot to post it. Doesn't matter. Thanks for looking.
Mainly I'm wondering why the mention of SS amp and imt together in the op, I.e. It sound like the OP is saying 'I'm playing through a SS amp and I don't have an imt' as if the SS factor is creating the issue.
I'm thinking if it's a SS guitar amp the question of needing imt is same as for any (most) guitar amp, SS or tube. It's about the mic. If you are gonna use LoZ mic, prolly want to use an imt with that.
But if it's an 'acoustic' amp, there's a chance it will have an input designed for LoZ as well as hiZ input.
Same with PA. Just about every PA will have inputs for LoZ balanced mics and many will have inputs for unbalanced also
MindTheGap
1931 posts
Dec 09, 2016
12:30 PM
True about the acoustic amp or PA typically having a Lo-Z, XLR input. But I was saying that the typical SS guitar amp, although it probably only has a hi-z input, may have enough gain that it will work fine with a lo-z mic as-is.

I have definitely used amps like that.

That's why I was banging on about what the IMT does, and what it doesn't do and what some people claim for it.

Last Edited by MindTheGap on Dec 09, 2016 12:31 PM
SuperBee
4329 posts
Dec 09, 2016
12:59 PM
Yeah I get that. That was actually a part of what my post-that-wasn't addressed; my story of the first time I plugged in a mic to an amp.
The mic: sm58
The amp: 5watt ss guitar amp
The result: disappointment! Without the exclamation. It was much less enthusiastic than that. Amp on 7 or 8 before I could hear above the acoustic sound of the harp.

That's how I got started on all this.
I found that document (the one which includes the claim that using a balanced mic with an unbalanced connector results in only half the signal coming through) and learned that there are hiz and loz mics and I had a loz one. So I bought a hiz mic and plugged it in and added the !
And a 30 watt tube amp but the mic was the thing.
Later I got an imt for my loz mics.
I've never had an amp with enough gain that I felt my loz mic was really delivering without an imt but that's just how I trained myself to feel. If I can't get the rig to feedback I figure it's not really giving me all it's got.
MindTheGap
1933 posts
Dec 09, 2016
1:55 PM
Yes I see. Disappointment would certainly would be the result with a lo-Z mic into a normal-gain, clean-channel SS amp, or a typical tube amp that gives a crunchy kind of overdrive with a guitar. There's not enough mic signal.

I'm thinking of those SS amps with a hi-gain/overdrive button or channel. With a guitar they're to give a heavy metal/shredding sort of sound.

I suppose the sound advice is really just do to the right thing and buy an IMT, then you've got the option.

Just to say, the first IMT I bought (which is even more unfeasibly long than the Little IMP) has a Lo-Hi switch in it, so I could try either or very easily. There was a period when I'd was trying out every amp I came across, just to see.

Although the simple XLR->1/4" jack does work in some cases with harp, I don't think it's helpful the manufacturers supplying one with those Lo-Z vocal mics, it must cause confusion. Vocalist will surely try plugging them into the Hi-Z inputs on PAs, or guitar amps, and find a weak signal, and be disappointed too.

Last Edited by MindTheGap on Dec 09, 2016 1:59 PM
Ian
394 posts
Dec 10, 2016
5:41 AM
@superbee. It's a 40 watt guitar amp. Just asking about these imt things as I've heard people natter about them!

OK so the next problem I have is after trying said 40watt amp out (it's not mine) I'm getting hellish feedback. As soon as I get enough drive and volume, through my American tone pedal, What can I do to try to avoid it!?
I don't have a harp shield or similar.
Is it the size of the amp? The make (fender champion)? The mic (superlux)?

This is turning out to be a bit of nightmare! ;)
MindTheGap
1937 posts
Dec 10, 2016
7:59 AM
Ah ha! I know for definite that you can make that combo work, even without an IMT. Especially your pyle pro without an IMT!

The American Sound pedal has buckets of gain range available, so it's easy to overdrive it horribly, and typically that gives you the feedback. So you need to back the gain right off until you get just a subtle overdriven sound. The Voice and Gain pots work in tandem, so if you turn them both down you'll be into the right territory.

Then don't use the models on the Champion, just the clean settings.

Then you have to adjust the output from the AS - the Volume pot. To make sure it doesn't overdrive the input of the amp. The AS is unusual in that it can actually boost the signal, so you have to be careful with the output volume.

That should be enough. If you do want to use the Superlux instead (which has a much higher signal output) you can back the gain off further and/or use the volume control on the mic itself to reduce the input. It has a centre detent so you could leave it there.

Alternatively, you can bypass the AS pedal altogether and use e.g. the Champ model on the Champion. That's quite nice too.

Hope this helps. Let us know how you get on.

Last Edited by MindTheGap on Dec 10, 2016 8:05 AM
MindTheGap
1940 posts
Dec 10, 2016
9:04 AM
...sorry if that sounds over-complicated Ian. Really it's just down to adjusting the volume/gain levels along the train.

Maybe a practical approach is to set them all really low, so you have a totally clean sound, then edge them up so you can hear the difference. For the 'tube sound' you don't want much distortion - much less than you might use with a guitar.
Ian
395 posts
Dec 13, 2016
1:59 PM
Mtg.
Thanks for all your advice. In related news...
I just got the deal of a lifetime on a vox av60....
£100!
Used for 3 months.
Tried it at the guys house, and it sounded great. I'll let you know how I get on with it.
It seemed really feedback resistant with my superlux. So we may be on to a winner here.
MindTheGap
1950 posts
Dec 13, 2016
11:44 PM
That sounds good. I read it's a design with a preamp valve in the power amp stage, fed into a SS amp. The idea being to get the coveted 'power amp distortion sound'.

As they say, if it sounds good then it is good.

Although it's a shame we didn't hear the outcome with the original SS amp - that Fender Champion is a good option for other beginners I think.

Last Edited by MindTheGap on Dec 13, 2016 11:48 PM
Ian
399 posts
Dec 14, 2016
3:31 AM
Well, the champion is thill there so I can still try it out... You know.... For science!


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