RE: [Harp-L] Wireless/Impedance/Adapters - Christelle

Hi, Funharp

This is a subject of constant confusion among many. Because I make volume controls I confront it every day. Let me try to clear it up for you. There are low impedance and high impedance mics. Duh, you knew that. Virtually ALL low impedance mics have XLR connectors. They are all wired the same way. The signal is on pins 2 and 3, and NEITHER of these is connected to ground, which is connected to the shield of the cable and pin 1 of the connector.

Unfortunately, SOME high impedance mics, like the later JT30's, Hohner BluesBlaster and some Shaker mics, have XLR connectors to. These are NOT wired like low impedance mics. Here, the signal is on Pin 2 OR Pin 3 and the ground/signal return is on pin 1.

The Shure 545 confuses the issue even more. The latest models have an XLR connector, but can be user-modified via a jumper on the back of the XLR connector to be high or low impedance.

Now -let's talk about the other end of the picture, the device you connect your mic to. This means a PA, a guitar amp, a wireless transmitter, etc. These devices have "impedance" too and the CORRECT way to connect a mic to the device is to be sure that the impedance is matched - either low at both ends or high at both ends. PA XLR inputs are ALWAYS low impedance. Guitar/harp amp inputs are ALWAYS high impedance. Whenever you see an XLR connector on a device other than a mic, you can safely assume that is a low impedance device, and when you see a mono 1/4" input you can safely assume it is high impedance.

Confusion arises due to what I call "the cheater cable." This is a cable that has an XLR connector at the mic end and a 1/4" male at the amp end. It is for connecting high impedance mics like the BluesBlaster to a guitar amp. High impedance at both ends - all is well, NOT cheating. However many owners of these cables use them to connect a low impedance mic to a guitar amp. This actually DOES work but it is technically incorrect -it is cheating - you have an impedance mismatch and you won't get the most out of the amp or the mic. The correct way to connect the mic to the amp is to use an Impedance Matching Transformer ("IMT"). Now, the "device the mic is connected to" is the IMT, which IS low impedance on the mic side. It has a transformer inside which steps up the impedance so the amp side is high impedance.

I make volume controls for both High and low-z systems. In the case of one for a High-impedance mic and cheater cable, it LOOKS just like the low impedance model (XLR at both ends) but the are NOT the same internally. My low impedance control won't work with a high impedance device at the other end, JUST LIKE THE FIREBALL volume control won't work this way.

As for wireless - it gets a bit more confusing still. First, remember that the mic only cares what it is connected to - in this case, the wireless transmitter. It doesn't matter how the receiver is connected to the amp. There are both high impedance (think "AKG Guitar Bug") and low impedance transmitters (think AKG SO40.) My high impedance controls work fine with the guitar bug. But the impedance of the wireless transmitters vary. The AKG and Samson are higher than a typical PA, enough so that I make a different low impedance control for them. This is what Jason Ricci uses, for example, with his SM57 and wireless transmitter. Some wireless transmitters, Shure beltpack wireless systems, are "universal" - they are very high impedance and will work with both low- and high-impedance mics. Because of that they won't work with my low impedance volume controls - so I have yet another design to cope with them.

The solution you propose, (two different adapters XLR to 1/4 female to plug in a "guitar bug" like the one from AKG. So to speak one High to High impedance (XLR to 1/4 jack), and one low to high (XLR to 1/4 including a impedance matching transformer) WILL work for you with the Guitar Bug.

As you can see, there is a lot of reason to be confused. But there are people out there who can help "just make it work." I build all my controls and adapters using a modular system. You choose the connectors at each end. In between, you can have nothing (i.e., just a straight adapter from one kind of connector to another), or you can add a volume control, an impedance matching transformer, or both. The reason I can be in this business and not worry about competition from high volume manufacturers is precisely what is discussed here. There is no one-size-fits-all solution, and often I have to exchange several emails with customers before we can determine what the best solution is for them.

I hope that helps!

/Greg

http://www.blowsmeaway.com
http://www.bluestateband.net


From: funharp <funharp@xxxxxx>
Date: July 30, 2008 3:00:58 PM PDT
To: harp-l@xxxxxxxxxx
Subject: [Harp-L] Wireless/Impedance/Adapters - Christelle


Hi all,

recently there was a thread about wireless systems.

I am still confused about some things:

for instance: the Hohner Blues Blaster and the Shure 545 both have XLR connectors, but I do need another cable than I use for a vocal mic like the Shure SM 58 or for the Fireball V. They are differently wired, because the first two are High impedance while the latter two are low impedance. Is that correct?

Could I use two different adapters XLR to 1/4 female to plug in a "guitar bug" like the one from AKG. So to speak one High to High impedance (XLR to 1/4 jack), and one low to high (XLR to 1/4 including a impedance matching transformer) ?

Or is there another way to use different mics (the above are the only ones I have - not much for a harmonica player ;-))) with as little as possible gear fot going wireless?

Thanks in advance

Otto

PS: before I forget: a question to Christelle: Is it only the volume control of the Fireball V not working when connected to the AKG wireless system or is there no signal at all?








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