[Harp-L] Re: Astatic (Crystal Balls) Problem


I know that he doesn't need my endorsement...lol...but I've had Greg work on three of my mics (including an Astatic crystal T-3), and high recommend him to anyone needing a microphone modified or repaired.

Greg was a great communicator ahead of the work, did exactly what I needed , and went above and beyond to check the devices out thoroughly. His work was clearly done professionally and neatly, and he documented what he changed in each instance, and then sent any removed or replaced parts back with the completed work. And, yes, in fact I found his prices were quite reasonable.

I particularly liked the modification he did to my Astatic T-3. This involved removing the old three-pin base connector on the pivoting "tail" of the mic, and replacing it with a custom extension that terminates in an Amphenol screw-on connector. This allows me to swap mics quickly and efficiently with my existing cables rather than carrying and goofing around with a separate one just for that microphone.

Any questions about Greg's work, feel free to contact me off list.



Date: Sat, 29 Oct 2011 08:25:48 -0700
From: Greg Heumann <greg@xxxxxxxxxxx>
Subject: Re: [Harp-L] Astatic (Crystal Balls) problem
To: harp-l@xxxxxxxxxx
Cc: richardtraffordowen@xxxxxxxxx
Message-ID: <3BDAFC80-CA16-4330-8C3A-FA4E29610FCA@xxxxxxxxxxx>
Content-Type: text/plain;	charset=us-ascii

Richard I think you're barking up the wrong tree here. Hum happens because your amplifier is receiving some 60 Hz RF - which is present to varying degrees all over the place. The higher impedance the input to your amp, the more sensitive it is. I'm willing to bet if you remove the disconnect the mic from the cable but don't unplug the cable, it gets a little worse. If you unplug the cable it goes away - because when you do this the amp's input jack shorts the signal directly to ground. A mic's element effectively places a resistor across the input of the amp. A dynamic mic has considerably lower resistance than a crystal mic and therefore more effectively damps out the 60Hz RF, for which your cable is an antenna.

For all intent no current flows from the amp when you plug in. Mics are "generators" and create the electrical current that the amp then amplifies. As your amp warms up, its input impedance may change or it's gain may increase and it is therefore going to make the hum louder.

My guess is that the problem is your element is getting old, output has dropped, and you've been slowly raising the volume on your amp to compensate. Your cable may have deteriorated too and the shielding quality ain't what it used to be. The solution is a new cable and a stronger element.

As for modifying the JT30 to take 1/4" - it is a real hack job to do it internally. A more common approach is to install a screw-on connector (which earlier JT30's had). I prefer a screw-on cable with that, but the Switchcraft 332A adapter will screw on and provide an external 1/4" input. I can do this mod for you if you wish.



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