KingoBad
728 posts
May 13, 2011
10:47 AM
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I have just picked up a very nice looking jt30vc that was purchased new in the early 90s and rarely used.
I purchased it for fairly cheap, as everything I tried it on sounded weak (as in previous duds I have purchased)but not horrible (I had to turn my amp all the way up).
My question is, does the xlr connector running through an impedance transformer change the nature of how the crystal mic performs? It is a MC151 element,
Would it benefit in switching out the type of connector, or does that make a difference in performance of this mic? (is it a dud)
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Danny
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5F6H
668 posts
May 13, 2011
10:58 AM
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The connector makes NO difference to the sound...as long as it matches the cable wiring. Use a guitar/instrument cable, rather than a multi conductor "microphone" cable, wired "pin 3 hot", pins 1 & 2 connect to ground & cable shield. If that's what you have already, it's worth tryoing a "pin 2" hot cable as I seem to recall some CAD JT30s were wired differently.
You can check cable wiring by checking continuity with a DMM from tip of the jack plug to XLR pin no. 3 (marked on the plug).
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Joe_L
1243 posts
May 13, 2011
11:36 AM
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When I tried an standard microphone cable, the output was very low. You need to use a different cable. I can't recall which pin was hot. I think it was pin 2. No impedence transformer was necessary.
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The Blues Photo Gallery
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KingoBad
729 posts
May 13, 2011
11:59 AM
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I'll have to check these options out.
I am using a standard xlr mic cable into a impedance transformer that converts to a 1/4 inch jack (the transformer does not have a switch, I bought the cheapest one I could find at guitar center for my sm58). I have no amp to try an xlr plug directly without a transformer.
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Danny
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tmf714
626 posts
May 13, 2011
12:29 PM
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Thats most likely your problem-your using a low impedence transfomer on a high z mic. It cuts your power quite a bit. That IMT is for a low impedence mic.
Last Edited by on May 13, 2011 12:30 PM
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12gagedan
37 posts
May 13, 2011
1:15 PM
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My very first mic was a JT30VC. Some nice guy at the local music store re-wired a cable for me when I couldn't get much sound out of it. If it's not the impedence issue, crystals do go bad. Heat, humidity, and percussive incidents (dropping) all negatively impact crystal microphones. Never, ever leave a crystal mic in the car on a hot day.
d.g.
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5F6H
669 posts
May 13, 2011
2:08 PM
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The IMT is pin 2 hot (this is where it would pick up signal from a PA mic...but pin 2 is not connected on a typical JT30, whatever it is picking up, it is not the audio from the hot mic terminal), you just need a pin 3 hot cable terminating in a 1/4" jack...you could just rewire the amp end of the cable, but I recommend an instrument/guitar cable with a pin 3 hot XLR at the mic end.
However if the IMT was pin 3 hot it would still bump up the mic signal...probably unhelpfully so.
The XLR cable has no impedance as such, the 3 wires are not connected to each other (open connection, infinite resistance/impedance)...impedance is just related to how the cable connections terminate.
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rharley5652
485 posts
May 14, 2011
12:04 AM
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here is the cable you need for the JT-30 VC:
www.harphouse.com/index1.html?399.html&1
The #JT30VC Astatic Bullet harmonica mics need this cable. First, because it's Hi-Z, and secondly, because it's 3 pin hot. That's right, you can have a cable look like this one, with the similar connectors and everything, but they may be only 2 pin hot in which case, they won't work with the bullet mics. Plus, you should buy this cable anyway - it's the most reliable we've found. 20' long with a 3 pin hot XLR connector on one end and a 1/4 jack on the other.
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Simply Unique Kustom Mic's By Rharley
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KingoBad
731 posts
May 14, 2011
9:22 AM
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I guess I'm gonna start with the chord then...
Thank you!
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Danny
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