swampboy
17 posts
Oct 04, 2010
12:56 PM
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Hiya guys,
I've just got hold of my first crystal mic and it's responding differently to my CMs and dynamics.
When tightly cupped with the mic volume up full and blowing at full blast the mic distorts...but not in a good way! It sounds like an intermittent crackling, or the mic is shorting out.
If I blow less hard, loosen the cup, turn the volume down, sub a lower gain preamp tube, etc the effect goes away.
My question....is this something I will have to live with and a result of high output/ impedance, or is it a fault?
Cheers, Swampboy
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5F6H
306 posts
Oct 04, 2010
2:37 PM
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Any info on mic/amp appreciated, will help us pin down the culprit. Could be big output from the mic, could be that the higher mu preamp tube is underbiased/too low a plate voltage/grid leak input rather than cathode biased input. Check that your amp has an input grid load, turn it off and plug in a mic lead, measure ohms from tip to barrel of the free end of the cable.
Why not use the lower mu tube if it cures the problem (I can appreciate that this could be a bind if your other mics don't like it)? Either way, there is a solution that will allow you to eliminate the problem
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MP
875 posts
Oct 04, 2010
2:39 PM
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it sounds like the crystal is dying or faulty. i say faulty because you didn't say whether the crystal was new or not.
i imagine it's not the higher gain tube because you have used your other mics in both situs?
an old crystal will cut in and out. sometimes they crackle. a crystal is exactly as the name implys- it is a crystal and crystals can crack. i once had a new crystal that was a lemon because it was cracked and the distortion was a BAD distortion.
it is possible you have a loose solder connection too.
best check your connections. then swap a working CM in the mic to rule out a bad connection.
good luck
MP
hibachi cook for the yakuza
doctor of semiotics
superhero emeritus
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swampboy
18 posts
Oct 04, 2010
2:55 PM
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Thanks for the response. The mic is a new Bluexlab:-
http://www.bluexlab.com/WP/?p=180>lang=en
I have tried it with other amps and cables, so the problem is not there. I don't have a problem using a lower gain preamp tube, but I'd like to get some opinions...do you think I should contact the seller?
Last Edited by on Oct 04, 2010 5:51 PM
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5F6H
307 posts
Oct 04, 2010
3:13 PM
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If the mic works fine with other amps & cables, it is most likely something pertaining to the only amp with which the problem occurs...what is it (the amp)? If it only occurs with one amp, I don't see that it is the seller's problem
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swampboy
19 posts
Oct 04, 2010
3:22 PM
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The problem is the same with all amps.
I'm mainly using a '63 Vibroverb Reissue.
Last Edited by on Oct 04, 2010 3:23 PM
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Greg Heumann
806 posts
Oct 04, 2010
5:26 PM
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A crystal element has a physical mechanical connection between the diaphragm and the crystal itself. A high pressure differential between the front and back (i.e, cupped with a very tight seal, hard draw chord) can hyper-extend the diaphragm and damage this internal connection to the crystal. Has nothing to do with the wires. After this it can become intermittent. I've ruined a few myself - although they were old and probably much weaker than when new.
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/Greg
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swampboy
20 posts
Oct 04, 2010
6:00 PM
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So the element is blown?
Thanks for the replies guys
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Greg Heumann
807 posts
Oct 04, 2010
8:18 PM
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Didn't say that - you have to eliminate other possibilities. Switch to a different cable. If the problem no longer occurs, it was the cable. If that doesn't do it, rewire the mic. If THAT doesn't do it then it is the element.
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/Greg
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5F6H
308 posts
Oct 05, 2010
2:45 AM
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I'm still a bit confused as to why the problem would go away with a lower mu preamp tube, or why turning the amp down a little would alleviate the problem (both of these things are later in the signal chain), (could be something perhaps that is only evident with the better hi end response with the 12AX7/volume up higher?)...if the problem is at the element/tight seal, it should still happen. As Greg says, I think there is a bit more troubleshooting to be done.
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toddlgreene
1867 posts
Oct 05, 2010
8:54 AM
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Did you say the mic was a new bluexlab? If it's new, I would imagine the builder would honor some sort of warranty. Contact him and send it back!
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Crescent City Harmonica Club
Todd L Greene, Co-Founder
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