fast_eddy
5 posts
Oct 16, 2009
11:04 AM
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All,
Can someone tell me the best way to test the output on a crystal element. I'd like to determine how close or how far mine is away from original spec, but don't want to ruin it in the process. Thanks in advance.
fast_eddy
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tookatooka
649 posts
Oct 16, 2009
1:15 PM
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Never worked with cystals but my first plan of action would be to measure the resistance of the crystal and see how much it differs from the original specification. You can do no harm by doing that. Just a thought.
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MrVerylongusername
565 posts
Oct 16, 2009
1:25 PM
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WHHHHHOOOOOAAAAAA!
Hold on! To measure resistance, don't you need to put a voltage across the element?
I'm no expert - check with Greg Heumann - but I really don't think that's a good idea unless you actually want to fry the crystal.
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tookatooka
651 posts
Oct 16, 2009
1:31 PM
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There's an amateur radio forum here
http://forums.qrz.com/archive/index.php/t-59429.html where they discuss crystal mics. The radio hams normally know what they're talking about when it comes to mics.
Last Edited by on Oct 16, 2009 1:36 PM
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MrVerylongusername
566 posts
Oct 16, 2009
1:35 PM
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Heat from a soldering iron will kill a crystal, so will dropping it, leaving it in a hot car, or a humid atmosphere. I really think you should get expert advice before you do anything. 1.5v from a multimeter might not be much, but these things die if you just look at 'em funny.
Last Edited by on Oct 16, 2009 1:58 PM
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MrVerylongusername
567 posts
Oct 16, 2009
1:52 PM
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Tooka - I'm not trying to challenge you. I'm just worried that fast_eddy will kill his element. I'm speaking from experience. I killed a Slim-x element once with over zealous soldering. Now I'm really paranoid about doing anything to crystal elements unless I'm 110% certain it's harmless.
The forum post you linked to talk about measuring the output voltage, which does make sense. They are not talking about measuring the resistance.
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tookatooka
653 posts
Oct 16, 2009
2:03 PM
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That's OK MVLUN. You are of course right, I shouldn't have suggested that in hindsight. As I said I never worked with crystals (mic's that is) but most electronic devices have a resistance so I thought it would be OK. I have worked with quartz crystals in electronic timing circuits but that's a different matter. Thanks for stepping in, you could have prevented a disaster. I hope fast-eddy reads the whole thread before taking any action. No challenge was recognised on my part. Thanks.
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MrVerylongusername
568 posts
Oct 16, 2009
2:12 PM
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Well you could still be right!
I'm hoping Greg will read this and help fast_eddy out. All I'd say to eddy now is if it ain't broke - don't fix it!
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fast_eddy
6 posts
Oct 16, 2009
9:38 PM
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All,
Thanks so much for your postings; I really appreciate the dialog here on this forum. I am very new to the forum, and only about 8 months into harp playing, but I am loving every minute of it. Who would have thought a bunch of harmonica nuts would create such a community?
Last month I purchased an Electar Tube 10 tube amp and what I believe to be a 1960's or 70's vintage Astatic JT 30 with MC 101 crystal element. The mic works, and the combo togehter gets kinda loud, but I'm not so sure it would keep up with a drum set for volume. (I need to work on my cupping too.) The mic works, but I hear "stuff" rattling in there if I shake it gently. Wondering if this is just some junk between the front of the element and the silk or if it's a crumbling salt crystal. I was assuming that if I could hear stuff rattling in the mic, and it was in fact a damaged crystal that there would be no output at all.
This was kind of a long reply, just thought I'd throw it out there. If I don't get many responses, I may start a new thread with the same text.
I look forward to Greg's comments should he read this post.
Thanks again.
PS - I haven't touched my mic with any type of meter yet. I'll wait on that until I have general consensus on acceptable methods.
fast_eddy
Last Edited by on Oct 18, 2009 9:37 AM
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MrVerylongusername
569 posts
Oct 17, 2009
4:48 AM
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Rattling isn't good, but it could be something else just like you say. You won't damage anything by opening it all up and seperating the element from the grill to see. As long as you're gentle.
I have a little Electar 10 too. If the mic is OK then you really ought to be able to get a good dirty sound without adding too much gain on the amp. I don't think it'd hold it's own against a drum kit at full tilt, but it can get uncomfortably loud in my living room. If you're struggling to get any 'dirt' into your sound without lots of gain, then I'm afraid the element is on its way out. There was an interesting post n Harp-L a year or so ago about repairing crystals, but I wouldn't do anything at all unless you are sure it's on its way out.
A new Astatic element will cost you a 3 figure sum now. Not worth it IMHO. There are other crystals that can sound as good, look out for those little tabletop, oblong shaped tape-recorder mics from the 60s - if you're lucky you'll find a good substitute in one of those. A Shure CM element (from a green bullet) is the usual replacement, then you have a smaller lighter mic with the sound of a GB. Plenty of choice!
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bacon-fat
1 post
Oct 26, 2009
5:31 PM
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Crystals and ceramics can't be measured with an ohm meter, like you might do with a shure cm to test coil dc resistance. Doing that would put a voltage across it and likely fry it.
They appear electrically to have infinite (ok maybe half that) resistance.
You can measure the output with an AC voltmeter like Harpwrench did, or an oscilloscope. Or just plug it in and compare it to your favorite mic.
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Deluxe8765
12 posts
Oct 31, 2009
11:25 AM
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Right. Not a good idea to test crystal elements with voltmeter. A. You could fry it, some say. B. You won't get an accurate reading as the resistance is way too high (infinite is more like it, like bacon-fat said). If you happen to have an oscilloscope, that would be ideal.
I use a test cable that I made with a 1/4" plug on one end, and alligator clips on the other end. Attach clips to correct terminals on element, plug into amp, use your ears to judge output. Tough to do if you have nothing to compare it to. I see a lot of misinformation on my infrequent visits here. Will try to check in more often. BTW, I have several crystals that rattle, but they still work fine. They are very tricky little mothers. Normally, a rattle would signal a dead crystal, but not always. The holy grail of crystal elements is a working Shure crystal. 99-131, R7, and the like. Once you hear one of those that is strong, you will understand what the fuss is about. Best harp tone in the world, many people think. Huge, warm bottom, plenty of output. 99% of them are dead. You could spend thousands trying to find a good one, and then it could die at any time. Not a pursuit for the faint of heart or light of funds. I just sold a great one to a lucky guy in England. He is one happy harp player now.
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Greg Heumann
156 posts
Oct 31, 2009
7:47 PM
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Sorry to be late to the party.
At this point I'm reiterating what others have said, but here goes:
An ohm meter won't tell you anything about a crystal and depending on your meter can damage the element. A crystal is NOT like a coil/magnet element and would measure very high if not infinite resistance.
You can safely solder if you know what you're doing - you should use a temperature controlled soldering iron. If the element already has leads, though, it is safer to heat sink them and solder to the lead ends.
The only way to test crystals to see if their output is strong is to have some good ones for reference - then blow through an amp and compare That's what I do. A strong crystal has about the same output as a CM or CR. There are MANY crystals that have partially died and their output will be lower.
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/Greg
http://www.BlowsMeAway.com
http://www.BlueStateBand.net
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