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Impedance matching Shure Beta 58A, connecting to iPod Touch
andy o
post Sep 8 2011, 10:10
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Hey guys, I've been reading up about connecting a Beta 58A which is 150 Ohm (pdf spec sheet) and my iPod Touch 4, which apparently has the same circuitry as iPhone 4, which supposedly doesn't detect any mic below 800 Ohm.

So I got the Hosa MIT-156 impedance transformer:
QUOTE
This adaptor is designed to match 600R output impedance to 2.5K input impedance. It may be used to connect a microphone to a portable recording device, camcorder, or PC.


I don't know the math of impedance matching so sorry if this is obvious. From that information, can you tell what will be the output impedance of the Beta 58 + MIT-156?

So far the Touch can't detect the rig (works for a computer mic I have though, so my cable adapters that come after the MIT-156 are working fine). And when I connect the mic to the PC via the mic inputs of either an Asus U1 or the built-in IDT sound device (on Windows 7). I get low signal and very loud hiss. What am I missing?
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mixminus1
post Sep 8 2011, 16:29
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Hmm, that Hosa adapter should at least be getting you close enough to get some kind of signal into the touch. Its 600 ohm input rating does mean that the signal will be lower than optimal with the Beta 58 (or pretty much any other balanced dynamic mic), but again, you should be getting something.

I've got an iPhone 4, and just for a quick test, I took the headphone out of my external USB Sound Blaster (which should be down around 5-10 ohms) through a generic camcorder A/V breakout cable (3 RCAs to an 1/8" tip-ring-ring-sleeve), and going in on the right channel RCA, I was able to get sound into the Voice Memo app. Judging by the amount of attenuation I had to dial in in foobar2000, it appears to be a fairly typical mic level input, so I'm not sure why you couldn't get anything at all - what are the additional cable adapters you mention?

As far as why you're getting a severe level mismatch going into your PC, those "mic inputs" are typically somewhere between a true mic level (-60 dB) and true line level (-10 dB) sensitivity - -30 dB is pretty common, so it appears that the Hosa isn't stepping the signal up quite enough.

FWIW, since there are no specs given for the Hosa, here is the manual for a very similar adapter from Shure (that costs almost three times as much as the Hosa). The Hosa *should* be constructed very similarly to the diagram shown in the Shure manual..."should" being the operative word here. Note how the Shure has the option to lower the input impedance in order to increase the output level...I wonder how closely Hosa copied their design? wink.gif


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"Not sure what the question is, but the answer is probably no."
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Posts in this topic
- andy o   Impedance matching Shure Beta 58A   Sep 8 2011, 10:10
- - mixminus1   Hmm, that Hosa adapter should at least be getting ...   Sep 8 2011, 16:29
- - Speedskater   Remember, a transformer cannot do both impedance m...   Sep 8 2011, 18:20
- - andy o   Thanks for the info. The other adapters are a 1/8...   Sep 8 2011, 18:48
- - DVDdoug   I'm thinking the problem is with the adapters....   Sep 8 2011, 20:08
|- - andy o   QUOTE (DVDdoug @ Sep 8 2011, 12:08) I...   Sep 8 2011, 21:38
- - mixminus1   Wait, andy o: you're taking the 1/8" TRS...   Sep 8 2011, 20:29
- - andy o   Gimme some time to process all the info I've b...   Sep 8 2011, 20:45
- - mixminus1   Hmm, without knowing exactly how the eBay adapter ...   Sep 8 2011, 22:08
- - andy o   No, you're right, I think it's wired exact...   Sep 8 2011, 22:24
- - andy o   Didn't work. I think something's funny wit...   Sep 8 2011, 23:23
|- - andy o   OK, I'm reviving this, cause, dumbass me, I ju...   Jul 27 2012, 06:38
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 27 2012, 01:38) I...   Jul 27 2012, 15:38
- - andy o   I'm getting a lot of hiss noise because the mi...   Jul 27 2012, 16:35
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 27 2012, 11:35) I...   Jul 27 2012, 19:44
- - mixminus1   Correct, the 58A is a dynamic, albeit a high(er)-o...   Jul 27 2012, 18:00
|- - andy o   QUOTE (mixminus1 @ Jul 27 2012, 10:00) It...   Jul 27 2012, 23:43
- - andy o   thanks for the recommendation, Arnold. I found it ...   Jul 27 2012, 23:59
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 27 2012, 18:59) thank...   Jul 28 2012, 00:03
- - andy o   I think that would be even better, I mean I was ju...   Jul 28 2012, 00:11
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 27 2012, 19:11) I thi...   Jul 28 2012, 10:49
- - andy o   What about this one AT2020? It's even cheaper,...   Jul 28 2012, 00:21
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 27 2012, 19:21) What ...   Jul 28 2012, 03:39
- - andy o   Great, thanks for the input.   Jul 28 2012, 03:59
- - andy o   I have some questions about mic specs, I'll op...   Jul 29 2012, 21:10
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 29 2012, 16:10) I hav...   Jul 30 2012, 11:40
- - andy o   I ended up getting the AT2035, found it for ...   Jul 31 2012, 00:58
|- - Arnold B. Krueger   QUOTE (andy o @ Jul 30 2012, 19:58) I end...   Aug 2 2012, 18:53
- - andy o   Thanks for the tip(s). I would never have consider...   Aug 3 2012, 02:26


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