I removed a transformer from a Shure mic with a HiZ output. Pretty straightforward connection to dynamic capsule and output connector. Figuring all transformers found within a microphone are for the purpose of HiZ output, I ordered a handful or "SM58 microphone replacement transformers"...
Only to find out that even the LowZ balanced output of such is <drum roll> transformer coupled.
Why is this? The capsule winding cant drive the few hundred ohm load directly? The transformer's BH curve and FR factors into the SM58 microphone's sound?
Now I have a few useless mic transformers, as I was expecting them to output a high Z level and they do not. More like 20 Ohms to 200... I'm trying to adapt low Z sources to ordinary HiZ guitar pickup levels and a transformer is a very convenient way to go. No pop when removing the 1/4" plug, no battery to eventually die.
Only to find out that even the LowZ balanced output of such is <drum roll> transformer coupled.
Why is this? The capsule winding cant drive the few hundred ohm load directly? The transformer's BH curve and FR factors into the SM58 microphone's sound?
Now I have a few useless mic transformers, as I was expecting them to output a high Z level and they do not. More like 20 Ohms to 200... I'm trying to adapt low Z sources to ordinary HiZ guitar pickup levels and a transformer is a very convenient way to go. No pop when removing the 1/4" plug, no battery to eventually die.
Are you measuring DC on those transformers to get 20 to 200 ohms? You need to measure impedance at about 1K AC instead.
Yes, I am and forgot to mention. The actual HiZ transformers I have measure 1.8k to 4.5k DC on the HiZ side. I have 6-7 in various configurations. Some are too valuable to destroy for the transformer inside; better to sell on epay and buy the correct part, which I see ranges from about $12 to $30, shipped. The expense is fine, but the time to have it in hand is more of a pain...
The SM-58 capsule DCR is only ~12 ohms, so the step up increases the voltage, and gets the impedance up to the "low impedance" 300-600 ohm range (~150 ohms actual), and increases the signal to noise ratio.
The transformer saturation when you scream into the mic is also part of the SM58 microphone's sound.
Shure did make a transformerless mic for a brief time with the SM-78, but that faded out of production quickly- a transformer works better with a wide variety of console's input impedance, and the transformer saturation was missed.
The SM-78 "matte suede" finish, available in multiple colors, turned to a dirty grey after a short time, that killed the deal for those who preferred their cleaner sound.
The 10/1 ratio of the transformers you bought should be similar to direct box transformers, though may not handle the voltage as well, you get what you pay for, specs and Mu metal shields that can match a Jensen usually cost more:
hi, I got a few replacement SM57/8 transformers, they are a bit bigger than originals. I wander is it possible to use those core to wind a ribbon mic transformer? And what number of primary turns are optimal? I might even wind foil primary, or is it overkill?
Its not possible to magnetise the transformer if the core material is 80% nickel as this material has very low remanance. 49% nickel isnt too bad
either. I do it all the time without problems to check winding continuity.
anyone have any info on SM 78?
i don't want to say that Mr Welter is wrong but i've never heard or come across that model before.
i'm going to have to review/relearn what i know about impedance, and mic's....there's something about impedance over frequency that's nagging at me.
i don't want to say that Mr Welter is wrong but i've never heard or come across that model before.
i'm going to have to review/relearn what i know about impedance, and mic's....there's something about impedance over frequency that's nagging at me.
So far it's Shure WH20, SM10 / VR230 style dymanic headset microphones. These are dipoles, as they're clearly vented on the back side and pickup sound from both sides, each being 180 deg out of phase from one another, of course. So far field they cancel. I'm picking up sound off an acoustic guitar's soundboard, with the microphone attached to the guitar, so I dont have to hold it like a vise relative to a stand mic.
I want a mic'd sound, not a piezo nor a mag (electric) sound.
One reason I want to bump up the signal level using just a tranny is I'm sick and tired of replacing batteries that support amplification circuitry. Plus no <kapow> when you plug in, as the ground ring hits the jack tip.
So far, it's barely working, of course, even with a known good Shure HiZ out microphone tranny. I'm chewing on just mounting up an XLR and connecting the guitar to the board like an ordinary mic; particular guitar I dont care that much about selling at some later date.
Microphone transformers are generally 30-300 ohms. If you want a higher impedance check out phono step up transformers 60-47k. Lundhal are worth looking at.
I have 3 Bogen stock balanced input transformers, I harvested from an amp I bought last year. Seen them advertised for that application; even seen a built box with 9 pin sockets and RCA connectors for that application.
Has me wondering if I need to go through two; 30-300 and then 300 - 50K. I suppose the Lundahl does it in one shot, being a "real" phono step up.
Few people remember the 28% lighter "Starmaker Series" SM77 and SM78 introduced around 1980 anymore.
They are listed in the 1981 Shure catalog:
https://www.musikding.rocks/index.php?file-download/13515/
I was surprised that Shure evidently was still making the transformerless SM-78 as late as 1987:
The "internal connections" show the direct connection from the cartridge to the XLR.
In 1989, the SM77 and SM78 were no longer listed in the Shure catalog..
Art
Those three mics all have cardioid (heart shaped, unidirectional) not dipole (figure of 8) patterns:
A dipole picks up equally on either side, many studio recordings are made with singers on both the front and back of the diaphragm, but not on the sides, where the null is located.
The smaller dynamic headset mic cartridges have considerably less sensitivity than a larger SM57/58, so will require more pre-amp gain.
Art
Art is it possible the x-former is built into/integral to the cartridge?
i did find it amongst the discontinued archive on Shure's website. there's no mention that it's transformerless, which you would think would merit a mention,no?
i did find it amongst the discontinued archive on Shure's website. there's no mention that it's transformerless, which you would think would merit a mention,no?
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those headset mic's the SM10 and WH20 have upper mid boosts and tailored low to deal with extreme close proximity effects and less than adequate placement problems. i can't see them making good acoustic guitar mic's.
What I'd always assumed about these mics, without a high-Z output... But along with other assumptions, not the case.
Unsure why they spec Cardioid. The holes in the back, right at the null or 180 around from the front screen; if you speak into them, sound comes through. Not as sensitive as the front side, but not zero by any means, as it would be if that side were solid plastic. Basis of that assumption there. Similar to their electret version of headset, where both cartridge and capsule inside had these vents.
I've noticed. I have the cartridge from the Shure "highball" mic I took apart for its impedance transformer; it's relatively huge.
+2.5 @4k and 8.5k? I suppose...
I could spend close to $300 on a Countryman ISOMAX 2 and get this instead
Also get the more ordinary "SM58 big cartridge" -57db sensitivity vs these Shure's crappy -47db.
Somehow I'm not buying this would work so great, unless the mic shown has little if any vibration pickup;
For more than the guitar is worth $300, I'd get just a Baggs system, install it and be done. But I like to play around, see what I can make work.
i've had the pleasure of working with the Countryman, well worth it and the mount attenuates mechanically transmitted noise but hey it's a microphone and it will still capture a thumb/finger drum/thump of the guitar top...which is great for songs like Clapton's "Layla"
No doubt it's a nicer mic; good to get others perspective on these things. Thanks for participating in my thread!
The placement of the holes behind the diaphragm make the mic a cardioid.
If the back was sealed, the mic would be an omni.
If the back was open, the mic would be a dipole (figure of 8 pattern).
I wouldn't suggest any standard mic element would work well without vibration isolation, just that larger elements require less gain, which was the reason you were looking for transformers.