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A Shure SM58 Hack for You
#3048443 06/10/20 11:57 PM
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So I was talking with Bryce about the Cloudlifter...and thought what if I plugged an SM58 into an interface's instrument input...after all, it's a dynamic mic? Once I wired up an adapter to do XLR Balanced -> Mono Unbalanced, all I can say is it makes a big difference. Much brighter, and more defined.

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Re: A Shure SM58 Hack for You
Anderton #3048455 06/11/20 01:52 AM
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Originally Posted by Anderton
So I was talking with Bryce about the Cloudlifter...and thought what if I plugged an SM58 into an interface's instrument input...after all, it's a dynamic mic? Once I wired up an adapter to do XLR Balanced -> Mono Unbalanced, all I can say is it makes a big difference. Much brighter, and more defined.

Paul Stamler did a project with a class of his students several years back where they experimented how different loads on microphones affected their sound. They decided, from listening tests with several sources, that loading an SM57 with 600 Ω smoothed out a lot of bumps in the frequency response. The level drops some from a more conventional 2,000 Ω or so preamp input, and the high end drops off a little sooner, but the mids and highs were a lot smoother with the heavier load. And their opinion, this constituted "better sound."

While rumors abound that ribbon mics need a lower than common preamp input impedance, Wes Dooley's mic preamps, which are optimized for ribbon mics (inclluding the classics) have an input impedance of 50 kΩ or higher. Works for him!

Re: A Shure SM58 Hack for You
Anderton #3048456 06/11/20 02:04 AM
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I have a couple of cables already wired up for that, no transformers.

I don't have an SM 58 or 57 - I know, heresy!!!!!
I do have a KSM 8 and some other dynamics including a Heil PR40 so I'll give it a spin.

I've heard of removing the transformer inside an SM58 too but I don't remember if they like it or not.


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Re: A Shure SM58 Hack for You
KuruPrionz #3048498 06/11/20 01:23 PM
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Originally Posted by KuruPrionz
I have a couple of cables already wired up for that, no transformers.

"Like that" being a cable with a 600 Ω resistor wired across pins 2-3?

In his article in Recording, Paul called it the "Gizmo" but I believe that name has already been used a few hundred times. The value for the resistor in the Gizmo is the value of the resistor that it takes when connected in parallel with the mic preamp's input impedance, to equal 600 Ω (assuming you're loading an SM57). So if your preamp's input impedance is, for example, 2.5 kΩ, you'd need a 790 Ω resistor in the Gizmo to give you a 600 Ω load on the mic. For a 1.5 kΩ input impedance, you'd need a 1 kΩ resistor. For an input impedance of 30 kΩ - typical of a "ribbon" mic input - you'd need a 612 Ω resistor. Of course "close enough" is usually close enough.

Here's a Handy-Dandy Calculator for two resistors in parallel.

Quote
I do have a KSM 8 and some other dynamics including a Heil PR40 so I'll give it a spin.

Well, there's probably nothing magic about a 600 Ω load on those mics. For the benefit of all your fellowmen, maybe what you should do is build a box with a male and female XLR on either side and, for a "normal" mic preamp input impedance, hang a 5 kΩ pot across the signal pins and twiddle it to find the sound you prefer. It might be different for different applications. There are a number of mic preamps that have selectable input impedance, generally in steps that will skip over your optimum value. The Cloudlifter-Z has a variable input impedance that covers a pretty wide range, and I'm starting to see instrument inputs with variable impedance as well.

Quote
I've heard of removing the transformer inside an SM58 too but I don't remember if they like it or not.

That's a different kettle of fish, and it depends on whether you like the transformer's distortion or not. As human nature predicts, the first experiments with bypassing the transformer produced a round of WOWEEEEE!!!!s, but then others chimed in with dissent, often saying that they'd rather take the distortion than lose the level boost that the transformer provides.

As in most things audio, it depends on both electrical and human factors.

Re: A Shure SM58 Hack for You
Anderton #3048509 06/11/20 02:44 PM
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Anotehr great post, Sir Mike!!!

I'd have to check the innards of the cables to confirm, probably no resistor. I have a Focusrite ISA One and a Presonus Eureka that both have switchable input impedence ( resistance?). Switching that does make my one ribbon mic - CAD D-82, sound different. The Heil sounds different too, on the Focusrite - haven't tried the Eureka.

The cords are thrift store finds, I'll try one with some dynamic mics and see what happens. Then I might open one up.

I've got more than enough "experiements" to conduct already so this makes it to the "back burner" list. Cheers, Kuru


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