Silly Questions about High Impedance Dynamic Mic, Shure Prologue 12H

[Paul]

I've got two of these mics, but their usefulness seems limited.

For one, if you try to improperly drive a low-Z mic pre, you still
get a signal, but a very small one, as only pin 3 is driven, with pin 2
left open, and pin 1 grounded.

And then the only XLR to 1/4" unbalanced cable that I had lying around,
was actually wired with pins 1 and 3 grounded, and pin 2 as the signal
wire. WTF??? I would guess there isn't a wiring standard going from
unbalanced XLR to unbalanced 1/4"?

Who decided it was a good idea to use an XLR connection for an
unbalanced output? Where one pin is not used at all? I assume
this was done just because of the popularity of the XLR, and
for the purpose of confusing the public? :)

Can I convert these mics to Low-Z, by removing the output transformers,
and driving pins 2 and 3 directly from the capsules? That would seem
to make them much more useful....

[Mike Rivers]

On 3/26/2016 8:16 PM, Paul wrote:
> I've got two of these mics, but their usefulness seems limited.
>
> For one, if you try to improperly drive a low-Z mic pre, you still
> get a signal, but a very small one, as only pin 3 is driven, with pin 2
> left open, and pin 1 grounded.

Well, that's not the best situation, but it's still workable if you wire
it correctly.

> And then the only XLR to 1/4" unbalanced cable that I had lying around,
> was actually wired with pins 1 and 3 grounded, and pin 2 as the signal
> wire. WTF???

It's a historical thing. Pin 3 used to be hot with respect to Pin 2, but
then about 20 years ago, the industry pretty much standardized with pin
2 hot with respect to Pin 3. You have an old mic with a new cable. But
if you're connecting it to a low impedance mic preamp, you need a signal
between pins 2 and 3, and if pin 2 is open on the mic, then you won't
get the voltage where you need it until you ground Pin 2 on the mic.

> I would guess there isn't a wiring standard going from
> unbalanced XLR to unbalanced 1/4"?

No, there isn't, because that's not a very common thing to do. Usually
an unbalanced mic has a 1/4" phone plug at the end of its cable, and an
adapter with a female 1/4" jack on one end and a male XLR plug on the
other end is wired so that the tip goes to pin 2 and pins 1 and 3 are
connected to the shield (ground).

> Who decided it was a good idea to use an XLR connection for an
> unbalanced output?

The bean counters. If they used the same parts on both the high and low
impedance version of what's otherwise the same mic, they can save some
money. They expected you to use the cable that they probably originally
provided with the mic, and they expected you to plug the 1/4" plug on
the end of that cable into a high impedance unbalanced input.

> I assume
> this was done just because of the popularity of the XLR, and
> for the purpose of confusing the public? :)

Nobody's confused but you.

> Can I convert these mics to Low-Z, by removing the output transformers,
> and driving pins 2 and 3 directly from the capsules? That would seem
> to make them much more useful....

Try the simple solution first. Modify an XLR cable so that you get
signal across the inputs of your mic preamp and see what that gets you.
Even though there will be some voltage drop across the high source
impedance, the output voltage of the mic for a given SPL is 16 dB higher
for the high impedance version than for the low impedance version, so
you'll probably have enough level. What you're giving up is the common
mode rejection offered by a balanced connection, and some high frequency
loss if you use a very long cable.

I don't know for sure, but I'd guess that the low impedance version has
a transformer as well, just a different transformer. Or maybe it's the
same transformer and you can convert it to low impedance by using a
different tap. E-V mics did this - they brought out both the low and
high impedance taps to a 4-pin connector (not an XLR) and you just wired
up the mating connector for low or high impedance as you needed it. I
couldn't find a detailed document for the mic on line, so I guess maybe
they don't want you to mess with it.


--
For a good time, visit http://mikeriversaudio.wordpress.com

[Paul]

Well, indeed, they had the Hi-Z AND Lo-Z versions of the same mic:

http://cdn.shure.com/user_guide/upload/1296/us_pro_prologue12_ug.pdf


Not sure if the transformer has another tap I can use.

"Try the simple solution first. Modify an XLR cable so that you get
signal across the inputs of your mic preamp and see what that gets you."

I tried shorting pin 2 to ground on one of these mics (is this the
same thing you suggested to do with the modified XLR cable? shorting
pin 2 to ground?). This makes one side of the pre-amp balanced
transformer go to ground, instead of open. It makes the signal
stronger, but not by a huge amount. Certainly not the same signal
level as my Lo-Z dynamics, obviously.

I guess it might be good enough...maybe I'll take one of the
transformers out, and see if it has another tap.....

Thanks for the feedback....

[Mike Rivers]

On 3/26/2016 11:32 PM, Paul wrote:
> Well, indeed, they had the Hi-Z AND Lo-Z versions of the same mic:
> http://cdn.shure.com/user_guide/upload/1296/us_pro_prologue12_ug.pdf

Yes, I found that instruction sheet. But what it didn't show was the
wiring of the connector, or of a transformer, but I guess you've taken
the mic apart and found one.

> I tried shorting pin 2 to ground on one of these mics (is this the
> same thing you suggested to do with the modified XLR cable?

What you want to do is connect pins 1 and 2 together. Pin 1 may or may
not be connected to the cable shield and/or the case of the mic.

> This makes one side of the pre-amp balanced
> transformer go to ground, instead of open.

Correct. You no longer have a balanced connection, but at least you have
signal continuity through the cable. With only one wire actually
connected to one of the signal pins on the mic preamp, the circuit is
completed only by capacitance, not by a DC path. That's why you get some
signal, but weak, and lacking in low frequencies.

> It makes the signal
> stronger, but not by a huge amount. Certainly not the same signal
> level as my Lo-Z dynamics, obviously.

Right. According to the spec sheet, the source impedance of the mic is
about 47 k Ohms. Assuming that your mic has an input impedance of about
2.5 k Ohms, about 47/50ths of the capsule voltage will be dropped across
the the mic's internal impedance, that represents an attenuation of
about 26 dB. Since the output level of the Hi-Z version is specified as
being
16 dB higher than that of the Low-Z version, that means that you'll get
about 10 dB less signal for the same source level (or need 10 dB more
gain to get back to the same level as with the low impedance version of
the mic.

Use it on a drum or an instrument amplifier. Don't use it on a dulcimer
or the crickets at dawn.

[Paul]

On 3/27/2016 4:50 AM, Mike Rivers wrote:
> On 3/26/2016 11:32 PM, Paul wrote:
>> Well, indeed, they had the Hi-Z AND Lo-Z versions of the same mic:
>> http://cdn.shure.com/user_guide/upload/1296/us_pro_prologue12_ug.pdf
>
> Yes, I found that instruction sheet. But what it didn't show was the
> wiring of the connector, or of a transformer, but I guess you've taken
> the mic apart and found one.
>
>> I tried shorting pin 2 to ground on one of these mics (is this the
>> same thing you suggested to do with the modified XLR cable?
>
> What you want to do is connect pins 1 and 2 together. Pin 1 may or may
> not be connected to the cable shield and/or the case of the mic.
>

Ok, yes, pin 1 is grounded to the case, so your suggested cable
mod would do the same.

>> This makes one side of the pre-amp balanced
>> transformer go to ground, instead of open.
>
> Correct. You no longer have a balanced connection, but at least you have
> signal continuity through the cable. With only one wire actually
> connected to one of the signal pins on the mic preamp, the circuit is
> completed only by capacitance, not by a DC path. That's why you get some
> signal, but weak, and lacking in low frequencies.
>
>> It makes the signal
>> stronger, but not by a huge amount. Certainly not the same signal
>> level as my Lo-Z dynamics, obviously.
>
> Right. According to the spec sheet, the source impedance of the mic is
> about 47 k Ohms. Assuming that your mic has an input impedance of about
> 2.5 k Ohms, about 47/50ths of the capsule voltage will be dropped across
> the the mic's internal impedance, that represents an attenuation of
> about 26 dB. Since the output level of the Hi-Z version is specified as
> being
> 16 dB higher than that of the Low-Z version, that means that you'll get
> about 10 dB less signal for the same source level (or need 10 dB more
> gain to get back to the same level as with the low impedance version of
> the mic.
>

Yep. For any newbies reading: 20*log(2.5/49.5) = about -25.9333dB

> Use it on a drum or an instrument amplifier. Don't use it on a dulcimer
> or the crickets at dawn.
>

Ok, great. Thanks for the engineering review and insight...how
many years have you been in pro audio?

I'll mod both mics to have pin2=Hot, and pin3=grounded, to match
the cable I have. Thanks again....

[Scott Dorsey]

In article <nd78jf$73o$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>I've got two of these mics, but their usefulness seems limited.
>
>For one, if you try to improperly drive a low-Z mic pre, you still
>get a signal, but a very small one, as only pin 3 is driven, with pin 2
>left open, and pin 1 grounded.

This is a communications thing. They often use pin 3 hot, with pin 2 used
for a push-to-talk switch.

>And then the only XLR to 1/4" unbalanced cable that I had lying around,
>was actually wired with pins 1 and 3 grounded, and pin 2 as the signal
>wire. WTF??? I would guess there isn't a wiring standard going from
>unbalanced XLR to unbalanced 1/4"?

For many years there wasn't any standard for balanced XLR, even. The
Pin 3 vs. Pin 2 people argued for years. Well, some of them are still
arguing.

>Can I convert these mics to Low-Z, by removing the output transformers,
>and driving pins 2 and 3 directly from the capsules? That would seem
>to make them much more useful....

Likely. There is a low-Z version of these microphones called the
Prologue 12L. Get the maintenance sheet from Shure. It likely has the
same element; if it's wired without any transformer, then try it. It's
possible that instead it has a different transformer in the box, though.

These were popular paging microphones for supermarkets and busses; they
are not going to be hi-fi. Might be interesting on a guitar amp though.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Mike Rivers]

On 3/27/2016 9:25 AM, Paul wrote:
> Ok, great. Thanks for the engineering review and insight...how
> many years have you been in pro audio?
>
> I'll mod both mics to have pin2=Hot, and pin3=grounded, to match
> the cable I have.

Oh, about 60 years, I guess. Hard to remember just when I started, or
when I became "pro."

[Paul]

Mike suggested drums, due to the low signal level when using with
low-Z pre-amps. So maybe these would be good as tom-tom mics, or for
the floor tom?

[Mike Rivers]

On 3/27/2016 4:25 PM, Paul wrote:
> Mike suggested drums, due to the low signal level when using with
> low-Z pre-amps. So maybe these would be good as tom-tom mics, or for
> the floor tom?

If you have drums to record, give 'em a try. At least you won't have an
overloading problem, unless the mics themselves crap out due to a higher
SPL than speech, which seems to be what they're mostly designed for. But
other than cymbals, the high frequency droop that you might due to a
long cable shouldn't be a problem. It would be about around a 6 dB drop
at around 5 kHz for a 25 foot cable here, not a big deal for toms.

Just this week I watched a session with Sylvia Massy producing, and she
used all sorts of odd mics on the drums, including a room mic consisting
of an SM-57 taped into one end of a garden hose draped around the drum
kit on the floor. And some conventional mics and mic positions, too.
Whatever works, you know.

My fantasy session now is working with her, recording The Maddox
Brothers and Rose. Too bad it'll never happen. ;)

[Phil Allison]

Paul wrote:

>
> I tried shorting pin 2 to ground on one of these mics (is this the
> same thing you suggested to do with the modified XLR cable? shorting
> pin 2 to ground?). This makes one side of the pre-amp balanced
> transformer go to ground, instead of open. It makes the signal
> stronger, but not by a huge amount.
>

** You sure your mic pre uses an input transformer ?

Very few do and active balanced circuit uses twin, identical inputs ( with phase reversal ) - so you can drive one or both.

It makes little difference if you short the unused one to ground.


... Phil

[Scott Dorsey]

In article <nd9fdt$rft$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>
> Mike suggested drums, due to the low signal level when using with
>low-Z pre-amps. So maybe these would be good as tom-tom mics, or for
>the floor tom?

If you put it into a low-Z preamp, not only will the signal level be low,
but the frequency response will be altered because the microphone is too
heavily loaded. Likely that means no top end.

Use a step-down transformer or modify the mike to be a Prolog 12L.

[Paul]

That's a good point, but it did get a bit louder after I did the
mod.....

[Paul]

On 3/28/2016 8:23 AM, Scott Dorsey wrote:
> In article <nd9fdt$rft$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>>
>> Mike suggested drums, due to the low signal level when using with
>> low-Z pre-amps. So maybe these would be good as tom-tom mics, or for
>> the floor tom?
>
> If you put it into a low-Z preamp, not only will the signal level be low,
> but the frequency response will be altered because the microphone is too
> heavily loaded. Likely that means no top end.
>
> Use a step-down transformer or modify the mike to be a Prolog 12L.
> --scott
>

Ok, I'm not sure if the transformers in these mics has another
low-impedance tap I could use, but if not, perhaps I could just remove
the transformer completely, and try driving pins 2 and 3 directly
from the capsule, as the differential signal?

[Scott Dorsey]

In article <ndcfj8$k90$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>On 3/28/2016 8:23 AM, Scott Dorsey wrote:
>> In article <nd9fdt$rft$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>>>
>>> Mike suggested drums, due to the low signal level when using with
>>> low-Z pre-amps. So maybe these would be good as tom-tom mics, or for
>>> the floor tom?
>>
>> If you put it into a low-Z preamp, not only will the signal level be low,
>> but the frequency response will be altered because the microphone is too
>> heavily loaded. Likely that means no top end.
>>
>> Use a step-down transformer or modify the mike to be a Prolog 12L.
>

> Ok, I'm not sure if the transformers in these mics has another
>low-impedance tap I could use, but if not, perhaps I could just remove
>the transformer completely, and try driving pins 2 and 3 directly
>from the capsule, as the differential signal?

Maybe, that's why I suggested you get the service manual from the Shure
website for the 12L, which is the low impedance version. Does it have a
transformer? Is it a different model transformer? When you know these
things, you can answer that question.

[Phil Allison]

Paul wrote:

>
>
> Ok, I'm not sure if the transformers in these mics has another
> low-impedance tap I could use, but if not, perhaps I could just remove
> the transformer completely, and try driving pins 2 and 3 directly
> from the capsule, as the differential signal?
>

** You need to try that idea.

The capsule is very likely 600ohm and not made by Shure - since the brochure is printed in Japan.


.... Phil

[Paul]

The Shure website only has the 12L user guide, which doesn't show
a schematic. But the Prologue 10H and 10L looks very similar:


http://cdn.shure.com/user_guide/upload/355/us_pro_10l_ug_27a2178_ec_.pdf

And you can see they simply remove the transformer to go from high
to low impedance, and separate the black wire from the case-ground tab
on the capsule, so they can drive pins 2 and 3 differentially from the
capsule directly.

Ok, since I have two of these mics, I will likely try this!

:)

[Paul]

[Scott Dorsey]

In article <nd8pk1$a1v$1...@dont-email.me>, Mike Rivers <mm1...@yahoo.com> wrote:
>On 3/27/2016 9:25 AM, Paul wrote:
>> Ok, great. Thanks for the engineering review and insight...how
>> many years have you been in pro audio?
>>
>> I'll mod both mics to have pin2=Hot, and pin3=grounded, to match
>> the cable I have.
>
>Oh, about 60 years, I guess. Hard to remember just when I started, or
>when I became "pro."

Oh, come on, Mike. When was the first time you got paid for recording or PA
work? I remember the first time I got paid, I was 14...

[Scott Dorsey]

It's certainly worth trying. The 12 might be different than the 10, but
I doubt it.

[Mike Rivers]

On 3/29/2016 9:30 AM, Scott Dorsey wrote:

> Oh, come on, Mike. When was the first time you got paid for recording or PA
> work? I remember the first time I got paid, I was 14...

My rabbi used to go down to U.S. Recording Co on South Capitol Street
and have them cut a disk of the chants we had to learn for our bar
mitzva service. Since each week, we would read from a different portion
of the torah, he couldn't just cut one disk and sell it to everyone.
When I was about 12 and preparing for my bar mitzvah, he got a tape
recorder so he could record the chants at home and then take the tape to
the studio. I helped him set up his recorder, showed him how to use it,
and how to make edits so he wouldn't have to re-record the whole thing
if he made a mistake. It was a Wilcox-Gay.

He charged $15 for the disks, but in exchange for my help, gave me mine
for free. I guess that was my first paid session, though it was more
consulting than recording. So, yeah, 61 years.

[Paul]

Aren't high-Z mics something like Beta tapes were back in the day?

Aren't they practically useless these days? No CMRR, etc.

Or do you think I should keep one High-Z mic just in case I
run into a high-Z input? The only time I can imagine needing
a high-Z mic is if I wanted to use a guitar amp to sing through,
and didn't have a balun transformer (XLR to 1/4").

[Phil Allison]

Paul wrote:

>
> Aren't high-Z mics something like Beta tapes were back in the day?
>
> Aren't they practically useless these days? No CMRR, etc.
>
> Or do you think I should keep one High-Z mic just in case I
> run into a high-Z input? The only time I can imagine needing
> a high-Z mic is if I wanted to use a guitar amp to sing through,
> and didn't have a balun transformer (XLR to 1/4").
>
>

** There are not many uses for them and very few left on sale.

The original uses were with things like with consumer grade tape recorders and paging amplifiers.

FYI:

Nothing stops you using a low Z mic with a guitar amp - for close miced speech or singing they have enough output level.



.... Phil

[Paul]

Oh, I've used Low-Z mics with a guitar amp quite often, using a
transformer balun.

It just seems like High-Z isn't very useful, and may not be worth
keeping in my mic locker.....

[Phil Allison]

Paul wrote:
>
> >
> > ** There are not many uses for them and very few left on sale.
> >
> > The original uses were with things like with consumer grade tape
> > recorders and paging amplifiers.
> >
> > FYI:
> >
> > Nothing stops you using a low Z mic with a guitar amp - for close
> > miced speech or singing they have enough output level.
>
>
> Oh, I've used Low-Z mics with a guitar amp quite often, using a
> transformer balun.
>

** I meant use with no balun transformer.

It is often quite unnecessary and only spoils the quality.

That low Z mics must be only be used with balanced inputs or gain some benefit from so doing is one of the most persistent myths in audio.



.... Phil


.... Phil

[Paul]

Ok, I'll try it without a balun.

But how many High-Z mics do you have in your locker, and how often
do you need to use them?

Have you ever run into a situation where only a High-Z mic will do
the job?

[Mike Rivers]

On 3/30/2016 2:02 AM, Paul wrote:

> Aren't high-Z mics something like Beta tapes were back in the day?

Not really. Beta was actually a better system than VHS. However, like
Beta videotape (and ultimately, VHS, too), high impedance mics have
become obsolete because the equipment that they were used with has
become obsolete. We had high impedance mics to use with equipment that
was built without transformers to save cost.

> Or do you think I should keep one High-Z mic just in case I
> run into a high-Z input? The only time I can imagine needing
> a high-Z mic is if I wanted to use a guitar amp to sing through,
> and didn't have a balun transformer (XLR to 1/4").

Since most high impedance (only) mics usually aren't of particularly
good quality, I'd rather have a decent transformer around than be
burdened with a mic that I'd rather not use, even in an emergency
situation. I was once working at a country music festival in rural
Virginia where the temporary power they brought in for the PA system
went out just before Jerry Lee Lewis was about to go on stage. They had
a generator for minimal lighting, so we plugged a guitar amplifier into
that circuit, put a direct box backwards between an SM-58 and the
amplifier for his voice, and The Killer put on a killer show for the 100
or so people who gathered at the edge of the stage.

And on the more practical side, Chicago style harmonica players have
traditionally played with a cheap high impedance radio dispatcher's mic
(the Shure Green Bullet) plugged into a guitar amplifier. They wouldn't
let Shure discontinue it.

[Phil Allison]

Paul wrote:

>
> Phil Allison wrote:
> >
> >>>
>
> Ok, I'll try it without a balun.
>

** Old Chinese staying: "Never try = never know".

> But how many High-Z mics do you have in your locker, and how often
> do you need to use them?
>

** None.

> Have you ever run into a situation where only a High-Z mic will do
> the job?

** As Mike R said, a harmonic mike is one - if the player is using one of those puny, tube practice amps made in the 1950s and needs to overdrive the shit out of it.



... Phil

[Scott Dorsey]

In article <ndfpvg$5ob$1...@dont-email.me>, Paul <quill...@gmail.com> wrote:
>
> Aren't high-Z mics something like Beta tapes were back in the day?
>
> Aren't they practically useless these days? No CMRR, etc.

They are still very common in the communications world, for short runs from
a desk mike to a radio, etc.

> Or do you think I should keep one High-Z mic just in case I
>run into a high-Z input? The only time I can imagine needing
>a high-Z mic is if I wanted to use a guitar amp to sing through,
>and didn't have a balun transformer (XLR to 1/4").

Maybe, but you should always keep matching transformers around.

[Paul]

Ok, thanks everyone for the feedback, it's been very informative.

I'll likely modify both of these 12Hs to Low-Z, and maybe sell one
on Ebay......those Ebay people will buy anything!

Haha!

:)

[Peter Larsen]

Always watch out, if you encounter a Sennheiser cable transformer at a
garage sale, buy it, it will probably be practical some day .... and
impossible to get on the day you need it.

> --scott

Kind regards

Peter Larsen