Topic: Phantom power vs. battery box for AT943's

[som]

I have read a few threads on here that rave about the improved performance when going from a battery box to phantom power on the AT943's and other SP-modded AT stealth mics.

In looking at the SP site, it says that most MD and DAT recorders that provide plug-in power will provide 3 or 4 v to the mics. The battery box will provide 9+ v, which inches up towards 10v, which is the "optimum voltage". I can see how that is an improvement.

Now, I know that these mics can't take straight 48v phantom power, and that some sort of voltage adaptor is required between the mics and the phantom power source. What does the adaptor regulate the voltage down to? If 10v is the "optimum voltage" and the battery box delivers 9+v, what is the huge improvement with adapted phantom power? What am I missing?

Thanks in advance for any info.

[Sean Gallemore]

it's not so much the voltage, as it is the resistance over which the phantom power is applied......or atleast I'd like to think

[som]

Thanks for the reply, but could you elaborate? I'm not sure what that means....

[Sean Gallemore]

the phantom adaptors drop the voltage down to 5V, so the "more volts is better" theory goes out the window, so it has to be something else

[leegeddy]

the phantom adaptors drop the voltage down to 5V, so the "more volts is better" theory goes out the window, so it has to be something else

i'm sure jon @ jklabs could provide some technical answers as well.

with a battery box operation, the supply voltage and the audio signal are carried along on the same lead (hot). with the phantom power modules, the supply voltage and the audio signal are separated: audio (pin 2), supply voltage (pin 3).  would this difference be the answer? i don't know. it's beyond my scope of understanding.

jon, where are ya?

marc

edited for stupid grammar mistakes!

[jk labs]

'

the phantom adaptors drop the voltage down to 5V, so the "more volts is better" theory goes out the window, so it has to be something else

i'm sure jon @ jklabs could provide some technical answers as well.

with a battery box operation, the supply voltage and the audio signal are carried along on the same lead (hot). with the phantom power modules, the supply voltage and the audio signal are separated: audio (pin 2), supply voltage (pin 3).  would this difference be the answer? i don't know. it's beyond my scope of understanding.

jon, where are ya?

marc

edited for stupid grammar mistakes!

I'm here. Just ain't able to overlook anything with "AT943" in the subject line.

The original poster is right. And so are the respondents! More or less 

The reported differences in performance are real enough: "P48 powering" is better than "9V-battbox" is better than plug-in-power. (The use of quotation marks will be clear in a second). 


Why the differences?

Voltage is part of the reason why plug-in-power doesn't measure up (low voltage together with high gain resistors force the AT943 beyond its linear region. The mic pre in typical consumer units don't exactly help on the situation either).


But that's about it as far as the voltage goes: 10 Volts is the official limit as was stated. So the proper voltage is within reach for a system built around a 9 Volts battery.     

If you look at electric current the tables are turned: the P48 scheme is limited to about 10 mA. The 9 Volts battery delivers 100 mA without a sweat. But 10 mA is plenty :-) 

So what is left?

Schwilly suggests resistors. Leegeddy the wiring.

In a grand scheme that's just it - the actual circuit topologies used causes the differences.
 
So the often seen statement that "P48 powering" is better than using a "battery box" just reflects the fact that current P48 powering schemes (PM-4, 8533 etc) are built so as to interface more properly with the AT943 than the current crop of battery boxes.  


As for jk labs.... (possible improvements w/ a hint of commercial flavor):
Having now analysed Kevin's AT943/PM-4 combo in detail, the very challenge of both modding/tweaking the transformer-coupled PM-4 and making an even better stand-alone 9V battery box solution for the AT943 is just, well ... irresistible ..  

Jon

(mildly edited for readability :-))

[som]

Don't resist, then!   

+T all around....

[Zaphod]

Thank you for that info Jon, +T.

I look forward to any updates you have for your P48 solution to the PM4/AT943 (as well as AT853?) combo.

[som]

making an even better stand-alone 9V battery box solution for the AT943

I hope you will follow through on this and keep us posted! I would be *very* interested in this, as I'm sure many others on the board would be.

[jk labs]

Thank you for that info Jon, +T.

I look forward to any updates you have for your P48 solution to the PM4/AT943 (as well as AT853?) combo.

Well, I could post a picture or two (by end of the week I imagine).

The solution I'm working on will work for all ATs mics of similar electronic build ( & terminated in a miniXLR). In fact it would probably work equally fine with a few bigger electret mics like Sennheiser K6, AKG BlueLine, C1000 guts, but I need to revisit their respective schematics to know for sure.

And of course Leggeddy's modded Nak 300s.....

[Zaphod]

Very nice.

[Sean Gallemore]

what about DPA 406Xs?  They both run off the same battery box

[som]

The solution I'm working on will work for all ATs mics of similar electronic build ( & terminated in a miniXLR).

I hope you will also look into the possibility of an improved battery box like you hinted up above, something that will work with a 1/8" mini-stereo plug. It would be nice to get a boost in quality but still have the stealthiness of a battery box / 1/8" plug.

[jk labs]

what about DPA 406Xs?  They both run off the same battery box

That's an interesting question. It's almost accidental that the AT mics (831 851 943 etc) and the DPA 406x can be run off the same plain vanilla 9 Volts batterybox.

Why is that? Well, the two mics are very different internally. So much so that by the time you are finished making a really sweet solution for the AT mics, the DPA 406x can't even be connected.

I think the optimum powering soluion for the DPA mics is very near a plain 9 V batt box but built wth good parts.

[Sean Gallemore]

what about DPA 406Xs?  They both run off the same battery box

That's an interesting question. It's almost accidental that the AT mics (831 851 943 etc) and the DPA 406x can be run off the same plain vanilla 9 Volts batterybox.

Why is that? Well, the two mics are very different internally. So much so that by the time you are finished makig a really sweet solution for the AT mics, the DPA 406x  can't even be connected.

I think the optimum powering soluion for the DPA mics is very near a plain 9 V batt box but built wth good parts.

why can't they be connected?

[jk labs]

what about DPA 406Xs?  They both run off the same battery box

That's an interesting question. It's almost accidental that the AT mics (831 851 943 etc) and the DPA 406x can be run off the same plain vanilla 9 Volts batterybox.

Why is that? Well, the two mics are very different internally. So much so that by the time you are finished makig a really sweet solution for the AT mics, the DPA 406x  can't even be connected.

I think the optimum powering soluion for the DPA mics is very near a plain 9 V batt box but built wth good parts.

why can't they be connected?

Because we are now talking about an optimized interface to (& for) the AT943 using three wires.

Then you come along with a DPA 406x. That means you have two wires. You try all possibilities
for connecting your two to the three available on the interface.

None of the combinations will give you a single mV of signal. The two are just not compatible.

This s where the difference shows up. Put differently, if you are looking for the ultimate battery box for the DPA you should not look at the box optimized for the AT943. They are not even distant relatives.

[Sean Gallemore]

what about DPA 406Xs?  They both run off the same battery box

That's an interesting question. It's almost accidental that the AT mics (831 851 943 etc) and the DPA 406x can be run off the same plain vanilla 9 Volts batterybox.

Why is that? Well, the two mics are very different internally. So much so that by the time you are finished makig a really sweet solution for the AT mics, the DPA 406x  can't even be connected.

I think the optimum powering soluion for the DPA mics is very near a plain 9 V batt box but built wth good parts.

why can't they be connected?

Because we are now talking about an optimized interface to (& for) the AT943 using three wires.

Then you come along with a DPA 406x. That means you have two wires. You try all possibilities
for connecting your two to the three available on the interface.

None of the combinations will give you a single mV of signal. The two are just not compatible.

This s where the difference show up. Put differently, if you are looking for the ultimate battery box for the DPA you should not look at the box optimized for the AT943. They are not even distant relatives.

DPA some how does it with their DAD60XX series connectors

[jk labs]

what about DPA 406Xs?  They both run off the same battery box

That's an interesting question. It's almost accidental that the AT mics (831 851 943 etc) and the DPA 406x can be run off the same plain vanilla 9 Volts batterybox.

Why is that? Well, the two mics are very different internally. So much so that by the time you are finished making a really sweet solution for the AT mics, the DPA 406x can't even be connected.

I think the optimum powering soluion for the DPA mics is very near a plain 9 V batt box but built wth good parts.

why can't they be connected?

Because we are now talking about an optimized interface to (& for) the AT943 using three wires.

Then you come along with a DPA 406x. That means you have two wires. You try all possibilities
for connecting your two to the three available on the interface.

None of the combinations will give you a single mV of signal. The two are just not compatible.

This s where the difference show up. Put differently, if you are looking for the ultimate battery box for the DPA you should not look at the box optimized for the AT943. They are not even distant relatives.

DPA some how does it with their DAD60XX series connectors

  When I wrote that it couldn't be done I was thinking of attempts at wiring the DPA mics _directly_ to the new AT box.

Yes you (or DPA) can make an interface between the 406x and the new AT box but you will end up with
a power scheme and signal path worse than that provided by even standard batteryboxes.

Jon     

[som]

Well, speaking for myself, I would love a unit that would basically replace my SP battery box (1/8" input from the SP-modded AT943's, 1/8" analog out) but would provide the benefits that I keep hearing about from a "true" phantom powered solution. Going from a 1/8" input to mini XLR's will make the setup bulkier and will require a mod to the SP AT943's.

Is part of the "problem" the wiring mod that provides an unbalanced 1/8" stereo terminator to the pair of AT943's? Is undoing this mod and restoring the balanced XLR's a necessary part of the solution?

(Note: I may be talking over my head here!)

Thanks again (and +T) for explaining all this stuff!

[jk labs]

Well, speaking for myself, I would love a unit that would basically replace my SP battery box (1/8" input from the SP-modded AT943's, 1/8" analog out) but would provide the benefits that I keep hearing about from a "true" phantom powered solution. Going from a 1/8" input to mini XLR's will make the setup bulkier and will require a mod to the SP AT943's.

Is part of the "problem" the wiring mod that provides an unbalanced 1/8" stereo terminator to the pair of AT943's? Is undoing this mod and restoring the balanced XLR's a necessary part of the solution?

(Note: I may be talking over my head here!)

Thanks again (and +T) for explaining all this stuff!

Hi there,

we certainly have covered some ground here. Not everything was spelled out to the same level of detail. 

But to be crystal clear:
In order to reap the benefits of this optimized powering scheme each individual AT mic has to be terminated in a three wire connector. The most compelling reason for going with miniXLR is that many AT's have these installed already.  In addition the miniXLR is relatively low profile and it's sufficiently rugged for this application.

Now, if you do look for alternatives a single 1/8" stereo mini per mic satisfies the criteria.  Or you could hardwire
into the box for the lowest possible bulk. Lastly a single five pin connector would accomodate both AT mics (ground is shared).

Jon

[som]

Ahhh, I think I get it now! The two-mics-terminated-in-a-single-stereo-1/8" is apparently a flawed (or limited) design that does not allow for optimum powering.

I'm on board, looking forward to what you come up with!

[leegeddy]

Well, speaking for myself, I would love a unit that would basically replace my SP battery box (1/8" input from the SP-modded AT943's, 1/8" analog out) but would provide the benefits that I keep hearing about from a "true" phantom powered solution. Going from a 1/8" input to mini XLR's will make the setup bulkier and will require a mod to the SP AT943's.

Is part of the "problem" the wiring mod that provides an unbalanced 1/8" stereo terminator to the pair of AT943's? Is undoing this mod and restoring the balanced XLR's a necessary part of the solution?

(Note: I may be talking over my head here!)

Thanks again (and +T) for explaining all this stuff!

Hi there,

we certainly have covered some ground here. Not everything was spelled out to the same level of detail. 

But to be crystal clear:
In order to reap the benefits of this optimized powering scheme each individual AT mic has to be terminated in a three wire connector. The most compelling reason for going with miniXLR is that many AT's have these installed already.  In addition the miniXLR is relatively low profile and it's sufficiently rugged for this application.

Now, if you do look for alternatives a single 1/8" stereo mini per mic satisfies the criteria.  Or you could hardwire
into the box for the lowest possible bulk. Lastly a single five pin connector would accomodate both AT mics (ground is shared).

Jon

thanks jon for some clarity about the benefits of running the AT mini mics. 

i just want to add that if you buy the ORIGINAL AT mics, they are all wired with the unbalanced 3 conductor outputs (eg., 1-ground, 2-audio, 3-supply voltage). only issues are the SP models that combine the supply voltage and the audio on a single rail to accomodate their 1/8" plug.

marc

[mattb]

Now if you could cram a nice little a/d converter into this (yet to be seen) box to provide optical out for us JB3 users, that would be the icing on the cake. Any possibility of something like that happening?
I'm currently running AT933 > PM4 > PS-2 > AD-20 > JB3 and I like the AD-20 a/d stage more than the JB3's. So I'm wondering how I could incorporate this box into my rig. It seems like all the EE work I've seen from you is analog only, so that may be outside your area of expertise or interest but I bet prople would be interested if it could be done in a practical manner.

Of course if it was just a replacement for my SP battery box when going stealth/light that would still be cool, but we always want more. 

[jk labs]

Now if you could cram a nice little a/d converter into this (yet to be seen) box to provide optical out for us JB3 users, that would be the icing on the cake. Any possibility of something like that happening?

I'm currently running AT933 > PM4 > PS-2 > AD-20 > JB3 and I like the AD-20 a/d stage more than the JB3's. So I'm wondering how I could incorporate this box into my rig. It seems like all the EE work I've seen from you is analog only, so that may be outside your area of expertise or interest but I bet prople would be interested if it could be done in a practical manner.

Of course if it was just a replacement for my SP battery box when going stealth/light that would still be cool, but we always want more. 

The picture included will give you an idea of the size. This is the box I am using to verify the concept mechanically and test/refine the new circuitry.
The final version will most likely be a box of the same size. Power is from a single 9 V battery mounted internally (taking up about 2/3 of the lenght).  I expect 50 - 100 hours run time per battery change.

Adding an A-D converter is an interesting route to take. Doing so mandates adding some mic-pre functionality as well.
The design is for all practical purposes already done (as part of other units completed or in progress).
But it's a competetive marketsegment and success depends on low unit costs obtained through high volume production.
That means high volume sales. It's a major undertaking. Selling 50 to 100 units wil not cut it.
 
The AD-20 was mentioned. The box above will be able to feed the AD-20 an appropriate signal. Obviously some connectors are needed to make the proper connection. If that is still too bulky I think there is enough space inside the AD-20 to allow a modification (among them remove the XLR ins). The AD--20 gets mini-XLR ports and all the necessary circuitry to support the AT mics. (Such a modded AD-20 is  no longer be a general purpose XLR input converter). 

Oppps, picture file was too large and I don't have the tools to reduce here now. In a day or so I will.

Jon

[mattb]

Thanks. I understand that would be a big undertaking and maybe a hard market to crack - but I'd definitely consider it if such a product became available at a fair rate.

That AD-20 mod sounds really cool too. LMK if you ever want to move forward on that. It would save a lot of space and connections in my rig.
Would you expect it to sound equivalent to my PM-4 > PS-2 > AD-20 setup or would it be different somehow?

Looking forward to seeing that prototype too!

[mattb]

Cool! Looking forward to seeing the fruits of your labor! +T

[jk labs]

A small update.... 

The AT943 spec sheet at Audio Technica states a sensitivity of -40 dB re 1V /Pa.
That means 10 mV signal rms in a soundfield of 94 dB SPL. This spec is for the mic
in "phantom power mode".  If we add 20 dB (10 times stronger) to the soundfield we
end up at 114 dB SPL. Now the mic delivers 100 mV rms. And by extension, at 134 we
get 1 Vrms. 134 dB SPL is close to the max signal excursion possible for the AT943. 

The PM-4 is 1:1. It passes the AT943 signal without altering its amplitude (or rather, 
the drop is about a dB or so).


The AT943 wired into a standard 9 Volts batterybox outputs a 10 times (+20 dB) stronger signal.
So at 94 dB SPL we get 100 mV, 114 dB SPL gives 1 Volt. And 134 .... well the capsule
has hit the ceiling long ago. Distortion is all we get.


This poses a slight problem for my "AT PP9" (AT Power Plant 9 Volt). My options are:     
A) I just ignore the 20 dB lower output. Users turn up their record dials or must use mic inputs. 
B) I add a 20 dB gain stage. That means the 9V batt box is asked to output 10 Volts rms when the mic is exposed to 134 dB SPL. That's plain impossible.
C) I add some gain. Like 6 dB and say "live with it"

or
D) a selectable gain feature is introduced. Features that will have an impact on bulk and cost.


I should have seen this coming but my focus was on getting the optimum sound from the capsules.
In light of jb3 users etc not having a functional mic-pre in the recorder this starts too look like
options from hell. All options (A, B, C & D) must be supported ...

But just to have said it. The situation is no worse than that of having AT mics -> PM-4 -> PS2 ->  That chain has the exact same need for gain.. 

thoughs? ideas?

[mattb]

Seems like this wouldn't be an issue for putting those circuits in a mod AD-20, since it will have that lower signal right now anyway, but it definitely poses a problem for those going without a pre.

For the direct to line people, it seems like some kind of gain stage would be best. The JB3 gain can be noisy, so the common reccomendation is to leave it at 0 and either adjust the input or bring it up later on your PC. So if you could do a variable gain stage that may be even better for the jb3 line in users.

[Sean Gallemore]

that's some great info jon, and I wish more people could view it.

at8533 > mp-2 > modsbm-1 is a bit bulky, but it works like a champ.

I thought you plan was to do something like PM4/PS-2/AD-20 all in one box with stepped gain.  Either way, thanks for trying this and listening to our opinions.

[som]

Okay, this just zoooomed waaayyyy over my head, but let me ask a question or two to clarify:

Currently, with my SP 943's and a 9-volt SP battery box, I get enough output from the mics at most shows to go line-in. Occassionaly I need to go mic-in, but since the volume is so low at these events, the D7 can handle it.

Are you saying that once these are powered with phantom power (or your upcoming "AT PP9") the output from the mics will no longer be adequate to go line-in without a preamp? (Or some sort of built in gain)

B) I add a 20 dB gain stage. That means the 9V batt box is asked to output 10 Volts rms when the mic is exposed to 134 dB SPL. That's plain impossible.

But didn't you say that the current breed of 9 volt battery boxes adds 20 dB gain? What do they do if the mic is exposed to 134dB?

Once again, any help in understanding is appreciated!



As to your question, I *personally* would like a replacement for the SP battery box that gives me the sonic improvement that I've heard phantom power will provide (and I realize this will require a mod to my SP-CMC8's to provide mini XLR terminiation). I would still like adequate output to to go line-in without a preamp (like I currently do). I would prefer to monitor and control the levels on my recording device, not on the "AT PP9".

That's what I *want*.....I can't tell you how to make it happen! And I'm aware that others may want something different.

Scott

[jk labs]

that's some great info jon, and I wish more people could view it.

at8533 > mp-2 > modsbm-1 is a bit bulky, but it works like a champ.

I thought you plan was to do something like PM4/PS-2/AD-20 all in one box with stepped gain.  Either way, thanks for trying this and listening to our opinions.

My plan was first to provide the PM4/PS-2 function in a truly small box (AT PP9). That is, I'd leave it to the customer to find a gain stage. Then my plan was to work in blissful serenity on a suitable gain stage & basscut in the smallest possible package (AT PP9-Pre). With the knowledge then acquired porting to a say AD-20 would be no challenge. But using the AD-20 as host is just one of several possibilities for running the AT mics in full performance mode.      

Now I have come to realize that the first unit will be used with a D100 (and a UA-5). And a jb3 owner is interested. So I realize I have to jump right on the development of the AT-PP9-Pre. The challenge isn't in creating the functions but the limited space into which I want to do it.

The plan I have with the AD-20, again due to limited space, is to install a dual continouos volume control with gain 10 to 45 dB.  Then use the stock rec. level controls for independent l/r fine control.
This project now hangs as I can't get the AD-20 to run at 48 kHz. (The DA-P1 accepts it as 48 kHz data but the M audio DIO 2496 does not see the ouput from the modded AD-20 as valid SPDIF data?. And my frequency counter is broken ... and,  well...). The mod for 48 kHz is something the owner wanted.  I might undo it till I get the right tools up and runnng.  

Seems like this wouldn't be an issue for putting those circuits in a mod AD-20, since it will have that lower signal right now anyway, but it definitely poses a problem for those going without a pre.

For the direct to line people, it seems like some kind of gain stage would be best. The JB3 gain can be noisy, so the common reccomendation is to leave it at 0 and either adjust the input or bring it up later on your PC. So if you could do a variable gain stage that may be even better for the jb3 line in users.

Agreed, with the AD-20 f. ex the low levels pose no problem.

I don't know the jb3 first hand. Care to just tell me what are the know issues and specifics with line-in and gain settings? Or point me in the right direction?

[jk labs]

Okay, this just zoooomed waaayyyy over my head, but let me ask a question or two to clarify:

Currently, with my SP 943's and a 9-volt SP battery box, I get enough output from the mics at most shows to go line-in. Occassionaly I need to go mic-in, but since the volume is so low at these events, the D7 can handle it.

Are you saying that once these are powered with phantom power (or your upcoming "AT PP9") the output from the mics will no longer be adequate to go line-in without a preamp? (Or some sort of built in gain)

B) I add a 20 dB gain stage. That means the 9V batt box is asked to output 10 Volts rms when the mic is exposed to 134 dB SPL. That's plain impossible.

But didn't you say that the current breed of 9 volt battery boxes adds 20 dB gain? What do they do if the mic is exposed to 134dB?

Once again, any help in understanding is appreciated!



As to your question, I *personally* would like a replacement for the SP battery box that gives me the sonic improvement that I've heard phantom power will provide (and I realize this will require a mod to my SP-CMC8's to provide mini XLR terminiation). I would still like adequate output to to go line-in without a preamp (like I currently do). I would prefer to monitor and control the levels on my recording device, not on the "AT PP9".

That's what I *want*.....I can't tell you how to make it happen! And I'm aware that others may want something different.

Scott

Hi there!

I am saying that the PM-4/PS-2 outputs 20 dB less signal than you currently get. I am saying that the same is true for my current "no-gain" solution (AT-PP9). Only you can tell how a loss of 20 dB impacts your record chain. But, if your line-in didn't have sufficient gain previosuly the situation is 20 dB worse now.

The price you pay for having those extra 20 dB taken out is a loss of 14 dB dynamic range and a rolloff of the highs above 10 kHz.

Your current combination of mics + batt box output a severely clipped signal if the mics are exposed to 134 dB SPL.  In fact it starts to occur at 124 dB SPL (I take the numbes from my head - look at the AT spec sheet for an idea of what AT claims for max SPL). At dB SPL above 122 or so your current setup is not suitable. I haven't tested but I expect, based on the properties and currents involved, the problem to present already at 118.. 119..

What you are looking for in the PP9-Pre is very much along what I was planning on. You adjust it for a healthy output based on location, anticipated SPL etc and do the rest from the rec. level control on the ADC.

[dklein]

The price you pay for having those extra 20 dB taken out is a loss of 14 dB dynamic range and a rolloff of the highs above 10 kHz.

I'm getting lost here...isn't this the punishment for having the extra 20dB? (as opposed to having the 20dB taken out)

i.e. SP 9v solution:  20dB higher output, max level ~120 dB
    PM-4/PS-2 or JKL: 20 dB lower output, max level ~134 dB

Why does that 20dB gap occur in the first place - is it the powering scheme, 2 wire vs. 3 wire config or what?
And what's this about a rolloff above 10 kHz?  Didn't spot that earlier in the thread.

[jk labs]

The price you pay for having those extra 20 dB taken out is a loss of 14 dB dynamic range and a rolloff of the highs above 10 kHz.

I'm getting lost here...isn't this the punishment for having the extra 20dB? (as opposed to having the 20dB taken out)

i.e. SP 9v solution:  20dB higher output, max level ~120 dB
    PM-4/PS-2 or JKL: 20 dB lower output, max level ~134 dB

Why does that 20dB gap occur in the first place - is it the powering scheme, 2 wire vs. 3 wire config or what?
And what's this about a rolloff above 10 kHz?  Didn't spot that earlier in the thread.

Hi

Very poor wording by me. Indeed I meant to say something to the effecting of the signal being 20 dB stronger.

As for max levels:
If we are to believe AT the dB SPL limit for the ES943C on phantom power is 138 dB SPL.

Why the 20 dB difference: 
With the "phantom method" you get whatever level the mic delivers. In the two-wire scheme the signal is
"developed" over an external resistor.  I've tried to avoid talking about this or that brand of battery box. The reason the difference is 20 dB is because the person who designed that all popular line of batteryboxes decided
20 dB would be a nice round number. Going higher isn't feasible (max SPL comes creeping down), making
it lower is accomplished by making the resistor smaller in value.

[Sean Gallemore]

are we assuming a 6 dB per octave curve?