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

[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?