Topic: What was I doing wrong?

[Tim]

I've also done a split with phantom on both. However you do it, keep in mind that level changes on one unit may affect levels on the other.

Yah - that sounds like great advice...

what's the problem? what he said is absolutely true

[hexyjones]

the idea is that phantom power can potentially color the sound of the pre and if you're doing a comp where one or both of the units does not have it's phantom on you are not really getting a true comparison of what both units sound like under actual show conditions.

Wrong...

[sygdwm]

the idea is that phantom power can potentially color the sound of the pre and if you're doing a comp where one or both of the units does not have it's phantom on you are not really getting a true comparison of what both units sound like under actual show conditions.

Wrong...

-t fuckhead for not backing your comment w/ some actual info.

[hexyjones]

I've also done a split with phantom on both. However you do it, keep in mind that level changes on one unit may affect levels on the other.

Yah - that sounds like great advice...

what's the problem? what he said is absolutely true

I just dont see how 2 phantom sources can power the same mics?'

Might be going out on limb - but I would think that of all the factors involved - phantom power would add the least amount of color...as long as its the right spec...

Do you see any problems with powering the mics and then splitting the signal...?

Think of battery powered mics...you wouldn't need two sets of batteries to split the signal...just split it.

[hexyjones]

the idea is that phantom power can potentially color the sound of the pre and if you're doing a comp where one or both of the units does not have it's phantom on you are not really getting a true comparison of what both units sound like under actual show conditions.

Wrong...

-t fuckhead for not backing your comment w/ some actual info.

Go ahead pal - use 2 phantom sources...

The whole idea is so fucked - I dont even want to try...

[SuperDave]

http://taperssection.com/index.php?topic=22724.0

Down the line on that thread they say something about using phantom on both pre's.

Although, I think I'd definitely go with corkscrew's idea of powering the mics before the split.  Every fiber of my being screams never to run phantom twice.  I'd probably expect fire to shoot out of the mics if I did.

Anyway, that's my 2 cents. 

[MattD]

Dual phantom in this manner is safe. The way the mics are set up with an XLR splitter, the phantom power is being applied in parallel. In parallel, the current load is divided among the two power sources (the ratio of which depends on the impedence of the mic inputs) and the voltage remains constant.

As for the level fluctuations, I learned that from experience (Derek Trucks show with Scott Brown where we split his 4022s to a V3 and ULN-2). I have the idea that changing the gain on the preamp slightly affects the impedence of the inputs which causes the balance of current to shift. Since we're talking small amounts of current and resistance, that would explain the slight effect on levels. If one of the more EE-minded folk here could confirm this or correct my theory, that'd be cool of you.

[SuperDave]

Dual phantom in this manner is safe. The way the mics are set up with an XLR splitter, the phantom power is being applied in parallel. In parallel, the current load is divided among the two power sources (the ratio of which depends on the impedence of the mic inputs) and the voltage remains constant.

As for the level fluctuations, I learned that from experience (Derek Trucks show with Scott Brown where we split his 4022s to a V3 and ULN-2). I have the idea that changing the gain on the preamp slightly affects the impedence of the inputs which causes the balance of current to shift. Since we're talking small amounts of current and resistance, that would explain the slight effect on levels. If one of the more EE-minded folk here could confirm this or correct my theory, that'd be cool of you.

Wow, great job of explaining it.

I'm wondering if you powered the mics before the split, would the change in gain on one pre, affect the other pre?   

[Todd R]

Go ahead pal - use 2 phantom sources...

The whole idea is so fucked - I dont even want to try...

Do you know anything about electric circuits when you say this?

By using a splitter to split the electrical signal to the mics, you create a parallel circuit.  In a parallel circuit, the voltage on each side of the circuit remains the same and the current varies.  Thus, applying +48v phantom power to both sides of the parallel circuit is not problematic in the least bit.  The available current increases (since both the V3 and the PS2 are supplying 48v phantom), but the mics will draw what current is necessary, so the additional available current isn't a problem at all.  (In fact, it could be a benefit if you needed to power current hungry mics like Earthworks.)  Both the V3 and the AD20 are expecting +48v phantom at their inputs, so they use DC blocking capacitors to block the DC phantom voltage and allow the AC mic signal to pass.  This is exactly how phantom power is designed to work.  So to reiterate, it isn't a problem at all to have phantom on from two sources.  No different at all really from wiring up two batteries in parallel to increase your runtime from using one battery.

It'll depend somewhat on the circuit design, but changing your levels on your preamp will change the impedence of the circuit.  This slight change in impedence isn't a problem either, but it will slightly change the mic signal levels the other preamp is seeing, thus the impact of changing levels on one unit on the other.  Not a problem, just inherent to using the mic splitter cables.  You could solve this by using a transformer based mic splitter.  In fact, if you used a transformer based mic splitter, you would absolutely need to run phantom power on both preamps since a transformer will not pass DC either.  (The m148 for example does not use blocking capacitors, but instead uses transformers to block the 48v phantom power.)

Bottom line, this idea isn't fucked at all, it is perfectly reasonable.  The only thing that is fucked is your advice.


EDIT:  Looks like Matt got this info out while I was typing up my response.  Yep Matt, you've got it exactly.  And yes, I do have an electrical engineering background.

[hexyjones]

Dual phantom in this manner is safe. The way the mics are set up with an XLR splitter, the phantom power is being applied in parallel. In parallel, the current load is divided among the two power sources (the ratio of which depends on the impedence of the mic inputs) and the voltage remains constant.

As for the level fluctuations, I learned that from experience (Derek Trucks show with Scott Brown where we split his 4022s to a V3 and ULN-2). I have the idea that changing the gain on the preamp slightly affects the impedence of the inputs which causes the balance of current to shift. Since we're talking small amounts of current and resistance, that would explain the slight effect on levels. If one of the more EE-minded folk here could confirm this or correct my theory, that'd be cool of you.

So since the AD-20 has no phantom circuit - the current wont flow that way? (my guess)

Again - I would avoid doing this...I dont see what you would gain...

The level shifts dont seem to realted to phantom...? That would happen with Dynamic mics as well wouldnt it...?

[hexyjones]

Go ahead pal - use 2 phantom sources...

The whole idea is so fucked - I dont even want to try...

Do you know anything about electric circuits when you say this?

By using a splitter to split the electrical signal to the mics, you create a parallel circuit.  In a parallel circuit, the voltage on each side of the circuit remains the same and the current varies.  Thus, applying +48v phantom power to both sides of the parallel circuit is not problematic in the least bit.  The available current increases (since both the V3 and the PS2 are supplying 48v phantom), but the mics will draw what current is necessary, so the additional available current isn't a problem at all.  (In fact, it could be a benefit if you needed to power current hungry mics like Earthworks.)  Both the V3 and the AD20 are expecting +48v phantom at their inputs, so they use DC blocking capacitors to block the DC phantom voltage and allow the AC mic signal to pass.  This is exactly how phantom power is designed to work.  So to reiterate, it isn't a problem at all to have phantom on from two sources.  No different at all really from wiring up two batteries in parallel to increase your runtime from using one battery.

It'll depend somewhat on the circuit design, but changing your levels on your preamp will change the impedence of the circuit.  This slight change in impedence isn't a problem either, but it will slightly change the mic signal levels the other preamp is seeing, thus the impact of changing levels on one unit on the other.  Not a problem, just inherent to using the mic splitter cables.  You could solve this by using a transformer based mic splitter.  In fact, if you used a transformer based mic splitter, you would absolutely need to run phantom power on both preamps since a transformer will not pass DC either.  (The m148 for example does not use blocking capacitors, but instead uses transformers to block the 48v phantom power.)

Bottom line, this idea isn't fucked at all, it is perfectly reasonable.  The only thing that is fucked is your advice.

If I read correctly -

He was not using the PS2 - he was expecting the V3 to do it all..

Pretty sure there is no onboard phantom on the AD-20

[Stumptown Matt]

I've also done a split with phantom on both. However you do it, keep in mind that level changes on one unit may affect levels on the other.

Do you see any problems with powering the mics and then splitting the signal...?

I only brought it up because some people may have two preamps both with phantom and no outboard phantom available ( such as the PS2).  If you have an outboard phantom unit it would probably be better to split the signal after the phantom to the two separate preamp units

[hexyjones]

I've also done a split with phantom on both. However you do it, keep in mind that level changes on one unit may affect levels on the other.

Do you see any problems with powering the mics and then splitting the signal...?

I only brought it up because some people may have two preamps both with phantom and no outboard phantom available ( such as the PS2).  If you have an outboard phantom unit it would probably be better to split the signal after the phantom to the two separate preamp units

Agree - I dont see what you gain from running two phantoms?

[Todd R]

If I read correctly -

He was not using the PS2 - he was expecting the V3 to do it all..

Pretty sure there is no onboard phantom on the AD-20

Phil wasn't using two phantom sources, I was commenting on your incorrect attacks on the advice in this thread to use two phantom sources.  As a general approach, that is perfectly reasonable and may be preferred for a number of reasons.

I do think you might be onto something though.  The problem may lie in the fact that AD20 uses a separate phantom and is not integrated like the V3.  

Phil was trying the setup Brian outlined above.  But since the AD20 doesn't have its own phantom power, it might not have blocking capacitors.  Rather those might be put in the PS2.  So if that is the case, I think two configurations should work to do what Phil was attempting.

1)  mics> PS2 (48v phantom)> splitter cable>  (1) V3 with no phantom on   and  (2) AD-20     <---- this looks like what you are advocating

2)  mics> splitter cable>  (1) V3 with phantom    and     (2) PS2 (providing phantom as well) > AD20

[Tim]

the idea is that phantom power can potentially color the sound of the pre and if you're doing a comp where one or both of the units does not have it's phantom on you are not really getting a true comparison of what both units sound like under actual show conditions.

Wrong...

-t fuckhead for not backing your comment w/ some actual info.

Go ahead pal - use 2 phantom sources...

The whole idea is so fucked - I dont even want to try...

You fucking moron. You have no clue what the fuck you are talking about. I tried to play nice in this thread but you're still the same clueless jackass you've always been.