Topic: What was I doing wrong?

[philR]

so the other night i wanted to split my mic signal and run it to 2 different pre's.  i have a pair of xlr splitters that i got from leegeddy here.  and used both a v3 and an ad20.  i had no problem getting a signal on the v3 side, but the ad20 side was giving me nothing.  anybody know why?  did i need to run the ps2 on the ad20 side too?

[hexyjones]

You should have been splitting the signal after the PS2...(if I understand you correctly)

[philR]

why is that?  doesn't the v3 provide the phantom power i need?

[hexyjones]

You only need one phantom power source...

The phantom power turns the mics "on" - thats all you need to do...

I would seriously advise against hooking it up that way again...Does all your gear still work...?

[philR]

yeah my gear is fine.  i'm curious why you think i should have put the ps2 before my split?  if i should only be running one phantom power source wouldn't the v3 cover that and the ad20 would be fine without the ps2?

           

[Brian Skalinder]

I'm unclear on exactly what you ran.  Is this correct?

       ---AD-20 > recorder
      /
Mics < splitter 
      \
       ---V3 w/phantom > recorder

If so, yeah - that should've worked as I understand it.

[philR]

that's exactly how i ran it brian.  and yeah, i figured it should work, but for some reason it did not work on the ad20 side.

[hexyjones]

Without the gear in front of me - I am at a disadvantage to offer an explantion why it doesnt work...the mics signal is being split before they get power...the splitters may play a role here...not sure how all these things are wired.

However - my instinct would be to power up the mics and then split the signal...

Mics > PS2 > Splitter > Downstream devices...

[Stumptown Matt]

I read something awhile back and if I remember correctly you would need to run a phantom power for each preamp.  It will not harm the mics to run phantom from two units to one mic if I remember correctly.  The original thread was concerning a comparison tape and Marc Nutter explained how it was ok to have two sources of phantom power.  The discussion was about a year or more back around the time the V3 came out.

[Tim]

whenever I've run splits I've run the phantom on both units....

[philR]

interesting.  +T's all around for the help.

[MattD]

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.

[hexyjones]

Fucking craziness I say -

Power the mics and split the signal - Dual Phantom? NONSENSE!

How do you guys think this shit up!

[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...

[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.

[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.

[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...

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.

Why use 2 phantom sorces? I defy anyone to give a reason to do this...

[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...

what's wrong ass clown? Care to explain? Your one word answer leaves a lot to be desired.

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...

I'be used 2 phanton sources at leats half a dozen times with no problems. Again, why is the idea "fucked"?

looks like you got handed your ass again in this thread...

[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.

Why use 2 phantom sorces? I defy anyone to give a reason to do this...

I gave you one. Your repsonse was "wrong". Well what exactly was wrong about it?

[hexyjones]

What was the reason? I missed it?

I gave the proper advice in response # 3

So buzz off...

[Tim]

What was the reason? I missed it?

HOLY SHIT!!!!!!!!!!

You have got to be, hands down, the most annoying person I've met in many a years taping.

Look, forget it... a real EE (Todd R) has shown, once again, that you don't have a clue what you're talking about. You're not worth my energy...

-T for being a complete ass clown

[hexyjones]

What was the reason? I missed it?

HOLY SHIT!!!!!!!!!!

You have got to be, hands down, the most annoying person I've met in many a years taping.

Look, forget it... a real EE (Todd R) has shown, once again, that you don't have a clue what you're talking about. You're not worth my energy...

-T for being a complete ass clown

Thats what I figured...

[Tim]

you don't have a clue what you are talking about. how many more times do you have to be proven wrong before you will just shut the fuck up and go away?

[hexyjones]

you don't have a clue what you are talking about. how many more times do you have to be proven wrong before you will just shut the fuck up and go away?

What was I wrong about...get back to me when you have a good reason to run two phantom sources...

[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.

Is this the "reason" Tim? Man those must be some smart electrons...!!!

[Todd R]

What was I wrong about...get back to me when you have a good reason to run two phantom sources...

You were wrong when you said the idea of using 2 phantom sources was fucked.  Matt and I have both explained that you were wrong and that it is perfectly acceptable and will not cause any problems.

Why use 2 phantom sorces? I defy anyone to give a reason to do this...

Reasons:

1)  if the mic splitter is transformer based, you will need to either use 2 phantom sources or will need to insure that the phantom you do use is on the pass through output side, not on the side that is transformer isolated.  A transformer based splitter will not allow changes in impedence to change the signal level on either side of the split (as was discussed earlier).  For this reason, professional sound companies running sound will use transformer based mic splitter boxes when they need to split the signal.  But a transformer will not pass DC voltage, including 48v phantom.

2)  Using 2 phantom sources will better insure you have adequate current available for the mics to draw from.  For example, Earthworks mics are very power hungry and consume about 10ma per mic, as opposed to most mics that consume 1-2ma per mic.  Many phantom power circuits do not have enough juice to power mics like these adequately.  Using two phantom power sources in parallel allows power hungry mics to get the current they need to operate at their best.

3) a poor phantom design may not have adequate current available, may not provide the standard 48v, may have unacceptable levels of noise, etc.  Using two sources (esp say if one was from a V3 which has good phantom powering) will mask this.  The overall phantom power might be worse than using the V3 alone, but would be far better than only using the preamp with crappy phantom.  So using two phantoms won't allow you to compare on the basis of phantom power, but at least it allows the mics to perform their best so the rest of your preamp comparison means something.

I guess if you know beforehand you've got one of your two preamps that is known to have good phantom power (eg the V3), you can only run the phantom on that unit alone and avoid issues with 2) and 3) above.  But if you don't know anything about either preamp you're running and don't know whether either has good phantom power, by running both together you insure you have an adequate phantom power supply.  And since their is no reason not to run two phantom power circuits, why not do it?

[Brian]

corkscrew - http://taperssection.com/index.php?topic=40548.0

[goose]

corkscrew said:

Why use 2 phantom sorces? I defy anyone to give a reason to do this...

How about when the two preamps you are comparing send 48v all the time, ala m148/m118?  No way to turn the phantom off on those oade boxes, so it would really seem strange to put a ps2 out front of that mix.

[Tim]

What was I wrong about...get back to me when you have a good reason to run two phantom sources...

You were wrong when you said the idea of using 2 phantom sources was fucked.  Matt and I have both explained that you were wrong and that it is perfectly acceptable and will not cause any problems.

Why use 2 phantom sorces? I defy anyone to give a reason to do this...

Reasons:

1)  if the mic splitter is transformer based, you will need to either use 2 phantom sources or will need to insure that the phantom you do use is on the pass through output side, not on the side that is transformer isolated.  A transformer based splitter will not allow changes in impedence to change the signal level on either side of the split (as was discussed earlier).  For this reason, professional sound companies running sound will use transformer based mic splitter boxes when they need to split the signal.  But a transformer will not pass DC voltage, including 48v phantom.

2)  Using 2 phantom sources will better insure you have adequate current available for the mics to draw from.  For example, Earthworks mics are very power hungry and consume about 10ma per mic, as opposed to most mics that consume 1-2ma per mic.  Many phantom power circuits do not have enough juice to power mics like these adequately.  Using two phantom power sources in parallel allows power hungry mics to get the current they need to operate at their best.

3) a poor phantom design may not have adequate current available, may not provide the standard 48v, may have unacceptable levels of noise, etc.  Using two sources (esp say if one was from a V3 which has good phantom powering) will mask this.  The overall phantom power might be worse than using the V3 alone, but would be far better than only using the preamp with crappy phantom.  So using two phantoms won't allow you to compare on the basis of phantom power, but at least it allows the mics to perform their best so the rest of your preamp comparison means something.

I guess if you know beforehand you've got one of your two preamps that is known to have good phantom power (eg the V3), you can only run the phantom on that unit alone and avoid issues with 2) and 3) above.  But if you don't know anything about either preamp you're running and don't know whether either has good phantom power, by running both together you insure you have an adequate phantom power supply.  And since their is no reason not to run two phantom power circuits, why not do it?

I went out to have a few beers after that last round.... nice work Todd....

[BCostigan]

WOW!

Pretty amusing thread!  I must admit my kneejerk reaction was to side with corkscrew thinking two differnet power sources = bad.  Once my AC minded brain realized we were in DC land it was instantly clear.

[Tim]

Pretty amusing thread! I must admit my kneejerk reaction was to side with corkscrew

I'm going to say that if you should ever find yourself in a similiar situation again just stop and do exactly the opposite

[F.O.Bean]

some people are so ignorant

[setboy]

dumb people are everywhere

[Tim]

[setboy]

T+ tim thats good stuff

[Tim]

backatahca

[sygdwm]

he deleted his account. +t's all around.