Topic: cable to block phantom?

[BayTaynt3d]

Brian,

Did you ever find a solution for this?

I just had this problem the other day. I plugged directly into someone's bass amp (they all seem to have built in DIs these days, direct outs), but I wanted to use a fourth mic and got paranoid that if I turned on phantom, it'd fry the guy's bass amp? I kind of doubt it considering the whole point of that direct out of the bass is to negate the need for a DI isn't it? So, I'd think it was designed to plug into a snake, etc., that might very well have phantom running down it (although most SBDs let you turn that off I guess, but some snake boxes are self powered aren't they?).

Anyway, if I could find an inline phantom-blocking adapter, seems like that'd have been the safest thing to use, but I can't seem to find anything like that on the web and this thread never posted a resolution except for homemade (which isn't something I'm capable of, lol)?

Unless someone could tell me that the direct outs on all bass amps will block phantom and not fry? I do that trick all the time, and yes I know it's a dry signal, but I get plenty of wet bass off my main stereo pair when I do this trick (for acoustic jazz recording).

Any help would be appreciated, thanks!

[Brian Skalinder]

Seems like transformer isolated splitter box is the way to go.  The cheap ones have low quality transformers, the expensive ones obviously high quality.  Most of the advice recommended staying away from the cheapos, and I didn't pursue it further.  However, never actually listened to a lower end transformer isolated splitter box, so I don't know the audible impact of the lower quality transformers.

Perhaps one of our TS tinkerers / retailers could make a good quality transformer isolated splitter box at a decent price point, dunno.  I'm thinking Church or Busman, though I'm sure there are others.  Chris and I actually talked about it a bit, but I neglected to follow-up.

[dean]

Wow, this is absolutely fascinating, seriously.  I don't really follow it, but it makes me sure of one thing, that I, along with each of you, am a complete, utter and hopeless NERD!!!

[rdfager]

I've had this problem too.  Add me to the list of people who would buy one if someone comes up with a reasonably priced inline device to remove phantom power.

[SparkE!]

What's wrong with just a series capacitor in both the hot and cold leads?

[BayTaynt3d]

Does anyone know the answer to my other question? Anyone have any experience with the direct out capabilities of newish bass amps? I got to think they block phantom just like a DI would don't you think? I guess I'm just not willing to risk frying someone's amp to find out, LOL.

[BayTaynt3d]

I looked through a few random user manuals for bass amps/heads last night, and the funny thing was that although they pretty much all had direct outs, they pretty much all were XLR out, and they pretty much all described it as a "built in DI," none explicitly said they'd block phantom. But all DIs block phantom right?

I guess the only really safe thing to do is to bring my own DI for these cases, but it's not only easier to just plug into the amp, but it also doesn't require putting my gear in the musicians chain -- not everyone is going to like that cause my cheap DI could color their sound, not to mention fail or something, causing problems for the performance. Whereas when I plug in directly, there's no chance of any of that.

I wonder if I could do something like this:

XLR-to-1/4" adapter > DI > XLR > R4

But the DI would be expecting unbalanced on the bass side, and in that scenario I'd be feeding it a balanced signal wouldn't I? Or could I do that if the XLR-to-1/4" was wired appropriately. Sorry, I don't know enough about the technical side of this to know any better...

[SparkE!]

A normal XLR to 1/4 adapter will not block phantom power.  It just sends the XLR hot to the 1/4 tip and XLR ground to the 1/4 ring.  The XLR cold is not connected.  So, if you have 48 V on the XLR hot and 0 V on ground, you end up with 48 V between the 1/4's tip and ring.

[bluegrass_brad]

A normal XLR to 1/4 adapter will not block phantom power.  It just sends the XLR hot to the 1/4 tip and XLR ground to the 1/4 ring.  The XLR cold is not connected.  So, if you have 48 V on the XLR hot and 0 V on ground, you end up with 48 V between the 1/4's tip and ring.

But he is talking about using the XLR > 1/4" TS to run into a DI box.  the DI box would block the power.

[BayTaynt3d]

A normal XLR to 1/4 adapter will not block phantom power.  It just sends the XLR hot to the 1/4 tip and XLR ground to the 1/4 ring.  The XLR cold is not connected.  So, if you have 48 V on the XLR hot and 0 V on ground, you end up with 48 V between the 1/4's tip and ring.

But he is talking about using the XLR > 1/4" TS to run into a DI box.  the DI box would block the power.

Yes, exactly. And as you said before, I guess taking that balanced XLR out of the bass amp and adapting it to 1/4" TRS (that's the cable I already have) and then sticking that 1/4" TRS into the input of the DI will still work? I ask cause I'm kind of clueless about this, I do know that typically you'd be putting an unbalanced 1/4" into the input of the DI. In a way it's like I'd be going DI > DI > R4 (yuk). But from what you said earlier, sounds like I probably don't have to worry about frying the direct out of the bass amp anyway?

[DSatz]

I don't know the configuration of the bass amp's output, but if it's using an output transformer, it shouldn't mind the phantom powering. If not, you might consider some of the toys on http://www.jensentransformers.com/iso_aud.html. Jensen transformers are among the best available anywhere. Pamper your signals a little ...

--best regards

[Church-Audio]

Seems like transformer isolated splitter box is the way to go.  The cheap ones have low quality transformers, the expensive ones obviously high quality.  Most of the advice recommended staying away from the cheapos, and I didn't pursue it further.  However, never actually listened to a lower end transformer isolated splitter box, so I don't know the audible impact of the lower quality transformers.

Perhaps one of our TS tinkerers / retailers could make a good quality transformer isolated splitter box at a decent price point, dunno.  I'm thinking Church or Busman, though I'm sure there are others.  Chris and I actually talked about it a bit, but I neglected to follow-up.

I will build you a transfomer isolated input if you need it let me know.


BTW there was mention of a "bass amp" what is this all about?

Chris

[George2]

Leave the +48 off on channels 3 and 4 and use one of these.

http://www.professionalsound.com/Catalog/48ph.htm

http://www.denecke.com/Products/Audio%20Accessories/audioaccessories.htm#PS1A