Topic: Any reason not to use a Denecke PS-2 before a pre?

[su6oxone]

Just wondering if there is any reason, like increased noise, decreased sound quality, or whatever, from using a Denecke PS-2 for phantom power to power a set of mics and then connecting it to a preamp.  In other words, is there any benefit from having a set of mics directly connected to a pre versus having a PS-2 in between the mics and the pre?  I haven't heard many people using a PS-2 for phantom with their pres, but have seen most people using external power supplies for their pres and using their pres for phantom as well.  Thanks for any input.

[bugg100]

Well, the answer comes back to whether YOUR current pre has phantom? If so, why bother? If not, moot point cause your mic(s) have zero noise(signal) without power...

[flipp]

In some cases you will get increased runtime from your recorder. I have a friend who powers his ADKs with a PS2 and his FR2LE with rechargeable AAs. He gets over 4 hours at 24/96 this way as opposed to just under 2 at 24/48 if he uses the LEs phantom. He doesn't use a pre, runs mics straight into the LE. Makes sense in this situation.

[bugg100]

He doesn't use a pre, runs mics straight into the LE.

Well, he does use a pre, just an internal one...

But true, that would be a good reason, if you don't mind an extra box...

[flipp]

He doesn't use a pre, runs mics straight into the LE.

Well, he does use a pre, just an internal one...

But true, that would be a good reason, if you don't mind an extra box...

Mics > PS2 > Recorder all with internal batteries vs.
Mics > Pre > Recorder + external power source

three boxes versus four, if it's a wally world batt then it's not that big a deal; however, if its lead, big weighty deal

as for whether there is any extra noise introduced using a PS2 vs. Pre's phantom, I have no idea but as long as the mics are getting sufficient voltage I doubt you would be able to hear it if there was some introduced noise

[su6oxone]

Thanks for the replies guys, +Ts.  To answer the question, I was thinking about using the PS-2 for phantom in order to increase the battery life of the MP-2 (by not using phantom on the MP-2).  So I guess there's not much reason to not use a PS-2 in front of a pre (MP-2). 

edit: did the ticket system change recently?  don't seem to see the buttons anymore.

edit2: nm... i see i need 96 more posts to +/- T.

[DSatz]

su6oxone, here's how I approach it, although I have no data to back this up, and I could and really should measure what I'm talking about here. In fact I promise to do so as soon as I can. But in the meantime ...

A stock Denecke PS-2 has electrolytic coupling capacitors at its outputs, while any transformerless preamp that offers phantom powering will generally have electrolytic coupling capacitors at its inputs. Electrolytic capacitors are fine as long as there's some DC voltage (of the correct polarity) across them. Take that away, though, and they may begin to add some distortion to a signal. (That's what I need to measure.)

The PS-2's output capacitors are kept charged by the phantom power supply itself, so no worries there. But the input capacitors of the preamp aren't, because (presumably) you turn off the preamp's phantom power circuit. So that's where the problem might occur, if it's a problem at all.

How I deal with it is that I own two PS-2s--one of which has had its output capacitors bypassed. This is a standard modification which Denecke can tell you how to do, or you can have them do it for you. I use that supply for situations such as you describe, while I use the other one with a Denecke AD-20 (a/k/a Zefiro InBox), since that unit's preamp can't tolerate DC on its inputs--it absolutely requires a phantom supply that blocks DC.

--best regards

[su6oxone]

any transformerless preamp that offers phantom powering will generally have electrolytic coupling capacitors at its inputs. Electrolytic capacitors are fine as long as there's some DC voltage (of the correct polarity) across them. Take that away, though, and they may begin to add some distortion to a signal. (That's what I need to measure.)

DSatz,
Thanks for replying, it's always awesome to get your expert opinion/knowledge.  I will be using the Sound Devices MP-2 preamp, which has Lundahl transformers.  Does this change your assessment at all re: maybe needing to mod the PS-2 for use with the MP-2?   

[su6oxone]

I don't really understand the technical aspect of it, but appreciate the input.

[DSatz]

su6, with a preamp that has input transformers, you won't usually have two sets of coupling capacitors in series, and the capacitors in the phantom supply will be kept charged by the action of the phantom supply itself. Thus there should be no problem at all of the kind I was talking about. If I'd realized you were using a Sound Devices preamp, I would have kept my mouth shut. I should have read your signature line, I guess.

Good input transformers on a preamp can be very helpful in a number of respects; this is one of them. To oversimplify greatly, I'm glad when I see (good) transformerless outputs and (good) transformer-equipped inputs on sound equipment.

--best regards

[Len Moskowitz (Core Sound)]

Just wondering if there is any reason, like increased noise, decreased sound quality, or whatever, from using a Denecke PS-2 for phantom power to power a set of mics and then connecting it to a preamp.  In other words, is there any benefit from having a set of mics directly connected to a pre versus having a PS-2 in between the mics and the pre?  I haven't heard many people using a PS-2 for phantom with their pres, but have seen most people using external power supplies for their pres and using their pres for phantom as well.  Thanks for any input.

In designing our 2Phant, we measured the PS-2 and it's very quiet (like -155).  I wouldn't be concerned about it adding any noise.

If your mic pre can power your mics, you shouldn't bother with it.

Other than the fact that it can't power mics that require high 48V current for very long, it's a fine product.
   

[su6oxone]

Thanks DSatz and Len, appreciate the info!

[Brian Skalinder]

Other than the fact that it can't power mics that require high 48V current for very long, it's a fine product.

Short-ish runtime with high draw mics (of which it doesn't seem like there are many that tapers regularly use) is easily resolved by either hot-swapping the batteries (IIRC, the PS-2 will maintain power for a short period during swap), or using a compact, inexpensive external power supply.  So, I think it's a fine product in either case.