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General Discussions => Drawing Board => Topic started by: geetar_king on March 20, 2009, 12:45:45 PM

Title: Phantom Power & true relay bypass - cut out the phantom when bypass engaged??
Post by: geetar_king on March 20, 2009, 12:45:45 PM
Quick question for you guys.

I'm making up a bypass using some relays in a method similar to Igor's schematic ( http://www.groupdiy.com/index.php?topic=29770.0 )
and I was wondering how phantom power interacts with the bypass.

Should phantom power disengage when switching into bypass or does this not really matter?  If 48V phantom was on to the hot and cold input pins while in bypass then the output would essentially have phantom power too?! (bad?)

My understanding is that phantom power should be applied on the circuit side of the bypass switch so that when the relay bypass disengages and switches to bypass mode, the 48V phantom is essentially lifted from the inputs. Is this right, or should it not matter if 48V is applied during bypass...?
Title: Re: Phantom Power & true relay bypass - cut out the phantom when bypass engaged??
Post by: valvehead on March 20, 2009, 02:50:47 PM
 ???

Are you saying want to put a bypass in a mic preamp? That would directly connect the mic to the line level output with no gain.

Or are you powering some line-level device with phantom power?
Title: Re: Phantom Power & true relay bypass - cut out the phantom when bypass engaged??
Post by: SSLtech on March 20, 2009, 03:19:29 PM
I think you haven't really thought it through properly before asking...

If the unit requires preamplification, why would you possibly want to bypass the preamplifier?

If the unit requires phantom to even produce a signal, why would you want to remove it?

In addition, VERY few devices which require phantom produce signal very quickly after phantom is reapplied... so removing and reapplying it seems like an act of folly.

Now I'll admit that I've jokingly said in the past: "No bypass, I don't believe in it!" -Apparently someone else got the joke because it's now their signature... and I'm tickled and flattered by that.

...But the one place where I really have to say "No bypass, I don't believe in it!" ....and actually MEAN it, would have to be a mic preamp.

If you really MUST bypass the preamp (although my brain simply cannot appreciate why!) but wish to still supply phantom, you just take the signal from AFTER the [DC blocking capacitors] / [input isolation transformer] -Simply delete as applicable, carry on with your fiendishly evil plans, and let us know how you get on.

;)

Keith
Title: Re: Phantom Power & true relay bypass - cut out the phantom when bypass engaged?
Post by: geetar_king on March 20, 2009, 09:54:33 PM
wow, yes i didn't think about it at all haha!  i'm using mic and line inputs, so yes the line inputs wont need phantom thus my problem is solved haha. jeeesus

why the hell would i want to bypass the mic input haha.  ...keith, feel free to delete this thread
Title: Re: Phantom Power & true relay bypass - cut out the phantom when bypass engaged??
Post by: SSLtech on March 21, 2009, 10:42:00 PM
Heh... well then I'm glad we can all laugh about it...

I thought you'd come up with an evil scheme to take over the WORLD!!!

;)

Keef