Samson TXM20

[jimcolmn]

Hope someone can advise, Our music club (strings and Things) were enjoying it's normal 6 hour Tuesday night jamming session when our phantom power went down on our Samson TXM20. This was the first time we have used the phantom power on this unit. the equipment connected to the unit was as follows: 3x Sure Sm58s, 4x guitars + DI boxes, 1x bass + DI box, 1x TC Helicon with 12 string electro acoustic and Sure sm58 connected and 1x TC Helicon voicelive touch.

[The Dude]

Couldn't find a manual with minimal searching. Possibly someone here has something. There isn't usually much to phantom power. It should be a simple DC supply circuit and I wouldn't think it'd be that hard to find. It may even be labeled +48 or something of the sort on a power supply connector. My best "stab", and it is just a stab at this point, would be that there is a fuse, low value resistor, or fusible link that has opened up somewhere in the power supply. You might be able to find it with a little DVM poking around. Somewhere there will be 48V or so and on the other side of the defective link there won't be.

[Enzo]

First, unplug all those things and use a voltmeter to see if the phantom is on the mixer jacks. One of those cables could be loading it down. If the phantom comes back, then plug them back into the board one at a time, each one alone, to see if one causes the problem.

What of that list actually uses phantom power?

How did you know the phantom went out? Light went out? Phantom powered thing stopped working?

We have all done silly things, perhaps someone pushed the button by accident and turned off the phantom?

Are you using a snake? If so, does plugging direct into the mixer and not using the snake allow the phantom to operate?

Contact Samson and ask for the schematics.

[Jazz P Bass]

Good question: "What in that bunch uses phantom power?"

[The Dude]

The mixers I've seen have a resistor in line with the phantom supply on each channel, so that if a short occurs on a particular channel it does not effect the others much. There isn't normally much current in the phantom circuit. Think how long a battery will last in a battery powered condenser mic.

My point is that I doubt any one mic/device would cause a global phantom failure. If you don't have any phantom on any channel, I would be more likely to suspect a failure of the supply itself rather than a load caused by something plugged into a single channel. It would, however, be a good idea to start by measuring at the XLR connectors to see what if anything is there in the way of phantom power.

[Enzo]

I had the same thought, the phantom has the 6.8k resistors or whatever they are. But around here, we never think up reasons not to check something.


And you are correct, phantom mics and such do not draw hardly anything... when they are working.


We don't yet know the OP. I was talking to someone about a mixer with 12 really low gain channels, only to ultimately find they were all bad because the master outs were bad. SO if someone presumes the phantom is gone, we may find it is the item that is bad, not the supply. And always thinking about the lurkers.

[The Dude]

Yessir Enzo,

And why take ANYTHING apart until you verify that phantom is missing with a meter. Always my first step is to get as much information as possible before the screwdriver comes out. It's really simple, for instance to stick meter probes in an XLR jack to verify. Or, (unrelated to this thread) stick your meter probes into speaker jacks and maybe find a shorted amp channel, etc., etc. It's always helpful to have a plan.

[jimcolmn]

Hi Guys, many thanks to ENZO, JAZZ P BASS and THE DUDE for you’re fast responses to my post. Apologies for the long reply but I will try and give answers to you’re questions.

I should say here that I am not a sound engineer and I have little experience with powered mixers or what you can or should not connect to it and the manual does not cover this point at all well.

Bits of kit needing phantom power are the DI box’s, these are active Behringer DI100 ultraG which can be powered by a 9volt battery or phantom power. We had no batteries so we used phantom.

“How did you know the phantom went out?” Firstly we heard a sound similar to someone unplugging a guitar from an active amp (this happened 2 or 3 times), then we lost sound from the guitars and the phantom power light went out.

“Are you using a snake?” Yes we are using a snake, when we lost power I first tried re-setting the mixer by turning of the unit leaving it for a minuet or so and powering back up. This did not work, I then plugged direct into the mixer, still no response, I then tried switching the phantom power on and off with no luck, however, when doing this some of the Signal LEDs flickered on then off again ?!?

I hope this has helped. I have contacted Samson about a copy of the schematics but no response as yet, does anyone have a copy of the schematic they could email or post I will of course cover the cost of postage etc.

Once again many thanks for you’re help.