ART 312A powered speaker problem

[fredcapo]

Got in a pair of ART312a powered speakers with complaint of no output- no other info. When I tested, they worked fine in "line" mode with xlr cable from preamp. When I put them in "mic" mode, nothing from the microphone with xlr or microphone with 1/4 inch jack, until I pulled out the 1/4 inch jack partially, then the mic worked. Not an intermittent issue but seemingly the 1/4 in jack is TRS. Both work same way.

The manual calls the two jacks, one 1/4 inch and one xlr, "jack/female xlr inputs bal/unbal"

Anyone know what is going on with this. Is it a problem with some input circuitry or do they expect some special wiring on xlr or 1/4 in plug on the microphone?

Thanks

[g1]

If you plug a mic into the xlr and have the switch set to mic, you should get sound. If not, there is a fault.

[fredcapo]

Thanks for the schematics, g man. But if you look at a wiring diagram for a 1/4 in to xlr adapter, tip goes to xlr pin 2. In the ART schematic, they are connecting ring to pin 2, thus it works when jack pulled partially out... What's going on...?

[Enzo]

You have a mic with a 1/4" plug?


I have a kit of adaptors around for connecting stuff. My XLR to 1/4" are wired both ways. I have a pair wired pin 2 hot (grounding pin 3), and I have a pair wired pin 3 hot (grounding pin 2). I use both types. In fact they can also be wired TRS to XLR. I don;t need that here. The adaptors themselves come from Switchcraft unwired, because they don't know what you plan to use them for.


I am concerned you were trying to use more than one jack. Was that the case? You can go in one jack and out another to daisy chain systems, but you can;t use two jacks for different purpose. Or have I misread you?

The balanced input should be differential, so you should be able to ground either 2 or 3, and use the other as a hot. But not with an adaptor in another jack.

[fredcapo]

Enzo Thanks. There were brought here by a school with only info "no output" so i dont know if they ever worked for them... I saw the input jacks were a bit shaky so I replaced with upgraded spec jacks with same results. I need to speak with the school and try to find out the history and how they plan to use...

I need to examine the schematics and try to figure out if the input circuit is designed to electrically adapt to a mono mic jack... is that likely???

[Enzo]

It is a common balanced input, and like any other of its type, you can usually ground one side and call it an unbalanced input.

That is why it says BAL/UNBAL beside it.

[g1]

I'm a little confused as to what you are plugging in when using the xlr with switch set to "mic". Are you using a balanced mic? What do you mean by "mono mic jack"?

[g1]

Anyway, after the switch it is the same for both settings of the switch. You said the xlr worked when set to line position. Then you should be able to switch to mic and the only difference should be the pad resistors switched out.
So any problem should be due to the jacks or switch or connections. You should not have to look beyond the output of the switch.

[fredcapo]

When driven with a signal from a preamp, it seems fine when the switch is in line or mike position (hotter in mike).

When using a microphone alone, it only works when hot lead of mike is tied to ring and ground lead of mike is tied to sleeve...

Maybe there is a problem with the filter board that one of the balanced inputs is bad and it only works with a true balanced signal...

[Enzo]

OK. Put it in MIC mode so it is more sensitive. Turn it on and turn it up.


Unbend a paper clip, ir grab a resistor, or otherwise hold some bare wire in your fingers. Insert the end of the bare wire into the XLR jack pin 1. Nothing should happen since pin 1 is ground. Now stick your wire into pin 2. Do you get hum out the speaker? Now try pin 3. Does that hum? Both pins 2 and 3 should make hum when touched - equally. If not, you have an input issue.

If they both work, then the input stage works, and the 1/4" jack is the suspect. At that point, plug a TRS plug into the jack and touch my bare wire to the tip and then to the ring connections, which should act just like the XLR.

[The Dude]

I count 4 resistors 2 caps and a switch between the inputs and the filter card. I'd start with checking all of those parts if you haven't. It shouldn't take that long.

[g1]

When using a microphone alone, it only works when hot lead of mike is tied to ring and ground lead of mike is tied to sleeve...

It still sounds like you are using the mic into the 1/4 inch jack, whether balanced or not I can't tell. Don't you have a lo-z balanced mic you can plug straight in to the xlr input?

[fredcapo]

After a few simple tests and thinking in terms of balanced input as per the suggestions, I have determined that only one side of the balanced input, the "cold" is working on both speakers. The speakers put out considerable output when driven by a mixer, and acceptable level of output with a microphone, when using ring and sleeve.

The owner is satisfied with using it that way so no fix will be attempted. Thanks for all the input.