Issue with M1TWA

[giesen]

I just installed an M1TWA, and having problems with very poor voice quality.
 
I wired up it per instructions (using the appropriate jumper cables) and used 18AWG to the speaker and 22 AWG to the microphone on an M1TWSF. The mic works great, but any announcements on the speaker are very crackly, and after 5-10 seconds of speech or talking through the dial-in interface, the sound drops out and I get a "pulsing" sound almost like the old pulse (pre-DTMF) telephones.
 
At first I thought maybe the board wasn't getting enough power, so I added an Aux 1A 12VDC power supply (the M1TWA calls for a max of 1A). Then I thought maybe that power supply isn't quite enough, so I swapped out the power supply for a 3.3A 12VDC power supply, but still same problem.

Anyone have any ideas what to try next?

 

[Del91574]

What's the impedance of the speakers? Have you adjusted the gain on the unit?
 
Sounds like an overdriven amp and impedance issue to me.
 
I think there was a discussion trying to figure out if the power needed to be isolated or made common when using an aux supply. I can't remember.

 

[giesen]

What's the impedance of the speakers? Have you adjusted the gain on the unit?
 
Sounds like an overdriven amp and impedance issue to me.
 
I think there was a discussion trying to figure out if the power needed to be isolated or made common when using an aux supply. I can't remember.

 
M1TWSF has an impedance of 32 ohms, within the range of 4-32 ohms specified by the M1TWA. One zone is turned all the way up, the rest all the way down and muted.
 
I think you may be right, I turned down the gain one zone 1 and it seems to have gone away. I'll keep watching it.
 
Thanks.

 

[Del91574]

What's your total impedance connected to that output? That's important, as wiring speakers isn't just either placing them all in parallel under terminals or in series.

 

[giesen]

It's a single m1twsf.

 

[giesen]

Hrrm now I'm starting to wonder if I have a short. I have a brand new m1twsf in the box that measures 31ohms across the terminals.

The one I have wired in (with the m1twa end disconnected) measures about 1 ohm.

Is my methodology correct?

 

[RAL]

It sounds like you might indeed have a short.  I just measured a spare M1TWSF that I had sitting on the shelf and can confirm that 31 ohms is correct.  So if you are seeing 1 ohm at the other end of the wire, something isn't right.

 

[mikefamig]

measure the impedance of the speaker circuit at the M1 controller. That way you are testing the entire circuit and seeing what the control is dealing with.
 
Mike.

 

[Del91574]

1 ohm, with the circuit disconnected from the unit would indicate a short, exceptionally close to the unit or possibly a blown speaker (stuck or similar) but typically you'd see higher than an ohm if there was a little cable length.
 
Verify your meter first, both by shorting the leads and off a known resistance (EOLR's are great for this).