My Audiosone / Sigcom amplifier has laryngitis

Something funky is going on with my voice evac amplifier.

A bit of background: This is an Audiosone / Sigcom AU-360-E amplifier. This is the “expansion” version; it has no message repeater or microphone preamp. The unit is powered from the 24-volt auxiliary output of the FACP. You connect a bell circuit from the panel to the amplifier. Normally, the amp lets the panel supervise the speakers. When the alarm goes off, the amplifier generates an alarm tone. You can override the tone using the line input and press-to-talk circuit, as illustrated in this video.

The amplifier has a special 120-volt input that’s used for supervision only. When the building has power, all is normal; the amplifier will constantly test its internal tone generator and allow the panel to supervise the speakers. When there is no power, the internal tone generator test is suspended to save the battery. The panel sees this as an open circuit, which means that when there’s no power, the speakers are not supervised.

ANYWAY, here’s the problem: as long as the amplifier sees 120 volts, the internal tone generator sounds awful. This is what it’s supposed to sound like (the supervisory circuit is disconnected in this video). Instead, it sounds like this:


I’m kind of at a loss on this one. My guess is that the panel has some internal fault, which is probably why it was so cheap on eBay. I’ve bypassed the problem by making a recording of the whoop tone and having the Raspberry Pi play it instead. But it’d be nice to get this working properly.

Does anyone have any experience with these old Audiosone systems? Does anyone have a schematic, by any chance? Would the fine folks at Sigcom waste their time helping me with a hobby system (an outdated one at that)? I’m not afraid to bust out the soldering iron and start replacing capacitors, just as long as I know what I’m doing.


Upon further investigation, it looks like it’s a function of how long the tone generator circuit has been active, rather than just the AC supervisor circuit. When the supervisor circuit is active, the tone generator makes noise but doesn’t broadcast it over the speakers. This way, the amp can make sure the tone generator is always working. So, because it’s on constantly, the tone generator has plenty of time to drop down to the “sick” sound.


What’s the voltage setting on the amp output? Are there any other devices drawing from the 24V power output on the panel, or is it just the amp? Is the is the 120 on the panel and the amp sharing the same ground?

This amplifier only outputs to 25-volt speakers. It’s the only thing receiving accessory power from the panel. The 120-volt supervisor doesn’t have a ground connection, although they are plugged into the same power strip.

This amp had the same problem when it was connected to my 4004 panel. I thought the batteries in my panel were going bad, but the same thing happens with the new batteries on the AFP-200, and even when I just power it with a big 24-volt (3 amp) power brick.

(Thanks, NickyVeee!)

Edit: Oh, also, the voltage on the accessory output remains constant at about 25.2 volts no matter what’s happening.

Also, which terminals are you using from the AFP-200 to provide power? If you’re using TB1 terminals 3 and 4 (non-resettable power), they’re only limited to 500mA. TB1 terminals 1 and 2 are rated for 1.0A in standby and 1.5A in alarm, the problem is it’s unregulated power which could be subjected to rippling.

Your particular amp draws 1.2A in alarm, and probably at the peak of the whoop is where it draws the most power, which is where you’re getting your distortion. In any case, it might be worth it to try using a dedicated 24V power supply. I think you can get them for like $20-25 online, electronics stores may also carry them depending on their selection.

I assume this is for a hobby system, so any 24V power supply that outputs more than 2A should work so long as you don’t require battery backup. Otherwise then you’d have to get an actual power supply meant for larger alarm systems and vocal amplifiers, like the Notifier AMPS-24, which could cost you quite a bit.