RS Wallwart for RS pro 404

[mediaseth]

The RS 404 says min 400 milliamp and 9v. So, I got the 9v 800. Then, the young RS employee who wasn't even sure what I was talking about at first fitted a "C" plug to the wall wart. It fits fine, but not super snug.

First, is RS's type C the right one?

Second, the polarity being correct, I get a loud hum. It's as loud as the desired signal. I just went back to batteries after a fit of cable jiggling.

Did RS outfit me with the right wallwart and right adapter? Is there something else I need to do to eliminate this hum?

Thanks

 

[KC5EIB]

Using External Power
You can power your scanner using a power source that supplies 9V DC and delivers at least 400mA. Its center tip must be set to positive and its plug must fit the scanner’s PWR DC 9V jack. The "B" or "C" tip will be fine.

The modern switching power supplies should not cause a loud hum in the radio. Are you using an external amplified speaker?

Be sure you are using the correct battery holder for the type os batteries you are using.

Place 4 AA batteries into the correct battery holder matching polarity symbols (+ / –):

Black – Alkaline (non-rechargeable)

Yellow – Rechargeable Ni-MH or Ni-Cd

 

[mediaseth]

Thanks, KC5EIB

As I said, I'm using a 9V DC rated for 800mA. The center tip is set to positive. The plug is a "C" tip.

The only external amplified speaker I can think of are my USB driven Alesis active monitors, which are tuned into the web stream. They are not connected to the scanner.

I am using the correct battery holder. I did not think I needed to keep batteries in it while it was plugged in, but tried both ways. I do not have rechargeables and so I did not try those.

With the batteries only in play and the power adapter unplugged, there is no hum, but the volume output is more than halved and I've had people complain that the stream is not loud enough. I have it boosted all the places it can be.

I hope I have provided enough details. Could I have a faulty adapter from RS?

 

[GTR8000]

With the batteries only in play and the power adapter unplugged, there is no hum, but the volume output is more than halved and I've had people complain that the stream is not loud enough. I have it boosted all the places it can be.?

Just to be clear, are you saying that you're using the scanner for a live feed, and the hum is coming through on the stream?

Do you hear the hum on the scanner itself when you disconnect it from the computer, or does the audio sound fine coming through the scanner's speaker?

It sounds to me like you are hosting a feed with the scanner, and that's where you're hearing the hum. If that's the case, then it's actually rather common, you're experiencing a ground loop. In a nutshell, the scanner and computer are at different ground potentials, so you get a low 60 Hz hum in the audio. The reason you don't get the hum when the scanner is running on battery power is because it's not connected to AC, and therefore not grounded.

The first step in trying to eliminate a ground loop is to make sure the scanner and computer are plugged into the same AC source. The same physical outlet, even if it's through a power strip or UPS.

If that doesn't solve the issue, you're going to need an isolation transformer on the audio cable. Radio Shack sells one that works well and is easy to hook up.

Ground Loop Isolator - RadioShack.com

 

[mediaseth]

Thanks, Chauffeur6!

 

[mediaseth]

Just to be clear, are you saying that you're using the scanner for a live feed, and the hum is coming through on the stream?

Do you hear the hum on the scanner itself when you disconnect it from the computer, or does the audio sound fine coming through the scanner's speaker?

It sounds to me like you are hosting a feed with the scanner, and that's where you're hearing the hum. If that's the case, then it's actually rather common, you're experiencing a ground loop. In a nutshell, the scanner and computer are at different ground potentials, so you get a low 60 Hz hum in the audio. The reason you don't get the hum when the scanner is running on battery power is because it's not connected to AC, and therefore not grounded.

The first step in trying to eliminate a ground loop is to make sure the scanner and computer are plugged into the same AC source. The same physical outlet, even if it's through a power strip or UPS.

If that doesn't solve the issue, you're going to need an isolation transformer on the audio cable. Radio Shack sells one that works well and is easy to hook up.

Ground Loop Isolator - RadioShack.com

I just bought that from my local radio shack and tried it. It does nothing to reduce the hum. Zilch. I'm about to try a USB soundcard (for another issue as well) as long as I can still use my other USB sound processors, as I also edit audio and video on this machine.

 

[m42duster]

Go to your local Goodwill store. They always have a pile of used wall warts of differing outputs. Pick a few up with your desired specs, check it with VOM.

Usually cost under a buck. Get all the class 2 u can find.

 

[mediaseth]

Go to your local Goodwill store. They always have a pile of used wall warts of differing outputs. Pick a few up with your desired specs, check it with VOM.

Usually cost under a buck. Get all the class 2 u can find.

I'll look around. It's just plain silly that radio shack doesn't sell a wallwart that plays well with its own product. Still puzzled and worried about why the isolation transformer had zero effect, too..thought it could tamp it down at least a bit.

 

[mediaseth]

Follow up. Got a regulated power supply, 9v 1000mA. Same issue. No change whatsoever. I give up. I'm going to get a double set of rechargeables and run off battery only. I'm boosting the audio with an external usb audio adapter. Done.

 

[GTR8000]

That's odd. Did you listen to the audio coming straight out of the scanner's speaker while running on AC, with no connection to the computer?

 

[mediaseth]

That's odd. Did you listen to the audio coming straight out of the scanner's speaker while running on AC, with no connection to the computer?

Yeah. I got a clean signal with no connection to the computer. Maybe my RF/EMI problem is just that bad or maybe there's a flaw with the RS Pro-404 scanner.

 

[pvf]

I also bought the 9V 800mA wart and it does nothing to power the scanner. I know the polarity is correct and the tip is snug to both inner and outer contacts. Has ANYONE figured out a AC adapter that works with the PRO-404???

If I'd known the RS didn't come with an AC, I would've paid the extra for the GRE, no question. This is ridiculously frustrating.