hum from radio

[grayghost]

???
we have a radio/cd player that the dealer installed.
when we have the trailer plugged into our generator or an outlet in our house we get a terrible hum from the speakers. when it operates off the battery in the tm there is no hum. any ideas, suggestions, solutions?

thanks

eileen

[RockyMtnRay]

Eileen...

The hum is most likely caused by a residual 60 cycle alternating current "ripple" that the standard 6300 series converter is leaving on top of the 12V DC power that it provides to the internal circuits of your TM. The issue was more or less addressed by Mike Laupp in the thread on LED lights (http://www.trailmanorowners.com/yabbse/index.php?board=7;action=display;threadid=935). As Mike points out toward the end of that discussion, removing low frequency AC from a DC system is not particularly easy...and can't be done with the usual "noise" filters sold by Radio Shack and auto stereo places (those filters are designed to remove high frequency alternator noise and other static).

Filtering out low frequency AC hum can be done though...but you will need to talk to a very competent electronics technician to either find a filter that's commercially made or have him/her design one for you. It's been long enough since I studied such circuits that I can't remember the details. Perhaps forum member Bill (who I believe is an electrical engineer) might have some circuit designs that an electronics tech could put together for you.

Another, albeit rather pricey, alternative is to simply replace the 6300 converter with a 7300 series converter...among other gains you would get is very clean and filtered DC power into your TM. Based on what Mike Laupp posted, that solution would run you around $280.

[RockyMtnRay]

Followup thoughts.

IIRC, three of the DC outputs from the 6300 converter are supposed to be "filtered" (I believe they basically use the battery as a filtering mechanism). At least one of those "filtered" outputs is routed into the area above the refer for the express purpose of providing power for such things as a radio/stereo. If the person who installed your radio/cd player didn't know this...and hooked up its power lead to an unfiltered DC circuit from the converter...you would indeed be getting a lot of hum. Alternatively, the radio/cd player that was installed is particularly sensitive to AC ripple on its power circuit.

Solving this may involve the services of a technician who has appropriate instruments to chase down the source of the AC ripple on your radio's DC input...and who can come up with a suitable fix (different supply lead, filter for current supply lead, etc.).

[Bill]

Ray and Eileen -

I'll reply since you have brought up my name, but you have already said the right things. You do have a battery installed, right - it will hum like mad if you don't. Assuming you do, in my opinion either the radio is on the wrong circuit (to check, pull the three right-most fuses on the fuse block in the converter - the radio should go off), or the radio is extraordinarily sensitive to the presence of 60-cycle ripple on the DC supply line. Any radio that cost you more than about $30-$40 should not be this sensitive, so unless you have a REALLY cheap (or old) radio, this should not be the problem.

The technical solutions are not handy. As Ray notes, pre-packaged filters are not among them. The real technical solution, after ensuring it's on the right circuit?
1) Add a voltage regulator to the 12-volt input line to the radio. Almost sure success. See the thread on LED lights for a link/pointer, or email me. Not handy - you shouldn't have to do this.
2) Solder 0.01 uF capacitors across the diodes in the converter. Maybe a 50% chance of success. Again, not hard but not handy, you shouldn't have to do it, hiring someone will cost more than a new radio. But if you have an electronic bent, contact me off line, and we'll go through it.
3) Buy a new converter. This is like buying a new car when you can't figure out how to empty the ash trays in the old one. Sure it will work, but this is the wrong reason to buy a new car (or converter) unless you have more money to spend than many of us.

A more practical solution is to buy another radio - ON APPROVAL - do a quick install, see if it hums. If it hums, return it.

No magic solutions here, I'm afraid, but if it hums only when you are plugged in, then this is not normal - and it should be curable. Feel free to email me with questions and results.

Bill

[mjlaupp]

Ray and Eileen -

...... or the radio is extraordinarily sensitive to the presence of 60-cycle ripple on the DC supply line. Any radio that cost you more than about $30-$40 should not be this sensitive, so unless you have a REALLY cheap (or old) radio, this should not be the problem.........

I installed a $450.00 Kenwood radio in my ill fated '02. I could hear the 60 cycle hum during dead air periods or between CD tracks. It wasn't loud but was enough to annoy. I had installed the radio using the TM provided filtered power lead behind the blank insert over the fridge. There is no hum with the same type installation in my '03 with the power converter upgrade installed.
MJL

[Bill]

Eileen -

Any progress on this? Mike is right, price alone is not a guarantee of hum-free operation. Even a really good unit can have a little hum. But you seem to be describing a LOT of hum. BTW, I have a relatively cheap Jensen unit from the Crutchfield catalog, and it has no hum that I can detect.

I continue to think that if your dealer sold and installed this unit for you, he will certainly want to make it work for you. Aside from the basic ethics of the situation, he wants you to be a satisfied customer. Have you checked with him? It is quite possible that he got a defective unit from his supplier, and that a replacement unit would operate just fine. Since the cabling is already in place, it would be quick and easy for him to slide your unit out and slide a second identical unit in. If the hum stops, you are good to go. If it still hums, then you (and he) know it is a design problem with that particular model, and you install another model.

Bill

[grayghost]

hi bill, no we haven't resolved the hum yet. the dealer suggested installing a ground wire from the back of the radio to the the frame. we haven't found the time to do that yet.

as far as a defective product, well i'm not sure about the dealer replacing it since he is 4 hours away from us. i called the manufacturer of the radio and got nowhere with them. but i don't think it's defective because there is no hum when running off the battery, only off ac or generator.

we have a guy installing electric in our barn and i would like to give him the opportunity to check it out.
i think he would have a heads up on what to do to fix this.

thanks for your help.

eileen

[DancinCampers]

Hi Eileen,

Another thought would be to check if the TM is wired on the AC side properly.

You can buy a polarity checker fairly inexpensively & plug it into your AC outlets. The lights will tell you if the system is properly wired.

I carry mine with me & always check after I hook up to electric power.

Let us know when you get the problem solved, very interested in the resolution.

Dan

[grayghost]

hi dan, would you believe we have not gotten back to that radio to check things out. it's on the short list for this week-end. trying to get everything squared away for our first ever trip next week. sure do hope i'll pack all the right amounts :) will definitely try the polarity checker. thanks.

eileen