| Ron39 | -- 11-18-2011 @ 11:11 AM |
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I have a 1939 Ford Tudor Sedan that I am restoring. It is a six volt system but I had a 12 volt stereo system put in it using a converter. The problem is that the radio sounds like sh*t when the car is running due to the "non resistor" plugs and wires of the six volt system. The stereo guy advised me that the only way to cure the problem was to convert the car to 12 volt. Does anyone know how to fix my problem without converting to 12 volt? Maybe a noise reducer or something?? thanks in advance!! Ron39 rutpd3@yahoo.com
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| supereal | -- 11-18-2011 @ 12:18 PM |
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If the radio noise is from the ignition, the inverter likely isn't at fault, unless the power lead is picking up the noise. In that case, we use a piece of TV coax cable for the input to shield it. Your "stereo guy" is blowing smoke at you regarding 12 volts. The only difference would be elimination of the inverter. The usual source of ignition noise can be a poor antenna connection, particularly at the base, where grounding occurs, or a bad antenna lead or connector. Ignition noise is common on the AM band, but FM or CD shouldn't be affected unless the inverter is the cause. If the noise is a whiring noise than rises with engine speed, it is likely from the generator. This can be reduced by installing a condenser on the battery post of the generator or regulator. Be sure that case of the radio is grounded, but only if it isn't at the same polarity as the power input. Most modern car radios are designed for a negative ground system, and old Fords have a positive ground, requiring the radio to be isolated from the vehicle ground. Same is true for the inverter. You can install resistor plugs and new plug wires with metallic cores, but don't expect much improvement in reducing spark plug noise. Good quality inverters are well shielded, and yours may not be. I'd get a second opinion from a shop that knows what they are talking about.
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| Gary M. | -- 11-18-2011 @ 5:34 PM |
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I also have a 39 Tudor with a modern radio and a 12v inverter. The inverter that I used is made for a 6v positive ground with the purpose of not having to isolate the radio from the frame. The owner of the company that makes the inverter tells me that grounding is simply a reference point and this affects the amount of voltage that needs to be fed into the device. For example,my modern stereo is 12v negative ground so my inverter must put out 18v to the stereo but since the stereo is grounded to a system which is 6v positive ground,6 of those volts will cancel out leaving only 12v to the stereo. My stereo works great with no static and I dont have bonded ignition wires. The company that I bought from is Meyers Electronics River Falls Wi.54022 www.pressenter.com/~cmeyer
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| supereal | -- 11-18-2011 @ 8:20 PM |
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It is an interesting theory, but if you feed a receiver with 18 volts, that is what it gets, and will cook the unit unless it contains some sort of input regulator such as a Zener diode. All solid state equipment is polarity sensitive. There is no "reference point" that reduces the voltage unless it is combined with a regulator, either in the inverter or receiver. This message was edited by supereal on 11-18-11 @ 8:28 PM
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| Ron39 | -- 11-19-2011 @ 6:36 AM |
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The noise is not really a "noise" but more of poor sound quality. The radio sounds mint when motor not running... then poor sound quality when running. This is also for FM AND the cd player. the radio is mounted under the dash and the power source is directly from the battery. Should I try to ground the radio itself?? The radio guy hooked up the radio directly to a 12 volt battery and it still sounded bad when engine running.
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| TomO | -- 11-19-2011 @ 7:07 AM |
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Ron, If the radio sound bad with the motor running even when hooked up to a external battery, I would suspect shielding in the radio is inadequate. Try wrapping the radio in aluminium foil to see if the improves the sound. If it does, build an enclosure out of metal to hold the radio and ground it. The other option is to buy a different brand of radio. Tom
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| supereal | -- 11-19-2011 @ 4:13 PM |
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Are you using the old speakers? The speakers for tube type radios are often unsuitable for solid state receivers. Many had grounded frames, while others had impedance ratings that don't match. Solid state units usually require 4, 8, or 16 ohm speakers. Before you swap receivers, I'd try new speakers with isolated frames and known impedance ratings. I've chased this stuff for decades, and know that old components are often at fault for poor performance.
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| Gary M. | -- 11-19-2011 @ 4:54 PM |
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I may have distorted the explaination on how the power inverter allows the 12v neg. gnd. radio to adapt to a 6v pos. gnd. car without isolating it, so I suppose for a better explaination there are schematics on line at the websight that I posted yesterday. There are various styles of the inverter depending on your application. Sorry for the confusion.
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| Ron39 | -- 11-21-2011 @ 4:52 AM |
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The speakers are brand new as is the stereo system.
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| supereal | -- 11-21-2011 @ 10:25 AM |
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In that case, it is likely that the receiver has a faulty output section. High distortion is the usual result of an output amp going "class C", in which the necessary "push pull" action is cut in half. This message was edited by supereal on 11-21-11 @ 11:06 AM
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| Ron39 | -- 11-22-2011 @ 4:18 AM |
So ... what do I do to fix it? Help!! 
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| supereal | -- 11-22-2011 @ 6:25 AM |
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The cure is repair or replacement if the diagnosis reveals that the unit,at least the output section, is damaged. If the receiver was fed a higher voltage than required, or incorrect polarity was applied, even the higher power transistors can be cooked. When that happens, either the unit doesn't work, or the audio is badly distorted. If it is new, warranty should cover it. Take it to a good shop and have it looked at. I spent a couple of decades as the chief engineer of a broadcast company, and I've encountered the problem many times. Old cars, with their badly regulated and "dirty" power present unique problems to sensitive equipment.
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