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Post by stan on Nov 23, 2017 22:34:04 GMT
Thanks will give that lot a try tonight (all being well) appreciate your advice on this one. As it's a -VE chassis it will have a connection to the -VE I would have thought? Years ago there was a floating earth radio I am bu**ered if I can remember the make? there was also a Philips with switchable polarity back then as well! I hope you get it sorted Stan  Thanks John. I had a moment of clarity today and some pennies dropped into position. I am annoyed with myself electronics both old and new were my thing for years. Anyway the previous owner had fitted a dc-dc convertor, which confused me as it had a 24v output? 24v!!! That would fry tge radio I thought so I took it out but I found this useful article mgaguru.com/mgtech/electric/et207.htmWhich explained everything, so the dc-dc convertor is going back in as will the aerial connections reverted back to normal again! Hopefully that will remove the sensitivity of the current set up but the engine suppression work shall also go ahead. Then you lot can have some peace and quiet from me on this subject. 😉 |
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Post by djm16 on Nov 23, 2017 23:05:19 GMT
You have already figured out that the 24V converter is a dodge to get around the polarity problem using a cheap, non-isolated DC-DC convert. It "may" work fine for a low powered 4W mono radio, but for a modern 20W stereo you will run into distortion. Why?
At normal engine speeds, the power rail on your car will be at around 15V (that is a typical value for the voltage regulator). The radio will therefore be powered by 24-15V in other words 9V. It may work fine, but the available power output will be halved (V^2 / R) and bass transients are likely to cause clipping.
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Post by stan on Nov 24, 2017 7:14:20 GMT
You have already figured out that the 24V converter is a dodge to get around the polarity problem using a cheap, non-isolated DC-DC convert. It "may" work fine for a low powered 4W mono radio, but for a modern 20W stereo you will run into distortion. Why? At normal engine speeds, the power rail on your car will be at around 15V (that is a typical value for the voltage regulator). The radio will therefore be powered by 24-15V in other words 9V. It may work fine, but the available power output will be halved (V^2 / R) and bass transients are likely to cause clipping. Thank you sir good point. Maybe thats why I thought the previous owners radio was rubbish quality? Will try it and see how it goes, I dont really want to do a negative earth car conversation just for 1 radio? But if I can't suppress the interference then it might be my only option? Thanks again for the valuable advice. |
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Post by djm16 on Nov 24, 2017 14:10:31 GMT
No need to convert the car, just get an ISOLATED 12V (15V?) DC-DC converter and common the +ve input (ground) to the -ve output (ground). After a while you will forget just how much the converter was.  |
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Post by stan on Nov 24, 2017 15:04:17 GMT
No need to convert the car, just get an ISOLATED 12V (15V?) DC-DC converter and common the +ve input (ground) to the -ve output (ground). After a while you will forget just how much the converter was. The one that came with it is rated 72w think they are £40?? Anyway its going back in tonight cost to me nothing but 30 mins faffing again in the cold. |
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Post by johnwp5bcoupe on Nov 24, 2017 17:02:20 GMT
No need to convert the car, just get an ISOLATED 12V (15V?) DC-DC converter and common the +ve input (ground) to the -ve output (ground). After a while you will forget just how much the converter was. The one that came with it is rated 72w think they are £40?? Anyway its going back in tonight cost to me nothing but 30 mins faffing again in the cold. 6 amps should do you Stan unless you are running 100w amps  |
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Post by djm16 on Nov 25, 2017 4:39:56 GMT
The "one that came with it" is almost certainly a NON-isolated DC DC converter. That means it has a common -ve rail. (£s)40 for a 10A NON-isolated converter is about right.
My ISOLATED 10A convert, which runs a 4x 20W head unit plus a 100W compact subwoofer, cost around (£s)200.
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Post by stan on Nov 25, 2017 21:19:47 GMT
The "one that came with it" is almost certainly a NON-isolated DC DC converter. That means it has a common -ve rail. (£s)40 for a 10A NON-isolated converter is about right. My ISOLATED 10A convert, which runs a 4x 20W head unit plus a 100W compact subwoofer, cost around (£s)200. After spending a couple of hours refitting the dc-dc convertor and checking various bits I just left it and walked away. There is something weird going on with the feed from the battery? I was having issues with my multimeter think the leads are loose so readings a bit all over the shop. One minute I get power then dead? Removed everything and just connected radio and nothing so thought it best to do this again during daylight hours and have a rest from it. Wish I had left it alone now! Oh well its nice listening to the straight 6. |
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