zcacogp Posted September 12, 2019 Report Share Posted September 12, 2019 Chaps, Not related to my suspension thread, my 987 Cayman is really kicking my butt in another area - in car audio. The standard radio was terrible so I've installed a Pioneer double-din head unit in the dashboard and an older 4-channel amplifier in the front boot. Head unit is new, amp is old but known to be good. I'm running it active - i.e. with two channels on the amp to the mid range speakers in the doors and two to the tweeters in the dash. I've run the RCA cables and speaker cables through the bulkhead in front of the passengers and then again through the bulkhead beyond the battery into the front boot to connect to the amp. I am having the most enormous problem with interference from the engine; there is a whine whenever the engine is started. And it's most annoying. I've done or observed the following: - Good amp and HU connections. HU now connected to it's own custom loom straight to the battery - No whine with RCA's disconnected. Whine occurs only when both sets of RCA's are connected - Whine seems to be related to the position of the RCA's and I think there may be a source of interference in the footwell, somewhere near the centre console. Such is the design of the car then routing the RCA's via any other path would be difficult. Has anyone else installed an amplifier in the front boot and if so then where did you run the RCA cables? Thanks for your help. Link to comment Share on other sites More sharing options...
Rooose Posted September 12, 2019 Report Share Posted September 12, 2019 Not installed an amp in a Boxster but first question I would ask is where/what is being used for the ground? I didnt see in your description if you had one in place. All interference issues I have had with audio whine have been due to poor or badly located ground wire. Sorry its unlikely to solve it but just wanted to mention it in case it has any value! Link to comment Share on other sites More sharing options...
zcacogp Posted September 12, 2019 Author Report Share Posted September 12, 2019 Roose, Thanks. I think that the earths are pretty much as they should be; I've made a dedicated loom for the HU and the earth goes straight to the battery, with another wire from the battery to the amp ground, and a thick wire from the amp ground to a nearby bit of bodywork. The whine doesn't seem to be being caused by any of the usual things and I'm confused. It doesn't follow any sort of logic and seems to be in some way related to the route that the cable takes through the footwell, hence my question about whether there is something that causes a lot of interference in there. The chunky cable from the alternator to the battery +ve terminal seems to run through the passenger side (if you follow it from the battery it goes to the nearside of the car) but there is a thick black cable of some kind that appears behind the pedals and I don't know what it does. It could be a vacuum line from the engine but I'm not convinced. Given that I am currently stumped by it then I am seriously thinking about relocating the amp to under the passenger seat and taking the RCA cables elsewhere entirely. This will be a lot of work but the whine is intolerable. Thanks again for your help. Link to comment Share on other sites More sharing options...
Def1 Posted September 13, 2019 Report Share Posted September 13, 2019 From my old sound off days , the RCA cables need to be kept well away from any power cables ,unless yo have a spare amp or cables to try to eliminate the issue 👍👍 Link to comment Share on other sites More sharing options...
zcacogp Posted September 13, 2019 Author Report Share Posted September 13, 2019 'Zactly! And my question is whether there are any big power cables in the footwells which could be causing this problem. I've tried a spare HU and am on my second set of RCA cables .... Link to comment Share on other sites More sharing options...
DaveEFI Posted September 15, 2019 Report Share Posted September 15, 2019 Sounds like a typical ground loop. Usual cure is isolating transformers in the phono leads between head unit and amp. Why many modern units use fibre optics for this. No chance of a ground loop. Link to comment Share on other sites More sharing options...
zcacogp Posted September 15, 2019 Author Report Share Posted September 15, 2019 Dave, Thanks. It's either ground loop or RCA interference. I don't think it's ground loop as there is a single wire that goes from the HU case to the Earth connection for HU to the Battery negative terminal to the amp ground. Then again I don't seem to get the noise when I run a signal from an independent source (i.e. my 'phone) directly into the HU end of the RCA's, so I'm confused. It seems that there are people who have run aftermarket amps in their frunks so it must be possible. Link to comment Share on other sites More sharing options...
DaveEFI Posted September 15, 2019 Report Share Posted September 15, 2019 Ground loops often defy logic. If you're getting pickup on the phono lead, convert to balanced - a transformer at either end. Or an analogue to Toslink converter. Link to comment Share on other sites More sharing options...
zcacogp Posted September 15, 2019 Author Report Share Posted September 15, 2019 This problem seems to defy logic, for sure! Analogue to TOSLINK is an option but it's a pricey and bulky one. I'm hoping it won't be necessary. What do you mean by 'convert to balanced - a transformer either end'? One option would be to make some new RCA leads with balanced cable - is this what you mean? Thanks for your input. Link to comment Share on other sites More sharing options...
DaveEFI Posted September 15, 2019 Report Share Posted September 15, 2019 Balanced uses special transformers (or electronics) which convert the signal into two legs of opposite phase. So any interference gets cancelled out when it is converted back to unbalanced at the other end. Dates back to the early days of telephones. Cable is commonly a twisted pair and screened - but the screen doesn't carry any audio. Still used in pro analogue sound gear. Trouble is decent transformers ain't cheap and you'd need four for stereo. I'd say converting to toslink would be cheaper - but more work to install, as the common units need 5v DC, so would need a power supply. Link to comment Share on other sites More sharing options...
zcacogp Posted September 16, 2019 Author Report Share Posted September 16, 2019 Thanks - that's a good explanation. If I was to go down the toslink route then what would I need? Link to comment Share on other sites More sharing options...
DaveEFI Posted September 16, 2019 Report Share Posted September 16, 2019 Have a look on Ebay etc for RCA to Toslink and Toslink to RCA converters. In the UK, about £25 each. They are stereo. But run off 5v DC, so you'll need couple of 12v to 5V PS too. Total size is small enough to hide OK. Since you've said running the amp from a self powered device like a phone works OK, it very likely is a ground loop and that will remove it. Link to comment Share on other sites More sharing options...
zcacogp Posted September 16, 2019 Author Report Share Posted September 16, 2019 Dave, Thanks - this is helpful stuff. I've ordered some good RCA cables (Krystal Kable) which should arrive today. These will either solve the problem of interference (fingers crossed, but I'm doubtful) OR show it to be a ground loop problem. I'll update this thread accordingly. Link to comment Share on other sites More sharing options...
DaveEFI Posted September 16, 2019 Report Share Posted September 16, 2019 Other thing to try is running the amp ground back to the same place as the HU ground. Link to comment Share on other sites More sharing options...
zcacogp Posted September 16, 2019 Author Report Share Posted September 16, 2019 The amp is grounded with a thick cable to the bodywork nearby but there is another (thinner) cable that links the amp ground with the battery negative terminal and the HU ground. Wouldn't this eliminate any ground loops? Link to comment Share on other sites More sharing options...
Recommended Posts
Archived
This topic is now archived and is closed to further replies.