# Spike on Pioneer deck preamp out when station changed. (Not shielding/ground/fuse)



## Jnitrofish (May 25, 2010)

Hello all, I'm new here. I stumbled upon this form after experiencing noise on my preamp outs on a Pioneer DEH-6700MP (and a DEH-6500MP, but not a DEH-2000...yes, I like Pioneer decks.)

This came after I installed a 4 channel amp in my car and rewired the front doors to run 4" speakers off the deck and then run the 8" woofers off the new amp (the rear channels of the amp will power my 6.5" once they get here).

Now the deal is is that I don't experience normal noise, like alternator or engine, I just get a nice pop (sudden positive spike) and weird low frequency (sub sonic) meandering (viewed by recording the preamp outs connected to my computer using audacity). This pop and meandering happens every other time I change radio stations or change inputs (to CD or aux), it only happens to the preamp outs (speakers connected to the internal amp don't experience this pop). By the way, the pop is relative to the volume and seems to happen more if there is louder music on whatever radio station or source I'm changing too.

Now here is what I have done to diagnose this:


Ran ground on the new amp straight to battery instead of the child seat anchors.
Changed RCA cables.
Swapped amps with my truck so I know its not my new amp.
Swapped head units with my truck (the DEH-6500), the pop persisted (it makes pops too).
Swap a spare head unit (the DEH-2000) and the pop *stopped*.
Disassembled the DEH-6700 and looked for a blown Pico fuse, and then realized that they shield is grounded anyways and the Pico is good (amazing I know)

It was after all this I realized it is not noise being introduced from the outside, but it is from the inside, straight from the center pin connection on the RCA/preamp outs.

So now I'm completely puzzled and if I cant figure out how to fix this or where to investigate next, I'm kinda left with a potentially damaging spike or buying new head units which I don't like.

Any help is appreciated.

Thanks.
-Jason


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## beerdrnkr (Apr 18, 2007)

Pico fuse?


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## Jnitrofish (May 25, 2010)

As discussed here: http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/13889-pioneer-rca-preout-noise-prevention.html

I checked the fuse protecting the ground on the preamp outs and its fine.

I have to admit I am guilty of hot swapping.

Edit:

Here is the picture of what happens to the preamp when I change stations.


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## beerdrnkr (Apr 18, 2007)

Jnitrofish said:


> Hello all, I'm new here. I stumbled upon this form after experiencing noise on my preamp outs on a Pioneer DEH-6700MP (and a DEH-6500MP, but not a DEH-2000...yes, I like Pioneer decks.)
> 
> This came after I installed a 4 channel amp in my car and rewired the front doors to run 4" speakers off the deck and then run the 8" woofers off the new amp (the rear channels of the amp will power my 6.5" once they get here).
> 
> ...


My bad I missed that. I have no clue what else it can be.


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## Jnitrofish (May 25, 2010)

hmm.

Well while the pop is coming and going as it pleases I have taken enough time to analyze my new system, and I have realized that I have to have the gain/level on my amp cranked all the way up to even match what the head unit is putting out, which is extremely annoying to me since I got a more powerful amp to make things louder, not to make things match exactly what I had driving them before.  (Not sure if I'm measuring the preamp out voltage right, but I'm only measuring 5 millivolts...)

Also, I managed to get a ground loop by hooking up a second set of RCA cables from my head unit to my amp for rear/sub channel, not sure how that happened, but I could hear my glow plugs cycling.


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