bigd480

I have a 97 w/ Bose and bought a JVC HU w/ 4.8v pre-outs, and a 70-7551 harness to connect it with.

I've read many posts that recommended this harness, and many others with people complaining about pops/whine when using this harness and wanted to know if the 70-7551 + 2 ground loop isolators is the best solution to add this HU, or if I should get something different like the PAC ROEM-NIS2.

Given the multiple ground wires, I'm wondering if the people that had pops just had grounding issues? (what is the best way anyway? The 2 ground wires from the 7551 and the ground from the HU all connected to one bolt? which bolt?).

I also read some people recommend adding a resistor/capacitor to the amp turn-on lead and others say that this didn't work.

Thanks for any input/experience. I know this topic has been discussed a lot but the posts span many years and there doesn't seem to be a definitive "this is what works".

nismos14

iTrader: (56)

The pac should keep the popping from happening....

bigd480

I've read that the popping has to do with the amp turning off and on. My last stereo was the 05 pathfinder Bose so my acc and amp turn-on lead are already jumpered. Wonder if that is actually the problem though.

My other question is does the metra 7551 actually pass the right type of signal or did they slap RCAs on it for convenience? I'm not really familiar with how high/low level signals work and bought the 7551 assuming that the amp pre-outs on my deck would provide the best signal.

Pearl96Max

iTrader: (151)

7551 isn't needed. 7550 works perfectly fine.

bigd480

Installed the deck temporarily while waiting for the stock brackets to arrive. With the 70-7551 I'm only getting popping when first turning the car on and if I take the volume all the way down to zero - not when switching sources/tracks. The sound is good and loud enough. I have a 4-channel ground loop isolator on the way that will hopefully take care of those pops.

I did get some really loud buzzing sound from inside the engine bay if I put it in ON instead of just ACC. Figured it was because the climate controls were disconnected.

bigd480

4-channel GLI installed - no pops, bass still good. Happy for now.

the one I purchased:

I thought that was an amazing deal for a 4-channel. Even cheaper at Monoprice's website if you're going to be buying other stuff and paying shipping anyway.

Pearl96Max

iTrader: (151)

And yet, you could have just used a 7550.

bigd480

My understanding was that using the 7550 would result in the Bose amps receiving an already amplified signal.

As far as I know, amps should only receive low-level signals, otherwise why would RCA pre-outs even exist (if it was fine to use speaker level outputs that are already there in every deck)?

Pearl96Max

iTrader: (151)

You're right, what do I know ? Just been doing this for a few decades.

You Do realize you are still comparing signal to signal right ? When you get a 2v generic deck or a higher (ie: older Eclipse) 8V deck... wouldn't your 'theory' still apply ?

Carry on as you wish with your issues. I will continue not having any.

bigd480

I'm not arguing with you, I'm telling you why I did what I did. If you don't have issues with the 7550, more power to you.

I don't understand your point about comparing signal to signal. It's high-level vs low-level, amplified vs non-amplified. I'm sure over the decades you've installed many LOCs because of this difference.

Whether the difference between line-level and speaker-level input is big enough to notice - who knows. I just wanted the cleanest signal possible if I'm keeping these 15yr old speakers/amps.

Pearl96Max

iTrader: (151)

Amplified IS 'high', non amplified IS 'low'. BOTH are simply voltage. So a 'high voltage deck' would be no different.

You wanted the 'cleanest signal possible' yes you added more to the chain to be counterproductive. You went backwards, not forwards my friend.

bigd480

I understand your point now, but still am trying to grasp if high-level deck output is equivalent to speaker-level output (6v?), why do pre-amp outputs even exist and why would people pay more for decks with higher voltage pre-outs if they could simply use a harness like the 70-7550 to achieve the same thing?

Is there something about the Bose amps in our cars that makes this an exception to the rule?

Pearl96Max

iTrader: (151)

First - Convenience.
Second - All amps have RCA inputs.
Third - Typically higher distortion with the 'high level' one the top end of the volume.
Measurable, but still fairly minimal, especially for an OE upgrade.

We actually do ALL Porche 996/997 this way to Aftermarket amps ! .. Zero issues.

bigd480

Thanks for the explanation - there are so many threads on this but no one has laid it out that simply.

One other question: what is it about the 7550 that doesn't cause the popping? One would assume the popping has something to do w/ the amp turn-on lead, which is the same in each case. Is it possibly the way the deck's RCAs are grounded?

Pearl96Max

iTrader: (151)

Not a problem.

Yes, typically in the RCAs and/or lack of information when changing sources. Amp is live, but nothing is going through. Once information is received it 'pops'. VERY typical in Fords as well and thus a resistor is needed to downstep the voltage (turn on is 5V).