ReZ-8

Ok so I need to get my signal before the stock amps for flat frequency, but won't it screw up the stock amps? Won't the resistance be half?

I'm planning on using the signal from the rears to feed my amp (has hi-level line-in). But I do not want to screw up the rest of the system, it's already bad as it is!

I've looked and I can't find a straight answer, help!

staticlag

To answer this question, use the equation:

1/R(total)=1/R(stock amp) +1/R(aftermarket amp)

R= resistance

But resistance is not what you should be worrying about.

What you are truly asking is: Will there be enough current for the stock amp?

In which case, use the equation: V=IR after you have gotten numbers from the above equation.

But what you really should be asking is:

Will the new combined total resistance load overdrive my headunit???

MrWigggles

If you use the speaker level inputs of most electronics they will either have plenty of input impedance or a very mild load.

I don't think you will hurt anything by using the speaker level inputs for the signals before the Bose amp.

With a decent multimeter you can test the speaker level input impedance (i.e. resistance) of the device you want to use while it is on. Or you can call the manufacturer. I would say anything over 1000 ohms will be fine. Anything less than 100 ohms I would avoid using. 100-1000 ohms is a bit of gray area.

Probably the best way to tell if you have a problem is to listen to the music level of the rest of the system before and after you attach your device. If the volume stays the same, you are not loading the signals and you are fine. If the music of the Bose speakers goes down in volume it means your device is loading the signals that go to the Bose amp which you don't want.

If your speaker level input do load the system then I would simply use the signals after the amp like most people do.

-Mr. Wigggles

rkostolni

I highly recommend not doing that. The speaker wires on the bose system, prior to the bose amp are a differential pair. If you use them, you will burn out your headunit. You need to get a convertor box that adapts differential pair to standard RCA's. PAC and Soundgate both make one. I am using the Soundgate LOCB.2, but I believe they now have a better one out that provides level control. That would be nice, essentially giving you control of the amp gain from your drivers seat.

rkostolni

As far as effecting the impedence of the circuit, it won't have any appreciable effect as both the convertor box and the amplifier inputs are very high impedence. When compared to the low impedence of the speakers, there will be virtually no change in the perceived impedenence of the circuit from either the amps or HU perspective.

If you don't want to buy the convertor box, then tap the speakers wires after the amp, but then you have to deal with the bose amp's dsp.

MrWigggles

Speaker level signals ARE differential pair. (Every modern HU uses Bridge Tied Load (BTL) outputs for speaker level signals.)

The only difference between the Non-Bose and the Bose headunits are their ability to drive current (i.e. speakers). The signals themselves are virtually the same. In fact one forum member had a Non-Bose HU accidentally installed in his Bose system and it work fine. The voltages are the same.

The important thing, and I think I made it perfectly clear, you don't want to pull too much current from the Bose HU. That's why it is important that you know the input impedance of your AMP/Processor/Etc. speaker level inputs. I guarantee it won't be 4 ohms. That would mean they would have to have a 25 Watt resistor inside the thing to disipate all of the heat. It is going to be over 10 ohms and probably much much higher. CALL THE MANUFACTURER IF YOU CAN'T MEASURE IT YOURSELF.

The Soundgate on paper is a great solution, BUT it is $90+ and it doesn't work all that great in back by the Bose amp. I've tried, personally. It might work great behind the radio - dunno.

If you keep the volume low and follow my suggestions in my earlier post, you won't fry anything.

-Mr. Wigggles

rkostolni

I would rather be safe, I remember hearing quiet a few stories of blown headunits from people tapping directly in before the bose amp. Why didn't you like the soundgate?

MrWigggles

The Soundgate had alternator whine when I located it back by the Bose amp. The instructions say to put it as close to the HU as possible.

For differential signals the location of the converter shouldn't be that critical but apparently in this case it is.

(BTW, I'm not possitive the circuit topology used by Soundgate. A good differential amplifier should have great common-mode rejection and the alternator whine should be gone. In the coming week I plan to make my own differential to single-ended convertor and see how well it does.)

-Mr. Wigggles

ReZ-8

Thanks for all the input... but i will post a new thread with a simplified request. :o