Calling all car audio experts

Voodoomelon

Hey all.

http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/154929-bm24-pre-outs-2.html

According to that link, the BM24 radio module I have in the boot (which doubles as the cars amplifier) outputs a balanced 5v line level signal to the speakers in the car, if you don't have the DSP system like me.

Thats great, however my new Apline PDX-F6 amplifier has an input sensitivity of 0.2V to 4.0V.

Would it be safe to solder RCA connectors to the four speaker cables coming out of the BM24 radio and run them straight into the low level RCA inputs on my amplifier? (it doesn't have high level inputs)

I have high-level to low level converters from Halfords but i really don't want to use them if possible.

What I really want to know is it possible to damage the amplifier's input by running 5V to it?

Thanks! :pac:

Owen

No, it's not about the voltage. The reason some audio systems run at 4/5 volts is to isolate their signal by lifting the reference point of the audio. Normal electrical items in the car run between 0-12 volts. By lifting that from 4-16 on an audio line, you're eliminating where a lot of the whining noise and static could come in from other car systems.

The voltage doesn't matter, but the wattage does. If you take your speaker connections, they're sure to be running at a minimum of 5 watts RMS, potentially up to 50 watts RMS, and if you don't have high level inputs, don't connect them. You'll pop whatever you connect them to, and risk popping the unit driving the signal too.

Use your convertors!

Voodoomelon

Hmm, its just others have done just that, soldered RCAs to the speaker cables no problem with the same radio module. The difference is that their aftermarket amps might of had a higher input voltage sensitivity.

Surely the wattage doesn't matter if its a balanced signal, most decent headunits output 50w per channel also no problem?

Owen

Wattage definitely matters. I play Guitar in a band, and if you put an 800 watt poweramp into a speaker which can handle 50 watts, it pops.

If others have done it, they must have the volume output of the module down to the bare minimum - even at that, it's a stupid thing to do. You should only use speaker outputs as an audio source into an amp, if the amp has high level inputs - level referring to power, not voltage.

I suppose you could think of it this way, a normal input has an amount of power that it can tolerate the input signal being, so something the size of a lemon. You're trying to squeeze a watermelon through that hole, and hoping for the best.

Voodoomelon

Thanks for that, I wasn't arguing, just trying to get my head around it.

I was under the impression that all those converters did was drop the voltage to about 2v or so, the norm for RCA input. I didn't think wattage had anything to do with it.

Owen

Sorry, you're right, I'm wrong. I'm thinking live audio equipment, not car equipment. Those autoleads thingies in Halfords are step down transformers AFAIK which drop the voltage, I'd still be very wary of using them though for power reasons. I just don't think it's a good idea to take an amplified signal, and put it into the input of an amp which is expecting a non-amplified signal, and even if that doesn't blow the input part of the amp, reamplify the signal and risk distortion of the audio.

Voodoomelon

But thats exactly what they're for, dropping speaker level signals to low level rca. Id have no worries in the slightest running the converters, just they aren't the best for sound quality.

However all my gear is in the boot away from all engine and electrical noise so there's probably no difference in using the converters compared to not using them.

Forums and online stores say that there is usually an RMS wattage limit on the converters as the resistors get too hot if they're overloaded, but I very much doubt the radio module can output more than 50w per channel, the mids I ripped out only output 40w RMS peak.