QuestionQUESTION: I have an old-school Nakamichi PA-304 4-channel amp I'd like to use with my head unit that has only speaker level outputs. It looks like the NAK has some level controls on its inputs so I was wondering if I can use my head unit with the NAK. I have no owners manual for the amp and can't find one anywhere. I would be very grateful for some help with this.
Thanks,
Mark
Ventura, CA
ANSWER: Hi Mark,
Just about all after-market amplifiers include level adjustments for the inputs; however, they're usually not designed to be connected directly to a head unit's speaker outputs.
The proper way to use an amplifier with a head unit that doesn't have RCA outputs is to use a device called a line output converter. This connects to the factory speaker wires and converts the signal to a low-level output that can be connected to the amplifier with RCA cables. You can use a line output converter on a speaker output, even if it's also connected to a speaker.
Just about any car audio store should be able to supply you with a line output converter.
Hope this helps!
Brian
---------- FOLLOW-UP ----------
QUESTION: Wow, thanks Brian. Do I need to buy a high quality one (expensive) to be worthy of the NAK amp? Also, I am doing this for my sailboat which is very sensitive to power draw when the engine is off. Therefor I want to run only the head unit direct to speakers for low-power draw and then run the head unit to the line output converter to amp to speakers when power is not an issue. To do this I plan to wire up an 8-pole double throw rotary switch at the head unit outputs so I can select the two configurations. Is this an OK way to do it?
AnswerHi Mark,
I don't think you need to spend a lot for a good quality, 4-channel line output converter. There are several models that sell for between $30 and $50. If you're buying online, you might consider the NE-774V adapter from David Navone, linked below (scroll down to see the NE-774V):
http://www.davidnavone.com/cart.asp?24&cat=7
I think the switch you're describing would work for switching the speaker connections between the head unit and the amplifier. Another option would be to use a pair of 4PDT relays.
From what you've described, though, I'm not sure about your wiring plan. It sounds like you intend to use the switch to divert the head unit's outputs: you're connecting the "common" terminals to the head unit's speaker outputs, then connecting the "normally closed" terminals to the speakers, and the "normally open" terminals to the line output converter for the amplifier. When you turn the switch, the power output that would normally be sent to the speakers is sent to the line output converter, instead. Is this correct?
The problem with this setup is that you'll need to have the amplifier's speaker outputs connected to the speakers, as well as the head unit's speaker outputs (through the switch). When the head unit is driving the speakers, the head unit's output power will also be routed to the amplifier's output terminals. That's not a safe situation for the equipment, even if the amplifier isn't producing sound at the time.
The proper way to use the switch or relays is to make sure the speakers are only connected to one power source at a time. To do this, connect the "common" terminals to the speakers. The "normally closed" terminals should be connected to the speaker outputs from the head unit; the line output converter should also be tapped into these wires (between the head unit and the switch). The "normally open" terminals should be connected to the speaker outputs from the amplifier.
In this way, when you turn the switch it will disconnect the speakers from the head unit's outputs, and connect them directly to the amplifier's outputs. Thus the speakers are never connected to both outputs at the same time.
One other addition: I'd put a toggle switch on the "remote" wire leading from the head unit to the amplifier, so that you can switch the amplifier off entirely when it's not in use. That's one advantage of using a set of relays instead of a 8PDT switch: a single toggle switch can turn on the amplifier and activate the relays at the same time.
Hope this helps!
Brian
