Any easy way for newbie to trigger 12V on subwoofer without receiver?

[Hogwild]

Hi all:

Let's assume I have next to no knowledge of electronics. I have a Nakamichi subwoofer here with built-in amp. I don't know if it's functional or not. It has a 12V trigger port to turn it on, but I don't have a receiver. Is there some relatively simple/easy way to get it to turn on without one?

Thanks

[themadhippy]

try shoving 12v up the trigger line,a 9v battery might even be enough

[Hogwild]

But as I understand it, you can't let the circuit pull to much current...you have to current limit it before entry. So, that immediately means more work to do this, right?

[SteveThackery]

But as I understand it, you can't let the circuit pull to much current...you have to current limit it before entry. So, that immediately means more work to do this, right?

Why do you understand that?  I assume the subwoofer is designed to work with a range of different amplifiers, so I don't believe it will rely on all those amplifiers limiting the current in the same way.

If, for some reason, the current on that 12V input needs limiting then surely they would put the current limiter inside the sub.

Just try it with a 9V battery. They won't provide all that much current anyway.  I suspect the 12V input just operates a relay which switches on the mains power to the internal amplifier. 

[Hogwild]

My reason for believing it had to be current limited was here:

https://sound-au.com/project156.htm

[David_AVD]

What model subwoofer?

If it has a 12V trigger input, that should be optional function. It should come out of standby once it has audio present on the input.

[Hogwild]

 Are you sure? I think I already tried that, but I'll try it again just in case.
I just remembered...I already tried that.

It's a Nakamichi Sound Space 12.

[David_AVD]

OK, that doesn't appear to be a regular subwoofer. It looks to be an amplifier for the front left and right speakers too. The pictures I saw online just say "power control" for that socket, not 12V.

[boB]

I don't think I saw  any speaker terminals on the back panel in the picture.
But I'm old and my screen is dirty so who knows

[oPossum]

.

[SteveThackery]

My reason for believing it had to be current limited was here:

https://sound-au.com/project156.htm

Yes, but I think the current limiter will be inside the sub. It would be a very dodgy design if it relied on the external circuit implementing the current limit.

[Hogwild]

Okay, I tried it with a 9V battery and fed it music with my passive preamp, fed by a CD player. It did indeed turn the unit on. I didn't realize the voltage had to stay there for the unit to stay on, but it does. As soon as I remove the battery, the sub/amp go off.

It sounded like the whole frequency range was coming through the sub. I assumed it had a high-pass filter on it. I guess not.



Now, I want to test both the sub and satellites at the same time via a receiver I have.
I guess I have to connect the other two RCA plugs to a receiver's outputs? The inputs on the subwoofer are labelled Front left and Rear Left.


What about the RCA jack labelled "subwoofer" on the receiver. Is that already amplified or at line-level? Does it contain some kind of crossover/filter? I want to know if I can connect it to the input on the Sub instead of the passive preamp.

[David_AVD]

For the remote on/off, how did think it would turn off if only a voltage pulse was required to turn it on?

Your sub was designed to be part of a system so the filtering is done before it gets to it.

Those PRE OUT RCA connections on the receiver are line level outputs .

[Hogwild]

For the remote on/off, how did think it would turn off if only a voltage pulse was required to turn it on?

Your sub was designed to be part of a system so the filtering is done before it gets to it.

Those PRE OUT RCA connections on the receiver are line level outputs .

I don't understand the first question.

Then you wrote:
"Your sub was designed to be part of a system so the filtering is done before it gets to it." So that's a "yes", the receiver will do the filtering? If so, I wasn't aware receivers had what basically amounts to active crossovers built-in.

[David_AVD]

As you found, the remote trigger needs to be held asserted (voltage applied) for the sub to stay on.

Yes, the receiver does all of the filtering via the DSP. You can go into the menus and tell it what the crossover point is and it will do the high pass (for the main speakers) and low pass (for the sub) for you. If it doesn't specifically have that option, it may have simple selections such as FRONT SPEAKERS: LARGE / SMALL and SUBWOOFER: YES / NO. It uses that info to decide what filtering (if any) to apply to the respective outputs.

[Hogwild]

Okay, I'm stuck. I can't get the sub to play music again, and I never got the satellites to play when connected to the sub/amp. I know that the satellite speakers work, since they play fine when connected to my Gainclone.

When I connect the outputs from my preamp to the subwoofer, I don't get any sound. This is puzzling since there was output on the woofer previously.
That signal chain is:
 
CD Player-->Passive Preamp-->Nakamichi sub/amp.

Now, I'm using a passive pre, so...are the Nakamichi amp boards expecting/needing higher voltage inputs than what my setup is using to be able to play? I'm way out of my depth here.

The receiver I was trying to use isn't working either, so it's out of the picture.

[David_AVD]

You'll need to find a schematic for the sub / amplifier unit or reverse engineer how the control input works.

Without knowing what signal(s) it's expecting you're just stabbing in the dark.

[Hogwild]

I have zero skills that would help me to do that. Does anyone know where I might find more detailed specs?

The only schematics I've found on the Internet are for the whole kit, and cost more than $USD 30.00.

[Hogwild]

I can't confirm this yet, but this post suggests sensitivity is 200mV

https://www.highperformancestereo.com/preamplifiers-surround/nakamichi-soundspace-12-new-old-stock.html

If correct, what does that mean in my situation?

[Hogwild]

No one? Really?

I assume that means I'd need an active preamp or source device with higher output than just my passive pre?

[themadhippy]

200mv aint much,you should hear something from most sources,even touching the input with your finger should get you a hum out the speakers.

[Hogwild]

Hmm..well, I just got a copy of the service manual for the MK II version (I have the original). So I don't know if it's the same.

That MKII manual states:
Input sensitivity (at rated power)
Front, rear, center speakers..........850mV +-2dB
Subwoofer................................1100mV +-2dB

So, would I need a preamp to be able to get output?

It's driving me crazy trying to figure out how I got output previously but can't get it now just using the same equipment as I did earlier.

[Phil1977]

As already said, touch the signal line with your finger while the 9V-switching voltage is present.

If the woofer and its amp are active, you should hear some noise and hum coming from the speaker. Then you have to search for the error at the pre-amp.

If you hear absolutely no noise, then the woofer is still off for any reason.

[Hogwild]

Even with the new sensitivity numbers I just posted?

I tried that, with my fingers. It did nothing.

[Phil1977]

Yes if the sub has its own amplifier, then you should hear at least a little noise when touching the signal wire.

You mostly even hear a little bit of white noise if the amp is just on and you have your ear near to the membrane - without touching any wire.

Did you check polarity of the switch-on voltage?