Any easy way for newbie to trigger 12V on subwoofer without receiver? - Page 1
Forum section: electronics / beginners

author: Hogwild
author_rank: Regular Contributor
timestamp: July 01, 2024, 08:41:18 pm
content: 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

author: themadhippy
author_rank: Super Contributor
timestamp: July 01, 2024, 08:51:29 pm
content: try shoving 12v up the trigger line,a 9v battery might even be enough

author: Hogwild
author_rank: Regular Contributor
timestamp: July 02, 2024, 05:19:35 pm
content: 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?

author: SteveThackery
author_rank: Super Contributor
timestamp: July 02, 2024, 08:06:45 pm
content: Quote from: Hogwild on July 02, 2024, 05:19:35 pmWhy 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 02, 2024, 10:44:57 pm
content: My reason for believing it had to be current limited was here:https://sound-au.com/project156.htm

author: David_AVD
author_rank: Super Contributor
timestamp: July 02, 2024, 11:29:20 pm
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 03, 2024, 12:08:27 am
content: 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.

author: David_AVD
author_rank: Super Contributor
timestamp: July 03, 2024, 12:32:10 am
content: 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.

author: boB
author_rank: Frequent Contributor
timestamp: July 03, 2024, 01:44:43 am
content: 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

author: oPossum
author_rank: Super Contributor
timestamp: July 03, 2024, 02:09:10 am
content: .

author: SteveThackery
author_rank: Super Contributor
timestamp: July 04, 2024, 10:14:19 am
content: Quote from: Hogwild on July 02, 2024, 10:44:57 pmYes, 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 05, 2024, 09:28:19 pm
content: 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.

author: David_AVD
author_rank: Super Contributor
timestamp: July 05, 2024, 11:07:16 pm
content: 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 .

author: Hogwild
author_rank: Regular Contributor
timestamp: July 05, 2024, 11:23:53 pm
content: Quote from: David_AVD on July 05, 2024, 11:07:16 pmI 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.

author: David_AVD
author_rank: Super Contributor
timestamp: July 05, 2024, 11:33:58 pm
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 14, 2024, 08:17:52 pm
content: 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.

author: David_AVD
author_rank: Super Contributor
timestamp: July 14, 2024, 08:48:46 pm
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 14, 2024, 09:25:46 pm
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 15, 2024, 04:04:40 pm
content: I can't confirm this yet, but this post suggests sensitivity is 200mVhttps://www.highperformancestereo.com/preamplifiers-surround/nakamichi-soundspace-12-new-old-stock.htmlIf correct, what does that mean in my situation?

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 01:17:31 am
content: No one? Really?I assume that means I'd need an active preamp or source device with higher output than just my passive pre?

author: themadhippy
author_rank: Super Contributor
timestamp: July 17, 2024, 01:31:56 am
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 07:20:38 pm
content: 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 +-2dBSubwoofer................................1100mV +-2dBSo, 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.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 07:42:41 pm
content: 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.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 07:49:30 pm
content: Even with the new sensitivity numbers I just posted?I tried that, with my fingers. It did nothing.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 07:56:05 pm
content: 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?

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 08:06:58 pm
content: Polarity of the switch-on voltage?Assume I know nothing. Would you please explain?

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 08:22:30 pm
content: Just the orientation of the 9V-block. Which pole you connected with which contact on the woofer?

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 08:32:14 pm
content: 9v-block? I have no idea what that is.Pole? I don't understand how poles apply here or what you mean.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 17, 2024, 08:51:56 pm
content: Sorry for my English, in Germany we usually call 9V-batteries "9V-blocks". And with "pole" I meant terminal.Both are "false friends" - for me it reads like correct terminology, but it seems it isn't

author: Hogwild
author_rank: Regular Contributor
timestamp: July 17, 2024, 08:58:01 pm
content: Oh. Thanks for that. Yes, double-checked that I was using proper polarity. And I heard a relay click each time I applied the power to that jack.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 06:08:03 pm
content: My 9V battery reads about 8V on a DMM. But I assume if I heard a click, then the relay was opened? It's either fully on or fully off, right?

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 18, 2024, 06:31:07 pm
content: Mostly yes but not necessarily.Do you have a power meter? Can you check the power consumption of the subwoofer?I´m quite sure it´s not active. Even if the input sensitivity is quite low, you definitely shoud hear a low signal if you connect any low level source.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 06:42:10 pm
content: Well, considering Nakamichi's documentation basically says it's active...I have a Kill-A-Watt. Would that do the job?

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 18, 2024, 07:00:59 pm
content: What kind of documentation do you have?Yes, a killawatt should show you a different power reading when the relais is on or off. If it´s the same the relais is probably not switching or some fuse is blown.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 07:03:55 pm
content: I'll try it. I have the schematic for all the modules but the amp/subwoofer. For some reason, I can't find those on the Web, except for a couple people who are selling them for between $USD 30.00 and 50.00. I'm not willing to pay that in this particular case.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 07:32:15 pm
content: I only connected it for a few seconds, but no change on the Kill-A-Watt. Measured 0.

author: Phil1977
author_rank: Frequent Contributor
timestamp: July 18, 2024, 07:58:08 pm
content: Then you have to open it and look for blown fuses and caps...

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 08:12:20 pm
content: I'll take a look at it.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 10:04:14 pm
content: I opened it up, but I can't seem to find a fuse at all, and no bad caps that I can see. Maybe I'm missing it.Attached, are a few photos.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 10:10:36 pm
content: Here's a couple more photos. I took all these photos before thinking that I really should've been focussing on the caps. I'll take another look at all the caps and photograph anything that looks suspect.

author: Hogwild
author_rank: Regular Contributor
timestamp: July 18, 2024, 11:43:12 pm
content: I just briefly checked continuity from the AC inlet to the inputs on the Power supply. The meter beeped, but sometimes it took a bit of moving the probes around. And the solder joints are pretty cold-looking. Is it worth it for me to try to reflow the solder on those joints, or is continuity usually a bit fussy to test for on solder joints?