Sub channel not working on Soundstream Rubicon 555

[gti16vman]

Been into car audio for quite some time and always wanted to try some of the higher end car audio stuff like Soundstream, Xtant, and Zapco, but back in the day I couldn't afford these. So when I recently got my new to me truck, I needed a fairly small footprint 5 channel amp to power the speakers I was putting in and a single 10" subwoofer for under the back seat.

The object of my 5 channel amp obsession was a Rubicon 555. Have always wanted one. So I recently found a really nice one on ebay that the previous owner claims he bought new and had it installed in his vehicle until he recently sold it. I got it and immediately verified that the 4 main channels worked, but didn't test the subwoofer channel. I did this because I knew that I wouldn't be able to get around to installing it for a few weeks.

Fast forward, I did the install, which included an OEM Nissan head unit that has mp3 capability going to an Audio Control LC6, which gives me 4 channels of output to the Rubicon. That powers a Kappa component set in the front and some Kappa Perfect 6.5" midbass drivers in the rear. Everything sounded great except for right at startup for a few minutes, I had a high pitched noise coming from the amp. I had purchased some replacement screws from Jaime and JandR electronics and asked him about it. He said to put some caulk on the transformer winding, and sure enough, that fixed it.

Finally, this weekend, I got around to building my enclosure and putting the sub in. Much to my surprise, when I hooked it all up, I have nothing coming out of the sub terminals. I tried everything that I could think of, but no matter what, I got nothing out of the sub output.

I disconnected the rear speakers from the amp and hooked the subwoofer to one of the rear channels and it worked, so I know that the subwoofer is fine. I have double checked all other connections, tried both summed 1-4 and sub inputs. It is in 5ch and local on the bottom switches, and tried the airbass switch in both settings. Have set it up just like the manual states with 4 channel or 6 channel input. Looked over the circuit board for any fried components and didn't see any issues. Am I missing something here? It seems like it is not getting a signal, but I know that it has to be when I move the rear signal over to the sub rca's and the switch is set to rca in for the sub. I am at a loss with this. Any ideas? Thanks in advance.

[jol50]

I'd check stuff before you took the board out. Nice amp, I have two 302s sitting here to try out when I get time. You can power it up with no speakers on it, then see what dc voltage you have to the sub. That could indicate what is going on; if you see maybe <50mv like the rest of the speakers then it may be working and not getting input signal to the sub section. Double check the controls settings again just to make sure.

Looking at this photo I would guess the sub outputs are the ones in the center by all the blue resistors and the six bolts clamp them. (With amp disconnected from anything, meter on ohms) I would check those to the sub terminal to verify (would see <1 ohm), then each for a short. If a short or very low ohms between the legs of any transistor in that group the outputs are blown. If I'm wrong here someone will correct me quickly, I have not worked on one of these just in case it has some strange setup. Usually the right leg of the transistors go through the larger resistor and to the speaker terminal they power. They might all go to + or if bridged half will go to + and half to - for the sub. On the other hand it could be a switch or RCA terminal or something like that.

[gti16vman]

Thanks for the response. Don't know how to explain it, but this morning on the way into work, it started working. This was 5 minutes or so into my drive, when switching from radio to cd. It may have been working the whole time, but radio was a bunch of talk, so not sure if it was working all along or not.

When I hooked it up on Sunday and couldn't get it to work, I decided to just leave it all connected. Must have been something that required a few power cycles to get it out of whatever state it was in. Hopefully it is back on for good now because I love this amp. Definitely the nicest that I have ever had.

[jol50]

That is good news, still might have a bad connection or RCA/etc someplace. I had a rear door speaker die in my car, I could hear only the tweeter in it. Three months later it came on one day.

[1moreamp]

Intermittent switch's, or bad solder on the sub channel driver card. Seen this a few times before. Seems to be a highly repetitive issue also...Good luck, its a simple one once you find it. Jaime can sell you all the parts you might ever need...

[gti16vman]

Thanks for the info. As long as it keeps working, I will leave it be, but if it starts acting up again, I will tear it apart and double check those things.