Adding a sub and an amp but the amp doesn't accept balanced inputs. Do I need the LOCB.2 or the LOCPREA?

 

What amp is it? How do you know it won't work with the system? Did you try taping into the amp feed with a set of RCA's?

JH

 

It was a hypothetical question.

I haven't bought the sub or amp yet but I did just win a Soundgate LOCB.2 on ebay for $10 shipped. Odds are it's broken, auction didn't say one way or ethe other, but I wanted to know if it would work incase it's NIB.

 

LOCB.2 is what I used and it works great for me. I tried a regular navone LOC and it had a huge cutoff below 80hz so it doesnt work very well at all for adding a sub. The LOCB2 does appears flat below 80hz on my cheapo o-scope

 

The difference between the 2 are that the locb.2 amplifies the line level inputs, while the locprea is passive and doesn't amplify the signals. The LOCB.2 will require tapping into a +12v source as well, and may cause noise/hiss to be increased in the amp output. I'm not sure what the voltage is on the stock HU, but if its decent like +2V, then I wouldn't amplify the signal using a LOCB.2. I would only amplify it its absolutely necessary such as with a <1V line level output. You may be able to hook the LOCB.2 without the power line, and it'll act like a passive LOC, and see if the gains on the amp can be set to a reasonable level, but if not, then you can try amplifying the signal and seeing if the amp gains can be set at a lower level.

 

the locb2 i received had an adjustable input level controlled by dipswitches. i set mine at one from the lowest possible setting (very little amplification)

 

LOC's are for high level out, why would you hook one into the low level signal coming from the HU? The signal comming from the HU is pretty low voltage, just run it into an amp. But not a signal processor of any kind. All of the amps I have tried worked fine, the crossover and EQ I tried both puked. I'd like to know why that happens.

JH

 

LOCs are for high output to low level true, but they are also for converting balanced differential signals to single ended signals, which is the reason we are using them. When I talk about the line level difference, its from 1V to 4V usually. A good deck has higher level preouts, >4V, some of the better decks go up to +8V etc. Lower end decks have ~2V or lower preouts. Without knowing the output level of the stock deck, its hard to determine if the LOCPREA or the LOCB.2 is the correct device to use. If the stock bose deck is in the range of 2V, then the LOCB.2 isn't needed since it only boosts output to 2.5V. Then the LOCPREA can be used. Higher preamp voltage means the amp gains can be set lower resulting in less distortion. However, boosting the preamp voltage to achieve this is similar to turning the gain up, there isn't a good way to boost the preamp voltage other than using a better deck that already had higher preamp outputs. As far as not needing a LOC at all, many people have reported issues with certain brands of amps that without using a LOC. You are one of the few who have gotten it to work on an amp other than JL Audio amps, so until more people report good results without using them, they are still necessary. I'm going to try it on my alpine amp and see if it works, but not all amps will work without a LOC.

 

What do you mean by puked? They actually died or just sounded horrible? Have you tried to hook them up to another car yet? Most likely the the internals of the EQ aren't grounded against the chassis of the EQ which means it doesn't accept balanced differential inputs which is making it sound jacked up. Try using the LOCPREA with the EQ and seeing if it works, that will tell you if that is the problem.

 

Yea, puked was a little vague eh. They both did the same thing, if you have the volume up to about 25 or higer, the system would start emmiting a loud squelching sound. Not a you're putting too much power into the tweets squelch. It was as though some kind of digital system was injecting noise. It's really odd, but both the clarion eq and MTX x-over did the exact same thing. None of the three amps I have tried have exibited this behavor. The chassis ground idea is intresting. But the eq and x-over were in the trunk using the amp chassis ground.

In a way, I tried your LOC trick. The alpine amp has an RCA pass through, I used that pass through to feed the eq to feed another amp that drove the speakers. The eq and x-over worked correctly in that instance. the eq and xover are fine, they just don't like the Hu signal. It's odd.

JH

 

Sounds like your alpine amp is accepting balanced inputs then, since the signal is fine after the amp. I spoke to David Navone about this, and the reason some amps work without a LOC is the way the circuit board is set up. Some ground the board against the chassis, while others "float" and thus cause sound problems. I'm purchasing an Alpine amp to run my sub, so hopefully it won't require a LOC, since your amp didn't. Do you know the model number of the amp or series so I can see if the one I'm going to purchase has a similar setup?

 

Its just an MRP-F420 that came from Best Buy. I'm currently using it as a 3 ch amp. I think I'm going to pick up another amp this weekend so I'll have a sub amp and a mid-hi amp. I've asked for amps that people know will fail, all I got was some 'MTX' and 'SONY' no model numbers. No solid answers. I may try a SONY just to see how it goes.
JH

 

did you mean f240? I can't find the f420 anywhere. Is it a 2005 model or 2006model? I going to pick up a M450, hopefully they are set up the same so I don't need a LOC