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Discussion Starter #1
I installed MS-8 to go between factory HU and JL HD900/5. Now I am trying to set gains using DMM the way JL says.

I can't get V readings anywhere near what they recommend. e.g. They say to get fronts to 20.0V. I am in the single digits. The sub is supposed to be 38.7V and I can't get above 11. If I go higher, the amp shuts off.

It's not like it isn't loud, I am just trying to set it "right".

I have tried changing MS-8 to Active, Defeated, Logic 7 on or off.

Any ideas what I am doing wrong?
 

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I installed MS-8 to go between factory HU and JL HD900/5. Now I am trying to set gains using DMM the way JL says.

I can't get V readings anywhere near what they recommend. e.g. They say to get fronts to 20.0V. I am in the single digits. The sub is supposed to be 38.7V and I can't get above 11. If I go higher, the amp shuts off.

It's not like it isn't loud, I am just trying to set it "right".

I have tried changing MS-8 to Active, Defeated, Logic 7 on or off.

Any ideas what I am doing wrong?
Is there a switch on the side to toggle between low level and high level input?

I once had the same problem and basically came to the conclusion that you cant set the gains the way JL wants you to because of the MS-8. This is because theres no way to defeat the auto-eq and therefore setting the gain through MS-8 will just be defeated next time the auto-eq is ran. Best bet is to use an oscilloscope.
 

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Is there a switch on the side to toggle between low level and high level input?

I once had the same problem and basically came to the conclusion that you cant set the gains the way JL wants you to because of the MS-8. This is because theres no way to defeat the auto-eq and therefore setting the gain through MS-8 will just be defeated next time the auto-eq is ran. Best bet is to use an oscilloscope.
that makes no sense. auto eq or not. even if it is eqd poorly and sounds like crap, there is still voltage coming out of the ms8 driving the amplifier. an oscope is still just gonna measure voltage. if it is not there, it is not there.

OP,

are you measuring this with test tones or music?
does the output from the ms8 have an ouput adjustment? can you turn it up?
 

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Discussion Starter #4
I am running test tones. I have used tones on CD and I have used tones from iPhone AudioTools app connected via AUX in port.

My DMM is a Fluke, but it is a tad old. I grabbed a new Fluke from work yesterday that reads "True RMS" and tried it again last night. Same result.

This newer meter even reads Hz. When I run a 1kHz signal, the meter reads the Hz just fine. Other frequencies, no so much.

So, sine wave playing in HU. HU volume at around 3/4. All speakers totally disconnected from amp. MS-8 "volume" set to -5 dB. DMM hooked to + and - of a speaker output on amp. Gains on amp all the way down. Input sensitivities set to LOW. All amp crossover functions off. MS-8 set to Defeat.

All I see is mV levels on fronts or rears running 1kHz. I can get up to 11V on sub when I play a 50Hz tone. If I turn up gains more than around 1/2 a turn, the amp will go in to protection mode and DMM goes to 0V.

So, you would suspect that I am just feeding the speakers with minimal power since that's what the DMM says. Well, I can guarantee you that your ears would disagree. It isn't that it sounds bad, either. I just want to set the gains for real and not just by ear.

I can turn the gains higher playing music than for tones. I guess that makes sense.

I have ordered a DSO Nano Quad. I suppose this will let me see where the HU starts to clip. I am running off speaker level outputs, so I don't know how much a voltage reading here will tell me. But, like minibari says, I should still see the same V coming from the amp.
 

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if you bypass the ms8 entirely what happens? (actually move the RCAs so it is HU-->amp )

I cant believe you can only get 11V out of it. that is only 121 watts at 1 ohm. just a stupid question (dont shoot the messanger ;) ) you do have the dmm set to AC voltage?
 

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Discussion Starter #6
I have not tried to take the MS-8 out of the signal path. I don't have RCA from HU, only speaker level from factory amp. And, my JL Amp doesn't have high level inputs.

JBL says the signal should be "pretty much" straight through. He says that the MS-8 is doing some processing at all times. So, no clear answer here.

Yes, I thought at first I might not be reading AC. But, I am.
 

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you got me stumped, lol
 

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Discussion Starter #8
I have two theories right now:

1. I am doing something totally wrong.

2. Either my HU and or the MS-8 is doing some sort of processing to the sine wave such that it isn't coming through as a single wave and the DMM can't lock on to anything to give me a reading. I have no idea if this is possible or if it is pure nonsense.

If I hook it up to speakers, I hear a single tone.

I guess I have to see what the scope shows me.
 

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most meters will measure AC to at least 1000hz. some several khz. so I dont think that is the case. but yes, the scope will give you must more resolution.
 

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Discussion Starter #11
Well, using DSO Quad, I was able to clearly see Peak to Peak Voltage as well as clipping. I cannot explain why I was unable to measure voltage using DMM. My best guess is that it has something to do with the signal going from the HU, to a factory amp, then to MS-8 high level inputs and then to JL amp. I think the signal just gets a little too fuzzy for a DMM.

As a side note, I learned that the rear channels are clipping way before the fronts. I could only put HU about 1/2 way up on rears and a bit over 3/4 on the front.

I think my solution to this is to go with a PAC LOC. This will give me low level out straight form the HU. The DSO showed me that the signal coming from HU to factory amp was very clean. Hopefully PAC keeps it clean. I have to believe it wil be a better signal than the factory amp. Plus, then the MS-8 can take L/R full range signals and process them instead of having to recombine factory EQd signals.
 

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Well, using DSO Quad, I was able to clearly see Peak to Peak Voltage as well as clipping. I cannot explain why I was unable to measure voltage using DMM. My best guess is that it has something to do with the signal going from the HU, to a factory amp, then to MS-8 high level inputs and then to JL amp. I think the signal just gets a little too fuzzy for a DMM.

As a side note, I learned that the rear channels are clipping way before the fronts. I could only put HU about 1/2 way up on rears and a bit over 3/4 on the front.

I think my solution to this is to go with a PAC LOC. This will give me low level out straight form the HU. The DSO showed me that the signal coming from HU to factory amp was very clean. Hopefully PAC keeps it clean. I have to believe it wil be a better signal than the factory amp. Plus, then the MS-8 can take L/R full range signals and process them instead of having to recombine factory EQd signals.
What vechicle is your set up in?
 
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