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Fx Loop's +4b Or -10db?


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Hello all,


I still can't quite wrap my head around the FX Loop +4db or -10db settings on my amp. I'm larely using my HD's modellers, bypassing my amp's preamp. I have my HD set on Line and connected via the FX Return as recommended by meambobbo's guide.


My question is, which setting should I have it on for my amp? +4db or -10db? Also, what's the explanation for it? Lastly, anybody know what's the difference between a series and a parellel FX Return on the Marshall JVM210H?


Thanks for reading!

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FX Loop +4db or -10db settings:


Audio equipment has these two as "standards" for how big a signal can be +4db = Line and -10db = Instrument level.


If you have a switch you set it to whatever the equipment on the other end of the cable is using, if both have switches then go for the higher level on both.


But as with most such "standards" there is a wide variation in what specific gear can output or receive and they often don't match.  The only thing you can do is experiment with the settings until you find one where it doesn't overload when you want clean sounds.  The HD500 has Line and Instrument settings that match the +4 and -10 settings on the JVM so both are adjustable.


Series FX Loops interrupt the main signal so that the FX Return is all that goes to the power amp, Parallel FX loops pass the primary signal though and you want the FX return signal to contain only effects without the original signal.  For using the HD500 you want to be using Series which is 100$ wet on the amp.


This link might help you:

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Thanks for that reply, really helped understand those two terms better. What do you mean by it affecting the clean tone? How do I know if it's good or bad?


Anyway, I was always under this impression that +4db are usually for stomp boxes while the -10db's for racks much like the HD.


What about the 'Line' and 'Stomp' settings on the HD? Does it follow the same rationale in which Line equals -10db while +4db's for Stomp?



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It is my understanding that both levels are line level.  +4dB is the professional standard for line level and -10dB is the consumer standard for line level.  This is with 0dB  being 1 Volt.  This also references a balanced or unbalanced cable.  If the same signal is sent down a balanced cable and and an unbalanced cable, the level at the balanced cable's end will be hotter than the unbalanced cable's end (if they're wired properly).   This gets back to the professional vs consumer level.  Professional equipment generally uses balanced cables and Consumer equipment generally uses unbalanced cables for the same signal. This explanation, by the way, is a MAJOR over simplification. 


There is no real standard for instrument level. A piezo pickup puts out more power than a guitar pickup and an active pickup even more.  It's basically somewhere between mic level and line level and varies between instruments.  The other part that adds to all the confusion is dB is actually a relative reference.  It can mean anything depending on what 0dB is determined to be.  It's why I referenced the 0dB being 1 volt.  One thing for sure.  Whatever the line level is, it is stronger than instrument level, so to say line level is -10dB and instrument level is +4dB is just wrong.

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