Can you help an old man wrap head around FX loop on JVM?

Discussion in 'Marshall Amps' started by lovehifi, Nov 15, 2019.

  1. lovehifi

    lovehifi Active Member

    Joined:
    Jun 4, 2014
    Messages:
    197
    Likes Received:
    141
    Trying to understand something and I guess my old brain is having a hard time understanding. I know what my ears tell me. Anyway I am running a Helix through my JVM205c using the 4 cable method. Just like I have been doing on my Freidman BE50. Here is what throws me off. Actually two things. There is a FX loop switch on the front of my amp and even when I have it off I can still here my effects on my Helix. Just running reverb, a delay, OD, Dyn Com. When I engage the switch on front things sound almost too compressed. I have tried adjusting the FX knob on the back of the amp but to me the FX switch off still sounds more open and musical. What am I missing or am I missing something? I just want it all hooked up and running the way it should and I can go from there. Any thoughts or help? Please in layman terms.
     
    Mitchell Pearrow likes this.
  2. G the wildman

    G the wildman Well-Known Member

    Joined:
    Feb 7, 2016
    Messages:
    504
    Likes Received:
    531
    Location:
    London UK
    Are you in the fx loop?

    Have you tried the parallel inputs?
     
    lovehifi likes this.
  3. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    1,418
    Likes Received:
    1,583
    Location:
    England
    The SERIAL/PARALLEL loop is the one on the right (for 205c). That is the one you should be using with a multi-effects in 4CM.
    Not sure about loop level button (-10dB setting I think from looking at the manual).
    The mix knob on the back should mix between dry (straight pass thru of the dry signal from preamp to power amp), and wet (signal processed by effects in the loop).
    The mix knob only affects the wet/dry mix of the serial/parallel loop
    Fully dry: you should hear none of the effects used in the loop.
    Fully wet: you should only hear the effected signal and get no phasing interference from the dry signal.
    The FX loop button on the front only switches the serial/parallel loop on/off.
    The other "POWER AMP INSERT / SERIAL" loop is a mystery to me! But it is non-programmable, and can be disabled with the bypass/active button next to it.

    This is how it should operate.

    BTW I do not have this amp, only access to the manual, and what I have gleaned from forum threads.
     
    lovehifi and Mitchell Pearrow like this.
  4. MonstersOfTheMidway

    MonstersOfTheMidway Well-Known Member

    Joined:
    May 1, 2008
    Messages:
    4,907
    Likes Received:
    2,423
    Hello.

    First, I have a recommendation for you: take the Helix out of four-cable method and connect it straight through into the JVM's "SERIAL/PARALLEL FX LOOP." Second, turn off the "OD" and "Dyn Com" in the Helix (you can keep using the reverb and delay from the Helix if you wish). Third, on the JVM set the "mix" control to "wet" and the "FX LEVEL" switch pushed in to the -10dBV setting. Fourth, adjust your Helix levels to your satisfaction. Does the sound improve?

    The JVM has two loop, so I'm not sure which one you connected the Helix because your post above doesn't say for certain. Second, I ask you to take the Helix out of four cable method in order to make sure that there's nothing wrong with the Helix or the JVM; if the sound improves, then you can be certain that both JVM and Helix are in good working condition.

    If the sound has improved, then perhaps the problem was that either you were connected to the wrong loop, the JVM "mix" control was not set properly, the JVM "FX LEVEL" was not set correctly. Also, check the cable routing of your four-cable method connection to make sure the signal is going to the connection ports on both the JVM and the Helix (I've used four-cable method before and it can be a little challenging sometimes).

    You can try reconnecting the Helix to the JVM with four-cable method and see if the sound quality improves. One thing you have to remember is that the Friedman BE50 uses a serial effects loop, which is different from the JVM's "SERIAL/PARALLEL FX LOOP." You can download a free copy of the JVM owner's manual/handbook from Marshall's website so you can learn more about what makes a serial/parallel fx loop unique.

    Good luck with your gear. Let us know how things progress.
     
  5. lovehifi

    lovehifi Active Member

    Joined:
    Jun 4, 2014
    Messages:
    197
    Likes Received:
    141
    Thanks guys. Big help. Sure enough I was plugged in to the wrong loop. I was hooked through the Power amp insert loop. Sounded pretty good though with the front FX button disengaged. However thanks to you guys I now have it hooked through the proper send and return. Do not know how I missed them. I adjusted the Wet/Dry knob to what sounded best to me which right now is about 80 percent. I also made sure the sure the -10db setting. Everything sounds right on the mark now and yes the front FX loop switch works as it should. I really appreciate the help. Glad I did not blow anything up. lol Oh and have downloaded the manual.
     
    Last edited: Nov 15, 2019
  6. RickyLee

    RickyLee Well-Known Member VIP Member

    Joined:
    May 22, 2010
    Messages:
    9,645
    Likes Received:
    3,127
    Location:
    Riverside CA U.S.A.
    Yeah, be careful with that JVM insert on the back. That one there puts out a massive 4VAC of audio signal with me playing my guitar on bridge humbucker! You could fry some FX gear in that insert loop for sure.
     
    Mitchell Pearrow and tce63 like this.
  7. Jethro Rocker

    Jethro Rocker Well-Known Member Premium Member

    Joined:
    Mar 11, 2011
    Messages:
    7,349
    Likes Received:
    7,646
    Location:
    Saskatoon, Canada
    So what is the insert in out for if not fx? I've never used mine
     
    tce63 likes this.
  8. SkyMonkey

    SkyMonkey Well-Known Member

    Joined:
    Oct 28, 2018
    Messages:
    1,418
    Likes Received:
    1,583
    Location:
    England
    As far as I can tell most people who do use it, use it either as a send-only to a different power amp, or to power the preamp of a different amplifier by the return jack.
    The voltages may make use in this way more akin to the internal voltages of the preamp/power amp connection after the S/P loop.
    Does the S/P loop step down the signal voltage for use with instrument level effects?
    If so that may explain the +4dBu/-10dBV switch.
    +4dBu for line level (with more headroom) and -10dBV for instrument level with less headroom.

    Just a guess!
     
  9. RickyLee

    RickyLee Well-Known Member VIP Member

    Joined:
    May 22, 2010
    Messages:
    9,645
    Likes Received:
    3,127
    Location:
    Riverside CA U.S.A.
    As SkyMonkey mentioned, that insert loop would be for connection to other amps. Obviously, if you wanted to connect two JVM's, that would be a good place to do it. I am not too familiar with external power amps signal levels, but you could run the JVM preamp into an external power amp from that insert point I would think.

    I will try to remember to take another reading, but I do not remember my level on the master volumes when I did that. I just remember that I was tinkering with a few delay pedals and having some issues with the S/P loop and took some voltage signal level readings on all the inserts.

    I would think you could compensate that high level by turning the individual channel volumes quite low.
     
    Mitchell Pearrow likes this.

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice