Code 100H Effects loop


Tried out the effects loop over the weekend and whether I run one pedal through it, or loads, tried different cables, power supply or battery, the loop adds a high pitched whine to the sound, which makes it pretty unusable.

I'm going to re-try a load of things, again different pedals, batteries and cables, but do Marshall have any suggestions?

Also is there a way to change the level/mix of the effects loop, or is it fixed?

CODE effects EffectsLoop whine

asked 02 Jul 2018 at 07:40 AM

Ian Watts
I have not noticed any sounds on mine. I have hooked up two different ways and both work great. My first hookup is guitar plugged into the 100h head input, then I use a Zoom G5n pedalboard then run my left out to the return on the code head, then run your send out of your amp back into the input where you guitar would plug in on the pedalboard as it does not have return on the pedalboard for some reason. I then set the amp to the Natural preamp as my pedalboard has all kinds of "other" amps. If I want to use only effects on the board I shut off the amp setting on my board and then can change the amp on the 100h head to Marshalls with all the effects off and slowly add what you want. When using the fx loop you must use both the send and return or you will have no signal. The fx loop to my understanding is after the preamp as well. My second hookup I tried is plug your guitar into your board or chain of footpedals and then run that directly into your guitar input on your 100h head. Doing this you will want to turn off the effects on the head or you can tinker with adding them in just keep in mind your effects plugged into the guitar input are outside of the amp so when you add effects on the 100h head you are essentially doubling the effect. Just have to play around a bit to get your sound. If you are using the Marshall Gateway they have the noisegate you can play around with which really does great. I have not found out how to get to it on the actual amp using the knobs and use it in the app only. Lots of folks are talking cheap about this amp but it is the best amp I have come across in the modeling real for the price. I'm also using the 412 Code cab and it sounds great as well. The cables I am using are Monster cables in case you have not tried but you may have done so. Also make sure your plug in is properly grounded as well. i had an old 40watt amp that I used prior to this one and if I plug into one outlet of the house I had a whine, so I plugged it into a different outlet and the whine was gone. I believe the fx loop on the 100h is fixed; however on my pedalboard I can boost and change the effects output on each effect I am using, you should be able to do as well and notice on the amp. - Steve R 02 Jul 2018 at 05:55 PM
Thanks for replying.

I've tried again tonight and its no better. I've tried two different boss pedals, different leads for send and return, different cabs, a 1x12 and a 4x12, different mains leads, different speaker cables and different rooms in the house with different power sockets. For both boss pedals I've used mains and batteries.

My conclusion is that there is a dodgy earth on the effects loop. As soon as the loop is complete, so send to input on the pedal, output on the pedal to return, the hum is really noticeable, when you engage the effects pedal, like a phaser its really obvious there's an effect. This doesn't happen in you go guitar, pedal input on the from of the amp.

Headphones are no use as they cut the effects loops off as well as the speaker. Looks like I'll be taking this one back to where I bought it from. I tested it for quite a while before I bought it but didn't think about trying the effects loop. Hopefully it's just a bad one in the batch, but if I try another one and it's the same, then it's bye bye Marshall. Which will be a shame as I've been using Marshall amps for a good 20 years.
- Ian Watts 03 Jul 2018 at 08:27 PM
Answers: 1


Sounds like impedence mismatch.  Heard great things about this but have not used.  I think Sweetwater may sell them.  Still a great amp but sucks your loop is bad.

answered 03 Jul 2018 at 10:32 PM

Steve R (12)
Taking it back to the shop on Saturday and going to try another one. - Ian Watts 04 Jul 2018 at 08:23 PM
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