Mark IV FX-Loop... Huh?

Ok, well I posted this a while back on Harmony Central cause I couldn't figure out how the hell to use the FX-Loop on my Mark IV and I just ended up giving up. However, now I want to use my Delay, Reverb and Noise Suppressor in the loop because (the first two) sound like crap distorted in front of the amp and I've been playing a lot more lower-gain stuff that they could be useful on.

I've used the FX-Loop on many amps and I just can't figure out why this one won't work.

When I try it through the footswitchable loop, it does absolutely nothing. When I try it through the normal loop, it cuts my volume DRAMATICALLY to which I had it loud enough to play with my band to where it was slightly louder than headphones at full volume on a CD player, etc, yet still, no effect can be heard. And yes, I'm using the send from the Mark IV, into my pedal, then the output from the pedal, into the fx return.

There's nothing wrong with the cables either as they work fine running the pedals in front of the amp. I also tried switching out the V2 (used for FX Return) as well as all the others in the preamp and that didn't work either. The owner before me used to run a G-Major through it, I don't understand how it can work for him fine, but not for me.

I just can't figure it out, wtf am I doing wrong?

(I have a '92 Rev A version if that helps)

Try just a patch cable in the loops and see if anything changes. I assume that you know about the switch on the rear of the amp to select which loop that you are using. Then there are the Effects Send levels that are controlled by the individual channel master volumes. Give it a shot, it won't cost a dime.

Make sure your not plugging into two sends or two returns or have the send and return backwards. I've done that before by accident while rushing to setup. Also, check the channel select switches for the loop too. Both of the rockers should be in the middle position for the loop to be on for all three channels. Also check that the Loop LED is lit up on the front panel when the footswitch is on.

JOEY B. said:

Try just a patch cable in the loops and see if anything changes. I assume that you know about the switch on the rear of the amp to select which loop that you are using. Then there are the Effects Send levels that are controlled by the individual channel master volumes. Give it a shot, it won't cost a dime.

Click to expand...

I hadn't thought of that before, I'll give it a shot tomorrow.

mr_fender said:

Make sure your not plugging into two sends or two returns or have the send and return backwards. I've done that before by accident while rushing to setup. Also, check the channel select switches for the loop too. Both of the rockers should be in the middle position for the loop to be on for all three channels. Also check that the Loop LED is lit up on the front panel when the footswitch is on.

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I've actually tried it all possible ways you could wire it just incase, (you never know ) and nothing seemed to work.

Well I tried just plugging a patch cable from the send to return to see if anything happens, no effect seems to happen from that, no volume cut or anything. It seems with my delay pedal, it cuts the least ammount of volume, but it doesn't really matter cause there's still no effect coming through.

MatrixClaw said:

Well I tried just plugging a patch cable from the send to return to see if anything happens, no effect seems to happen from that, no volume cut or anything. It seems with my delay pedal, it cuts the least ammount of volume, but it doesn't really matter cause there's still no effect coming through.

Click to expand...

List all of your settings on the MkIV, front and rear panels. If you used a patch cord in both the normal and switchable loops with no adverse effects on volume noticed, it sounds like an input signal strength issue at your effects chain.

JOEY B. said:

List all of your settings on the MkIV, front and rear panels. If you used a patch cord in both the normal and switchable loops with no adverse effects on volume noticed, it sounds like an input signal strength issue at your effects chain.

Click to expand...

Lead:
Gain: 8/Pulled
Highs: 6.5
Bass: 4
Mids: 5
Drive: 8
Presence: 6
Master: 3

R1:
Gain: 4
Highs: 7
Bass: 3
Mids: 4.5
Presence: 6
Master: 7

R2:
Gain: 9
Highs: 7.5
Bass: 3
Mids: 4.5
Presence: 3.5/Pulled
Master: 4

Triode
Simul-Class
Harmonics

MatrixClaw said:

JOEY B. said:

List all of your settings on the MkIV, front and rear panels. If you used a patch cord in both the normal and switchable loops with no adverse effects on volume noticed, it sounds like an input signal strength issue at your effects chain.

Click to expand...

Lead:
Gain: 8/Pulled
Highs: 6.5
Bass: 4
Mids: 5
Drive: 8
Presence: 6
Master: 3

R1:
Gain: 4
Highs: 7
Bass: 3
Mids: 4.5
Presence: 6
Master: 7

R2:
Gain: 9
Highs: 7.5
Bass: 3
Mids: 4.5
Presence: 3.5/Pulled
Master: 4

Triode
Simul-Class
Harmonics

Click to expand...

Nothing too strange there. It could be your noise suppressor cutting off the decay of the reverb or the repeats of your delay. Try the noise gate out front with the reverb and delay in the loop. If there are any input level controls on your reverb or delay, turn them up. Try turning off the noise gate and see if your effects come through stronger.

JOEY B. said:

Nothing too strange there. It could be your noise suppressor cutting off the decay of the reverb or the repeats of your delay. Try the noise gate out front with the reverb and delay in the loop. If there are any input level controls on your reverb or delay, turn them up. Try turning off the noise gate and see if your effects come through stronger.

Click to expand...

I've actually been running each by themselves in the loop with nothing out front but a Maxon OD-808. I use an EHX Holy Grail for reverb and a Boss DD-6 for delay (not the greatest, but I don't use it much anyway), the only one that has a level is the Boss. I've always found my ISP Decimator does more in front of the amp anyway, but I just wanted to make sure with the Mesa, especially since it doesn't seem to get as much feedback as my 5150 did and the problem seems to be more of a hum when idoling than anything so I figured I could get rid of it by putting it through the loop instead.

Any ideas before I take it to a tech?

MatrixClaw said:

Any ideas before I take it to a tech?

Click to expand...

I was hoping that using a patch cord in the normal loop would flush out any problems within the amps' circuits. The switchable loop uses LDR's which can sometimes fail. But after thinking about it, a faulty FX Return jack might cause some of the problems that you are having. Good luck man.

I just want to add to this 11-year-old thread, in case there are other people troubleshooting the mark iv FX loop. For me, the suggestion to just use a patch cable, from the FX’ send to return, confirmed that there was nothing wrong with my effects loop. In my case, I had a few issues: a bad Send cable, settings on a delay pedal in the loop that caused silence, and old preamp 12AX7 tubes. Changing the tubes cleared up the volume discrepancy issues I had with loop on and off— and, unrelated to the loop, low volume in channel 1. The fx loop is now transparent.The amp sounds better than ever! FYI, the tube that works with the fx loop send is V2.