I dont think the mark v fx loop is fully serial.

[diddlydan]

Was trying out my mates mark v earlier (sounds amazing) and i tested the loop.Im pretty sure its not fully serial.A small bit of signal leaks through on all channels.I tested it with a tuner.When i put the tuner between the guitar and amp and engaged it there was no sound.When i put the tuner between the fx loop send and return and engaged it a small amount of signal was leaking through.This makes digital pedals pretty much unusable in the loop as there will be slight phasing.Anybody else notice this?Its a small issue that wont turn me off picking one up as I have no intention of using delay etc on the gain channels.Ill use those mostly for rhythm as i use a fuzz for solos, so delay etc in the front end will be fine.Still though its a bit of a disappointment.This happen on anybody else v?

 

[SteveO]

It's a serial loop, but there is a very small amount of bleed that passes some dry signal through.

 

[barryswanson]

Digital anything with an analogue amp should be banned.

 

[bandit2013]

Digital delay is awesome in the FX loop. All depends on what you have I guess.

I have had issues with the Fx loop since I barely ever use it. When I did recently ( few months ago) it did not work. Had clean the rotary switch (with amp on and active rotate the FX selector knob, movement of the contactor with current cleans better than just the wiping action of the contactor). If you plug in two cable ends into the FX loop, there will be some residual signal if the loop is an open circuit. it will not be much or barely noticeable. You need to use both jacks. However, the send jack could probably double as a send to other (perhaps an other amp) if you leave the retrun jack unused. The Return jack has the built in disconnect but the Send Jack does not.

 

[LesPaul70]

I made the same observation a long time ago and (incorrectly) thought, because of the bleed, that it was a parallel loop and not a serial one to begin with. Whenever there was anything at all in the loop, the fx return sound would be slightly out of phase with the uneffected (bleed) sound. Heck, you would get that ugly out-of-phase quack even when you had nothing but a patch cable in the loop. It didn't matter whether your effects pedals were digital or analog, boutique-made or chinese plastic.

However.

At least on my V, the bleed is really audible only when your overall volume is very low (think bedroom volume). At band volume I never hear it. So try raising the master volume and you can no longer hear the bleed. Nor the out-of-phase quack. Works for me at least.

 

[dino2sf]

I put a Radial Big Shot Mix pedal at the end my loop chain. Im only using it only for its phase 180 degree switch. Seems to take care of the out of phase problem. Loop sounds killer!

 

[bandit2013]

I can offer 2 cents.
The phase shift will be there as long as the FX loop is set to active. What causes the phase shift is V6 and is nothing more than an inversion of the signal and should not be noticeable unless you are playing though a parallel amp that creates the signal 180 out of phase of the Mark V. If you are having issues with the FX loop, try cycling the FX loop selector control on the back of the amp. I previously had an issue that prevented use of a delay in the loop as well as caused similar characteristics most of you described. the delay went into full loop back mode as if the input was connected to the output. Changing the FX loop selector control on the back of the amp several times corrected the issue.

 

[Ytsejammer777]

See this thread:

http://forum.grailtone.com/viewtopic.php?f=33&t=48502

 

[bandit2013]

Like others, I too have the schematics. However, I do understand there is some details missing that are proprietary. The complete relay switching network is missing, logic for channel selection, etc... Due to the nature of the small signal relays used, if the amplitude of the signal is beyond its isolation rating for cross-talk interference, it may be the source for the issue. The small gap on the relay effectively creates a small capacitance. This parasitic capacitance is enough to pass a weak signal across the hard by-pass connection. Since two relays used to isolate the signal path though V6, increasing the master output from each channel will allow for more of the signal to couple thought the associated capacitance of the contacts. I would not doubt that there is also some mutual inductance contributing to the issue. It could also be caused by a ground loop or layout of the PCB that may have considerable stray capacitance or mutual inductance between traces that may be the cause. Doubtful since the signal is in the low frequency range, however the amplitude of the DC supply in relation to the signal level may be a factor. I may buy the parasitic capacitance of the relay contacts first since that is the only part of the circuit that would bypass the V6B triode.

 

[bandit2013]

Just for kick, I wanted to hear for myself what the big deal is.. Figured I would try it with the RA100. That made a really strange sound. I should have turned off the reverb. Most of the signal was passing though the reverb circuit.
Second in line was the Mark V. Sure it is there but does not seem to be cause for why some effects work and some do not. I tried it with reverb and without which did not make any difference. Third in line was the Roadster. That does it too but not as loud as the Mark V (RA100 was loudest due to reverb circuit but does not effect performance of effects I have used in the loop). Having two signal cables going no where resulted in audible hum that was louder than the bleed over signal. I have not tried the Mark IV (uses Varactors compared to JFET and Relays, there are a few relays but they are much larger than the small signal relays and probably have a larger contact gap). I do recall having something similar with that amp long a go when I left the pedal that I wanted to use at the time plugged in and the battery was dead). The effects loop is serial, but if the impedance in the loop is larger than the leakage path it won't be. Typically if the effect has a hard bypass or is in active mode, the impedance of the effect will be much lower than the leakage signal path.

Some of the old effects I used to use with the Mark IV do not work so well with the Mark V due to signal clipping on the input. Signal may be too hot for most effects that are expecting a lower magnitude (1 Volt or less).

 

[Archlute75]

I've never had a problem with this, and I've been gigging out hard with this amp since last March using both analog and digital pedals in the loop. I kind of think it might be a bedroom player issue? Even then, I've not noticed anything substantial when working in my studio at lower volumes.

Also, some of the stuff you guys come up with... Why would you ever use only the send or return alone in a loop, or plug two cables into the inputs while the outer ends were left dangling? Of course you're going to hear wierd **** :roll:

If you play at volumes for which the amp was meant to be played live or studio recorded, and use the send/return in a proper setup and at properly adjusted levels, I think you're going to be alright.

 

[domct203]

I've never had a problem with this, and I've been gigging out hard with this amp since last March using both analog and digital pedals in the loop. I kind of think it might be a bedroom player issue? Even then, I've not noticed anything substantial when working in my studio at lower volumes.

Also, some of the stuff you guys come up with... Why would you ever use only the send or return alone in a loop, or plug two cables into the inputs while the outer ends were left dangling? Of course you're going to hear wierd sh!t :roll:

If you play at volumes for which the amp was meant to be played live or studio recorded, and use the send/return in a proper setup and at properly adjusted levels, I think you're going to be alright.

+1

I have three Mesa's and do not have any issues with the FX Loop at band volumes when using gear designed for the signal level. My G-Major sounds great in all three FX Loops, I feel the Roadster's loop sounds the best, followed by the MKV. The Stiletto really doesn't get all that much use lately, but IIRC when set to "Kill Dry" the G-Maj was fine there as well.

Dom

 

[4406cuda]

My Flashback Delay sounds great through the loop.