Oscilatting Feedback Fx loop Delay

sumpe

Member
Messages
372
I got a mesa boggie rocket amp with parallel Fx loop.
After long hours trying to set the Mix (10 to '100%' wet) of the parallel loop, changing the delay pedal on boss me70 in front of and behind the amp, changing output levels on both the master output and eq output (using the EQ) on the bos me70 I STILL GET OSCILATTING FEEDBACK when running delay or delay with modulation (phaser, tremolo, etc).

I don't know if this can be fixed. My set up is: OD > Fuzz > amp > Parallel FX loop > send and return to boss me70.

I also tried with boss me70 in front of the amp - I read a post from years ago offering options such as modifyng the amp into a series FX loop (which it seems would be a permanent solution though I am not sure) or trying diffrent delay pedals.

Here is the issue: I need a 'real solution' for this because I ultimately want to run multiple delays and infinite delays with reverb on the Fx loopo. AND and I want the nice tone of my amp to remain AND trails on effects - is this wanting too much? PS: I do not want to part with the amp because of its tone and sheer volume power.

The only thing that I can do now is set delay level to the express pedal on the boss me70, and by taming it i can control the oscillation, but seriously if feels like the amp will explode if i don't do that - scary - especially since i want to focus on playing not making sure the amp explodes
icon_neutral.gif


Given the predicament of wanting to maintain amp tone, anyone that found a true solution to this (by the way I am by no means an amp technitian, but can contact one to see if they can do said solutions you present)

thank you very much.
 

Adsy

Member
Messages
145
If are you are using amps drive you will want to use the loop . Loop mod would be the easiest and cheapest solution if your happy with multi-fx. I have a 2007 dual recto with the same loop. I use everything up front and run overdrives before chorus,term,delay and reverb through the clean channel as the loop has some suck to it.
FWIW delays that work in the loop are DD -20, Echo Puss and Alter ego v 1
 

sumpe

Member
Messages
372
cheers and thanks Adsy.
Loop does suck some tone but not much if I keep the mix to 30% or thereabouts.
Issue is I use the amp drive for high gain! i do not want to run everything in front of the amp - the high gain sounds is 1/2 the reason I got the amp in the first place

would you know what the loop modification would mean sound wise? if i got it all as series instead of parallel, would that suck tone? would i still be able to keep OD, fuzz etc in the front and use the high gain sounds of the amp BEFORE running modulation, reverb and delay??
 

sumpe

Member
Messages
372
Yes even at 100% wet. However, I would run the 'mix' in the amp at 30%, but can run it at 100% as well and the same problem happens
 

rumbletone

Silver Supporting Member
Messages
8,034
I have no idea why it would oscillate unless (i) the feedback is set too high on the delay (even if it doesn't oscillate out front with the same settings, it may in the loop due to the hotter level), or (ii) it's plugged in backwards in the loop (i.e., the out of the delay is plugged into the send of the fx loop). Modding the loop to serial (which should be easy - may be as simple as disconnecting one wire) shouldn't be necessary to fix the problem you're having.

Have you tried a different delay in the loop (just for troubleshooting purposes)?
 

sumpe

Member
Messages
372
thanks rumbletone. i was maxing out on output and feedback level yes.
interestingly, when putting it in front of the amp, i also got oscillation when cranking the settings with two delays running at the same time though much more difficult to achieve this. i think the feedback artifact is massive on that amp. the delay is not be in the wrong order as it is coming from the bossme70 which i connected - send of Fx loop into Input and return of amp into Output of boss me70.
i have yet to try other delay pedals with the amp.
my concern is i want to play ambient stuff/post-rock and metal...

a) would the serial loop modification alter the tone of my amp if I put pedals on the loop (compared to parallel where I can set the mix of signal from 10% to 100%, thus controlling the amount of mix of the pure amp signal with the pedal)?
b) also i read somethig about attenuators for the amp (i.e. the Express mesa boogie series explaining one needs one - but I am not finding luck in understanding what I need to do and whether this is easy to set up (quotation from Mesa Boogie Express Manual)

" The Express incorporates an internal EFFECTS LOOP to handle the interfacing of outboard processing. This circuit is a patch point between the preamp and the power section and it is wired in series with the dry (un-affected) signal. Since this loop is a series-type loop (as opposed to parallel - where the loop signal runs alongside the dry signal) it is important that you use good quality processors “in the middle” of your amp....
NOTE: The EFFECTS LOOP is optimized for professional quality rack mount processors. Most pedal type effects work better in the“front-end” between your instrument and the INPUT. You will experience some tonal changes because of the additional cable and the fact that your instrument will no longer be going straight into the grid of the first tube. It’s up to you to decide if the trade off is acceptable."
 

sumpe

Member
Messages
372
Bump. I am trying to figure this out still and it is giving me lots of trouble.

I am considering the series modification to the amp effects loop but am worried this may in the end not solve my problem whatsoever. So any more input is much appreciated!

I am putting down my set up to see if it helps - maybe something on my chain can help resolve this
option a) guitar > tuner (TC polytune) > JOYO vintage overdrive > Bigg Muff > mesa rocket44 amp input > effects loop (parallel) send into boss me70 input > ditto loop station > return of effects loop.

I am trying to run the mix for the effects loop around 30-40%. The boss me70 is at maxed output, as I am

Ultimately I want to have the following on the effects loop: 1 to 2 delay pedals, 1 to 2 reverb pedals and modulation (phaser, chorus, tremolo, octave - maybe in a mutimodulation unit like Strymon Mobius)

Delay pedals I am considering: Nemesis, TC Triple Flashback Delay and Timeline (Strymon)
Reverb pedals I am considering: Eventide Space, Reverb Empress, TC Hall of Fame, Boss RV-6
As for other modulation I am considering running the Mobius Strymon or a Phaser, Chorus and Tremolo stompboxes.

Cheers
 

drbob1

Gold Supporting Member
Messages
29,936
I don't think series is going to solve your problem. The series mod means that ALL the signal will run thru the processor, with the impact that any impedance mismatch problems will get worse. The parallel loop isn't the problem. What is the problem is that the Boogie loop is rather limited. You don't have control over the expected input impedance/level of the device you're putting in the loop, or the recovery, and that loop is designed for rack gear whereas the pedal is designed for guitar input. So the Mesa is likely sending a +4 level signal and the pedal is expecting a -10 or even -20 dB signal (roughly 16-32 times louder than the ME70 can tolerate). So, you've got a couple of choices:

1. Add a clean boost set to cut the volume in 1/2 before the ME70 in the loop (it'll have to be something that can tolerate a really hot signal, like the Creation Audio Labs, or a purely passive device).
2. Better: upgrade to a professional level device in the loop. You can get the Boss Se70 or the Yamaha SP90ii, which are old school but have some good sounds, for just over $100. Or go all out and get a Lexicon MPX1 for $300 that will bury your ME70 for quality and variety of effects. Or spend $500 on a Lexicon PCM80/81/90/91 and have absolutely "best ever" sounds!

Oh, and if you're going to use delay/reverb in the loop, and you're going to spend Strymon money, just don't. Get the MPX1, you'll be way happier (the MPX1 can do anything the Eventide H9 can do except fuzz and distortion, and do SOOOO much more if you learn to program it a little).
 

sumpe

Member
Messages
372
hi drbob1. thanks a bunch! this is good.
i am more of a gigging - pack and go - guitarrist.
the racks MPX or Lexicon though amazing is something I am trying not to get into to. Therefore, I was looking into pedals.
From your response I get that I need to do more searching on boosting. My concern is whether I will manage to get delays 100% wet if I cut down with the boos - forgive me if this is a stupid assumption, but I thought that if I am cutting my signal by half, I might not hear a delay with 100% feedback.

Any 'pro' pedals that work with the Mesa Boogie parallel loop? I thought the ones I put down (on the parallel loop, as in front of the amp I am not as fussed because the JOYO and Muff are plenty for my needs there) are pretty good ones

cheers
 

rumbletone

Silver Supporting Member
Messages
8,034
IF the issue is just level and impedance matching, consider a simple device that shifts from line level to instrument level - then you can run whatever pedals you want in the loop (rather than trying to find pedals designed for instrument level that also work at line level). Radial and other make solutions for just that scenario.


hi drbob1. thanks a bunch! this is good.
i am more of a gigging - pack and go - guitarrist.
the racks MPX or Lexicon though amazing is something I am trying not to get into to. Therefore, I was looking into pedals.
From your response I get that I need to do more searching on boosting. My concern is whether I will manage to get delays 100% wet if I cut down with the boos - forgive me if this is a stupid assumption, but I thought that if I am cutting my signal by half, I might not hear a delay with 100% feedback.

Any 'pro' pedals that work with the Mesa Boogie parallel loop? I thought the ones I put down (on the parallel loop, as in front of the amp I am not as fussed because the JOYO and Muff are plenty for my needs there) are pretty good ones

cheers
 

sumpe

Member
Messages
372
thanks rumbletone. i am looking into that.
here are some devices I found (please note as I am just beginning this journey the devices may not be appropriate, so don't take me word for them as I have not tried them myself)

- Whirlwind IMP 2 Direct Box
- Ebtech LLS-2 2-channel Line Level Shifter
- Behringer ULTRA-DI DI400P Passive Direct Box


Any particular devices you could name for me to check? Looking at Radial devices I was not sure which one would work for me.

Also, another question I have is, IF I use a Line level to instrument converter before running the boss me70, will I need to boost the signal again before returning it to the amp effects loop?

Your help is much appreciated before I spend money on things that would not likely solve the issue.

cheers!
 
Last edited:

rumbletone

Silver Supporting Member
Messages
8,034
I'd try the Ebtech LLS - simple, passive, affordable, designed for exactly this type of scenario.

I checked Radial website and I don't see a standalone 2-way shifter like the Ebtech - though a ProRMP between the fx send and the first device in the loop would likely get you most of the way there as that's, in my experience, the bigger issue (I.e., plugging the output of the fx chain into the fx return would likely be fine without shifting back to line level ... which is your second question I guess - so the answer is 'probably ok without shifting back, but will lose quite a bit of gain, which may or may not matter depending on your rig and how hot you're running it').


thanks rumbletone. i am looking into that.
here are some devices I found (please note as I am just beginning this journey the devices may not be appropriate, so don't take me word for them as I have not tried them myself)

- Whirlwind IMP 2 Direct Box
- Ebtech LLS-2 2-channel Line Level Shifter
- Behringer ULTRA-DI DI400P Passive Direct Box


Any particular devices you could name for me to check? Looking at Radial devices I was not sure which one would work for me.

Also, another question I have is, IF I use a Line level to instrument converter before running the boss me70, will I need to boost the signal again before returning it to the amp effects loop?

Your help is much appreciated before I spend money on things that would not likely solve the issue.

cheers!
 

sumpe

Member
Messages
372
thanks for info rumbletone. I am about to try it out.
as for awallace. yes. I am aware. but I am getting serious oscillation even if not maxing out on feedback level. The mesa parallel loop does seem to need to be tammed down in any event.
I will try this out and see what goes...
cheers,
 

drbob1

Gold Supporting Member
Messages
29,936
The cheapest way to try this out would be a passive volume pedal before the ME70 in the loop. You're just cutting the voltage coming into the ME70 down to the level a guitar or pedal would produce. Should be minimal effect on tone and will give you a clear answer if my guess for what the problem is is correct. If it is, then some line level shift would be right. The problem with a direct box is that you need it to go the OTHER direction! The direct box is taking the low level, high impedance signal from your guitar rig and converting to a balanced, low impedance signal. You need to convert from a high voltage, low impedance signal to a low voltage, high impedance signal... The impedance is less important in this context than the straight up voltage. You can run some passive direct boxes backwards to accomplish this but you'll need an adapter to get your TS guitar signal into the XLR input correctly.
 

rumbletone

Silver Supporting Member
Messages
8,034
The cheapest way to try this out would be a passive volume pedal before the ME70 in the loop. You're just cutting the voltage coming into the ME70 down to the level a guitar or pedal would produce. Should be minimal effect on tone and will give you a clear answer if my guess for what the problem is is correct. If it is, then some line level shift would be right. The problem with a direct box is that you need it to go the OTHER direction! The direct box is taking the low level, high impedance signal from your guitar rig and converting to a balanced, low impedance signal. You need to convert from a high voltage, low impedance signal to a low voltage, high impedance signal... The impedance is less important in this context than the straight up voltage. You can run some passive direct boxes backwards to accomplish this but you'll need an adapter to get your TS guitar signal into the XLR input correctly.

In my experience it depends on the amp and the fx devices. For example, amps that have a level control pre-loop already allow you to attenuate the signal - and often that's not enough (i.e., the impedance mismatch is still a significant problem). But it's certainly worth a try - I have found in some cases that attenuation of the level is sufficient.
 

sumpe

Member
Messages
372
Upadate.
Using the Ebtech level shifter I managed to control the oscilation.
Method:
Run Fx Loop Send to +4bd of Ebtech Channel 1 and then run -10db from Channel one into Pedal input.
Run Pedal Ouptup back into Ebtech, Channel 2 at -10db, and then use +4db of Channel 2 to connect back to the Fx Loop Return on the amp.

My mix for the Parallel loop is about 45%-50%.
Because my main effects are delays and reverb, I am considering still the Series Mod.

Thanks again for the help. This change alone brought hope back to life in this amazing amp. If the series modification is recommended then it may be that I'd finally get it all set.

cheers for everyone's help!
 
Last edited:




Top Bottom