5150 Effects Loop Noise / Bleed Through - Decimator G String - Not Hum

[C.N.]

EDIT: Before you read the rest of this this, I'm starting to think this is not and FX loop / noise gate problem, but rather that somehow signal gets past the master volume of the 5150/5150ii/6505/6505+ in parallel.

CORRECTION: FX loop seems to be located after master volume, and signal gets past the master volume AND FX loop.

This issue happens with my 5150, 5150 II, and 6505

I have an ISP Decimator G String noise gate, and when the gate kicks in, I can still hear the guitar barely coming in. At ultra high volumes, it's not much of a problem because the noise/bleed doesn't get any louder (no matter if you have the master set to 1 or 11, the noise/bleed is the same volume). However, at low and even medium levels, it's significant enough to be bothersome.

I don't expect it to be absolutely silent since we are talking about a tube amp, but the guitar signal still bleeding through when the gate should be eliminating at least that completely?

Anyone else have this problem?

 

[Brandon E.]

Replace your battery maybe? I know the G-String will do that when the battery is dying...You should expect it to be absolutely silent, BUT the 5150 has a pretty sucky effects loop...if worst comes to worst you might want to not run it in the effects loop and just put your boost in between the 2 gate stages, that's how I run mine since I've had problems with shitty effects loops in the past. It is probably NOT the decimators fault.

 

[C.N.]

I was running the Decimator G string from an outlet. Put in the battery and the same issue persists.

Haven't had a chance to run the Decimator G string in front of the amp yet, but I believe that will partially fix the issue...

However, I still believe the main issue is with the amp. I'm not sure if this is common with most tube amps, but this is at least what I believe happens with at least the 5150 family:

Even with the master at 0, guitar signal/noise still comes through, albeit extremely muffled.

As you turn up the master, all of a sudden, the sound you are supposed to hear starts coming through, although it is coming through on top of the noise/bleed through.

In effect, the noise/bleed through kind of acts like a built-in noise floor that bleeds through constantly (which shouldn't be there because the signal is supposed to be cut off, especially since using a noise gate).

At low volumes, what you are supposed to be hearing has to compete with the muffled noise/bleed through, making the overall guitar sound like crap, until you go well past 1 on the master volume.

However, it is not until you start getting pretty loud that the noise/bleed through doesn't bother you too much because then the difference between the full sound and the noise/bleed through is greater, so the noise/bleed through sounds relatively quiet.

With the 5150, unless you want distortion from the power tubes or driving the speakers hard, you should get a relatively good sound from the amp being at a low volume, because you are getting most of your sound from the preamp; however, with this noise/bleed through competing with you main signal, it becomes difficult to get a good sound, not to mention the impossibility to get a dead quiet stop using the noise gate.

So in conclusion, I believe that somehow, some of the output of the preamp is bypassing the master volume section completely and going straight to the power amp.

Now, I don't know if this is done somehow through radio interference, or if there is some way that signal gets through in parallel to the master control section... It could even be that there is something wrong with the master volume pot bleeding through; however, I doubt that would be a problem with all three of my amps, especially since the same thing happens with all 3 of my amps and additionally, they all have different brand volume pots installed.

To explain a little more about what I am doing....

I am able to get a pretty decent sound at low volumes by:

1) Removing outer tubes and halving the impedance switch to obtain half power.
2) Running a Boss 7 band EQ in the FX loop, turning the volume all the way down on it (might be different on other EQs), boosting the far low frequency only half a notch, and the far high frequency 1 notch (this may be to compensate for the noise/bleed through muddiness/muffledness).

I've had several people compliment in surprise the sound I get from the 5150 at low volumes, when many online swear that you have to crank the amp to get a good sound (in all honesty, my experience in doing this makes the 5150 at low volumes sound even more amazing vs the amp normally cranked).

However, at the same time, the noise/bleed through makes the noise gate useless at low volumes, and additionally, I could probably get to even lower volumes if this issue was eliminated or significantly tamed. At the moment, I am competing with my better half's TV watching and having difficulty going low enough not to wake anyone up nearby.

 

[C.N.]

If anyone is having trouble understanding what I am explaining, try this.

1) Turn your amp on and get your nasty nasty nasty 5150 sound out of it

2) Turn the master down to 0 (notice a muffled signal still coming through when you play your axe)

3) While still playing with one of your hands, slowly turn up the master.

Eventually, at some point under or at 1, you should notice a clear and more desirable signal coming through all of a sudden. You should also notice that you have to turn up the master a bit more for the clear signal to start overtaking the muffled signal.

If not, I'd like to know what you are doing, since this happens with all 3 of my amps.

Anyhow, what you were hearing at zero is pretty much what still coming through my amp when my noise gate in the effects loop is engaged.

I would thing that placing the noise gate in front of the amps preamp instead of the effects loop might help this, although the Decimator G string is designed to work in the effects loop!

I suspect this is a big reason why Killswitch Engage uses a Decimator and an NS-2 simultaneously?

If there was another way around this, perhaps one "side chaining" noise gate would suffice?

 

[bryan_kilco]

I know what you're saying about the sound coming through when the volume is at 0. But I also have a screwed up FX loop and when I switch the loop ON, I get a HUMONGOUS drop in volume - to the point where it sounds like the volume is on 0.

Try cleaning you FX loop jacks maybe. I haven't done this, but I've tried patching the FX Loop Send - return with a patch cable and it did nothing.

 

[C.N.]

The jacks were cleaned recently, which fixed a lot of problems I was having before such as volume drop and making the sound very brittle.

Still, when I switch the FX loop off on my 5150II, I still get noise/bleed through with the master at zero, and besides, I can't imagine now that it would actually be an FX loop problem because the FX loop still feeds back in before the master... If it didn't, wouldn't you still hear a delay effect that was turned on in the fx loop come through at full volume when cutting the master to zero?

Somehow, I think the signal is getting past the master volume (in parallel?).

*If this could be eliminated, the noise gate would totally cut the sound when engaged (albeit you might still get a tiny, or even microscopic bit of hiss, natural from the power amp).
*Not only that, then you get to even lower volumes while keeping the signal clear.

Anyone who is an experienced 5150 tech care to chime in and offer an explanation?

 

[C.N.]

Anyone one else have a comment pretty please?

 

[amarshism]

i remember reading something about the bleed through going across the two sides of the fx loop preamp tube

 

[C.N.]

i remember reading something about the bleed through going across the two sides of the fx loop preamp tube

Makes sense as to why the fx loop is noisy or what not, but I still can't understand how the signal gets around the master...

 

[guitarguru777]

when was the last time you cahnged tubes and rebiased?

I bet its a microphonic tube

 

[C.N.]

when was the last time you cahnged tubes and rebiased?

I bet its a microphonic tube

It happens with all 3 amps I have.

I just biased all three last week. It happens with several sets of tubes.

I cants see how the powertubes would be getting a signal that shodnt be there with the signal shut off at the master volume anyhow..

 

[Kazrog]

Here's my opinion based on having 3 of these amps myself, purely on experience and inference (NOT based on any technical knowledge of the internals of the amp):

The 5150's "Post Gain" knob is NOT a master volume - in other words, it has no effect on the power amp. It is, in my estimation, a preamp level knob. It is also my opinion that the 5150's power amp is ALWAYS ON FULL BLAST, and that is why the amp is so noisy, and also why it sounds the way it does. I could be wrong about any or all of this, but the behavior of the amp suggests this to me.

In any event, signals sent into the FX return are seemingly not affected by the Post Gain knob at all. Again, I've had 3 of these amps, and they all were the same in this respect.

If there is anyone with an electronics background who can comment on this, the 5150 schematics have been published online for many years, and maybe somebody can finally enlighten us all about what is going on inside this great amp!

 

[kev]

This is what happend to me... http://www.ultimatemetal.com/forum/equipment/650991-another-5150-thread-effects-loop-hum.html

 

[kaomao]

The 5150's "Post Gain" knob is NOT a master volume - in other words, it has no effect on the power amp. It is, in my estimation, a preamp level knob. It is also my opinion that the 5150's power amp is ALWAYS ON FULL BLAST, and that is why the amp is so noisy, and also why it sounds the way it does. I could be wrong about any or all of this, but the behavior of the amp suggests this to me.

yes to me it seems the same, a preamp level!
If I put something in the return like a distortion pedal the post gain does nothing. I have to check it out to be honest, since last time I did this was some time ago.

 

[C.N.]

Hmmmmmmm you guys are right... The FX loop is after the master... becuase when I shut the master off with delay in the FX loop, the delay continues to ring out.

So.... for further testing, I put another EQ in the FX loop and turned the volume and gain on the eq pedal totally off.... but the same thing still happens.

The interesting part is that no effected signal gets through at all... It's still the signal that comes from the preamp section getting through...

So... I guess the signal is bypassing the master & FX loop (post master) somehow...

I wonder if installing a master volume at the last possible point in the amp that you can would do the trick? OR Maybe there is something still going on somewhere in the FX loop circuit after the return that can be fixed...

 

[TheWinterSnow]

The 5150's "Post Gain" knob is NOT a master volume - in other words, it has no effect on the power amp. It is, in my estimation, a preamp level knob. It is also my opinion that the 5150's power amp is ALWAYS ON FULL BLAST, and that is why the amp is so noisy, and also why it sounds the way it does. I could be wrong about any or all of this, but the behavior of the amp suggests this to me.

Yeah not correct. If you are not slaving amps together, the post gain is controlling the final signal to the power amp. The volume control is before the post gain but that does not change its effects, it would do the same thing that a MV control would do after the FX. The concept you have about the power amp being of full blast is completely irrelevant and makes no sense in regards to how power amps work.

Hmmmmmmm you guys are right... The FX loop is after the master... becuase when I shut the master off with delay in the FX loop, the delay continues to ring out.

So.... for further testing, I put another EQ in the FX loop and turned the volume and gain on the eq pedal totally off.... but the same thing still happens.

The interesting part is that no effected signal gets through at all... It's still the signal that comes from the preamp section getting through...

So... I guess the signal is bypassing the master & FX loop (post master) somehow...

I wonder if installing a master volume at the last possible point in the amp that you can would do the trick? OR Maybe there is something still going on somewhere in the FX loop circuit after the return that can be fixed...

You have crosstalk among the FX driving tube, no way around it. Get better tubes and/or get a gate in front of your amp as well.

 

[Jormyn]

Sorry for necroing this thread, but I've got a related problem.

I'm using a 6505 combo, which has the same bleed-through problem on the effect loop. Even better, though, is if I put my delay pedal in the loop; since it's digital and introduces a teensy amount of latency, the return signal ends up cancelling with the bleed and producing a hollow, scooped tone. It even does this if I turn the pedal to 100% dry. According to Google, a few other people have had the same issue, with various delays.

Since the bleed itself seems to be largely unfixable (aside from trying to find the least crosstalky tube possible), can anyone suggest a solution or workaround for this particular situation? All I can think of would be to use a different power amp altogether, but that's not the most practical idea.

Cheers.

 

[C.N.]

I hate to be the guy to revive :zombie: thread but...

After d*ck*ng around with the Axe-Fx II for almost 2 years, I'm going back to the 5150 for a change and have a couple comments/insight/theories to add.

You have crosstalk among the FX driving tube, no way around it. Get better tubes and/or get a gate in front of your amp as well.

I guess this is probably the main reason several like KSE/Periphery use(d) two gates, one around the boost pedal in front of the amp and another in the fx-loop.

* I also read somewhere that Adam Dutkiewicz got his Soldano SLO with the mod removing the FX loop. *

I'm pretty sure this whole situation is the reason amps (at least 5150/SLO related ones or others with similar FX loops) sound better without the FX loop (at least at low to medium volumes). My understanding is that most people who use 5150 get most of their distortion from the preamp and not the power amp, so in theory, a 5150 should sound pretty good at low volumes. However since the FX loop is a problem, the amp kinda sounds bad at low volumes (or at least has to be adjusted differently to compensate for the bleed through, by adding more treble, bass and presence to compete with the muddy cross-talk).

This might also add to the syndrome where players adjust their settings at home, but when they go to play live, their sound falls apart at high volumes. Of course this is also combined with the Fletcher-Munson curve effect, but I'm pretty sure the cross talk exacerbates the overall problem.

Besides using the two gate technique, and instead of ripping out the effects loop as in the SLO effects loop removal mod, it would of been sweet if all amps using these effects loops also had a switch to disable the fx loop entirely (maybe at least by cutting the fx return off sometime AFTER the tube where the crosstalk occurs). This wouldn't give us spill-over, but it would definitely fix an issue a lot of 5150 (etc) users have.. An issue that many aren't even aware of but affected by. Dual noise gates help alleviate the issue (you get less noise from an OD but the amp's preamp is still kicking through), but sometimes you don't really want to use noise gates.