FX Loop Bleeding

[brasuca]

Hi there,

I have purchased a Marshall Vintage Modern 2266 50w Head a month ago and recently I realized that ~5% of the dry signal is bleeding through when I use the FX loop.

I wanna know if this is a common issue, and how to solve it. Marshall in the US (Korg) seems pretty primitive. I called them and explained the problem and they said they would have to do some tests with the amp (apparently their amp?) and never called me back. On the other hand the local dealer where I bought it said it could take more than 6 weeks to get it repaired through warranty. Furthermore, I read somewhere that Marshall (Korg) may not really fix the problem... and I am afraid of sending it for repair and getting it back in the same condition after such a long wait. Well, in that case, I might as well find a good tech and do the mod on my end.

So, did you guys have had similar issues in the past? Any advice?

The amp is really great, but this FX loop shortcoming is very disappointing.

Thanks a lot!

[SteveD]

Hi brasuca and welcome to the forum :)

This is the first time I've seen this 'problem' reported. It seems very strange because it's a series FX loop, and when enabled, diverts 100% of the signal to the Send; there is no parallel path to bleed through like on a parallel loop. :? therefore what comes back to the Return is solely what is coming back from your FX.

If you enable the FX loop and connect only a short lead to the Return socket (or prefereably a shorted jack plug) and nothing else, play your guitar and there should be no signal getting to the power amp at all until you bypass the loop.

If you're amp doesn't behave like I have described above then there is indeed something else going on that shouldn't be.

Please let me know or describe your issue in more detail in case I am misunderstanding you.

[brasuca]

Hi SteveD, thanks for your response and the warm welcome!

So, I did as you said: enabled the loop, plugged a short patch cable to the FX loop return jack, and plugged my guitar.

Then, if I dim the master volume, I can hear the guitar through the speakers in a volume equivalent to 1 when the FX loop is bypassed (however, the signal has a lot more treble).

This seems to happen regardless of other amp settings...

[SteveD]

I have just tried the same test with a 2466 and there is some bleed through but at an extremely small fraction of the actual signal (when the loop is bypassed). I wouldn't have thought it to be a problem as I would expect it to be inaudible when the loop signal is enabled.

[TonyC]

It's the same on my 2266 and it's impossible to hear the bleeding signal through the normal signal. This is a proven fact in acoustics and it's called the Masking Effect.

However, if you have a volume pedal in the loop as I have, things change when you lower the volume with he pedal. At a certain point the bleeding signal starts to come through, and with the pedal at zero volume the bleeding signal is obvious. This is not really a problem for me anyway since the bleeding signal is very faint.

[brasuca]

So, you guys are saying that the bleeding I'm hearing is probably normal? That's good, at least my unit is not defective!

However, I'm really trying to get some clean tones by passing the preamp using the so-called 4-cable method and the G-System (which actually succeeds in removing the preamp out of the signal path). However, since it does feed the preamp with some signal, that signal ends up bleeding through and affecting my clean tone quite a lot specially when the preamp is set to the high dynamic range.

I'll have to think of a workaround for that then, I have actually multiple choices:

1) try to mute signal fed to the preamp when it is out of the signal path;
2) mod the amp to prevent bleeding;
3) forget about it and live with the clean provided by the preamp in the low dynamic range;
4) ...

Is number 2 worth trying?

Thanks again!

[TonyC]

I also use the 4-cable method, but with a Boss GT-8. I don't know how loud your bleeding signal is, but mine is so week so it's out of the equation really.

Option (1) seems to be the best solution and it should be possible with the G-System. If you bypass the loop of the G-System the signal should go straight to the VM power amp (to 'Return' of the VM loop). Or does the G-System output a signal from its 'send' even if its loop is bypassed? With the normal 4-cable method the VM preamp is inserted into the signal chain via the loop of the outboard gear.

[brasuca]

To make some justice, I just got a call from someone from Korg USA stating exactly the same: the amp does bleed a little bit and it's more accentuated when it's set to the high dynamic range. It took 3 weeks, though, for them get back to me.

Anyways, TonyC, the G-System does output the signal even when its loop is bypassed. Unfortunately, this is a feature for some (you could plug a tuner there or something).
I need to know now if it's viable to add an option for muting the send signal in their firmware, and how willing TC would be to incorporate that into their next upgrade.

[TonyC]

Yeah, let's hope TC listens. Too bad you can't mute the send.