Ghost delay in FX loop

[macktruck]

I am getting a ghost delay in the fx loop of my roadster. When the delay is set to 1 echo ( feedback at 0 and mix at 50) I get after the 1rst repeat 2 others ghost delays (1 weak, 1 very weak) at the same tempo, with a very degraded tone (harsh, with a lot of hi frequencies).

I also did another test, increasing the feedback. After a couple of echoes, I could d hear a serious tone degradation (the repeats are getting more and more distorted, and with more and more hi frequencies). This only happens when the delay is in the fx loop. When in front of the amp it sounds fine.

I have been experiencing that with my eventide time factor but also with a tc nova system. So I think the issue is really with the fx loop.

I got in touch with Mesa and they did some tests with the time factor. They were able to reproduce the issue not only with the roadster but with a bunch of amps (Mark V, Lone Star, RoadKing, Electra Dyne). Right now they are investigating this issue along with Eventide, but Mesa thinks this is more of a delay issue, and eventide thinks its more of a fx loop issue!!

I would like to get more feedback from other users if you can definitely do some tests and tell me what you get. I'll upload a mp3 sample later.

 

[94Tremoverb]

It is absolutely an amp FX loop issue. It's caused by the extremely crude way Mesa implement parallel mixing, which allows some of the signal from the return to bleed back to the send and hence feed the FX unit's output back into itself. I'm amazed Mesa need to investigate this issue at all (unless they're just doing what software companies try when they know they've got a problem...) because the cause is completely obvious from the schematic.

Even without this, with some of the amps (eg the new Dual Rec with the series loop) there is still a slight problem with bleed-through because the send and return are done with the same 12AX7 and there is a small amount of crosstalk between the two halves. This is much less noticeable though. Even without *this*, there can sometimes be signal transfer from the FX return to the send via the power supply, which can cause trouble if the FX unit has enough gain.

 

[domct203]

It is absolutely an amp FX loop issue. It's caused by the extremely crude way Mesa implement parallel mixing, which allows some of the signal from the return to bleed back to the send and hence feed the FX unit's output back into itself.

The Roadster's loop is series, not parallel.

Even without this, with some of the amps (eg the new Dual Rec with the series loop) there is still a slight problem with bleed-through because the send and return are done with the same 12AX7 and there is a small amount of crosstalk between the two halves. This is much less noticeable though. Even without *this*, there can sometimes be signal transfer from the FX return to the send via the power supply, which can cause trouble if the FX unit has enough gain.

This could be an issue. How high do you have your channel masters/FX Loop send levels?

Dom

 

[macktruck]

It is absolutely an amp FX loop issue. It's caused by the extremely crude way Mesa implement parallel mixing, which allows some of the signal from the return to bleed back to the send and hence feed the FX unit's output back into itself.

The Roadster's loop is series, not parallel.

Even without this, with some of the amps (eg the new Dual Rec with the series loop) there is still a slight problem with bleed-through because the send and return are done with the same 12AX7 and there is a small amount of crosstalk between the two halves. This is much less noticeable though. Even without *this*, there can sometimes be signal transfer from the FX return to the send via the power supply, which can cause trouble if the FX unit has enough gain.

This could be an issue. How high do you have your channel masters/FX Loop send levels?

Dom

Channels Volume at about 11 o'cock, Master Volume at 10, and FX send at 100%.

 

[domct203]

Wow, with the Ch master at 11:00 and the Send level all the way up that's alot of signal going into the FX loop. Have you tried backing off the FX Send to Noon?

The distorted ghost delays may be from clipping the effects input and the A/D converter

Dom

 

[macktruck]

Wow, with the Ch master at 11:00 and the Send level all the way up that's alot of signal going into the FX loop. Have you tried backing off the FX Send to Noon?

The distorted ghost delays may be from clipping the effects input and the A/D converter

Dom

Sure I ve already tried that but it did not help. It reduces the send fx but since it's serial also the overall level.

 

[domct203]

Wow, with the Ch master at 11:00 and the Send level all the way up that's alot of signal going into the FX loop. Have you tried backing off the FX Send to Noon?

The distorted ghost delays may be from clipping the effects input and the A/D converter

Dom

Sure I ve already tried that but it did not help. It reduces the send fx but since it's serial also the overall level.

It lowers the OA level regardless if serial or parallel.

I hope you get this sorted out. I have a G-Major in the loop of my Roadster (FX Loop Send level at noon) and it works flawlessly.

Good luck, be sure to post back how you make out.

Dom

 

[macktruck]

I have been in touch with Mesa and I am still waiting for a solution. I'll keep you updated, hoping they'll figure something out.

 

[ironjose]

i also have a roadster and the first time i plug a delay into the effect loop (it was a EHX deluxe memory man) i've also heard this ghost delay fading out... but then i realize the effects loop was clipping the delay... so you might want to check on the levels...
other than that... now when i connect my gt8 to the effects loop that ghost delay is gone...

 

[macktruck]

I've been trying every set up I could think of but it just did not help.
I got in touch with Mesa and surprisingly they told me they could experience the problem also in front off the amp, which is definitely not my case. I will try to call them later today to figure it out. But based on what I have been told, I am afraid it's just the wait it is with Mesa'fx loop

 

[elvis]

Hook up this way:

Roadster FX send -> Delay pedal Input
Delay pedal output -> separate power amp (FX return of another amp, or any stereo power amp)

This will remove the Roadster FX loop return circuit and power amp from the setup. Still have ghost delays? If no, then it is likely feedback in the FX circuit. I would suspect the FX valve as well, maybe microphonic. Change it.

If yes, then likely the send circuit doing something wierd.

I also recommend turning the FX SEND and MASTER controls down. Turn up FX RETURNOUTPUT LEVEL to compensate. Mesa's master controls are generally pre-loop and affect loop level. I'm not sure about the output level on the Roadster.

Also, make sure the input and output level switches on the delay are LINE, not INSTRUMENT/GUITAR/HIZ/whatever.

 

[macktruck]

Thanks for the suggestion, I will try that.

I called Mesa and I feel like we are stuck here. They told me they are waiting from Eventide's answer, when Eventide told me they are waiting for Mesa's answer... I don't think they want to admit this is a problem with the FX loop. I have tried 3 different digital delays and ended up with the same problem. Mesa told me they also tried with an analog delay, and it worked fine. What is more surprising is that they told me they also experienced the problem in front of the amp, which is definitely not what I have.

So this is definitely an issue between digital delays and FX loop. I tried all the setups possible with the delay (line, guitar levels, kill dry...) but so far it did not help. I will try to find the right settings with the FX send.