Mesa Subway Plus preamp

[Michael Eisenman]

In that vein, any suggestions to approximate the sound of a B-15?

 

[ImTheOnlyOne]

Totally loving my second hand Subway+ DI... and...

It appears to put out some high frequency noises when only certain uncommonly used effects, the clearest example being the wild, "Harmony Delay", are placed in its effects loop using an HX One.

I've done extensive, if not thorough, troubleshooting. Rule out a defective HX One. I have two and both do it. Rule in the Subway+. Other amps and preamps tried don't replicate the noise, all else being equal. Everything powered via a CIOKS7. I've the HX One powered via battery pack, but same issue.

I have not yet tried the DI on 9v battery power.
I have not yet run the HX One before or after the DI.

Hoping to assess whether I may have a faulty Subway+, or something else is at play.

 

[squish]

Totally loving my second hand Subway+ DI... and...

It appears to put out some high frequency noises when only certain uncommonly used effects, the clearest example being the wild, "Harmony Delay", are placed in its effects loop using an HX One.

I've done extensive, if not thorough, troubleshooting. Rule out a defective HX One. I have two and both do it. Rule in the Subway+. Other amps and preamps tried don't replicate the noise, all else being equal. Everything powered via a CIOKS7. I've the HX One powered via battery pack, but same issue.

I have not yet tried the DI on 9v battery power.
I have not yet run the HX One before or after the DI.

Hoping to assess whether I may have a faulty Subway+, or something else is at play.

I've had a few FOH engineers point out that there is an ultra high frequency present but it really doesn't amount to anything audible.

 

[agedhorse]

I've had a few FOH engineers point out that there is an ultra high frequency present but it really doesn't amount to anything audible.

It's normal for that pedal to have a very low level ~22kHz -25kHz signal that's just a power supply switching residual, way above the audible range. It's between 50 and 60dB below rated output, the ONLY reason that it's a "problem" is because with the crazy extended range metering on some digital consoles, -60dB can be made visible.

Back in the day, extended range meters on the finest consoles could achieve -40dB and the residual doesn't even begin to show on that scale. In reality, it's a total non-issue.

 

[ImTheOnlyOne]

It's normal for that pedal to have a very low level ~22kHz -25kHz signal that's just a power supply switching residual, way above the audible range. It's between 50 and 60dB below rated output, the ONLY reason that it's a "problem" is because with the crazy extended range metering on some digital consoles, -60dB can be made visible.

Back in the day, extended range meters on the finest consoles could achieve -40dB and the residual doesn't even begin to show on that scale. In reality, it's a total non-issue.

Tested just now...
Even the Subway+ tuner output into the HX One presents the squealing noise when using the problematic effects, ruling out the DI's fx loop. Same whether powering the DI from CIOKS or battery. Utilizing the One's noise gate mitigates partially.

HX One into Subway+, no issue.

Only when Subway+ into HX, and only audible with certain HX effects.

Does the Rosette behave likewise?

 

[agedhorse]

Tested just now...
Even the Subway+ tuner output into the HX One presents the squealing noise when using the problematic effects, ruling out the DI's fx loop. Same whether powering the DI from CIOKS or battery. Utilizing the One's noise gate mitigates partially.

HX One into Subway+, no issue.

Only when Subway+ into HX, and only audible with certain HX effects.

Does the Rosette behave likewise?

There are some effects units that use charge pumps that are quite electrically noisy and have large switching residuals in the 15kHz range. Under some circumstances, when two dissimilar residuals combine, difference frequencies can be generated. For example, a 22kHz and 15kHz signal can combine to generate a new 7kHz signal (which is generally fairly low level but can be high if the 15kHz residual is high).

These multi-fx units can be problematic at times with some effects which result in new signals being generated (usually frequency modulating effects). This is why I no longer use this type of switchmode power supply in audio, there are just too many new variables and devices that have been introduced since this circuit was utilized over 10 years ago. It was still a common solution 5 years ago but is falling out of favor as there are better solutions now.

The Rosette Pre-DI uses exactly the same circuitry unfortunately. For 99% of users this isn't an issue, but for those who it is, it's not something that can be corrected.

 

[ImTheOnlyOne]

Really appreciate the replies.

It's a minor issue, certainly. I fight to keep my HX One in the path, I like aspects of it so much, even with the understanding that it's notoriously interactive with some pedals. Placing it before the Subway+ works around the noise, but isn't where the One works for me. If Line6 'fesses up to their misstep and releases an "HX Two", I'd likely bite.

All that said, I'll keep plugging away at it. The Subway+ DI is easily the best all around 9v-battery-ready bass preamp tone-to-go I've encountered.

 

[ImTheOnlyOne]

Managed the high freq noise by placing a Tech21 Para Driver in the S+DI effects loop.
Some noise cancelling voodoo happens when the Para blend is at 50%.

 

[agedhorse]

Managed the high freq noise by placing a Tech21 Para Driver in the S+DI effects loop.
Some noise cancelling voodoo happens when the Para blend is at 50%.

What's happening is that you are effectively injecting an inverted version of the noise, summing with the original noise, effectively cancelling most of it. You may be able to minimize the noise by varying slightly off of the 50% mark too.

 

[ImTheOnlyOne]

There are some effects units that use charge pumps that are quite electrically noisy and have large switching residuals in the 15kHz range. Under some circumstances, when two dissimilar residuals combine, difference frequencies can be generated. For example, a 22kHz and 15kHz signal can combine to generate a new 7kHz signal (which is generally fairly low level but can be high if the 15kHz residual is high).

These multi-fx units can be problematic at times with some effects which result in new signals being generated (usually frequency modulating effects). This is why I no longer use this type of switchmode power supply in audio, there are just too many new variables and devices that have been introduced since this circuit was utilized over 10 years ago. It was still a common solution 5 years ago but is falling out of favor as there are better solutions now.

The Rosette Pre-DI uses exactly the same circuitry unfortunately. For 99% of users this isn't an issue, but for those who it is, it's not something that can be corrected.

Do you expect all of the above will be true of the new Subway+ Bass DI-Premp II?

Really happy to see this new bass pedal release

 

[agedhorse]

Do you expect all of the above will be true of the new Subway+ Bass DI-Premp II?

Really happy to see this new bass pedal release

No, it does not use a charge pump, it's completely immune from these issues.