MarkBass effects loop issue

[VifferMike]

I have a BBE 362NR (Sonic Maximizer with a noise-reduction circuit) in my rack that I run through the effects loop of my amp, per the recommendation of a BBE rep on TB a few years back (and per recent owner's manuals for more current such units). I've had no issues with this setup while using it with SWR, Eden and Genz-Benz amps. However, the effects loop on the Markbass TA 501 that I have now is causing some weirdness.

First, there's some noise being generated in the circuit. I can deal with that. But the big issue that I'm having is that there's a marked difference in output level when the the 362NR is switched on and the sonic maximizer is activated versus when the 362NR is switched on and the sonic maximizer is deactivated.

With the maximizer on, the volume output is roughly the same as if the unit was switched off completely, but the tone sounds overdriven (and the sonic maximizer effect, to my ears, sounds lessened). When the maximizer's off (but not the entire unit), the volume is decreased at least 5 dB, and probably more.

Does anyone (especially the BBE reps that lurk on TB) have any insight as to why this is happening? Is the Markbass' effects loop designed differently than the other brands? Did my 362NR somehow fry itself in between my old GBE600 and the TA 501?

I tried posting this in the Effects forum but got no response ... and now that I think about it, it's the amp that's the likely mitigating factor, not the BBE SM. Anyone have any insight?

 

[JimmyM]

Try cleaning it with contact cleaner. It's cleared up more than a few buggy effects loops.

 

[VifferMike]

... and no effect (pun intended). I also tried the BBE's other output channel; no effect. The volume-output boost is still there.

To narrow down the problem, I just inserted two other effects into the loop in place of the BBE; one with a level knob (SansAmp BDDI), then one without (Boss CE-2B Bass Chorus). Both didn't cause a volume-output spike in the effects loop like the BBE does. (I run all of my effects except for the BBE between the bass and the amp's input).

So it does appear that the issue is inside the BBE unit, and it's not dependent on either Channel A or Channel B. Drat (but at least it's not my amp!). Time to try a new BBE unit, it appears, unless someone else has another suggestion ...

 

[Jeff Scott]

For the BBE to be effective the FX loop must be set to series, not parallel, which is the default setting for that amp, I think. It sounds like this is your problem.

 

[VifferMike]

... I had no idea that an amp's effects loop had that option. So I'm to assume that the SWR, Eden and Genz-Benz that I ran before with the BBE all had their effects loops set to series? I wonder why Markbass runs theirs in parallel ... ?

Anyone have any idea how I can switch this in the Markbass? Or do I have to *gasp* take it to GC to have it done? I REALLY don't want to do that ... I trust GC with gear about as much as I trust Jack Bauer with the keys to my car ...

 

[Jeff Scott]

With SWR amp the loop is a parallel loop but with the blend control FCW it effectively becomes a series loop; I don't know about the others.

 

[VifferMike]

KJung forwarded me the instructions on how to switch the Markbass LMII's effects loop from parallel to series (thanks!). Using it as a guide, I switched the jumper inside my Markbass TA501 from parallel to series (this is the jumper next to the send and return jacks at the rear of the amp).

However, the BBE unit is still exhibiting the same behavior. Drat.

BUT: there are TWO jumpers that need to be switched in the LMII, according to the instructions. The second jumper is at location CN3 on the LMII's preamp circuit board, which is marked "PARALL" (for parallel) next to the jumper. I could not find an equivalent jumper in the TA501 - the jumper at location CN3 is marked "CALIBR" (for calibration, I'm surmising), and I could not find another jumper marked anything resembling either 'PARALL' or 'SERIES' anywhere else in the amp.

Markbass hasn't been responsive (it's been a week) to a request for the TA501's effects loop mod instruction sheet, so ...

... has anyone else done the parallel-to-series mod in the TA501 (or any other Markbass amp other than the LMII, for that matter) that could shed some light onto what step I'm missing here?

 

[B String]

This is an issue for me too. Markbass heads are set up so
that if you use anything in the effects loop, it sounds the
same in series or parallel mode. Great amp though.

 

[Peter Murray]

KJung forwarded me the instructions on how to switch the Markbass LMII's effects loop from parallel to series (thanks!). Using it as a guide, I switched the jumper inside my Markbass TA501 from parallel to series (this is the jumper next to the send and return jacks at the rear of the amp).

However, the BBE unit is still exhibiting the same behavior. Drat.

BUT: there are TWO jumpers that need to be switched in the LMII, according to the instructions. The second jumper is at location CN3 on the LMII's preamp circuit board, which is marked "PARALL" (for parallel) next to the jumper. I could not find an equivalent jumper in the TA501 - the jumper at location CN3 is marked "CALIBR" (for calibration, I'm surmising), and I could not find another jumper marked anything resembling either 'PARALL' or 'SERIES' anywhere else in the amp.

Markbass hasn't been responsive (it's been a week) to a request for the TA501's effects loop mod instruction sheet, so ...

... has anyone else done the parallel-to-series mod in the TA501 (or any other Markbass amp other than the LMII, for that matter) that could shed some light onto what step I'm missing here?

Hi there,
To start with I'm not sure why you feel the need to use a Sonic Maximizer with your amp, but I'll leave that discussion out of this!
Our effects loops are run in parallel partly because that way you never lose your signal if something happens to your effect, cables, battery, power supply, etc.
If you want to run in series, best option is to run through your effect and then into the amp.You could argue that this degrades your signal, but if you were really concerned about that you probably wouldn't be using a sonic maximizer! (sorry, there's that opinion again)...
Our amps are NOT user servicable, for legal and safety reasons. We can therefore not give out schematics, or encourage you to modify your amp. I know there are some schematics floating around but we do not support their use except by authorized repair centers. If you have modified your amp already, you have already voided your warranty. We spell this out clearly in our manuals.
Sorry I can't be more help to you, but unfortunately we just can't encourage user modification, it could get us into a lot of trouble.
Peter

 

[VifferMike]

Markbass' position on this, Mr. Murray. I greatly appreciate your insight and post. I've sent you details about my conundrum via PM.

 

[VifferMike]

The switch from parallel to series in the TA501 worked like a charm.