FX loop, "Solo" only on Ch1 ?

[Induktionator]

Proud new owner of a MarkV, I have some odd behavior I don't quite understand. I searched the forum here, but mostly found issues of noise and signal levels with effects processors. I think my problem is different.

It seems the FX loop only works as I expect for channel 1. The "Solo" control also works only for channel 1. Here's what I see:

I have a BOSS Looper, digital delay, and a Volume pedal, in various combinations.
On channel 1, the looper can record and play back as usual, the volume pedal can control the amp's overall volume (Just not quite to 0 as on other amps. I think the loop isn't completely series - 5% dry, 95% wet I guess). The Solo control works as the manual describes.

With Channel 2 and 3, it behaves like the effect loop return functions, but not the send. The volume pedal does nothing, effects like the Delay do nothing, and I can't record anything with the looper. I can play back a loop recorded with channel 1, though.

With Channel 2 and 3, the Solo control also does nothing. The LED on the footswitch lights, and that's it. No increase in volume.

channel 1 master: 12:00
channel 2 master: 7:00 (Or else it is a bit loud...)
channel 3 master: 7:00
output: 8:00

Things I've checked:

With the "hard bypass" switch on, the FX loop, output and Solo feature are inoperative. this is clear. From a schematic I found, this makes sense.

Depending on the setting of the FX select knob on the back, the FX light is 'forced' on for 1 of the 3 channels and the footswitch button allows to turn it on/off for the other 2. Or else it is always on, or else the footswitch button can control it for all of them. This is now clear. The setting of this knob doesn't affect the problem, just the ability to turn the FX loop on and off.

I found a schematic, and this problem would appear impossible from the schematic, so I guess it is an older revision. Probably someone 'leaked' it. Beggars can't be choosers, I guess.)

Any advice?
I would like to rule out that I haven't set something wrongly before calling the store to tell them it has a problem.

 

[SteveO]

Have you tried selecting "on all" on the rear knob?

 

[Induktionator]

The rear knob just allows to "override" the footswitch for one or all channels.

I found the issue.

There is a fixed amount of signal that bypasses the individual Master volume controls, effect loop, and Output controls. For Ch1 it's practically nothing, but for Ch2 and 3 it's bedroom playing level. If you don't know this and adjust the Masters to balance the channels when using the effect loop, the result is to have ch2 and 3 too low.
The channel masters basically set the Effect Send, but then the Effect return gets mixed with this low fixed volume signal.
(If you connect only the effect return (Or use a 1Mohm dummy plug), the outout volume of the amp is fixed at a low level, independent of the channel masters and output)

Basically, the effect loop with Ch2/3 isn't useful with Ch2/Ch3 masters below 9:00 or 10:00 or if you play the amp too quiet.
At low volume levels, expect the wonderful sound of the amp, and forget about the effects loop on Ch2/Ch3.

With the channel masters below 9:00, the effect loop send is nothing, so teh result is 100% dry, 0% wet.
Wit the channel masters around 10:00 it is about 50/50, and around 12:00 is is about 75/25. You can never really reach 100% wet because of this fixed-level signal that never goes away.

If the channel masters of ch2/3 are too low, depending whether effects invert or add a phase shift to the signal, it could sound bad due to phase addition/cancellation because the signal to the power amp isn't 100% wet.

If someone knows a trick to achieve a 100% wet effect loop it would be helpful. My guess is there's a resistor somewhere that doesn't appear on the "leaked" rev.1 schematic. Maybe I'll ask Mesa.

 

[SteveO]

Interesting to know. I generally keep my channel masters around noon and use the overall master to control output volume, so that explains why I haven't encountered this anomaly. I do know about the dry signal bleed in the loop, I encountered THAT issue when I was switching between the Boogie's preamp and a second one through the loops in my G-System.