FX Loop Question

[mrsunnybunny]

I have a question regarding the Mini Rectifier 25 FX Loop, although I am sure the same will apply to any other Mesa amp with an FX channel.

I currently have my looper plugged in the FX channel. This is to enable the recording and looping of the signal after the pre-amp stage; eg record a loop on the clean channel and play over it on the overdrive which works really well.

I noticed that when I play the loop through the FX channel and change the master volume of the channel, the volume of the loop does not change at all. For example, I can turn the master volume all the way up or even completely down and the volume of the loop does not change. Basically, the loop volume always seems to be set to the same volume which it was recorded at.

This doesn't really make sense to me as I would have thought that the FX loop is post the pre-amp but pre the post-amp tubes. Thus, any signal would still have to travel through the final amplification stage. Am I wrong and how does the wiring of the FX loop really work?

 

[afu]

That's normal. The loop is after the channel volume. If there was a dedicated master volume for the power amp, like the Output on a regular Recto, it would be after the loop.

 

[mrsunnybunny]

That's normal. The loop is after the channel volume. If there was a dedicated master volume for the power amp, like the Output on a regular Recto, it would be after the loop.

I think this makes sense... So the regular recto has another dedicated master volume which is after the loop? As the mini does not have this, does the final 'output' always run at the same power? Do I need to worry about effects pedals being run through an amplified stage of the amp?

 

[afu]

That's normal. The loop is after the channel volume. If there was a dedicated master volume for the power amp, like the Output on a regular Recto, it would be after the loop.

I think this makes sense... So the regular recto has another dedicated master volume which is after the loop? As the mini does not have this, does the final 'output' always run at the same power? Do I need to worry about effects pedals being run through an amplified stage of the amp?

Q1: The bigger amps have the Output control, which is a global MV, just after the fx return.
Q2: The final output level depends solely on your channel volumes and gain.
Q3: The routing is like this: input preamp stage - gain - more preamp - volume - loop - power section. The distortion is being generated (for the most part) before the loop. If it's a single, stomp box, pedal, a loop could overdrive the pedal, because it's an instrument level device and the loop is line level. Modern multi-fx units usually give you a choice between line level and instrument level input, a pad on the input, or provide an fx loop to run to an amp's fx loop.

 

[mrsunnybunny]

That's normal. The loop is after the channel volume. If there was a dedicated master volume for the power amp, like the Output on a regular Recto, it would be after the loop.

I think this makes sense... So the regular recto has another dedicated master volume which is after the loop? As the mini does not have this, does the final 'output' always run at the same power? Do I need to worry about effects pedals being run through an amplified stage of the amp?

Q1: The bigger amps have the Output control, which is a global MV, just after the fx return.
Q2: The final output level depends solely on your channel volumes and gain.
Q3: The routing is like this: input preamp stage - gain - more preamp - volume - loop - power section. The distortion is being generated (for the most part) before the loop. If it's a single, stomp box, pedal, a loop could overdrive the pedal, because it's an instrument level device and the loop is line level. Modern multi-fx units usually give you a choice between line level and instrument level input, a pad on the input, or provide an fx loop to run to an amp's fx loop.

Thanks but now I am even more confused! If the loop is at the end of this (input preamp stage - gain - more preamp - volume - loop), then surely I should be able to control the volume of my looper pedal (which is playing back a recorded sound) by turning down the channel volume? This however is not the case. I can turn gain and channel volume all the way down, keep the looper running and the playback volume will not change... Similarly, I can crank channel volume and gain all the way up and the loop I am playing will not increase in volume.

 

[afu]

Well, the loop volume doesn't change, because the looper is driving the return stage. It's sending a signal in after the volume control.

Edit: Since the volume control is before the loop, whatever you play into the looper stays at the recorded volume. You'll need a volume pedal or something in the loop (after the looper) if you want to control both.

 

[mrsunnybunny]

Well, the loop volume doesn't change, because the looper is driving the return stage. It's sending a signal in after the volume control.

Edit: Since the volume control is before the loop, whatever you play into the looper stays at the recorded volume. You'll need a volume pedal or something in the loop (after the looper) if you want to control both.

Ok, that makes sense, thanks! In the mini, would the power section then always run at the same power (ie 25W or 10W), while in the normal Rectro, this power stage can further be controlled by the master volume?

With that in mind, it would seem that the 'preamp stage - gain - more preamp - volume' stages would run at relatively low power (eg not enough to power a speaker by themselves). This 'low power' signal is then taken by the power stage and amplified to 'speaker' level.

 

[afu]

Ok, that makes sense, thanks! In the mini, would the power section then always run at the same power (ie 25W or 10W), while in the normal Rectro, this power stage can further be controlled by the master volume?

Yes and no, respectively. The volume for most amplifiers goes up or down by manipulating the level of the preamp; whether it's individual channels or a master volume after all of the channel volume controls. All of them come before the power amp.

I presume the difference with your amp is that the Output as a MV is absent from the end of the loop. Your volume controls behave exactly like the larger ones do when the loop is bypassed, except you still have the option of using a loop.

With that in mind, it would seem that the 'preamp stage - gain - more preamp - volume' stages would run at relatively low power (eg not enough to power a speaker by themselves). This 'low power' signal is then taken by the power stage and amplified to 'speaker' level.

Pretty much. There's a more complicated answer about the output transformer, but you've got the general idea.

 

[waygorked]

Is there any simple way to add a master volume to the power amp, short of adding an external attenuator like Bad Cat Unleash?

I've been trying to find a way to run my Mesa TA30 and Mini Rectifier together in stereo using the effects loops for some time, to no avail. I really want to use the loops in stereo for my Strrymon Timeline and Big Sky. Unfortunately Mesa designed the TA30 with a really hot send and padded down return on the top boost channel, which pushes my stereo reverbs into distortion when used with the MiniRec as the other stereo input. If I route the Timeline's output around the big sky and blend it back into the reverb output with a mixer pedal, so that only one input hits the reverb, then everything goes back to the returns in stereo it works ok. Unfortunately that also renders the second channel on the TA30 useless, as this has an entirely different loop gain structure.

I really love the sound of my TA30's top boost channel, and really want to run stereo effects. I don't want to buy a second TA30 to pull it off, which Mesa suggested was the only solution. If I could run the send from the TA30 as the only input into the Timeline, then go stereo out into the MiniRec's return, the problem would be solved. But, as if designed specifically to thwart me, the MiniRec's loop return is after the master volume, rendering it useless for this purpose.

Is there any simple way to move the location of the master volume in the MiniRec, such that it could function essentially as a slave amp for the TA30? Alternatively, would running my Morely mixer pedal prior to the MiniRec's return as an attenuator work?

 

[afu]

You could use a volume pedal for that, too. You could also use a buffer pedal with a volume control.

Another thing would be a DIY, passive volume box with just a 10 uf capacitor into a 10k audio pot. That'll cut the bottom off below 15 hz at Noon and 1.5 hz at full volume, so it basically won't hurt anything you need and its output impedance is a max of 2.5k. With a DIY'er, you can take a marker and mark a line where it needs to be set, or, just not install a knob so it is harder to twist. Ignoring the cost of an enclosure, since that could be a re-purposed item, two jacks, a cap, a pot, and some wire is less than $10.

If a passive, DIY box cuts highs, adding a simple treble boost circuit is, like, $1 to $2 for a resistor and a cap.

 

[waygorked]

If I set it up with a volume pedal, or any other form of passive attenuator prior to the MiniRec's loop return, I am not entirely sold that would solve the problem. The level of the loop send on the TA30 is different between channels. The top boost channel has a hot send and a padded down return, whereas the tweed/gain channel has normal send-return level matching. After setting an appropriate level for the MiniRec to slave to the TA's top boost channel, switching to the tweed/gain channel would create a big level drop, correct?

 

[afu]

I am not as familiar with your amp. If a midi pedal switcher with the option of channel switching is used, the switch to tweed could be setup to not use the pedal. Unless the pedal switcher has enough amp switchers, a device like the Voodoo Control Switcher could be used for the amps and set up to do additional (or all) channel switching, while the pedal switcher can activate pedals depending on the patch, and be the midi controller.

A setup like that removes both Mesa pedals from the floor, both amps gain midi control, plus pedal switching without tap dancing, and there can be 128 combinations recalled.

You'd be looking at $500 or so for, say, a Decibel Eleven Switch DR, a Voodoo Control Switcher, and a volume pedal. If you already have an effects unit with stereo outs and level controls for each out, the volume pedal can be left out and it's more like $440 for the first two. If something like that sounds good, shop around and look at different units. The Switch DR is cool, because it's both a controller and a switcher for a low price and good reviews.