Question on effects loop on LS (prolly same for all Mesas)

[strumminsix]

I am gonna run some modulation effects through my mesa and have no idea how this works on the LSC.

I see a send level and read the manual which assumes a return level on your device.

Makes sense.

But then I see this "unity gain" and I have no idea what that is on amps.

Is it really as simple is send a strong enough signal to drive the processor and return a strong enough signal to match what you had before you put something in the loop?

Hope so, but still dont' understand unity gain.

 

[ylo]

I don't know the context, but I think "unity gain" here means the signal coming back from the EFX unit is the same level as the signal sent. In this case, the volume remains the same with and without the effect in the loop.

 

[Anonymous]

Post removed.

 

[strumminsix]

Okay, played with it last night and now I'm more confused than ever!

When I have the loop engaged so I can use the Solo function even without anything in the loop and nothing in the jacks, that unity gain level still controls volume!

I am so lost.

 

[Dann'sTheMan]

Hi strumminsix,

Don't give up - indeed you should be congratulated for reading the manual in the first place. 8)

First of all, unity gain simply means a gain of 1. In amplifier design, the gain factor is an indication of how much amplification will take place on an input signal: e.g. if there was 1V at the input and 2V at the output, this would represent a gain factor of 2. In the serial FX Loop it's desirable to have a gain factor of 1 (i.e. unity gain) so that everything electrically behaves as if there was no FX processing in place (in theory).

The way this is set up involves setting one control (set the Output control on the front panel to 12 o'clock - more on this later), and then adjusting two controls: the send level on your amp, and the output level on your FX. The send level on your amp is to make sure your FX unit is seeing a "good" signal: too small, and the result is noisy, lacking resolution, and sounds bad; too big and the result is clipping and it also sounds bad. Then, the output level on your FX is used to adjust the signal returning back to the amp. When set correctly, then the level of the signal (and the volume of the amp) will be about the same as if the FX unit was not connected - this is unity gain.

Now, finally, set the Output control on the front panel to where you really want to set the overall volume. The reason for this is that the Output control is really part of the FX loop return circuitry (the Solo control is also part of this circuitry). It needed to be set high when setting up unity gain on the other two controls (amp send level, and FX unit output level). Now that unity gain has been achieved, you can set it where you really want it.

As long as the "Loop In" switch is selected, the amp's controls for Send Level, Output and Solo are part of the circuitry. If you select "Hard Bypass", then those three controls are disabled, and you have to rely on the Channel Masters - a bit like my lean and mean F-series amp.

Big smiles,

Andy.

 

[strumminsix]

Wow, thanks so much, Andy!!! It's starting to make sense.

Now other things are starting to click. I wanted to use my XTL for modulations and reverbs and figured running it in the loop. It didn't sound all that good and a bit noisy (like a bad pedal). But now I realize that it's a hotter signal (like active pups) and I should have pad'd the signal and I'll try that tonight.

So it sounds like I should have had that set at noon the whole time, yes? And that's because it is a bit of a bump going through a couple other tubes (halves) and a couple jacks and a solo pot and a master volume pot, yes?

Okay, things are clicking...

BTW, I unpligged the processor (XT) last night, off'd the loop, both down to 50W, tube rectification, tweed power and fell in love with my XTL all over again.

The signal and tone was just wonderfully simple and pleasurable to my ears.

 

[Janglin_Jack]

The way this is set up involves setting one control (set the Output control on the front panel to 12 o'clock - more on this later), and then adjusting two controls: the send level on your amp, and the output level on your FX. The send level on your amp is to make sure your FX unit is seeing a "good" signal: too small, and the result is noisy, lacking resolution, and sounds bad; too big and the result is clipping and it also sounds bad. Then, the output level on your FX is used to adjust the signal returning back to the amp. When set correctly, then the level of the signal (and the volume of the amp) will be about the same as if the FX unit was not connected - this is unity gain.

Now, finally, set the Output control on the front panel to where you really want to set the overall volume. The reason for this is that the Output control is really part of the FX loop return circuitry (the Solo control is also part of this circuitry). It needed to be set high when setting up unity gain on the other two controls (amp send level, and FX unit output level). Now that unity gain has been achieved, you can set it where you really want it.

As long as the "Loop In" switch is selected, the amp's controls for Send Level, Output and Solo are part of the circuitry. If you select "Hard Bypass", then those three controls are disabled, and you have to rely on the Channel Masters - a bit like my lean and mean F-series amp.

Big smiles,

Andy.

What if you have something like an Analog Delay Pedal and a Chorus that do not have volume controls. How would you establish the FX unit output level??) Should you just turn up the amp send level up as high as possible without distorting the pedals?? It seems to effect the total output of the amp. Higher the send, the higher the output.

Jack

 

[Dann'sTheMan]

What if you have something like an Analog Delay Pedal and a Chorus that do not have volume controls. How would you establish the FX unit output level??) Should you just turn up the amp send level up as high as possible without distorting the pedals?? It seems to effect the total output of the amp. Higher the send, the higher the output.

Jack

Hi Jack,

The pedals you've described have likely been designed for unity gain - and if they haven't there's not much you can do.

Theoretically, you should do the following:
step 1) set the Output control on the front panel to 12 o'clock
step 2) adjusting the send level on your amp so that the FX unit is seeing a good strong signal without clipping.
step 3) now you cannot adjust the output level on your FX unit, however you can unplug the jacks from the FX loop and check whether the amp is at a comparable volume level with and without the FX connected (revisit step 2 until it is).

In practice however, because the Lonestar has a tube buffered FX loop, you may like to set a hotter than theoretical signal through this stage. As long as the FX unit isn't clipping, then you can set the controls where they sound best, but the above is a good starting point.

On my F-50, I like to turn the Channel Masters up high (equivalent to the Lonestar's Channel Volumes and the Send level), and then reduce the returning level (equivalent of the Lonestar's Master and Solo controls). This approach gives me great tones at low volume levels on my F-50.

Big smiles,

Andy.