Laney Pro-Tube Lead (100w) - Fx-Loop volume control

[stonerbox]

Hi guys!

Got somewhat of a unusual question, at least for this forum due to its main focus on stompboxes and such..

I play in a "stonerrock" band (down tuned+fuzz+psy and sh*t). We usually play pretty loud but at some shows we're force to turn the volume down. This is where my problem steps in, not that my sound changes from a less warm and driven amp but that my FX-loop has +8db boost. Now, on higher volumes the difference is not noticeable at all but as soon as the volume is set around noon on the amp the FX-loop boost way too much. So, I ask for your help on how to install a volume control at the FX-Loop on my Laney Pro-Tube Lead (100w).

I will be doing some research on my own but I figured asking you guys for help wouldn't hurt. Any ideas or help would be greatly appreciated since we're going on another gig this satuday!

Love this forum to death, Ben

[stonerbox]

I just realized that it says "line in/out" at the back.. but it's basically a FX-Loop, right?

[thelonious]

Hey Ben,

Do you have a schematic for this? I didn't find one with a quick google.

BTW, line level is fine for rack gear and some pedals with a lot of headroom, but it's pretty hot for your average pedal. Most of them are designed for instrument level. That might be part of your problem, unless I'm misunderstanding.

[stonerbox]

I haven't had any luck finding a schematic either. All I know is that it's pretty close to the JCM800 but with some popular mods people used to add to the Marshalls back in the days. That, and the fact that it's a 80's-something amp.

[stonerbox]

Found something here, http://www.el34world.com/Forum/index.php?topic=7789.0

EDIT: AOR100MV Schematic: http://www.mediafire.com/file/nmtygrveyum/AOR100MV.pdf

[stonerbox]

No love for this? Bump..

Could I just add a pot in between the "line in" and C19?

[PRR]

> my FX-loop has +8db boost. Now, on higher volumes the difference is not noticeable at all

8dB is very noticable.

That you don't notice a difference suggests you are running the _100_Watt_ amp at FULL blast, wiping-off any increase of level.

Then you turn-down to say 25W, add 8dB, you attempt 158 Watts and get the full 100W just as before.

Why does the FX loop have 8dB gain?

I'd think about a permanent turn-down pot in *the FX chain*, not the amp, so the FX chain runs unity gain. This could be a 10K trimmer in a box.

[slacker]

Where is the boost coming from? On that schematic, the volume pot is right before the line out, there's nothing to add any boost to the "fx loop" after that.
Unless I'm missing something, adding a volume pot after the line in is just the same as turning the existing volume pot down.

[stonerbox]

> my FX-loop has +8db boost. Now, on higher volumes the difference is not noticeable at all
That you don't notice a difference suggests you are running the _100_Watt_ amp at FULL blast, wiping-off any increase of level.
Then you turn-down to say 25W, add 8dB, you attempt 158 Watts and get the full 100W just as before.

That is definitely the case, as long as there is no headroom everything is fine.
The potential problem with a "pot-in-a-box" is that the (weird) 8dB+ boost only activates when a pedal is engaged. The weird thing is that I can't seem to find the "booster part" in  the schematic and what part of it that recognizes that a pedal is turned on. Just like Slacken wrote.
I only have a booster and a delay pedal and I certainly don't want one of them in "the loop" all the time.

Why does the FX loop have 8dB gain?

Reasons why beats me too!

Where is the boost coming from? On that schematic, the volume pot is right before the line out, there's nothing to add any boost to the "fx loop" after that.
Unless I'm missing something, adding a volume pot after the line in is just the same as turning the existing volume pot down.

Yeah! I could not find it either. This is truly a mystery.  

[defaced]

Do you hear a volume boost if you simply insert a jumper cable into the loop?

[stonerbox]

Do you hear a volume boost if you simply insert a jumper cable into the loop?

Actually I don't know? All I know is that when any pedal (in the fx-loop/ line-in/out) is engaged it boosts but as soon as I disengage it drops back to "normal" volume again.  
I just moved the amp back to the rehearsal today so I will have to try a patch cable (later this week).

If so, does it give us any future clues? Could the boost be regulated by impedance?