express effects loop

[Mont]

Can anyone point me in the right direction?

[geetarpicker]

Yes. Put together a wet/dry rig and put the effects totally post amplifier. Truly an effects loop in an Express is a big compromise.

[Mont]

do you have a schematic?

[Reeltarded]

It is done like any other. Passive? Inline after tone stack. 2 switching jacks.

Mr. Geetarpicker is right though. You break the topology. You turn your amp into an (some might say 'even') thinner Marshallish thing.

[Colossal]

do you have a schematic?

Mont,

Geetarpicker describes his approach in another thread. The premise though is a dry/wet setup. Your Express would be driving your usual cabinet of choice, totally stock amp, and totally dry (and totally badass). Then you mic your speaker cab, add your effects, and run this effected signal to a mono (for dry/wet) or stereo power amp (for wet/dry/wet). I believe (IIRC) Geetarpicker is using a line out either just after the output transformer or built into his attenuator to tap the amp dry signal. The wet cab(s) need not be huge, a simple 1x12 will do. This will thicken the resulting sound dramatically. With a stereo setup, your amp remains stock (as it was intended...no effects loop tone suckage) and you can bask in the stereo image

[geetarpicker]

I've done it two different ways, though I've never actually used a microphone in the system to drive the wet side. I think Eric Johnson, and others have used mics in their wet/dry rigs to keep things truly isolated. Years ago (early 90s) I would run my original Express straight to the 4x12. Then the 2nd speaker jack went to a box with a 2 resistor pad to bring it down to line level. I think it was something like 47k in series that was then terminated to a 1k to ground, the + and - being across the 1k. The 47k can be trimmed + or - to adjust the net line level. Then on to a rack processor (I had a Yamaha SPX900 back then) then to small power amp, then a 1x12. I also tried a 4x12 for the wet, and even a stereo wired single 4x12 one side dry the other wet. That said, my preference was for the separate 1x12 wet, 4x12 dry. Then I'd have the sound guy mic both and blend them 50/50 give or take.

More recently I've been using my Phaustine Phantom attenuator (sadly they are discontinued) in my setup. Typically at most gigs these days I need about 4-6db of attenuation. My Phantom has a speaker emulated line out that sounds quite decent. So, I run the 4x12 off the regular output of the ATT then the speaker emulated line out goes to the effects, then to reamp the wet signal I use a 1kw QSC K10 powered monitor. Then I have the sound man mic the 4x12, then I use the XLR feed through jack on the K10 to send the sound man the wet side no mic needed there.

The main difference is in the 1st version you need a guitar speaker to get the wet tone correct, and you need a separate power amp. In the 2nd version the powered monitor simplifies the rig, but then you need some sort of speaker emulation circuit in the system to get the correct tone on the wet side.

Currently my wet/dry setup uses a couple TC Electronics Toneprint pedals, and I just added a Strymon Timeline. The Toneprint pedals have selectable killdry options which are key to a wet dry rig for certain effects. The Timeline also has killdry but the current firmware needs a little more tweaking in it's killdry function but is expected soon. With the pedals I also use a small mixer to blend the effects. It's a little trickier to put together than a rack processor, but having the pedals instead of a rack unit makes live tweaking much easier.

Hope that helps! GK

[RJ Guitars]

Mont,

I just added an effects loop to my own version of the Express. It works, but it's really an idea under development so I won't say that it's the answer yet. Here is a link to previous discussion on this topic - http://ampgarage.com/forum/viewtopic.php?t=8437 and here is the link with a few details on my recent work on this topic. Go to page 7 on this link - http://ampgarage.com/forum/viewtopic.php?t=17524 -- since this is a new implementation of this idea, you should see some additional work done on it over the next few weeks...

I will make sure I say that Geetarpicker knows these amps extremely well and has really explored the many ways you can get the most out of an Express amp. If you want the ultimate sound, the way he describes to do things will most likely give you the ultimate solution.

rj

[variableresults]

Has anyone tried Metro's Zero Loss FX loop? It's buffered and (supposedly) puts out exactly what is put in, just with the added FX.

http://metroamp.com/store/index.php?mai ... cts_id=499

Seems like a pretty big hit on the Metro forums. Not sure if it would work on an Express, of course, which is why I ask (considering doing it myself whenever I get around to getting a kit ).

[variableresults]

I just did a little bit more schematic/layout scanning on the Metro FX loop and I (tentatively) think this could work. The instructions are mainly centered around the Marshall design (treble pot middle lug -> PI/MV), which obviously doesn't match up with the Express, but I think you should be able to duplicate the idea by inserting the loop between V2 pin 1 and R9 going to the PI.

I still don't know how effective it would be with a goosed Express since so much of the distorted sound is coming from the power tubes (and thus distorting any time based FX, too), but it should be better than FX inserted at the front end since you're bypassing the 12AX7 gain stages. It's hard to say what this loop would do to the dynamics without trying it, of course, but assuming it sends out exactly the signal it takes in (+ FX), I assume it would depend more on any buffering built into the FX you are running rather than the loop itself.

I could be completely wrong, though, as I've been out of my amp building hobby for a while and just got back in

[martin manning]

The usual place for a loop is just before the PI, but in this circuit I really don't see any good solution. The second and third 12AX7 stages have no attenuation at their outputs so the signal levels will be very high, high enough to overdrive the loop. Then the return signal is not at all likely to be equal to the send. The distortion begins building from stage 2 on into the PI and power stage, and interrupting that process will certainly alter if not destroy the character of the amp. The output from the tone stack is more or less line level so a loop could be inserted there, but that would miss the point entirely by putting the effects before the distortion is created.

[Reeltarded]

I only like passive loops for top secret parametric eq inserts, and then the amp goes on a load that feeds effects and secondary power.

An Airbrake with a variable direct is something I am interested in, and it works for every amp in the pile. One size fits most.

[jjman]

Tapping after the 3rd stage is key as mentioned. That stage compresses when it's clipping so time-effects need to be after it when it's clipping. This happens only at high setting on the volume, higher than the setting where clipping (in the outputs) starts.

My parallel loop tap's off a voltage divider after stage 3 reducing the send signal down to line level. After the effects, I bring the wet into half a 12ax7 (you have a spare triode) to boost it back up as much as possible before recombining with the dry. I used a phase flipping small tranny to bring the phase back in line with the dry. Then a wet/dry mixer pot before the PI.

If I was doing it again, I would modify the PI to allow input to both sides of it (like a Marshall 18watt with trem does) and have the loop return (after it's boosting triode) to the "other" side of the PI for phase harmony. This would eliminate the need for the phase flipping tranny. The key is you have to send a signal that's near line level while tapping it post 3rd stage. Parallel seemed the only practical approach to me.

It's not "pure" and using a separate amp probably sounds better and keeps the "Express" an "Express." Mine is far from pure in more than one respect.

[pablogt]

I was thinking of installing a Metro FX loop on a K50 too. I discarded the idea for the same reasons stated above.

After trying a dry-wet setup with my TAD Silencer's speaker emulation output I started thinking of incorporating an on-board speaker emulation output instead of the loop. I think it would be a great addition to this kind of amps. And their layout have that empty space just in the right place! (I think I suffer some kind of agoraphobia related to chassis and faceplate void spaces).

Can anyone point me to a known good speaker emulation schematic?

Pablo

[El Chiguete]

How about using one of this for a loop?

http://www.ceriatone.com/productSubPage ... -lator.htm
http://www.ceriatone.com/productSubPage ... ulator.htm