Sound Garage Tales » Guitar Amplifiers

The Loopy Effect Loop

Gabi — Thu, 07 Jan 2010 18:12:27 +0000

A common question I am being asked frequently is if my amps have an FX loop. The answer is a BIG NO. Here is why…

Guitar pedal board routing

Long Live FX Loops (but not in my amps)!

Honestly, I have nothing against effect loops. They have their role in certain high gain amps and do what’s needed to be done greatly: tapping into the preamp output signal, and making it available (via a tube or a solid state buffer to level out any possible impedance mismatches) to external FX processors then returning it in the amp’s power stage.

But if I graft a typical active FX loop as we know it, (and believe me, I tried it) in any of my Low-Gain Gabriel V18 or V33, the tone morphs into something way far from the typical character and dynamics, with a noticeable gain loss that results in a wimpy sound, something that is the last thing on my menu.

High Gain vs Low Gain Amps

Leaving all “class-talk” behind, there are generally two kind of guitar amps on the market today:

High Gain amps, where the signal gets over driven in the preamp, then served further to the power section that does little more than just amplify it. So in a high-gain amp, the majority of the tone characteristics are typically shaped in the preamp.
Here, the effect loop makes great sense since the signal sent to the effect processors has already an identity without loosing anything of its original character.

Low Gain amps where the tone is not saturated in the preamp section (the signal is quite clean at the preamp output) but rather by the power tubes when driven at higher volume levels. This results in a very characteristic overdrive shape distinct to these kind of amps. The Gabriel amps fit in this category.

Now, besides the fact that grafting a buffered effect loop into my low gain Gabriel V18 or V33 might come close to a blasphemy punishable by being burned at the stake, it would make no sense since the clean preamp signal still needs to receive its character and overdrive from the power tubes and an effected preamp output signal will alter the final character of the tone, robbing it of its precious gain and dynamics that’s so needed for the power tubes to do their magic.

The Workaround

As I often mention, the 18 watt Forum is a wealth of information with a lot of folks who are willing share their guitar amp building tips and wisdom. And that’s how I found out about this cool way of wiring your Gabriel V18 or V33 (or 18 watt amp for that matter) so it can simulate a wet/dry scenario of an FX Loop. In fact it is more than a simulation – it is a real effect routing with separate control on the dry and wet signal.

Simply, go with your guitar in the BRIGHT channel, then with another guitar cord, patch in the parallel jack of that same BRIGHT channel (this is your FX Send) and plug it into your FX chain input. The output of your guitar pedal board (FX Return) will go into the NORMAL channel input (I like to use the lower input jack).

This way you control your dry signal with the BRIGHT channel and the wet signal with your NORMAL channel. Simple as that! Diagrams below to help explain:

Pseudo FX Loop Diagram

Now, you can get creative here. You can group your pedals per channel having even more control over the levels.

For instance you can have all your overdrive pedals right in front of your amp going into the BRIGHT channel and have all modulation pedals placed in the FX Loop, going into the NORMAL channel.

This way you have independent control (on the NORMAL channel) over the amount of modulated signal from your modulation pedals grouped within the FX Loop. The guitar signal going into the modulation pedal group FX Loop will already be ‘effected’ by the overdrive pedal group you have going into the BRIGHT channel – but in this routing you control your balance between the over driven and modulated tone. Diagram below that explains what I mean:

FX Loop 2

Yes, the two channels are out of phase on my amps. So if you would patch the two channels directly with a cable, the tone will sound boxy. But when there’s a pedal chain on its path, it really doesn’t matter since the tone is already processed and you cannot perceive the out of phase coloration.

Here’s a detail of the amp channel connection:

It is a very simple setup that literally gives you the same options that an FX Loop would offer but without compromising the tone, or any of the internal circuitry, and having the full rich tone of the overdriven power tubes.

Fender Hot Rod Deluxe Electric Guitar Amp Demo

Gabi — Wed, 27 Aug 2008 14:44:54 +0000

Jason Spencer demonstrates the Fender Hot Rod Deluxe electric guitar amplifier. Sweet one!

Duration : 0:4:42

[youtube z0mgUGoP7_0]

Thermionic Eye Candy

Gabi — Fri, 04 Jan 2008 17:22:46 +0000

There is a superb NOS photo library at www.tubemongerlib.com that one of my friends from Great Britain turned me on (Thanks Craig!!!).
So, browse and drool.

Uploaded with Skitch!

Two amps today!

Gabi — Tue, 18 Dec 2007 16:44:54 +0000

It seems much more productive when my day isn’t interrupted by small, quick tasks (at first), like run and drop off packages at the FedEx office, or realizing that I am out of solder and need a quick trip to the Rat Shack store (I really like their solder!).
So, today I finished wiring the power supply on two amps. It is easier to work on one process at a time.
Seemingly the mind is setup to function well once is wound up. It takes me a generous amount of time to have my mind setup for a task. So, back to… wait what was I doing before writing this blog??

Ferarri Yellow Voxer 33?

Gabi — Fri, 05 Oct 2007 18:36:52 +0000

I just couldn’t resist not painting my transformer end bells yellow. And dang! It does not look that BAD after all! I am to the point of offering chassis only instead of being housed in a cabinet. Too good looking to be hid, right?

Postal Service & Elephants

Gabi — Wed, 03 Oct 2007 15:22:56 +0000

Check what happened to this package of tubes sent in Europe. It is not only the fact that the tubes in it are broken. They are FLAT!!!
This can only be done two ways. Either the post handlers are usually placing the heaviest packages on top of the smaller ones or, the post man got caught on a elephant crossing.

Buzzy G (solved again)

Gabi — Sat, 29 Sep 2007 04:36:38 +0000

Well after suspecting the speaker, then the casters on the cabinet, I zeroed in on the back panel. And yes, indeed the buzz source was coming from there.
It seems like the closed-back structure and small debth (9″) was contributing to bring that back panel buzz to surface, thing that usually does not happen on a open-back cabinet.
I solved this one with using a convertible back as I have on my 2×12 Slant cabinets. The two braces that join the three-pieced structure reinforces the whole back panel system so that it keeps everything snug and no unwanted vibrations or buzzes occur.

Buzzy G 2 (solved)

Gabi — Mon, 24 Sep 2007 16:33:41 +0000

Yes, the amp was fine. The culprit was the 1×12″ cabinet. Something with the speaker or at least a rattle of some sort that resonates with that “G” note.
He will drop it off this week to take a look.
So yes in the end – the amp was just fine.
I guess we’ll have to go through the reverse-troubleshooting process next time: from speaker backwards.
Actually – that wouldn’t be relevant in a case where the guitar cable is bad. Hmm…

Buzzy G

Gabi — Thu, 20 Sep 2007 17:20:47 +0000

It happens sometimes that some amps just have this buzz or noise on only certain lower notes. For example I had a local customer calling in telling me of this certain noise when he was hitting the G or G# on the lower string. So I had him bring in his amp for a check.
Funny thing is that I played it and didn’t hear that yesterday. There was however a different setting. He has a 1×12 cabinet with a Celestion Blue, and I tried it through a 1×12″ with a Greenback, using my LP.
Will try it later today with a Blue also. Things like these are harder to track down and they can be cured hopefully by just replacing the tubes. We’ll see…

Voxer 18w Guitar Player magazine review!

Gabi — Sun, 10 Dec 2006 14:29:33 +0000

Folks!

It is confirmed!

The Voxer 18 will receive another glorious review in the Guitar Player Magazine in the upcoming February 2007, issue done by no one else but David Hunter, the author of “The Guitar Amp Handbook”, former editor of “The Guitar Magazine” in the UK, contributor to books such as Aspen Pittman’s “The Tube Amp Book” Deluxe Revised Edition.

David has wrote a very favorable and positive review of the amp so stay on the lookout.
So all in all the Voxer 18 will be getting some serious fans throughout the continent and the whole world.

in Tone,
Gabi (Gabriel).

Sound Garage Tales » Guitar Amplifiers

The Loopy Effect Loop

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