Modding an Amp to add an effects loop

[Kiteboarder]

Is it possible to modify an amp to add an effects loop? Reason I ask is I want one of those new Mesa Transatlantics, but I need it to have an effects loop. I know it'll void the warranty, but that is a risk I'm willing to take.

Any of you know how to do this or can recommend someone? Can it be done at all?

Thanks, Danny

 

[djw]

Hmmm... I dunno, I'm going to take a wild guess that the reason we don't see fx loops in these lunchbox amps (Vox Night Train, Orange Tiny Terror, etc) is simply because there isn't room. Generally they require two jacks, sometimes a level control (pot or switch), and another preamp tube. All of that stuff takes up space that simply isn't there. If you think about all the little switches and the capabilities that are crammed in there -- the Transatlantic already has scads of features that those others completely lack. You might be able to stuff a loop into it, but it would probably at the cost of at least a couple of those features... there's just no where else to put it.

I'd love to be proven wrong though.

 

[Kiteboarder]

Thanks for chiming in Damon. The main problem here is the amp is brand new. It hasn't been out long enough for techs to experiment.

 

[msi]

Thats what I was going to say. It would probably not be possible to add a tube fx loop due to space and power requirements. But depending on if the power transformer provides a low voltage tap, you might be able to do a solid state FX loop that would be better than a tube loop. Fx loops shouldn't and noise or distortion and many tube fx loops are bad at that. Solid state FX loops are better because you don't want distortion in the fx send or return, and solid state fx loops excel at that. There is just the stigma people have against solid state, even when solid state devices are better suited.

 

[b0nkersx]

Thanks for chiming in Damon. The main problem here is the amp is brand new. It hasn't been out long enough for techs to experiment.

I don't know if this applies to the TA, but I've read that people have had very bad results from adding an effects loop to a Vox Night Train. If the effects loop is THAT essential and you want a smaller amp, just get an Express 5:25 or Lonestar Special or something. These lunchbox amps are designed to be portable amps you can crank easily for poweramp distortion, not to be do-it-all amplifiers.

 

[94Tremoverb]

It's theoretically possible to add an effects loop to any amp if there's room for just one TRS ('stereo') jack, which you can use as an insert point. You need to break the signal path at the right point and run it via the jack, which needs to be switched so it's bypassed when there's no plug in it.

But there are some problems...

First, in a tube amp the signal level at any point late enough in the circuit to make it worthwhile (ie after distortion) will be pretty high. This means that it almost certainly won't work correctly with anything other than line-level processors, and maybe not even then. You can solve this with an external step-down/up box though, to cut the level coming from the amp, run it through the effects, then boost it back up to the original level again - essentially the same as the circuit that's inside the amp if it has a proper loop.

Second, if the amp has a post-phase-inverter MV (which I think the Transatlantic may do, if it's loosely based on Vox/Matchless-type circuits), it isn't really possible to put the loop after the distortion, because at that point the signal is in two parts, reverse phased with each other. In theory you could do it by using a true stereo FX processor running in Dual Mono, but you'd need two separate loops. (And you'll still definitely have the level problem.)

Third, if the amp is using mostly power tube distortion, there's really no point anyway, since it isn't possible to put the loop after the distortion at all.

I've fitted simple loops to quite a few tube amps over the years, and almost always run into one or more of these issues, especially with smaller amps. If you really want to use FX after the distortion, it's much easier and probably better just to get a bigger amp with a proper loop, use a pedal or outboard preamp for the distortion, or just add the FX in the mix.

 

[Kiteboarder]

Thanks 94Tremoverb, that was VERY informative. It's out of the question then. Thank you. I'm going to stick with my Lonestar for the louder stuff, but I'm going to go with the Egnater Rebel 30 for my little portable amp. I prefer Mesa, but in this case I need to go with what works for my given situation.

Again, thanks, Danny