ABY BOXES NOT SO GOOD?

[MEKer]

So here is Fulltone's take on ABY boxes. Never used one, been thinking about getting one for the Y function with my 2 amps at the same time, and then I read this and it puts a damper on my enthusiasm.


"TITLE: Why doesn't the definitive ABY box exist?

First, let's mull over the problem with ABY boxes!

There are 2 types of A/B boxes out there:

Passive A/B boxes

These are simple, inexpensive units using a footswitch to toggle between two outputs... some adding a second footswitch to combine the ouputs for the "Y" function. (both amps on) This can work fine when the AB box is placed AT THE END of a chain of various effects pedals, right before the amps.

The first problem arises when (like me) you use a separate effects setup for each amp, placing the A/B Box BEFORE all the effects. THIS is when you will experience horrendous POPPING sound while switching between amps.
The second problem (if you use fuzzes or hi-gain pedals) being a very loud white-water sounding HISS should you ( for example; have a fuzz on side "A") then switch to side "B" without turning off said Fuzz.
The third problem is that you will get "loading" between the amps when running in "Y" mode where both amps are on at the same time, taking away highs and muddying up your sound.
The fourth problem can be "phase issues" when running both amps in "Y" mode. When 2 amps are out-of-phase it can be very odd sounding, with an apparent loss in volume instead of the expected increase and a very strange EQ, like a wah-wah being on in a fixed position.
The fifth problem can be dangerous as well as noisy; when a "ground loop" happens while connecting two amps via an A/B pedal, the result can be a constant loud HUM and could result in a nasty shock, especially hazardous when stepping up to a vocal mcirophone!

Active A/B boxes

Some active boxes can alleviate the loud popping sound, but do nothing for the other problems common to Passive A/B/Y boxes. And they introduce a new problem; They convert your guitar's native Hi-Impedance signal to Lo-Impedance. And most great distortions and Fuzzes simply do not like to see Lo-Impedance signal! They lose volume, dynamics, become trebly sounding... it just changes everything for the worse.

© Fulltone"

This can be found at
http://www.fulltone.com/faq/why-does...-aby-box-exist


Comments?

[line6man]

The thing about physics and music is, just about everything you do is a compromise of some factor or another. The question is which compromises you accept, or what means you will go to to alter them. Trying to run one signal to two input gain stages will drop the impedance if you simply run them in parallel. Conversely, attempts to sum outputs passively kills output, and active buffering opens the door to increasing noise, decreasing headroom, and altering the nature of the signal impedance. I'm not convinced of their fourth and fifth problems, however. Issues of phase are not significantly different running one signal to two outputs than running two signals (Dual outputs) to two outputs. That's inherent to the nature of having multiple amplifiers trying to reproduce the same thing at the same time. In any case, if it becomes such an extreme issue that it is noticeable, you have the option to add a phase-shifter (Not to be confused with the flanger-like effect, that is something different.) to your signal chain. There are rackmount signal processors available for live-sound applications, but a simple opamp circuit can be built to adjust phase delay, as well.
As far as ground loop issues, that is something to worry about with all sorts of things, not just AB boxes. Sometimes it is an issue and sometimes it is not, depending on the application.

[MEKer]

Sheesh---maybe I'll just forget the whole thing.

[gdavis]

If all you want is the Y function, you can find a Y cable pretty cheap to give it a try. Problems are possible but often things work without a hitch.

You might have a ground loop, you might not, it depends on the amps. The problem can often be solved by using a cable with the ground disconnected from the Y to one of the amps. You can even buy these cables or hack your own.

Phase again, maybe, maybe not, it depends. If it is a problem it can be solved by hacking a speaker cable to reverse + and - at one end.

This all assumes your not doing anything crazy with effect, just Y straight to amps.

Best solution may be napalm

[MEKer]

usually is.........

and it smells great in the morning

[gdavis]

BTW, the framptone amp switcher is about the closest you'll get to the ultimate AB/Y box and address most if not all the issues you'll see, but it ain't cheap.

[line6man]

Originally Posted by MEKer

Sheesh---maybe I'll just forget the whole thing.

I've never seen anyone make a big deal of this. Most people use AB boxes without even knowing such issues can be of concern.

[Munjibunga]

One word: Lehle. Here's a demo of their Dual SGoS switcher.

Here's the specs.

[Smilodon]

Why wouldn't switching between two preamps work?

They can be switched without too much noise, and if you set up two low impedance amps (That are switched) and two high impedance preamps (more like a buffer) on each output you could take care of all those problems as far as I can see. (Except for the cost)

(My knowledge about analogue electronics is pretty rusty, though... )

[Rockin Mike]

Lots of things work fine in the real world, and I only find out they are problematic by reading about them on Talkbass. Not saying the experts are wrong, just saying the problems are subtle enough I wouldn't have noticed them until someone brought them up.

I imagine ABY boxes might fall into that category. I would say try one out and see if it sounds good.

[line6man]

Originally Posted by Smilodon

Why wouldn't switching between two preamps work?

They can be switched without too much noise, and if you set up two low impedance amps (That are switched) and two high impedance preamps (more like a buffer) on each output you could take care of all those problems as far as I can see. (Except for the cost)

(My knowledge about analogue electronics is pretty rusty, though... )

For all practical reasons, buffering is the way to go. That is the traditional means of sending one signal to multiple outputs. (Look at mixing consoles, for example.) The concern laid out in the article, however, is that certain effects may be engineered to want to see a specific impedance. I personally wouldn't bother with such things, as I'm of the belief that instruments should have buffered outputs from the start. I like multi-effects units, but if I were buying individual pedals, I would choose them wisely. In any case, this issue is typically addressed by the "Does this pedal jive with active basses?" threads I'm sure people post daily in the Effects subforum. This is a non-issue if you don't use a lot of effects, though.

[Unrepresented]

Originally Posted by Munjibunga

One word: Lehle. Here's a demo of their Dual SGoS switcher.

Here's the specs.

I am satisfied with the Lehle Little Dual A/B/Y and it addresses the biggest issues of the OP's list. The switching is silent and there's an available phase inversion button. As for the issues with dirt pedals being noisy, that's more an issue with the dirt pedals, not the switcher.

[Biggbass]

I recently removed the Whirlwind AB box from my pedal board due to loud ground loop hum. Was wondering if it had anything to do with the battery inside the box, which is supposed to be there just to illuminate the LEDs. But diagnosis pin pointed the AB box as the source of the hum. Could be that it just went kaput and it's time for a new one. Need to open it up and take a look at the guts though.

[TimboZ]

I went with a t1m mini buffer with dual outputs.

http://this1smyne.com/shop/mb-mini-buffer/

[MEKer]

Well, I went to the mini-buffer site---saw the lil things. One jack each side. Cannot see how my one jack from the bass cord ends up going to 2 amps simultaneously like an ABY.

Researched the Lehle Little Dual and that seemed really nice.


Hmmmmm.

[grisezd]

Rather than split the signal before the amp, I like to plug into amp 1, then out of amp 1 (preamp out, second input, effects out, etc) to the second amp. If you have that option on your amps you might give that a try. Just don't plug a speaker out of one amp to an input of the second!

[bongomania]

Originally Posted by MEKer

Well, I went to the mini-buffer site---saw the lil things. One jack each side. Cannot see how my one jack from the bass cord ends up going to 2 amps simultaneously like an ABY..

Look at the pull-down menu of "options".

[SGD Lutherie]

Originally Posted by MEKer

And most great distortions and Fuzzes simply do not like to see Lo-Impedance signal!

That's nonsense. I use a number of distortions and fuzzes with active basses, and have been doing so since the mid 70s. The only ones it doesn't work well with is something like a Fuzz Face. And actually it works fine, it just sounds different.

Currently I use a modded Boss ODB-3, EH Bass Microsynth, Brassmaster clone, and I had a green Russian Big-Muff but sold it.

[line6man]

Originally Posted by Biggbass

I recently removed the Whirlwind AB box from my pedal board due to loud ground loop hum. Was wondering if it had anything to do with the battery inside the box, which is supposed to be there just to illuminate the LEDs. But diagnosis pin pointed the AB box as the source of the hum. Could be that it just went kaput and it's time for a new one. Need to open it up and take a look at the guts though.

Why would a pure DC source have anything to do with hum issues? Batteries do not have ripple like poorly filtered DC supplies rectified from AC.

[drewfx]

Originally Posted by line6man

I'm not convinced of their fourth and fifth problems, however. Issues of phase are not significantly different running one signal to two outputs than running two signals (Dual outputs) to two outputs. That's inherent to the nature of having multiple amplifiers trying to reproduce the same thing at the same time. In any case, if it becomes such an extreme issue that it is noticeable, you have the option to add a phase-shifter (Not to be confused with the flanger-like effect, that is something different.) to your signal chain. There are rackmount signal processors available for live-sound applications, but a simple opamp circuit can be built to adjust phase delay, as well.

I suspect the phase "problem" wasn't referring to simple phase cancellation between 2 amps but to the possibility that you might have a pedal in one chain that inverts the signal.

But IMHO most of these "problems" are either only a problem in specific cases involving certain equipment or are overstated.