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What's the deal with true bypass?
The term "true bypass" is rapidly becoming as diluted as "fat-free" (where "80% fat free" actually means that it's got 20% fat in it). But do we really need to worry about our effects when they're not on? Isn't the "true bypass" craze just a hype, designed to allow "boutique" pedal manufacturers to charge insane amounts of money for their products, and for guys to be able to make a living modding effects? Read on...
True bypass?
This means that the signal passes straight through the box - directly from input to output jack, touching only the switch/relay - when the effect is bypassed. This kind of bypass arrangement is only possible to create with some sort of mechanical switching - either with a good old stompswitch, or with an audio relay. The switching is done simultaneously at the input and the output, to route the signal around the electronics in the effect, and when bypassed, the effect/tuner is completely disconnected from the input signal. This is important, because as we will see later, this is a simple way of knowing if the claim that a certain pedal tuner is true bypass, is true or not. Here's a simple sketch of how it works:
True bypass switching can be wired inside a pedal, or inside a separate true bypass box which the pedal connects to. In that case, the pedal is kept constantly active, and the signal gets routed through or around it from the box.
Other variants
FET (electronic) switching: Widely used in Boss/Ibanez type of pedals, it has its perks. First of all, the switching is completely silent, without any clicks or pops. Second, both input and output is buffered, to keep the impedances constant - the signal "looks" the same to the amp, regardless of if the pedal is bypassed or active. Third, for a big-time manufacturer it is much cheaper to include the extra components in the pcb design, and control the switching via a dead-cheap tactile switch, than to install a big mechanical switch that needs to be hand-soldered. The drawbacks are that this type of switching introduces a lot of components not needed for the actual job the effect is supposed to perform, and the pedal will not pass any signal if it loses power. Read more about this type of switching here.
Mechanical output switching: Also known as "half-assed bypass", this type of arrangement is to be avoided at all costs (unless you plan to keep the pedal active at all times - then it doesn't matter, of course). You'll find it in Electro-Harmonix pedals produced before 2002, MXR (original as well as modern Dunlop reissue versions), many of the Maxon "vintage" pedals, and of course in most wah pedals. You will even find this switching system in Maxon "nine" series pedals produced before 2004 (they were/are advertised as being True Bypass - read all about it here). In this system, the guitar input is hardwired to the effect input, and only the output signal is switched. The presence of the electronics will affect the guitar signal, something you won't hear when the effect is active but will definitely notice when it's not (especially if this bypass arrangement is the first thing the guitar meets, with no other pedals in front). The input impedance of the effects circuit will also effectively be placed in parallel to the input impedance of the next pedal (or amp) - lowering the combined input impedance to half what it should be... About the only perk to this switching system is that the bypass signal will pass through even if power is lost (which is not an indication of true bypass - more about that later).
Eh... those two are the only other major variants out there - with minor alterations every so often, of course. But for the most part, everything else is just sales blurb and new, 'exciting' terminology. So let's investigate those a bit, shall we?
Terminology
This is like shopping for single malt whisky - you have to check the terminology very carefully. If the broschure says anything other than "True Bypass" (in that order, with no other words in between), assume that the switching is one of the other variants. If it actually says "True Bypass", assume they are lying, and investigate...
Hardwire bypass (sometimes even called "true hardwire bypass"): This only means that the switching isn't electronic. In 90% of the cases, it's the good old half-assed bypass with a buffer section in front, to ease the signal loading. In the final 10%, the pedal simply doesn't have the buffer. For instance, MXR uses a buffer at the start of the effects circuit, which is designed to present a high enough input impedance to be "electrically transparent" - the idea being that the electrons will not even try to move that way, when the bypass line is open. I've even heard Dunlop techs repeatedly refer to this system as True Bypass. Well, it isn't. True Bypass depends on the effects circuit being physically disconnected from the input signal, in bypass mode. But does the Dunlop/MXR system (sometimes referred to as "electronic true bypass" - an oxymoron if I ever heard one) work as intended? Not really - it may be as "invisible" as it wants - it will still drop the overall input impedance the pickups "sees", compared to when it's active (thus changing the tone).
There's one exception to the above - Digitech markets a line of pedals under the name "Hardwire", and contrary to their name, they actually seem to be true bypass for real. They use relay switching to provide true bypass in a Boss-esque stompbox, and according to their own description, the circuit is disconnected at both ends in bypass mode, leaving only a straight in-out connection. True bypass, in other words. Thumbs up for Digitech (although the pedal series' name can be a little misleading in this case).
Also, MXR have recently put out at least one pedal which is actually true bypass, namely the Carbon Copy Analog Delay. It uses the same switch as the others, but uses a Millennium-type circuit to run the LED, which means they can now have true bypass. I'm not aware of wether this system is in use in any other of the new batch of MXR pedals (GT-OD etc).
Hardware bypass: A variant on the above, used by Hughes & Kettner. In their sales blurb, they say: "The sophisticated hardware bypass ensures the instrument signal remains 100% unaffected in the bypass position." Very interesting... but no cigar. The wiring is the same as in the earlier example. They even go so far as reference the MXR system, but they stop just short of calling it 'True Bypass'. Read here: "The TUBEMAN features a real audio treat, the hardware bypass. This type of signal routing, popularized by the MXR® Classics, ensures the instrument signal remains 100% true and unaffected in the bypass mode." Pffft...
True (hot-wire) bypass: I just spotted this one, and frankly I don't know what it is supposed to mean. Or rather, I know what it is supposed to make you think it means, but I don't know what it really means. My hunch is that it's the same as the other ones - a direct connection from input to output, but with the effects circuit still connected.
Split bypass: This term was introduced by ModTone effects, and so far I haven't been able to verify exactly what it means. It does, however, sound suspisciously like the mechanical output switching system used by MXR/Dunlop etc. And since they advertise some pedals as having buffered bypass and some as having true bypass, they don't seem to use the "split bypass" as a decoy. So it probably is the MXR-style mechanical output switching, but without trying to pass it off as something else...
Virtual bypass: This can be anything, really. Many times, these pedals have a round metal stomp switch that control the switching transistors in an electronic switching arrangement. Other times, it is the same as the Hardwire bypass, with a buffer to ease the loading, with extra high input impedance. Again, the theory is that once the gateway directly to the amp (via the switch) is opened, the high input impedance of the effect will make it "invisible" to the guitar signal. It's a nice heory, but it doesn't work in practice... no.
Passive bypass: Used by Marshall, among others. I'm guessing it denotes a mechanical switching system of some sort, and I'm also guessing that it is the same output switching system as in the others. After all, if it were true bypass for real, they'd definitely want to use that term...
Side chain: Some of the signal is tapped off to the side, into a separate chain. This is the thinking behind the "tuner out" jacks on volume pedals - the signal is tapped before the volume control, so you can tune with the volume off. Also, since it is a "side chain" it doesn't have anything to do with the main signal chain, right? Neat, but it doesn't quite work. Take a look at the "mechanical output switching" figure above - that is a side chain... Aside from the lack of a switch to select between them, that system is exactly the same as what you get when connecting your tuner to the "tuner out" on a volume pedal.
A true bypass means that the circuit is physically disconnected from the input jack/bypass line. If a pedal doesn't do this, it is not true bypass. Period.
Terminology, part II
Clearly, deciding what to call what and having everybody stick to it isn't as easy as it sounds. Unless someone can actually register the term "True Bypass", together with a clear description (with circuit diagrams) of what constitutes a true bypass, there will always be the risk that manufacturers may take liberties with the language. But do they? Is the term "true bypass" increasingly losing its meaning, due to manufacturers using it frivoulously? I don't think so. In fact, the term "true bypass" - while often misunderstood by the general public - seems to have settled by now, and the manufacturers generally won't use it unless they can back their claim up.
To date, there are only one (and a half) exceptions that I know of - as mentioned earlier, Maxon used the term "true bypass" in the advertising for their "nine" series, when they clearly were not (read the article here). As of late 2003-early 2004, all Maxon "nine" series pedals are true bypass for real, so now their claim has merit. The half example comes from Dunlop, or rather from their tech guys, who - probably sick of having to repeatedly answer questions about the bypass system on their pedals - has stated to inquiring customers that the current production Dunlop/MXR pedals are indeed true bypass. Of course they are not (see the above discussion), and Dunlop/MXR has never officially tried to market them as such.
Still, some maintain that we need a new term, because the manufacturers has soiled the old one. Howard Davis, EE - who used to work for Electro-Harmonix as a circuit designer - is one of them (or rather, the only one, to my knowledge). While his intentions may be good, I strongly believe he is only confusing the issue. In his terminology table, he states that "true bypass" is the same as the other not-quite variants that only switches the output. This is of course totally wrong, and it doesn't help anyone, except the manufacturer who wants to market his pedals as "true bypass" even when they are not. I fail to see what he is trying to accomplish here. The universally (or close to, at least) accepted term is "true bypass", and a lot of work has gone into promoting that term, making it known, and keeping people from misusing it. We're nearly there now. In fact, we are so close these days that there's only one (serious and otherwise trustworthy) place on the internet where you will see "true bypass" being claimed to be the same thing as "virtual/passive/hardwire bypass" - and that is Howard Davis' site... Why???
How do I know?
I often hear people wonder if their so-and-so pedal is true bypass or not. Sometimes I wonder if this is the same I-need-to-know urge that makes us want to know for certain that the fridge light actually does go out when we close the door... My response is always the same: you only need to worry about it if you notice a degradation in your tone. Basically, if it works, don't fix it. But of course I want to know too... So in the interest of public knowledge, or at least to have some fun for myself, I decided to list and kill off a couple of myths about True Bypass:
- If I take the battery out and it still works in bypass mode, it's true bypass, right?
Nope. Sorry. What the battery-out test will tell you is if your pedal has a mechanical switch that carries signal or not, and if there are any active electronics in the main signal path. Take a look at one of the SPDT diagrams again - when the effect is powerless, the bypass line will of course still function as intended, but the effect input is still attached to it. No true bypass there, then. If your pedal has a buffer stage in front of the switch, or if it has electronic bypass switching (such as in Boss/Ibanez-type pedals), it will of course not pass any signal when powerless. But - again - you can not use this test to verify that a pedal is true bypass, only that it isn't.
- You need a 3PDT switch if you want true bypass and a status LED.
Wrong again. Did you think it was true? If so, you're in good company. Even Mike Fuller seems to believe this one. Here's a quote from the Fulltone site:
"If your pedal has an LED and doesn't have a 9 pole switch, it ain't True-Bypass."
And you'd think he'd know better... He probably does, but he's a businessman, and the "9 pole switch" he's referring to is of course his own triple-pole, double-throw (3PDT) switch. Kinda funny that he slags other manufacturers for using catch phrases like "virtual bypass" etc, and at the same time makes a claim of his own that is untrue... Granted, for me the easiest way to add an LED to the switching system would be to add a third row on the switch and run it from there. But the truth is that you don't even need to redesign the whole circuit to accomodate an LED to indicate on/off status. Even an "aftermarket" true bypass mod with LED can be done with a DPDT. It's called the "Millennium bypass" and was invented by R.G. Keen. Read all about it here (scroll down a bit in the article and you'll find it), and here you'll find even more stuff, this time about the "Millennium 2". Personally, I wouldn't bother with it, though. The amount of components and effort needed to make it work is not worth it, IMHO. Especially when you consider that a 3PDT switch is only $3 more than the Carling 316PP at Small Bear... I'd definitely recommend you to go for a 3PDT switch if you absoutely need to add an LED. But that still doesn't make Mike's statement true!
- In bypass mode, the circuit is electrically invisible, so therefore it is, in effect, true bypass.
Sorry... well, in theory this one is actually correct. If the circuit's input impedance is sufficiently high, it shouldn't even register to the signal. As we know, current will always choose the path with the least resistance, and if we can make the path leading to the amp that much more inviting than the path leading to the effect, it would qualify as a true bypass (since none of the electrons will choose to veer off into the effects circuit). But in real life, this doesn't seem to work. I have no scientific proof of this, only lots and lots of observations where effects which are supposed to be "invisible" in bypass mode still have affected the tone...
- True bypass actually degrades the signal, rather than help it.
No, it does not. That is a myth propagated by people who are trying to sell their own (buffered) pedals. A true bypass connection does not do anything to the signal - it simply leaves it alone. But since it doesn't do anything to the signal, it means that when a pedal is off, the cable following it will be part of the chain. So if you have all true bypass pedals, the guitar will "see" the entire cable length to the amp when all pedals are off. This will shave off some treble. And using a buffered pedal somewhere in the chain will help with this loss. But it's not the true bypass that is "degrading" the signal - it's the cables.
Come on - I really do want to know...
If you really, really want to know if your effect has true bypass or not, you have to open the pedal up and trace the circuit. That's the only way to find out where the signal goes and doesn't go, when the pedal is off. You can use an ohmmeter to measure this, if you like, but you still have to do some circuit tracing. Locate the input to the circuit (on the circuit board), and the main input point on the input jack (you can use a patch cable in the input jack for this). Then measure the resistance between the two points while you press the switch - if you get zero resistance in both switch positions, the pedal is not true bypass. A true bypass will disconnect the circuit input from the main input jack in bypass mode, showing up as infinite resistance on the meter.
Measuring straight through (from input jack tip to output jack tip) will not show true bypass - it will only reveal the same things as you'll learn when pulling the power. If you want to measure, you need to use the method described above.
And finally - a word of warning:
Removing your pedals from the chain when they're not in use will not only get rid of their tone sucking, it will also remove their buffering (their ability to drive long cables). This means that the amount and quality of cable between the pedals and amp will have a greater impact than before on your tone. When I was A/B testing a true bypass modded CryBaby recently, I was struck by the amount of treble I lost whenever I had the wah in the chain - quite the opposite to what the mod was all about... After a while it dawned on me that the difference in treble response came from me not only unplugging the wah to go straight into the amp - I was also unplugging some 5 metres of cable, giving me lots more treble. True bypassing your pedals might therefore send you into another tone-hunting frenzy, this time looking for the cable with the least capacitance (treble loss). George L's, Klotz GY107 LaGrange or Sommer Spirit cables work great for this purpose, but anyway: You have been warned!
The best compromise would be to have a really good buffer at the start of the chain (or as early in the chain as fuzz pedals will allow you to), with the rest of the pedals being true bypass. That will give your guitar pickups a consistent input impedance to work with, while the low impedance output from the buffer helps drive the long cable to the amp. Some like to have another really good buffer or slight booster at the end of the chain, and that is also an option. Keep in mind that you don't absolutely have to buy a dedicated buffer unit (while they are generally quite good, they are also generally quite expensive) - if you have a Boss/Ibanez-type (electronic bypass) pedal that you like the sound of even when it's turned off, it will do the job just as nicely. For a long time, I used an old Ibanez TS-9 as my main buffer... Then I moved to a t.c. preamp, then a custom built buffer unit, and now I'm using my Korg DT-10 tuner in that position.
© 2002 - 2008
