Buffered vs True Bypass Switching
By Phil O'Keefe |
Is One Really Better Than the Other?
By Phil O'Keefe
If you've been hanging around on guitar forums for any length of time, or reading effects pedal ads online or in magazines, you've no doubt run across the term "true bypass", and maybe even seen references to pedals with "buffers" or "buffered bypass switching." Each switching method has its share of fans out there and the debate over the merits and disadvantages of each can sometimes be intense, and for those unfamiliar with the differences, it can be a bit overwhelming and confusing. In this article I'll try to keep it as simple as possible from a technical standpoint while pointing out some of the advantages and disadvantages of true bypass switching, as well as buffers.
What is a buffer?
The output of passive guitar pickups is a very low level, but high impedance signal. Such signals are prone to suffering from all kinds of problems when run over long lengths of cable, including signal loss - especially in the high frequencies, as well as being susceptible to interference and picking up noise along the way. A buffer (or buffer amplifier) is a electronic circuit that is used to convert impedance. By their nature, most pedals are buffering the signal when they're active, regardless of the type of switching that is used. In the case of the buffer circuits that are typically used in effects pedals, the buffer is engaged whenever the pedal is bypassed. This keeps the pedal's output impedance low and constant, even when it's turned off, and this low impedance signal is better suited to driving longer cable runs without suffering the same degree of high frequency loss that a unbuffered high impedance signal will. Buffered bypass switching systems also offer other advantages, such as the ability to keep your signal levels healthy, and silent, click and pop-free switching.
There are some potential disadvantages with buffers. As with any active electronic circuit, a buffer can add noise to your signal. There is also the potential for "tone suck" when a buffered pedal is bypassed, depending on the design of the buffer, and even in some cases, where the pedal is placed in the signal path. Not all pedals work well with a low impedance buffered signal feeding them. Multiple buffers can compound these effects, leading to increased tonal degradation. In many cases, there will be two buffers per pedal, with one for the input and one for the pedal's output. When combining multiple buffered pedals, you'll have several additional circuits in the signal path, even when everything is "turned off" and bypassed, and this can lead to a less than ideal bypassed or clean tone.
Buffered bypass pedals can also cause issues when placed in front of some fuzz pedals and other pedals that are designed to interact with the high impedance pickups and electronics of your guitar. The ability of some pedals to respond well to adjustments of your guitar's volume control can also be negatively affected if a buffer is placed between them and the guitar. Often it is best to put fuzz pedals and envelope based effects (auto-wahs, envelope filter pedals, wahs, etc.) first in your pedal chain for this reason. If a buffer is used in such a setup, it's usually placed further down the chain, after those other types of pedals.
Impedance is always an important consideration, and improper impedance matching is often a big cause of "tone suck" in pedalboard setups. For an excellent overview of impedance, and some easy how-to instructions on how to test the impedance of your pedals, be sure to check out Craig Anderton's excellent article on testing input impedance to prevent tone suckage.
Digital pedals can sometimes be a bit of a special case. They often have buffers, as well as Analog to Digital (A/D) and Digital to Analog (D/A) converters, and sometimes their "bypassed" output is a post-A/D converter signal, even when the pedal is bypassed. Having the audio signal running through the A/D and D/A converters all the time can have an audible effect on the "dry" or bypassed sound; the amount being largely dependent on the quality of the converters and the accompanying analog circuits.
What is True Bypass?
The earliest effects pedals used less than ideal switching methods that kept part of the pedal's electronics connected at all times and loading down the guitar, even when the effect was in bypass mode. This usually leads to undesirable changes to the sound of the guitar, even when the pedal is bypassed. Such switching systems are still sometimes used today, particularly on reissues of some vintage designs, but this type of switching has largely (but not entirely) been replaced by pedals with buffers or with true bypass switching.
True bypass is a switching method that takes all of the effect pedal's circuitry out of the signal path when the pedal is bypassed, creating a direct wire path from the input jack to the output jack, with no other circuitry in between. This is most often accomplished with a double-pole, double-throw (DPDT) or triple pole, double-throw (3PDT) mechanical switch. A pedal equipped with true bypass switching of this kind will often pass audio through when bypassed, even if no power is supplied to the pedal, and all the other electronic circuits of the pedal are disconnected when the pedal is in bypass, preventing the circuitry from "loading down" the guitar.
True bypass switching can also be accomplished with relay switches, which are triggered by a footswitch, but activated by an electrical current instead of mechanically. True bypass switching systems that use relays are electronically more complex and more expensive, but they allow for more complex switching than a DPDT or 3PDT mechanical switch is capable of, and also are usually free of the clicks and pops that plague many mechanical true bypass switching setups. Pedals that use relays will often not pass signal when the power is removed, so you can't always determine if a pedal is really "true bypass" that way.
True bypass does have some drawbacks. If you use too many true bypass pedals without any buffering, you can wind up with high frequency signal loss, plus the mechanical switches themselves often create audible pops and clicks (mechanical as well as electrical) when you step on them.
What's in a name?
Hard bypass, pure bypass, hard-wire bypass… there are a lot of different names that are used by various manufacturers, and some pedals use switching systems that have been given names that sound similar to "true bypass", but that aren't actually true bypass pedals. The various terms used by different companies are often confusing, and there is no universally used naming convention when it comes to pedal switching, so you have to do a bit of research to be sure of what you're really getting. Identifying the switching type used by a pedal can be difficult, and the only way to be certain is to trace the signal path of the pedal and see what happens when the switch is hit. If this doesn't sound like your idea of a good time, you can always check the manufacturer's website to see if they clarify what type of switching system is used on the pedal you're considering, or stop by the Harmony Central Effects forum and ask your peers.
True bypass looper pedals
For getting around the negative aspects of pedals with poor sounding buffers, or for pedals without buffers that use tone-sucking, old-style non-true bypass switching, true bypass looper pedals are sometimes used. The input and output of the effects pedal is connected to the loop jacks on the true bypass looper pedal, and the input and output jacks of the looper are connected to the rest of the pedal chain. The effect pedal is left active, and brought into the signal path when desired by clicking on the true bypass switch of the looper pedal. This allows it to be turned on and off with a single click of a footswitch, but keeps it out of the signal path entirely (true bypass) whenever it is not being used, thus avoiding the negative effect of the pedal's inferior switching system, while keeping the pedal itself stock and unmodified.
Is there a clear winner?
Actually, there is plenty of room in the pedal world for both true bypass and buffered bypass switching configurations. Both have their advantages as well as disadvantages, which is probably why both have remained popular and in common use. On my personal pedalboards, I use primarily true bypass pedals, but each of my boards also has at least one buffer on it. Some true-bypass fans may advise you to avoid buffers entirely, but this is not recommended unless you're only running a few pedals, and using short cable runs from the guitar to the pedalboard, short patch cables between pedals, and a short cable from the pedalboard to the amplifier. For larger setups with more pedals and with longer cable runs, adding a pedal or two with buffered bypass switching or a dedicated buffer pedal will generally result in a better sounding rig, since the buffers will compensate for the high frequency signal loss you'd get from running without a buffer. Of course, the number and quality of the buffers you use will also have an effect on the way your rig sounds, and having too many pedals with less than stellar buffers in your signal path can lead to less than ideal tone when everything is bypassed. As always, the order you place your pedals in matters as well, and while there are guidelines and suggestions that many people reference when it comes to pedal order, nothing beats experimentation! You really need to try your various pedals in different configurations until you find what works best for you. If you need advice and suggestions about effects order, buffers, true bypass switching, and about what type of bypass a specific pedal uses, be sure to stop by the Harmony Central Effects forum.
Here are a few links from various manufacturer's websites, explaining their position on the subject of buffers and bypass systems: