True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

[ratherdashing]

This is easily one of the most misunderstood topics in the subject of guitar gear. Far too often I see people either confused about bypass types, making mistakes about bypass, or outright making up nonsense about the whole thing.

In the past couple of years, I have learned a lot about effects circuits by studying them, modding them, and eventually building my own. I hope this post will help share that knowledge and remove some of the mystery about this topic.

I should first point out that I don't hold any one type of bypass as superior or inferior to any other. Each one has its pros and cons which I will do my best to explain here. This post isn't meant to lecture you on why one type of bypass is superior, or how one type "sucks tone", and so forth. That is specifically what I am trying to avoid here. My only goal here is to educate.

Anyway ...

Buffered Bypass

To understand what buffered bypass is, we have to first understand what a buffer is.

A buffer is a circuit that changes the impedance of a signal. It is more properly called a "buffer amplifier" since there are lots of buffers in the electronics world, but we can call it a buffer for simplicity. All buffers use some sort of semiconductor - either a transistor or an operational amplifier (aka op amp) - and they require a power source (a battery or a DC power supply).

TIP: if you have a pedal that has no power source, such as a passive volume pedal, it is definitely not buffered.

The signal coming out of your guitar is a high impedance signal. This is another way of saying it is very weak. A buffer lowers the impedance without changing the fundamental character of a signal. There is no net gain; only a change in impedance.

Why do some effects have buffers? Because they work better when given a stronger, low impedance signal. This is especially true of digital effects, like delays and choruses, but most overdrive and distortion pedals also rely on a buffer for good tone. It's like building a bridge out of pine versus building a bridge out of steel girders.

This brings us to buffered bypass. In a buffered bypass effect, the buffer is always on and lowering the impedance even if the effect is off. There are a few good reasons you'd want to build a pedal this way; the main one being to maintain the volume level between the effect being on and the effect being off. Some pedals without a buffered bypass are a lot louder when you turn the effect on.

A buffer also helps your guitar signal make it to the amp if you have a lot of cable to go through. An unbuffered signal will degrade over a long enough distance, causing loss of high frequencies in particular.

Lastly, most buffered bypass pedals use what's called a "logic switching" system to turn the effect on and off. The switching is accomplished with transistors. This eliminates any audible pops or clicks when switching.

The downside to buffered bypass is that some buffers will affect your tone. Some people talk about buffers "dragging down" their tone, or they use the obnoxious "tone suck" term. With buffered bypass, the buffer's negative effects are in play even when the effect is off.

Additionally, some pedals, especially vintage fuzz circuits, actually expect a high impedance signal coming in. If you put a buffered pedal in front of them, they may behave unexpectedly (i.e. they will sound bad).

Examples: any BOSS pedal, the Ibanez Tube Screamer (all versions), DOD, Digitech (except Hardwire).

(continued in next post ...)

 

[Sporky McGuffin]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

If I might make one comment on an excellent post, it's possible to make a buffer with no semiconductors - using a valve.

 

[Uk Ant]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

If I might make one comment on an excellent post, it's possible to make a buffer with no semiconductors - using a valve.

Well he is trying to keep it simple, and very few pedals will have a valve buffer in there

 

[Simon_F]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Very interesting reading - looking forward to the other posts :fing2:

 

[elscorcho]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Very interesting reading - looking forward to the other posts :fing2:

+1:thanks:

 

[Sporky McGuffin]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Well he is trying to keep it simple, and very few pedals will have a valve buffer in there

Absolutely. I'm just petty and pedantic.

 

[elscorcho]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

*gets dictionary*

 

[ratherdashing]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Simple Bypass

As its name implies, simple bypass is the simplest design by far. Unlike buffered/logic bypass, the effect is physically cut out of the signal path when you hit the switch. It uses a single pole double throw (SPDT) switch to route the guitar signal either to the effect, or directly to the output.

Since there is only one switch involved, the simple bypass design has one critical flaw. Even when you turn the effect off, the effect circuit is still "dangling" from the signal path. Imagine you have a clothesline with a chain wrapped around it. You cut one end of the chain and it falls off the clothesline, but the other end keeps hanging on, dragging the clothesline down. This is how simple bypass works. The signal isn't flowing through the effect, but the effect is still partially connected to the signal path interfering with the bypass tone. This usually comes in the form of high frequency loss. The effect loading down the signal exacerbates the problem that buffering is trying to solve.

As you might imagine, simple bypass is how most vintage (60's and early-to-mid 70's) effects are wired. Transistors weren't cheap enough yet to make logic switching feasible, and nobody really seemed to care much about the issue anyway.

There aren't many upsides to simple bypass other than cost. Aside from a few hold-outs, most effects builders are now using either buffered/logic bypass or some form of true bypass.

Examples: almost every effect built before 1977, pretty much anything MXR/Dunlop makes.


True Bypass (mechanical)

True mechanical bypass is similar to simple bypass in design, except it fixes the "dangling circuit" problem. Instead of a single pole switch, a double pole switch is used - basically two switches that are activated by a single button. The effect circuit is cut at both ends and the bypass signal flows directly from input to output with no interference or buffering.

In theory, true bypass seems like an ideal switching system. It does offer the advantage of no tone change when the effect is switched off. It is not without faults, however. Without a buffer to raise the bypass signal up, or a dangling effect to drag the bypass signal down, true bypass is the most prone to changes in volume between effect on and off.

There is also a problem that will sometimes occur when a true bypass effect is first in the chain with no buffers in front of it. The mechanical switch is not very fast, and there is a very brief gap between the two positions where nothing is connected. This causes the signal to go from infinite impedance to low impedance, and the result is an audible pop. There is a way to prevent this, but it is not perfect (it's called a pull-down resistor, and some say it ... you guessed it, "robs tone").

Examples: Fulltone, some Keeley, BYOC, Teese


(one more ...)

 

[elscorcho]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

good stuff, nice thread!

btw which will you use on the FTL LITE?

 

[ratherdashing]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

True Bypass (relay)

The concept of true relay bypass is the same as true mechanical bypass: the signal is switched at both input and output to ensure a pure, direct path through the pedal. Instead of using a mechanical switch, however, true relay bypass uses something called a solid state relay (SSR). It is a semiconductor that lets a signal flow through it when current is applied to one of its pins. Basically, it's an electronic switch as opposed to a mechanical one. The switch you push with your foot activates a set of SSR's that send your signal either through the effect, or directly to the output.

There are a few advantages to using SSR's instead of a mechanical switch. Since SSR's switch very rapidly (only a few milliseconds) there is no pop or click heard when switching. There is also a cost advantage; the foot switch used for true mechanical bypass is only made by a handful of companies and it's quite expensive if you're buying it in bulk. SSR's are far easier to obtain and cost pennies if ordered in large quantities. They also have a much lower failure rate. For these reasons, big pedal manufacturers will almost invariably use SSR's if they want to make a true bypass pedal.

Despite its many advantages, true relay bypass is often not viewed as "real" true bypass by purists. Even when the effect is off, the guitar signal is flowing through the SSR's on its way to the amp. This is not the same thing as a buffer, but there is some concern that the SSR's color the tone in some subtle way. Whether this is a valid concern or not is unclear - in theory the right SSR should not interfere with the signal at all.

Examples: Digitech Hardwire series, Korg Pitch Black

 

[ratherdashing]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

good stuff, nice thread!

btw which will you use on the FTL LITE?

Both FTL Drive and it's younger brother use true mechanical bypass. I added a pull-down resistor to prevent the pop sound.

 

[Sporky McGuffin]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

I'm unsure about a few of these.

Pops in TB aren't caused by switching lag - they're caused by DC offset in the effect circuit. Pulldown resistors can help this by bleeding off this DC offset if the decoupling caps aren't up to the job on their own, but they're best as part of a belt & braces setup - the correct way to design out DC offset is to use appropriate decoupling caps and to minimise decoupling stages.

I'd also query the idea that any circuit using SSRs can be described as TB - given that they involve circuitry on the signal line when in bypass. "Proper" electromechanical relays do constitute TB (even though there are potential setups whereby they don't pass signal without power).

Generally excellent though.

 

[ratherdashing]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

I'm unsure about a few of these.

Pops in TB aren't caused by switching lag - they're caused by DC offset in the effect circuit. Pulldown resistors can help this by bleeding off this DC offset if the decoupling caps aren't up to the job on their own, but they're best as part of a belt & braces setup - the correct way to design out DC offset is to use appropriate decoupling caps and to minimise decoupling stages.

You are right. That said, I believe we are both correct. Mechanical switching does cause pops in and of itself.

I'd also query the idea that any circuit using SSRs can be described as TB - given that they involve circuitry on the signal line when in bypass. "Proper" electromechanical relays do constitute TB (even though there are potential setups whereby they don't pass signal without power).

Generally excellent though.

I suppose you would have to take that up with the manufacturers who advertise SSR switching as "true bypass". I am only relaying (pun intended) information. In their defense, the signal is only flowing through the SSR's in bypass, not any other components.

 

[Sporky McGuffin]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

You are right. That said, I believe we are both correct. Mechanical switching does cause pops in and of itself.

I've only ever had a problem with MTB (saves typing ) when there's been a DC offset generated inside the effect circuit. If there's no DC offset then there's no energy for a pop. Unless, I suppose, you've got some weird composition for the switch that's generating static between actuations.

I suppose you would have to take that up with the manufacturers who advertise SSR switching as "true bypass". I am only relaying (pun intended) information. In their defense, the signal is only flowing through the SSR's in bypass, not any other components.

It's probably quite a good system to be fair. My general concern is how well a bypass system works, and to be honest (as a purveyor of TB systems) a good buffered bypass is probably the best system. The boutiquers, though, are generally (there are exceptions) lacking in the design nous to make a really good buffered bypass, so instead they hype TB and denigrate BB.

Half arsed bypass (simple bypass in your list) is bloody awful. The other sare all good if done well.

 

[PFDarkside]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Half arsed bypass (simple bypass in your list) is bloody awful. The other sare all good if done well.

I'll take TB any day over a poorly designed buffer!

 

[RLee]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

I prefer TB throughout as well... I have one dedicated buffer in my signal chain, an MXR Microamp (that is true bypass itself), for when I drive a line level input from my pedals instead of an amp. In other words, use buffers where needed, not where they're not needed.

 

[\m/(00)\m/]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

so what are some good pedals that have buffered bypass, that don't color your tone too much?

 

[ratherdashing]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

I prefer TB throughout as well... I have one dedicated buffer in my signal chain, an MXR Microamp (that is true bypass itself), for when I drive a line level input from my pedals instead of an amp. In other words, use buffers where needed, not where they're not needed.

The Micro Amp is definitely NOT true bypass unless you modded it. Stock MXR pedals are simple bypass.

 

[kramer.geetar]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

Great thread, thanks for this. If you don't mind I would like to add some information regarding the complete opposite of all of this. This was written by Pete Cornish, who if you all know has made pedals, pedalboards and rigs for people such as David Gilmour, Janick Gers of Iron Maiden and so. Anyways, its an interesting read.
Here is his take on the whole by-pass craze. This was taken from Pete's site directly.

CASE AGAINST "TRUE BYPASS"

The "true bypass" function, which is promoted by some, can create dreadful problems with a system that uses many pedals. Take for instance a 15 ft guitar cable linked to ten pedals, each linked by a 2 ft cable, and then onto the amp by a 30 ft cable. If all pedals have "true bypass", and are off, then the total cable length hanging on the guitar output will be 63 ft. This will cause a huge loss of tone and signal level particularly if the guitar is a vintage type with low output and high impedance. The amp volume is then turned up and the treble control increased to compensate for the losses. The inherent background noise now increases by the amount of the gain and treble increase and is usually, in my experience, too bad for serious work. If one of the pedals is now switched on, then it's (hopefully) high input impedance (and usually low output impedance) will buffer all the output cables from the guitar and the signal level will rise due to the removal of some of the load on the pickups (i.e.: 17 ft instead of 63 ft of cable). The treble will rise and the tone and volume will not be as before. If that pedal was say a chorus or delay, devices which are usually unity gain, then your overall signal level and tone will vary each time an effect is added...not a very good idea.

Some pedals have an input impedance which is far from high in real terms; the input impedance of the vast majority of amps is 1 Megohm (one million ohms) and in my experience there are few effects pedals that have the same input impedance. A load on the guitar of less than 1 Megohm will reduce the volume and high frequency content of the pickup signal thus giving rise to complaints that "this pedal looses tone/volume" etc. Many effects I have tested have an input impedance of less than 100 Kilohms (ie: only one tenth of the amp input impedance) and cause serious signal losses in the effects chain.

My system, which I devised in the early 70's, is to feed the guitar into a fixed high impedance load, which is identical to the amp input, and then distribute the signal to the various effects and amps by low impedance buffered feeds. This gives a constant signal level and tonal characteristics, which do not change at all when effects are added. The proof that this works are in the recordings of our clients: Roxy Music; The Police; Queen; Pink Floyd; Bryan Adams; Lou Reed; Dire Straits; Paul McCartney; Sting; Jimmy Page; Judas Priest; Black Sabbath....

So the answer to your question re "true bypass" is no, I do not use this system in my EffectsBoards/Racks as it can seriously degrade your sound. All my current effects pedals (excluding Vintage Series) which are derivedfrom our large systems have, as the main input stage, a fiendishly clever pre amp that has the same characteristics as the input of a tube amp (1 Megohm/20pF), a highly efficient filter to eliminate the possibility of radio breakthrough and a low output impedance so that any following pedals/ cables etc. will not impose a load on the guitar signal. This pre amp is fitted to all our large stage systems and has always met with huge approval; not only from the guitarist but also the PA operator who is so happy to have constant level and tone presented to his mixing board. I go further with large systems and provide several inputs, each with the isolating pre amp and a gain compensation pre amp so that many different guitars can be level matched into the system. In addition a 20 segment PPM type display provides visual indication of signal level in our Effects Boards and Rack Systems.

 

[RLee]

Re: True Bypass vs. True Mechanical Bypass vs. Buffered Bypass etc.: an explanation

I agree absolutely with Pete's statements, but it's not a case against true bypass. It's a case against trying to drive a big pedal board and a long cable run without a buffer. This is not at all calling true bypass "bad", just the mis-application of it. Or, as I stated in my previous post, use a buffer where it's needed, but not where it's not needed.