# Exactly what is true bypass ?



## GuitarsCanada (Dec 30, 2005)

Is it really a true bypass? What is the technology here


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## mhammer (Nov 30, 2007)

"True" bypass removes the circuit entirely from the signal path.

The history....

In the early days of stompboxes, the most available (or perhaps only available) stompswitch was a SPDT (single-pole, double throw), that could reroute a single contact to one of two alternate places. The way that this was implemented in pedals was that the input jack would be hard wired to the circuit board, and the stompswitch. The switch was wired to the output jack and the connection to the output jack would select between the input and the output of the circuit board; so, effect, no effect.

The effect that remained connected at its input ran the risk of loading down the signal a bit, but so long as musicians were using only one pedal and were plugged into a high input-impedance tube amp, that did not pose a problem. The pedals were designed to provide equivalent output levels when they were on or off (and this included factoring in what the loading did).

As musicians moved from only one pedal to maybe 2 or 3 (Hendrix, master of FX had three, count 'em, THREE pedals on his pedalboard. No, wait a sec, he didn't HAVE a pedalboard. NOBODY had a pedalboard. They had a couple of pedals with patch cords.), however, the combined effect of the loading produced by all of those pedals, even when they were off, started to become noticeable.

And "tone-sucking" was born!

The solution was to have a switch that not only disconnected the output of the circuit board, but the input as well, so that the input jack would be directly connected to the output jack. This is what some in the audio world refer to as a "straight wire" connection.

Switches that could accomplish that task, using TWO sets of contacts (DPDT or double-pole/double-throw) were developed and available, but they tended not to be as reliable as some manufacturers might have liked. Remember, as well, that if the two sets of contacts do not change over in perfectly synchronized fashion, you can get dropouts or pops. 

As well, with more musicians in the mid-1970s starting to use ever more pedals (I had 4 or 5 in my 1978 rig), there was an emerging need for them to be able to tell at a glance, and without making rude noises, what was on and what was off. So, companies like Roland started developing solid-state switches using field-effect transistors that could go from a very low to a very high resistance. These circuits had the advantage of only needing to make one contact (no issues with synchronized contacts), and the ability to power an LED that could indicate on/off status. Is a field-effect transistor that can go from, say 100 ohms to tens of megohms, the same thing as a switch that can go from zero ohms to open circuit? More or less, in a great many circumstances, I suppose. But people would continue to argue. 

One thing was certain, though. The support circuitry needed to use the FETs bothered people insomuch as it wasn't a "pure" signal path. And while they were fine if you had 3 or 4 such pedals in series, with people in the 80's and 90's starting to have pedalboards with 6, 8, and 12 pedals, all those "buffers" in series added up to a bit of hiss and some trimming of both top and bottom end. There was also something to be said for the risk of introducing things like "group delay" as a cumulative effect of all those buffers and especially having the signal go through all those capacitors along the way.

In the late 1990's Mike Fuller's Fulltone company started enjoying success with his clones of some classic distortions. Fuller had two challenges, though: providing the true bypass that many pros treated as a kind of guarantee of signal quality, and providing a status LED so they could tell what was on and off. Fuller arranged for a Taiwanese or Chinese company to make a stompswitch with a third set of contacts, and thus was born the true-bypass with indicator: one set of contacts for the input jack, one set for the output jack, and one to turn an LED on and off accordingly.

Was this "better"? Opinions varied....widely, and still do. On his website, Pete Cornish (pedalboard-maker to the stars) has a thought-provoking diatribe in which he takes true-bypass down a peg or two. The thing to keep in mind is that even if the path between the input and output jacks is a piece of wire, those input and output jacks are always going to be connected to something else, and THAT is a weak spot. Cornish maintains that the presence of a well-designed quiet buffer to combat what connecting cables do is going to trump what true-bypass does inside the pedal every time. Like I said, opinions vary.

Boss and company have never seen fit to change from their non true-bypass switching. It works for them and people like it. And if they don't like it, the market now provides a plethora of other switching solutions such that you can keep your FET-switched Boss/DOD pedals, and use a master true-bypass switch to disconnect the lot of them. Problem solved.

True bypass can be accomplished directly, via a switch that redirects the contacts itself, or indirectly, via a momentary switch that actuates a relay, and the relay lifts the connections to the circuit.

In some instances, there can be "in-betweenie" arrangements. For example, some Boss-type circuits need to use a pair of FETs to isolate both the input and output of a circuit (usually a fuzz or distortion). Is this TB? Many would say no because the pedal still requires a buffer at the input and output for the switching to work.

Completely lifting the connections from the input and output of a circuit can entail risk of audible popping when switching. Yet one more reason why some companies have never seen the need to switch over from FETs (which don't have that problem). And as some have pointed out, the tradition stompswitch technology was actually developed for things like switching on your high-beams in the car, or turning on a vaccuum cleaner: both higher voltage and/or higher current situations. The upshot is that the humble DPDT or 3PDT switch has been forced into servitude in a function it was never designed to do in the first place; yer askin' for trouble.

That answer your question?


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## GuitarsCanada (Dec 30, 2005)

I don't understand all of what you have written, only because of my own lack of technical savvy, but I now know a lot more than I did when I asked the question. Appreciate that very detailed explanation


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## mhammer (Nov 30, 2007)

Let me know what needs clarification and I'll fix it.

I'm guessing terms like "loading" and "buffer", as well as the FET stuff, is a little baffling?


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## The Grin (May 5, 2009)

my understanding is that other pedals while turned off, still effect the over all tone. True bypass is suppose to be like it the pedal does not exist at all. Thats the impression I get anyway.


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## keeperofthegood (Apr 30, 2008)

I THINK I have this right.  It is late or early depending. But if it helps in thinking of Transistors and FET's maybe it is a good talking point:










The next two important parts of a circuit to know about are Capacitors and Resistors. In a DC circuit, resistors oppose the flow of charge but do not stop it, while capacitors retain charge and essentially act as a wall to the flow. In an AC circuit, resistors oppose the flow of charge but do not stop it, but on each change of cycle the capacitor alternates between storing and then relinquishing charge and so AC will flow through a capacitor.

So, if you look at a cut down of just the 'typical' input and out put of a pedal, you have essentially capacitors and/or resistors and switches.










In the top circuit, the bypass is not 'true' because the caps and resistors remain across the input the red arrows showing the path signal is still flowing in. In the bottom, the circuit is completely removed.

Hope that helps a tad


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## GuitarsCanada (Dec 30, 2005)

mhammer said:


> Let me know what needs clarification and I'll fix it.
> 
> I'm guessing terms like "loading" and "buffer", as well as the FET stuff, is a little baffling?


Oh it's just the ohms and megohms stuff that I don't really understand. But that is fine. I at least now understand the concept, intention and some history, which I was lacking. You hear the term all the time and just accept it as something that works without really understanding the workings. So I like to at least try and understand the technical aspect of these things and what they are indeed accomplishing.


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## GuitarsCanada (Dec 30, 2005)

That diagram also help, Keeps.


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## epy33 (Mar 7, 2006)

Very familiar with the concept, but this was a great read. Excellent explanation of true bypass.


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## jimihendrix (Jun 27, 2009)

I found this article by Pete Cornish...in an argument against true bypass...

http://www.petecornish.co.uk/case_against_true_bypass.html


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## mhammer (Nov 30, 2007)

Cornish makes a lot of sense, and the debate about his points has come and gone several times over at the diystompbox forum.

I have a copy of the Dave Hunter Guitar Effects Handbook. There are a number of criticisms one could levy at the book, but one of the nice things about it is the soundfile CD included. Several of the soundfiles compare a buffered feedthrough (using some Visual Sound pedals) against true bypass, and the buffered feed kicks the TB's ass up and down the block.

Now, having said that, there are some qualifications that must be raised. First, Pete Cornish does not normally deal with clients who play small urban bars where the guitar player and bass player share a mic and stand 6 feet from the drummer. He deals with clients who play much larger stages, where 80-100ft cable lengths are par for the course. Loading and cable capacitance effects are a function of cable length, so there are contexts where things that can be done to overcome cable weaknesses matter more and matter less.

Of course, a "regular" player with a 20ft cable to the pedalboard and another 20-footer to the amp may not think of themselves as being in the same league as Pete Townshend or David Gilmour with respect to stage size, but with no buffering between those two cables, that's still 40ft of cable, which *can* make a substantial audible difference.


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## jimihendrix (Jun 27, 2009)

These vids say that any tone loss is due to cable length...not the circuitry of the pedal itself...they say pedal buffering is the better way to go instead of true bypass...

[video=youtube;MOBn75-WN30]http://www.youtube.com/watch?v=MOBn75-WN30&NR=1[/video]

[video=youtube;RFw6uIDluUc]http://www.youtube.com/watch?v=RFw6uIDluUc[/video]


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## bobb (Jan 4, 2007)

One thing to keep in minds is that most of the "experts" in this subject are home players who have never been in a band situation. Most of what they think they are hearing is between their ears and not through their ears. Look at some of the snakeoil threads floating around on the "audiophile" forums debating the perfect AC cable to power your stereo.

Personally, I'm more interested in playing for an audience than sitting at home debating with myself over the ultimate tone. Especially in a band situation, the chance of any audience member being able to tell what is true bypass and what isn't is next to none. It's also very unlikely that same audience member could tell the difference between a $300 boutique OD and a $50 Boss unit. In other words in my case, I'm more interested in making the crowd happy by getting the job done effectively than blowing a crapload of money on pedals and cables that make no real difference anyway.


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## mhammer (Nov 30, 2007)

I don't think it is a question of "ultimate tone" (though I would agree with you that rabid pursuit of tiny differences that add nothing is a waste of everyone's time). Rather, I think a lot of players can find themselves in a position where the clean sound of their guitar can genuinely suffer from the very things that TB and buffered bypass were meant to address. There is making the audience happy, which IS important, but there is also making the audience happy via making yourself happy with how you sound. 

Concerns about tonal loss via cable issues and how you switch are probably more true for those playing single-coil pickups into cabs with wide bandwidth than they are for those playing overwound HBs into an amp set for overdrive. Stated another way, a *guy* may not be able to feel the difference between not shaving for 1 vs 2 or 3 days, but his *wife or girlfriend* probably can; some things just matter more to some people for very legitimate reasons. Bob Weil, shown in the first video that jimihendrix links to, bases Visual Sound in a suburb of Nashville. As I walked down Broadway there a few years ago and peered in the windows of the honky tonks, you could see a lot of players using VS pedals. And many of them were Tele players, aiming to chicken-pick you into submission. For those folks, preserving as much twang and brightness as possible is "mission-critical".

So, I applaud your very pragmatic approach, but I wouldn't be so quick to dismiss ALL concerns about switching approaches.


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