| # out/16 · Editado por: MauricioBahia|
Ismah: Tudo bem Bahia, mas não é necessário que tenha buffer para ser eletrônico, esse é o ponto que estou martelando.
Ok. Você concorda que todo bypass bufferizados é ativo, portanto necessita de energia para que mantenha o sinal. Eu já havia concocordado e explicado. Ponto final! :)
True by pass eletrônico que o cara cita, provavelmente usa um circuito flip flop com dois transistores, formando cada chave. Lá fora se chamam de jfet switching.
Ok, JFET, mas que pra funcionar necessita energia. É um transistor. Estamos novamente numa ambiente NÃO true bypass! Esse é o ponto.
Pra ser TBP "verdadeiro" é necessário estarmos bypassando o circuito do efeito através de um sistema exclusivamente mecânico e por fora de qq elemento que atue com resistência significante . Onde eu explico aqui: http://forum.cifraclub.com.br/forum/7/72741/p11#9182531
Para mais informações, tá tudo no artigo abaixo, até as múltiplas terminologias em http://stinkfoot.se/archives/501
Colando, antes que a página suma... Depois eu traduzo!
"TRUE BYPASS? 15 NOVEMBER, 2010 ANDREAS
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…
What is true bypass?
”True bypass” basically means that when a pedal is turned off, the signal passes straight through the box – directly from input to output jack, touching only the switch/relay. 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. 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. It can be achieved using a good old mechanical stomp switch, or – which is becoming increasingly popular – using relays. The trick with relays is that the switch you stomp on doesn’t handle the audio switching at all, so it can be a soft-touch momentary switch. Either way, as long as the condition mentioned above (signal passing straight through, without touching anything but the switch or relay) is met, it is true bypass.
The other two bypass types are…
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 guitar ”sees” the same thing, and the signal ”looks” the same to the amp, regardless of if the pedal is bypassed or active. The drawback is that it introduces lots of circuitry just to pass the signal along – in each fully buffered (Boss/Ibanez type) pedal, there are two buffer stages and one transistor mute stage. Each such stage will inevitably alter the signal a tiny amount, which isn’t so bad if there’s one or two. But if you have five such pedals in a row, that’s 15 transistor stages just to pass the dry signal along…
Mechanical output switching: Also known as ”half-assed” or ”hardwire” bypass. This type of arrangement has none of the benefits of the other two, sadly. In this system, the guitar input is permanently connected (”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 is effectively placed in parallel to the input impedance of the next pedal (or amp), which lowers 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?
There are a million different terms floating around, but as we already covered, there are only three major types of bypass systems… Here are a few of them explained:
Hardwire bypass: This one we covered earlier – it’s the ”half-assed bypass”, which does not do your signal any favours. Dunlop/MXR uses this one quite frequently (though it should be mentioned tat they’ve started moving over to proper true bypass wiring when designing new pedals). And then there’s the Digitech ”Hardwire” series pedals, which actually are true bypass (if a bit weirdly named).
True hardwire bypass: This is what Dunlop/MXR call it when the pedal is actually true bypass. For instance, the Carbon Copy analog delay has the same DPDT switch as the ”hardwire” MXR pedals, but with a Millennium-type circuit to run the LED.
Hardware bypass: A variant on the ”hardwire” term, used by Hughes & Kettner. This is the same thing as the ”hardwire” system, so no true bypass.
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 most of the other ones – a direct connection from input to output, but with the effects circuit still connected.
Split bypass: Again, it’s the ”hardwire” mechanical output switching.
Passive bypass: Used by Marshall, among others. It’s – you guessed it – the ”hardwire” system once again.
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 no. 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.
Well, enough of that for now. Just keep in mind that 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. If it does this – regardless of if it does it with an old-fashioned clunky stomp switch or a smooth momentary switch and relays – it is true bypass.
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… One tip that always seems to come up is this one:
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.
But really, how can I know if my pedal is true bypass?
Well, assuming you’ve already ruled out the presence of any active buffer stages (which the battery-out test will let you do), the only way to know for sure is 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 any buffering (the ability to drive long cables) they might do. 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.
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.
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 TC Electronic preamp, then a custom built buffer unit, and now I’m using a Korg DT-10 tuner in that position…"