True bypass on effects

The Tube screamer series generally are OK for treble bleed (or tone sucking) that's why alot of people will just play them stock. Certain pedals (i.e - Dunlop Crybaby Wah) don't have a very high input impedence which causes this tone sucking.

Basically there are a couple types of bypass: True bypass, buffered bypass and non-buffered bypass. True bypass has a switch that will bypass BOTH the output and the input completely, so when the effect is bypassed, absolutely none of your guitar signal is presented to the effect pedal, thus the signal is not loaded down.

Buffered bypass is probably the next best option, it's used in most Boss pedals and is used in the original tube screamer circuits. Buffered bypass usually only has a switch that bypasses the output of the effect, but the input is "buffered" by a high impedence circuit. This circuit is generally between 500k to 1M Ohms. If all this goes over your head, don't worry, the main idea is that although true bypass loads none of the signal down, buffered bypass is a VERY close substitute for this: it is used in alot of pedals because it is cheaper to build.

Non-buffered bypass is used in alot of older or cheaper effects and just has the output bypassed, which leaves the input of your guitar attached to the effect, even when it is bypassed, this causes a noticeable effect on treble depending on the circuit impedence.

If you're not a technical guy then the important thing to note from all this is that although true bypass seems like the ideal answer, buffered bypass can be very good as well (honestly, I have both true bypass and buffered bypass pedals and I can't hear much of a difference), but if you have some older effects it can load your signal down, so it's important to know what kind of bypasses you use, especially if you use alot of pedals.

If you only use a couple pedals (say, up to 4), I think the buffered bypass of the tube screamer would be fine.

Once I read that the buffered bypass has a positive lateral effect when you use many pedals and total length (cable+pedals) form the guitar to the amp is large. They say those pedals help to "regenerate" the signal. I don't remember exactly the link, it is possible that was an interview to John Mayer.

Interesting article:

http://www.tech21nyc.com/tech_notes/tech_truebypass.html

And another, this from GuitarPlayer:
Pete Cornish on True Bypass vs. Buffering

“The true-bypass function can create dreadful problems with a system that uses many pedals,” says legendary effect and pedalboard designer Pete Cornish. “Take, for instance, a 20-foot guitar cable linked to ten pedals, each linked by a one-foot cable, and then onto the amp by a 25-foot cable. If all pedals have true bypass—and are off—then the total cable length hanging on the guitar output will be 54 feet. This will cause a huge loss of tone and signal level—particularly if the guitar is a vintage instrument 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 its 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. Consider the change to approximate using 22 feet of cable, instead of 54 feet. But 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. This is not a very good idea.

“My system—which I devised in the early '70s—is to feed the guitar into a fixed high-impedance load that 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.”

Pete Cornish's article is a very sensible analysis of the bypassing issues and his approach. Not that he needs my validation, but he hits the right points with solid reasoning ... and doesn't seem to be a zealot about it.

“My system—which I devised in the early '70s—is to feed the guitar into a fixed high-impedance load that 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.”

On a high-level this makes sense - the original signal needs a kick in the pants. But for non-techies how does this translate?

- "..into a fixed high-impedance load that is identical to the amp input". Some bufferboost device at the beginning of your chain? Examples, and how do you match the amp input?

- "..then distribute the signal to the various effects and amps by low-impedance buffered feeds". Clueless.

Domo:)

- "..into a fixed high-impedance load that is identical to the amp input". Some bufferboost device at the beginning of your chain? Examples, and how do you match the amp input?

- "..then distribute the signal to the various effects and amps by low-impedance buffered feeds". Clueless.

Domo:)

Basically I think he's just saying that he uses a high impedence buffer at the system's input, just like most effects and amps. A characteristic of any half-decent amplifier is a high impedence input and a low impedence output.

As for the second part, buffers have two primary characteristics: a high impedence input and a low impedence output. The low-impedence output is to minimize any sort of electrical losses. It seems that in the article he might be talking about a parallel effects system, as opposed to series (or 'daisy chain') effects system that most of us use. If you use a parallel effects system, you could plug your guitar into multiple effects or amps at the same time, however if you don't use buffers for this then you will create a mess of problems.

Examples,

A VHT Valvulator line driver is a commercially available example of what Cornish might be using.

<snip>

Basically I think he's just saying that he uses a high impedence buffer at the system's input, just like most effects and amps. A characteristic of any half-decent amplifier is a high impedence input and a low impedence output.

Shouldn't assume the non-techie knows what impedance means. It's this simple: The guitar "sees" what looks like the amp's unadulterated input (straight in!), and the amp "sees" what looks like a guitar driving it. And neither of these change much -- if at all -- when the effects are switched in and out -- only the signal is processed by the effects. The net effect should be just like a guitar straight into the amp, but with an effect(s) added. This supposedly uses the guitar and amp "as designed," and preserves the uniqueness that may result from a particular guitar/amp combo.

Shouldn't assume the non-techie knows what impedance means. It's this simple: The guitar "sees" what looks like the amp's unadulterated input (straight in!), and the amp "sees" what looks like a guitar driving it. And neither of these change much -- if at all -- when the effects are switched in and out -- only the signal is processed by the effects. The net effect should be just like a guitar straight into the amp, but with an effect(s) added. This supposedly uses the guitar and amp "as designed," and preserves the uniqueness that may result from a particular guitar/amp combo.

What you describe sounds like a best case scenario - guitar out, amp in, with no negative effects from pedals in between, cord length, etc. like attenuation or the pedals bleeding off strenghttone?

Is impedance strictly a matter of signal strength? For example, can you put a multimeter on your guitar jack (say it's 7K output) and you want that as close as possible when you plug into the amp to keep the 'original' tone?

And the effect pedals have {minus any impact on impedance) should only effect the qualities of the tone, but not the strength?

Shouldn't assume the non-techie knows what impedance means. It's this simple: The guitar "sees" what looks like the amp's unadulterated input (straight in!), and the amp "sees" what looks like a guitar driving it. And neither of these change much -- if at all -- when the effects are switched in and out -- only the signal is processed by the effects. The net effect should be just like a guitar straight into the amp, but with an effect(s) added. This supposedly uses the guitar and amp "as designed," and preserves the uniqueness that may result from a particular guitar/amp combo.

What you describe sounds like a best case scenario - guitar out, amp in, with no negative effects from pedals in between, cord length, etc. like attenuation or the pedals bleeding off strenghttone?

It's entirely possible to create an approximation of the guitar-direct-to-amp situation as Pete Cornish describes. And this will result in a more predictable result when inteconnecting the guitar, effects and amp. But you need to forget about impedance equaling signal strength. That's an incorrect extension you (and many others) are making due to a crude method of characterizing the number windings (wire length) in pups. That chain of reasoning is higher output may be achieved by more turns on the coil = longer wire = more resistance = one part of impedance. Somewhat useful in identifying pups, but useless here (and most situations). The real importance of input and output impedance is the level (function of freq) and phase (function of freq) in signal transfer from one device (guitar or effect) to the next (effect or amp). Pete Cornish is saying he approximates the guitar-direct-to-amp impedance relationship in his design. The first benefit of that being realized when all effects are "OFF": The setup should sound very much like a guitar straight into the amp.
Is impedance strictly a matter of signal strength? For example, can you put a multimeter on your guitar jack (say it's 7K output) and you want that as close as possible when you plug into the amp to keep the 'original' tone?

Nope. impedence is a complex number that expresses the relationship between the voltage applied across a device and the resulting current that flows through that device. Impedances can be adjusted and changed in designs at the same time gain or loss blocks specified independently "deep inside" a device. A very simple model for describing an amp includes its input impedance, its output impedance and its gain (as a function of freq). Note that the gain must be spec'ed with a signal source of a specifed test impedance is connected to its input and a (usually different) specified test load impedance connected to its output. Once these are known, then the effect of the amp on a signal can be predicted based on other input and output devices connected to that amp -- as long as one knows both the output impedance of device on the amp's input (e.g., pup) and the input impedance of the device at the amp's output (e.g., amp). Knowing all that, one can calculate/predict the signal transfer from the first device (our pup) to the last device (amp). None of this is about absolute signal level (such as volts), but about total gain/phase versus frequency end-to-end (volts/volts = dimesionless).
And the effect pedals have {minus any impact on impedance) should only effect the qualities of the tone, but not the strength?

Effect pedals change signal strength (as a function of freq = tone) based on not only their own input/output impedances and gain characteristics, but also the impedances of the devices connected to them. This is the way the physics (electronics) works. If every designer agreed on standard input and output impedances for guitars, amps and effects, then the effects of interconnecting these would be far more predictable. But they don't. So for the most part, we use common sense and some trial and error to find configurations that will give us the tones and gains we want. Pete Cornish has developed a buffering design that helps minimize non ideal impedance interfacing between devices. The result is more predictable behavior.

Sorry if that explanation is not entirely clear. But unless you study some basic electronics, it's going to be difficult to give you satisfying explanation.

No, your explanations are very helpful.

I've a couple of electronics books on the way. Speaking of which, do you have any book recomendations for a electronics introduction, possibly focusing on music gear, etc? My goal is to have a decent understanding of the whole chain, to help make decisions on what to buy and how to setup. At some point would like to try making my own effects, wiring a guitar myself ( or at least play around with different pup combinations ).

All that, and it's really interesting :)

Related to the topic: Why do true bypass pedals sometimes make a popping sound when switched? And how come not all true bypass pedals do this?

Popping during switching of audio circuits often is indicative of DC voltage offsets from one state (e.g., EFX on) to the next (e.g., bypass). What's going on and how to mitigate the offsets/popping depends upon the sources of the voltage offsets, pedal DC bias/blocking design and what's connected to the pedal. Might not always be the pedal that causes the offsets, but some designs may deal with offsets better than others.

That probably didn't help much.