Question about the bypass functionality in two popular effects pedal switching systems

G

gene12586

Member
Hey all,

So I’m in need of a pedal switcher, and I’m deciding between the Carl Martin Octaswitch MK3 and the Voodoo Labs PX-8, each of which have 8 effects loops. I’m having some uncertainty with understanding the bypass functionality for the two pedals. So for the Octaswitch, the manual says the following:
“Your eight effects plug into the eight effects-loops on the back of this unit (all true-bypass, impedance free gold relays so you can run any of your pedals, new and old without problem), and then by turning on or off the numbered switches in each of eight DIP Bank switches, you determine which effects you wish to use simultaneously in each Bank. There is also a buffered (or not....switchable) Mono input and a stereo Output. On large stages when running long connected cables, there is a definite drop in the high end of your guitar sound (more or less depending on the input impedance of your amplifier). The solution is a built in buffer circuit at the input, so the user can choose between 100% true bypass, or buffered bypass to ‘beef’ up the signal.”
So, let’s say I press one of the footswitches and turn on a particular combination of pedals programmed into that footswitch, and let’s say the buffer switch is set to off. As I understand it this means that all of the pedals that are not part of the footswitch I pressed will be true bypassed. Now if I were to flick the buffer switch to on, what happens? Does that mean that the pedals not part of the footswitch are no longer true bypassed but instead buffer bypassed? Or does it mean that all of the pedals that are not part of the footswitch are still true bypassed but that there is a buffer added to the input of the Octaswitch (where the guitar goes into the Octaswitch) and to the output of the Octaswitch (which sends to the amp)? Or would the buffer only be applied to the input? Or are none of these explanations correct?
As for the Voodoolabs PX-8, the manual says:
“Each of the 8 audio loops of PX-8 PLUS are true bypass and completely isolate each pedal, keeping disengaged effects, along with any unwanted noise they might add, completely out of the signal path for the purest tone possible. The audiophile-quality output buffer of the PX-8 PLUS ensures your tone will be preserved even with long cable runs to your amplifier.”
This seems much more straight forward to understand. As I understand it this is just saying that if I press one of the footswitches and turn on a particular combination of pedals programmed into that footswitch all of the pedals that are not part of the footswitch I pressed will be true bypassed, and then there is a buffer at the output of the Voodoolabs PX-8 (which sends to the amp). Is that right?

And my final question is: Based on your answers to the above questions, ONLY taking bypass functionality into account, which of the two pedal switching systems is better?

Any help is much appreciated!





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"Stand by yer beds!" Hobby horse about to trot out!

"True Bypass" is a cheap ass' function used in pedals which has, by some clever marketing BS been elevated to a "desirable" state. At its simplest a TB circuit leaves its operation at the mercy of the source impedance, passive guitar say and its output level and quality at the mercy of the load imposed on its output.

It is basic electronic engineering 101 that a device should operate in the 'real world' with little to no regard to those limitations. This desirable state is obtained by the use of "Buffers". These are op amp section connected such that at the input they present a high impedance, for passive guitar* that needs to be be some 1,000,000 Ohms, a figure very easily achieved. The output of a buffer will be low impedance, at most 1k Ohm but 100R would be better. A low output impedance has two good effects. The level is not affected by the following gear. The output can drive the capacitance of long cables with minimal HF loss. The cost of such buffer chips is well under $1.00 for 2.

Given the highly desirable properties of buffered ins and outs and their paltry cost it is a continuing wonder to me that TB is still touted as a "Good Thing".... Bottom Line. get stuff with buffers and don't pay over the odds for the choice between it and crappy TB.

Now, before someone else kicks in! Yes, there ARE some very early pedal designs, mainly OD and fuzz jobs, that were TB and relied for their effect on the impedance of the guitar to some degree. We have got cleverer than that now tho'but!

*For a piezo acoustic you want 5-10 meg.

Dave.
 
I don’t no to be certain but I also noted their buffered blurb was linked to the stereo output so just designed to allow left and right to be unaffected by combining them into mono? So something you have to do to retain the stereo, but allowing the word to be used in the ad catching people out. I’ve not thought people would still be using relays in these kinds of devices. That’s kind of 70s design!
 
rob aylestone said:
I don’t no to be certain but I also noted their buffered blurb was linked to the stereo output so just designed to allow left and right to be unaffected by combining them into mono? So something you have to do to retain the stereo, but allowing the word to be used in the ad catching people out. I’ve not thought people would still be using relays in these kinds of devices. That’s kind of 70s design!
Click to expand...
Oh yes they do! (seasonal?) Rob. Relays are found in a great deal of 'high end' kit, notably some monitor controllers where they are used in a 'ladder' attenuator to effect volume control. (see Duggy Self's book) Relays have next to zero contact resistance and thus produce virtually no distortion. That is not quite the case with other forms of electronic switch, FETs for example. Some controllers use VCAs but excellent though these are they must introduce some noise and distortion. There is also virtually infinite isolation between the 'control signal' and the audio with relays.

Relays are of course more expensive, use significantly more power and can be acoustically noisy but..."yer pays yer money"!!

Dave.
 
The trouble with them in guitar based gizmos was that there is always the tiny noise in the gap while switching that then needs adttional components to trap out. Like those old big switches coloursound used, where the throw always had the click as the two DPDT wipers flew across! The no circuitry, no electronics approach with guitar stuff worries me.
 
rob aylestone said:
The trouble with them in guitar based gizmos was that there is always the tiny noise in the gap while switching that then needs adttional components to trap out. Like those old big switches coloursound used, where the throw always had the click as the two DPDT wipers flew across! The no circuitry, no electronics approach with guitar stuff worries me.
Click to expand...
Hmm, "switching noise" from relays is not a problem in the kit I mentioned because they use 'sealed' and shielded relays. You certainly would not want 'clicks' from a $1000 controller! When using bogo standard DPDTs to switch audio you have to be VERY careful to fit blocking caps AND drain resistors to keep any trace of DC off the contacts.

The guitar electronics industry is at times barely out of the "ball of string and lump of chalk" design era!

Dave.
 
ecc83 said:
"Stand by yer beds!" Hobby horse about to trot out!

"True Bypass" is a cheap ass' function used in pedals which has, by some clever marketing BS been elevated to a "desirable" state. At its simplest a TB circuit leaves its operation at the mercy of the source impedance, passive guitar say and its output level and quality at the mercy of the load imposed on its output.

It is basic electronic engineering 101 that a device should operate in the 'real world' with little to no regard to those limitations. This desirable state is obtained by the use of "Buffers". These are op amp section connected such that at the input they present a high impedance, for passive guitar* that needs to be be some 1,000,000 Ohms, a figure very easily achieved. The output of a buffer will be low impedance, at most 1k Ohm but 100R would be better. A low output impedance has two good effects. The level is not affected by the following gear. The output can drive the capacitance of long cables with minimal HF loss. The cost of such buffer chips is well under $1.00 for 2.

Given the highly desirable properties of buffered ins and outs and their paltry cost it is a continuing wonder to me that TB is still touted as a "Good Thing".... Bottom Line. get stuff with buffers and don't pay over the odds for the choice between it and crappy TB.

Now, before someone else kicks in! Yes, there ARE some very early pedal designs, mainly OD and fuzz jobs, that were TB and relied for their effect on the impedance of the guitar to some degree. We have got cleverer than that now tho'but!

*For a piezo acoustic you want 5-10 meg.

Dave.
Click to expand...
I get what you're saying generally I think, though some of the terminology is above my head. So buffers are the way to go (and you're saying to find some other cheaper switcher system that just has buffers)...
But in the case I'm still considering the Octaswitch, do you have some idea about what the answer to my questions are regarding the Octaswitch (as in my initial post)?
Thanks.
 
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It has a buffer at the input. Before your guitar goes anywhere else, it hits a buffer. Then all the pedal loops are true bypassed.

the difference between input and output buffer is that with the output buffer, the load on your guitar depends on which pedal is first in line OR the buffer if everything else is off. With the input buffer, the load is always just that buffer.

If you have old school fuzz pedals which depend on a low InZ for their tone, you might do better with the output buffer, else you’d have to put them before (separate from) the switch box.
 
Thanks! So you're saying that when you flick the buffer switch there's a buffer at the input and the output, and everything in between is true bypass. Correct me if I'm wrong.

Will keep in mind what you're saying about turning the output buffer on for old fuzz pedals cuz have been considering ordering one of the vintage Big Muffs
 
gene12586 said:
I get what you're saying generally I think, though some of the terminology is above my head. So buffers are the way to go (and you're saying to find some other cheaper switcher system that just has buffers)...
But in the case I'm still considering the Octaswitch, do you have some idea about what the answer to my questions are regarding the Octaswitch (as in my initial post)?
Thanks.
Click to expand...
I am sorry if I have confused you. I am always prepared to explain specific points in greater detail if you wish.

I do not have any direct experience of the Octaswitch but the mention of "True Bypass" raised the hackles! For a very long time the 'professional' audio world has embraced the engineering principle of high input impedance and low output impedance* as this gives the lowest signal loss overall and keeps the HF loss to a minimum even over long cables. If there is an option 'with buffers' take it.

ONLY in the guitar electronics world has this principle been abandoned and worse than that, TB is elevated to some mythical status as a "good thing"...'king ain't. The ability to provide these desirable ins and outs has never been easier and cheaper confounding the felony.

*Line inputs should be a minimum of 10k Ohms but it is easy to make them much higher. Passive guitars should 'see' 1M Ohm but don't sweat it 50% either way. Output impedance, as said before needs to be less than 1k Ohm but again, beer into water to make it a tenth of that.

Dave.
 
ecc83 said:
I am sorry if I have confused you. I am always prepared to explain specific points in greater detail if you wish.

I do not have any direct experience of the Octaswitch but the mention of "True Bypass" raised the hackles! For a very long time the 'professional' audio world has embraced the engineering principle of high input impedance and low output impedance* as this gives the lowest signal loss overall and keeps the HF loss to a minimum even over long cables. If there is an option 'with buffers' take it.

ONLY in the guitar electronics world has this principle been abandoned and worse than that, TB is elevated to some mythical status as a "good thing"...'king ain't. The ability to provide these desirable ins and outs has never been easier and cheaper confounding the felony.

*Line inputs should be a minimum of 10k Ohms but it is easy to make them much higher. Passive guitars should 'see' 1M Ohm but don't sweat it 50% either way. Output impedance, as said before needs to be less than 1k Ohm but again, beer into water to make it a tenth of that.

Dave.
Click to expand...
Thank you!! Got it, makes sense. :)
 
I mean the description you posted for the Octaswitch didn’t say anything about an output buffer and I’m not actually familiar with it. So when I was talking input vs output, it was more about the difference between the two units you were talking about. If any of the loops is engaged, we’d expect that it has a least one pedal actually on and active, so it doesn’t actually need an output buffer. If none of the loops are active, thats when you might want a buffer, and in that case it doesn’t much matter whether it’s at the input or output of the board as long as it’s in between the cable coming from your guitar and the one going to the amp.

Now, different pedals do have different InZ. Even if we’re not talking about fuzzface types, you might find that one pedal is good and high at 1M, another is a bit lower at 500K, and yet another might be somewhere in between. If these were just buffers (no other effect) you might actually hear a subtle difference in the very highest frequencies the guitar can pass when switching between them. Or course, if they were just buffers you wouldn’t bother. These pedals make some effect and have some specific tone, and that tone might be ever so slightly different if it’s not connected as the first active stage (if there’s an input buffer on the board or an active pedal earlier in the chain). For most pedals you’d probably never notice unless you were doing super nitpicky a/b testing, but…

When I was talking about “old school fuzzes” with deliberately low InZ, that impedance is a lot lower than most. You definitely would notice that it doesn’t sound quite right with a buffer (or any active pedal) before it. These are the really old fuzzes like fuzzface. No version of the Big Muff falls in this category. They all have essentially buffered inputs so another buffer before can’t hurt anything.


tl;dr: The buffer (input or output) is only to help maintain your clean all-pedals-bypassed tone and for that it doesn’t matter if it’s at the input or output of the board. Input vs output only matters if you have a fuzzface or similar.
 
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Ah ok, I took following line in the octaswitch blurb that I posted to mean that there is both input and output buffer: "There is also a buffered (or not....switchable) Mono input and a stereo Output."

What you're saying makes sense. So buffers are only really useful in this scenario when I'm bypassing the octaswitch entirely.... Or I also imagine the buffers would be of use if you're playing at some massive stadium and have to run super long cables.

Thanks for your detailed reply!
 
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