true bypass test that works?

[tomvelsor]

okay, so i know the old "no battery bypass" thing isint completely accurate..but i think i found a way to test for true bypass that might be accurate, and if anyone can tell me how this works or if i'm right..thatd be cool.

what i did was, i plugged my ipod directly into a 1x12" speaker cabinet once- out of curiosity..and i actually got a reasonable amount of volume, about as loud as the average stock computer speakers. then what i did was ipod into a pedal into the cabinet, and i found that with non true bypass pedals, weather the pedal is on or off, the signal will be VERY quiet (youll have to put your head against the cabinet to hear anything) but with true bypass pedals, when theyre bypassed the signal is the same as if its not there, but when its on it gets very quiet, as with the non-true bypass pedals..

is this because the ipod is putting out so little power that a non true bypass pedal will suck that much power out of the signal, and its only so noticable because an ipods signal is so weak? (thinking of it like, any given non-true bypass pedal will take x amount out of your tone, off the top, and if you start out with a weak signal, youll end up with next to nothing?)

is this test even accurate? i tested i believe 11 pedals, i think 6 of them are non-true bypass and the trend followed through on all of them

[nad]

http://www.stinkfoot.se/andreas/diy/articles/bypass.htm

Interesting article. Hooray Google!

[diechris]

list your pedals...

[niftydog]

Originally Posted by tomvelsor

is this test even accurate?

It's essentially no different to the 'no-battery' test.

The most reliable way by far is to simply open the enclosure and physically trace the switching circuit.

The easiest way is to post your pedals here and ask the question - or even search the forums for the answers.

[Parabolic Box]

Originally Posted by nad

http://www.stinkfoot.se/andreas/diy/articles/bypass.htm

Interesting article. Hooray Google!

Hurray for FET switching, I say. A superior concept. Just remember to keep fresh batteries in the box.

[niftydog]

Perhaps people would like to know a bit more detail.

Regarding the uselessness of the 'no battery' test:
On some pedals that claim to be true bypass the input of the effect circuitry remains connected AT ALL TIMES. This is not consistent with the accepted definition of real true bypass (wherein the circuit is completely disconnected when bypassed) and the 'no battery' test (or anything similar) is incapable of determining such a pedal from a proper true bypass pedal.

Regarding the iPod connected to speaker thing:
Firstly, I recommend you DO NOT try this - speakers have a nasty property whereby under certain conditions they can create a very high voltage spike which may damage equipment that is not designed to handle it.

An iPod output is a headphone output - designed specifically to drive headphones, which are in effect just tiny little speakers. It can deliver relatively high current into a relatively low impedance. So, in a way it's not surprising that an iPod is capable of driving other speakers.

The output of a pedal, on the other hand, is NOT designed to drive speakers directly. It has a relatively low output current and expects to be connected to a relatively high input impedance.

So, the phenomenon you are observing is simply due to the fact that the output device of the pedal (eg. op amp or transistor) is incapable of driving the speaker - or perhaps we should say it is less capable of driving a speaker than the iPod output is.

[bongomania]

Originally Posted by niftydog

The most reliable way by far is to simply open the enclosure and physically trace the switching circuit.

The easiest way is to post your pedals here and ask the question - or even search the forums for the answers.

I've all but given up on both of those. For one, if the switch isn't an obvious 3PDT, tracing the circuit can be very difficult unless you are an electronics pro. Say you have a trace running from a microswitch to an IC. How does the layperson know whether that circuit is advanced and well-designed enough to be called a "true" bypass, or just a crappy old tone-sucker? That problem upsets the second answer as well, as the majority of people posting here are not actually experts on how any one buffer or relay was designed. So except for the obvious 3PDT's, a lot of the TBP answers I've seen here have been "best guesses" rather than solid facts.

Beyond even that, manufacturers change their designs midstream: if someone comes on here and asks "is a Big Muff TBP" or "is a Punch Factory TBP" or "is a Maxon CS9 TBP", what do you think the correct answers are?

Still more, manufacturers play fast and loose with their own claims. So it is perfectly legitimate for someone to say "X pedal is TBP" when they read on the X pedal website that it is TBP. But what is TBP really?

Maxon makes a big production out of the 4PDT switching in their higher-end pedals, but I refuse to call it TBP because it just looks like a typical buffer to me (as a layperson), and on the pedal I'm looking at (a CP9Pro+) there is such a drastic difference in signal level between engaged and bypassed that it becomes impossible to use the bypass.

DHA, I like Dave on a personal level, and I like a lot of what he's doing, but he has the whole TBP concept all wrong. He advertises his pedals as TBP just because they pass signal even with the power source removed, but obviously if the signal is loaded by the passive part of the circuit, altering the tone in bypass, then it's not TBP. But even then, that's just my interpretation and bias; he believes he's saying the right and true thing.

Lots of tuner pedals advertise themselves as TBP when they're not. The worst offender is Dean Markley IME. They have a non-bypassable unmuted "TBP" output in parallel with the mutable output. You can mute your signal with the footswitch, but from that output it is not TBP. You can use the unaffected "TBP" output, but then the mute switch doesn't do anything. It's fake TBP, and they are liars.

When I reviewed the BBE Opto-Stomp, I noted that it had a 3PDT switch wired in the way you'd expect a TBP switch to be wired. So I said in my review that it was TBP (which I still believe to be true, incidentally). But when I Googled for references to my review page, I found a forum where they used that claim in that review as an example of the "many technical inaccuracies" in my reviews. They asserted the BBE was not TBP. Who's right? Maybe theirs was an early production model that was not TBP. Maybe mine was the early model, made properly, and BBE later switched to a non-TBP system. Maybe there was some minor point in the 3PDT switch wiring that was inconsistent with TBP, and I didn't see it. Maybe the guys in the other forum were just plain wrong. (I prefer that view of it.) But clearly if someone goes onto that forum and searches, they will find an answer regardless of whether that answer is correct.

IOW, I've about had it with trying to determine if a pedal is TBP by looking at it, and I certainly don't believe what I read here or elsewhere on the subject. The only thing that matters to me anymore is how the bypass sounds; and then we get back into subjective land. It's frustrating to be sure.

[niftydog]

So once again, caveat emptor!

Addendum to my comments above:
The reliable way is not easy. The easy way isn't reliable!

It's like the old engineers saying - you can have it fast, cheap and reliable, provided you only pick two!










...and at the end of the day TB is all hooey!

[musicelectronix]

Originally Posted by bongomania

But what is TBP really?

The answer to this question is simple. There are two kinds of true bypass arrangements:

1- Mechanical true bypass: The circuit is literally taken out of the signal path while the input and output jacks of the pedal is connected together. One more important thing, the input of the circuit should also be grounded. Many claimed TPB mass production pedals do not use this because of drastically increased costs and can not be done on an automated assembly line (In theory, it can be done. But most of amplification based designs [especially overdrive/dist/fuzz family, but certainly not limited to] will be prone to squelling and interference). Some boutique pedal builders do not ground the input (especially in older days), which is actually worse than buffered bypass

2 - Electronic true bypass: Can be done with a 2PDT switches (a 2PDT can also be wired as TBP, but there would be no status LED), so actually tactile switches can be used, which are the common with the mass produced pedals. It operates similiar to mechanical ones, but the trick is shutting down the LED by using open-gate operation of a transistor. Earlier Rats used this kind of bypass and I always wondered why current production models do not...

[DHA]

Originally Posted by bongomania

DHA, I like Dave on a personal level, and I like a lot of what he's doing, but he has the whole TBP concept all wrong. He advertises his pedals as TBP just because they pass signal even with the power source removed, but obviously if the signal is loaded by the passive part of the circuit, altering the tone in bypass, then it's not TBP. But even then, that's just my interpretation and bias; he believes he's saying the right and true thing.

Hi Bongo,

Sorry but I have to correct you here. My pedals are TBP, I will explain.

I use a DPDT relay as the by-pass switch, so both the input and the output are disconnected from the circuit when the relay is not powered. There is a short circuit on the PCB across 2 of the relay poles and a relay is really just a powered switch and has no effect on tone. I could have used a 3PDT switch instead but there can be a switching thump with these which is a problem with all TBP pedals. Instead a use DPDT footswitch and just switch the 12VDC to drive the relay, this way if you lose power it switches to TBP.

I hope that helps

Dave

[Hookus]

There are plenty of well designed bypasses out there that are not TBP, but sound just fine. Who cares if it is or is not, you should only care how they sound. Most switching systems that provide similar benefit to a 3PDT switch TBP, but use a 2PDT or relay stem from one of two things, cost, and the voltage thump (which may be caused by the LED in a poorly designed TBP).

[Toasted]

Plug it in with your bass and amp, and listen if you can hear any tonesuck. If you can't - it doesn't matter.

[bongomania]

Originally Posted by musicelectronix

The answer to this question is simple.

I disagree. What you described afterward is accurate, but far from simple- especially when manufacturers lie like dogs, and also especially when is it not "simple" for a layperson to see whether the the 3PDT or 4PDT is wired in the correct manner, or whether the electronic bypass is "true" or not. Again, in order to know the truth you have to be so knowledgeable about switching electronics that you could have designed the given switching circuit yourself.

[bongomania]

Originally Posted by DHA

My pedals are TBP, I will explain.

OK, I accept your explanation and apologize for my earlier statement. That said, with some of my gear I can hear the ground noise of the power supply of your pedal while the pedal is bypassed, and I do not have that issue with other TBP pedals I own. Clearly TBP in all of its various forms is not perfect in all circumstances or combinations with other gear, so the issues I ran into are not the "fault" of your pedal design, but it still illustrates how non-simple, non-obvious, and prone to misunderstanding the different systems are.

[tomvelsor]

Originally Posted by niftydog

Perhaps people would like to know a bit more detail.

Regarding the uselessness of the 'no battery' test:
On some pedals that claim to be true bypass the input of the effect circuitry remains connected AT ALL TIMES. This is not consistent with the accepted definition of real true bypass (wherein the circuit is completely disconnected when bypassed) and the 'no battery' test (or anything similar) is incapable of determining such a pedal from a proper true bypass pedal.

Regarding the iPod connected to speaker thing:
Firstly, I recommend you DO NOT try this - speakers have a nasty property whereby under certain conditions they can create a very high voltage spike which may damage equipment that is not designed to handle it.

An iPod output is a headphone output - designed specifically to drive headphones, which are in effect just tiny little speakers. It can deliver relatively high current into a relatively low impedance. So, in a way it's not surprising that an iPod is capable of driving other speakers.

The output of a pedal, on the other hand, is NOT designed to drive speakers directly. It has a relatively low output current and expects to be connected to a relatively high input impedance.

So, the phenomenon you are observing is simply due to the fact that the output device of the pedal (eg. op amp or transistor) is incapable of driving the speaker - or perhaps we should say it is less capable of driving a speaker than the iPod output is.

makes perfect sence..thanks. as far as damaging the speakers goes, its an old cabinet thats been abused way too much throughout the years, so thats why i was willing to try these things on this cabinet...


the one pedal that im unsure of is a visual sound jekyll and hyde, and im unsure because the way it opens doesent really let me see anything inside..i cant tell if the switches are TBP or not...im 80% sure its not though..

[niftydog]

I just think it's interesting to note how the discussion of bypass schemes has massively elevated since some bozo invented true bypass! Before then it seemed as if nobody gave two hoots!

[tomvelsor]

Originally Posted by niftydog

I just think it's interesting to note how the discussion of bypass schemes has massively elevated since some bozo invented true bypass! Before then it seemed as if nobody gave two hoots!

nah, back in the day people were aware of tone sucking pedals (mutron III, anyone?) there was just no other option..either a tone-sucker, or no pedal at all.

[Jazz Ad]

Originally Posted by niftydog

I just think it's interesting to note how the discussion of bypass schemes has massively elevated since some bozo invented true bypass! Before then it seemed as if nobody gave two hoots!

Boss partly built success on the quality of their electronic bypass. It was 25 years ago.
Bob Bradshaw has been assembing and troubleshooting pedalboards for about as long.
Nothing new under the sun.