[66] True Bypass Misinformation

Date: January 21st, 2008 | Comments : [15] | Categories: Uncategorized.

true bypass switch

I’ve seen a lot of misinformation written about true bypass switching, and little of it is confirmed by the actual measurements that I have made on the currently available switches and multiple pedal setups.

The modern DPDT and 3PDT switches used for bypass switching in pedals were specifically designed for audio use and are not old sewing machine switches. I measured the capacitance between poles of two types of footswitches (dpdt and 3pdt) and could not measure ANY capacitance to a resolution of 0.001nF (+/- 2pF). Also, the contacts of the footswitches used currently have a resistance of less than 50 milliohms (0.05 ohms), and may even be silvered for better performance.

The actual measurements of a string of true bypass pedals with one-foot interconnects show that there are minimal changes in series resistance, capacitance or inductance that could have an influence on the sound. The quality of cable used between the guitar and the pedalboard will be much more critical to maintaining the original guitar tone.

What about buffered pedals? Let’s say you are a Boss pedal user and have a BD-2 Blues Driver, AC-2, CE-2 chorus and a DM-3 echo in your pedal chain.

With all pedals bypassed, you have 3 transistor buffers active in the BD, 2 transistor buffers in the AC, 1 transistor buffer and 2 opamp buffers in the CE, and 2 transistor buffers and 2 opamp buffers in the DM!!!!

To summarize: that is 8 transistor buffers and 4 opamp buffers in your signal path at all times, even when none of the pedals are being used! There are also 4 jfet switches in the signal path and the opamp circuits are doing a pre/de-emphasis in the CE and DM. And that is only with 4 pedals; not an extreme example.

I guarantee all of this will have an impact on the sound that even the most tin-ear will be able to discern.

Every electronic circuit that you insert in a signal path adds some noise. They also add a bit of distortion and possibly some hi-freq loss. If you say that each buffer adds 1db of noise (and it is more than that with the cheap transistor buffers and opamps) then the 4 pedal example that I used has 12db more noise than the straight signal.

This doesn’t mean that buffers are bad – on the contrary, they have important uses. However, stacking a series of buffered pedals can lead to signal degradation… in the end, let your ears be the guide!

Some digital effects do not even have a real bypass; they process the signal even when the effect is switched out. The input signal is sent to the analog-to-digital converter and then straight to the digital-to-analog converter and on to the output. Even in bypass mode, the signal in the digital bypass is always subject to the limitations of the A/D to D/A conversion process including bit depth errors, distortion, Nyquist limits and conversion delays. That’s certainly not better than a couple of pieces of wire going through a 50 milliohm switch!

The easiest test is to make a simple bypass box and bypass the entire pedal chain so that you have either the straight signal through the bypass box or the buffered signal through the pedal chain with all of them switched to bypass. You should be able to hear a difference… if it sounds okay then use the chain of pedals, if you perceive a tone loss that is unacceptable, then consider alternatives.

More reading:

True Bypass Measurements

Basic Buffers

AMZ Super Buffer

Pedal Impedance

Buy a pedal for its sound… not its bypass switch!

 

15 Responses to “True Bypass Misinformation”

[273] Mark Hammer Says: 3:27 pm, January 21st, 2008

Choice of bypass system shold be a pragmatic one not a matter of religious faith or electronic ideology, as some folks seem to approach it. Unfortunately, the underinformed buyer is left at the mercy of the seller’s advertising copy. While that copy may do a fine job of underscoring the reasons why the manufacturer chose that bypass system, it often tends to overexaggerate the qualities of that bypass system versus any others, simply for marketing purposes, ignoring user context.

Fundamentally, the problem is that while many pedals may be used in a chain, no manufacturer has any idea if the pedal one buys from them is the only pedal, or one of many, so in some cases they design around the assumption of it being the only one, or the first one, while in other cases they design around the assumption of it being at least the second pedal in line (with the first having a nice buffer).


[274] Web Surf Says: 11:34 pm, January 21st, 2008

Would like a graphic that shows what really is a True Bypass.


[275] admin Says: 12:02 am, January 22nd, 2008

It is in the “True Bypass Measurements” article listed above.

regards, Jack


[276] David Says: 7:03 am, January 24th, 2008

In the case of a chain with several buffered pedals in it, would it be better to move the switching outside the pedal? By that, I mean that instead of the pedal being in the chain, several boxes with nothing more than a stomp and four jacks are in the chain? Two jacks are for the chain, one it out to fx, the other in in from fx. That way that buffer is removed from the chain when the pedal is on bypass?

I hope that makes sense! How about-

Instead of

–[]–[]–[]– (pedal chain with buffered fx)

it’s

–{}–{}–{}– (pedal chain with bypass boxes)
|| || || (to/from fx)
[] [] [] (buffered fx)


[277] admin Says: 6:56 pm, January 24th, 2008

That might be okay, depending on the pedal. It would be better to mod the pedals to eliminate some of the buffer duplicates, which should be fairly easy.

regards, Jack


[278] DDD Says: 8:47 am, January 25th, 2008

Bypassing several pedals with the single switch may cause oscillation due to the switch capacitance. The most “dangerous” capacitance is the capacitance between poles that is usually works as the capacitance between input and output.
I’ve made a high-gain stompbox with couple band-pass filters and maximum gain of about 110dB. The gadget works well but oscillates at maximum gain and resonance settings. Taking away stompswitch eliminates the problem at all. Connecting the 5,6 pF capacitor between input and output causes oscillation at the same frequency as the switch does.
Switch is DPDT model PBS-24. So I think its capacitance is close to 5,6 pf between poles.
To drastically reduce the said capacitance one can use 3PDT switch with the central section grounded (all of the three pins).


[284] analogmike Says: 10:58 am, February 6th, 2008

You can easily stop oscillations by connecting the bypass switch correctly. Ground our the SEND or TO CIRCUIT line when the switch is off. This should be explained in the above articles.


[365] BrotherTank Says: 3:39 am, March 9th, 2008

The discussion of true bypass (DpDt) vs 70’s style (SpDt) creates quite the quandry, with many people taking different sides or opinions as to which is more appropriate.

In all the discussions that I have read over the years, I’ve seen the same arguments about the 70’s tone sucking, vs the True Bypass giving a truer, more pure sound – even with the arguments about patchcord capacitance and switch contact capacitance affecting the sound slightly. And yet in all these discussions you also see these people looking for the same sound from their favorite player from the 60’s, 70’s, 80’s, etc. – But they still want the “True Bypass” and are worried because the pedals may be buffered and don’t want the tone sucking. They have been quazi brainwashed into thinking that TrueBypass is the answer, but then go nuts trying to find the settings and exact pedal combinations to achieve the sounds of their guitar idols.

The fact is that the 60’s-70’s tone sucking – simple SPDT switching is exactly what made those artists sound the way that they did. Hands off to the folks that want true pure DPDT or 3PDT switching to get the effect completely removed from the signal chain…

But I’ll stick to my original set of 70’s MXR tone sucking SPDT switching pedals,into my MusicMan 210-65 Amp… I have the sound I want… I have the sound of the greats… from a very exciting time in music where experimentation of various pedals and manufacturers produced some of the most amazing music of all time.

Sure… the tone changes in my effect change, but it changes the same way it did back then…. Tone sucking was part of the way the sound of the 60’s and 70’s created.

Greg
BrotherTank

PS: As an electronic technologist, I understand completely all the test results and the effects of each type of bypass.. In the end all that really matters is “Do you like the sound you have?” – Yes… Great.. If not – and if you are looking for the sound of your guitar god like Clapton, Hendrix, Eddie VH, and soooo many others… Remember… There sound came from those Tone Sucking Pedals you have been told are Bad…

BT


[411] charmboy Says: 9:03 am, April 16th, 2008

Great point BT, although I suspect that those heroes didn’t have effects that they weren’t using inline and switched off on all those great studio recordings. To really prove your point you’d need to rely on live performances from that era and quite frankly, even the greatest of guitar heroes had their share or crappy live tones in comparison to the sounds they got on studio records.


[424] Great page about true bypass vx. non true bypass Says: 2:19 pm, May 10th, 2008

[…] page about true bypass vx. non true bypass AMZ-FX Guitar Effects Blog Blog Archive True Bypass Misinformation It’s been discussed here a few times so I thought this might be interesting for some of you. […]


[425] Alan D Says: 10:38 am, May 11th, 2008

I have a Dunlop 95 Cry Baby Wah and i find that it does “suck the tone” as the say. when i’m using it it’s fine and im happy but it does affect the rest of my chain when i’m not using it. Do any other people have this ? Any suggestions ?

Cheers
Alan


[435] BrotherTank Says: 9:26 pm, May 16th, 2008

Agreed Charmboy… to a point… 🙂

Many of the greats back then like Hendrix for example, used only a few basic pedals and those were what gave them their sound. Back then, I couldn’t imagine Hendrix not going into the studio without his own pedals and specific guitars. Minor differences might have be found in different recording sessions or studios with different equipment used to mic and put the sound to tape.

Fortunately, I was born in the early 60’s and heard many of the greats play live.

Later into the 80’s and 90’s people started looking at tone sucking as the safistication of the studios and their equipment evolved. But even then (and probably to a lessor extent now) guitarists would want to take their setup into the studio as they wanted the same sound on the album that they were playing with in practice and on stage.

Now with studios being mostly digital, and all the modellings that software can provide, I guess it becomes a little less likely that todays musicians are dragging in their complete stage setup to replicate their sound… Although, one band that does come to mind is Boston. Scholz created the Boston sound – patented it really – And recorded the first 3 albums using nothing but his own equipment that he tailored/built completely to create and keep the sound consistant – both on and off stage…

Greg
BrotherTank


[813] WTFBAMLOL Says: 11:24 pm, October 7th, 2009

I never buy a pedal for it’s bypass swich, i don’t even think about it.


[460638] Steven Malm Says: 4:41 am, December 17th, 2014

I admit that I am considerably late in this thread, but I think the opinion on true bypass has changed a little in the last 5 years, or at least it should.

The one thing you did not mention when you did the pedal testing through your monitoring program was, how long was the complete cable length from guitar to amp?

I think it’s about 18 foot and the cable attenuation begins to drop signal at an audibly noticeable rate, true bypass cannot compensate for this whereas a signal buffer, such as found in a Boss pedal, can.

Imagine having a 25′ cable between your guitar and pedal array, an average of 1′ per 2 pedals, and a further 25′ cable from your pedal array to your Amp. At a mere 50′ there will be considerable signal loss and a noticeable decrease in volume, especially in the high range. A buff will compensate for this.

Just thought I’d through that into the mix, even at this late date,

Steven.


[492756] admin Says: 5:52 pm, December 29th, 2014

In the monitoring test at http://www.muzique.com/lab/bypass.htm the cables are only 6 inches long and the test program response has been calibrated to remove any impact of the cables. Only the bypass systems are impacting the response.

regards, Jack




 

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