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Truth in advertising...?

- an in-depth look at the bypass system in the Maxon OD-9

[All the latest news can be found here, but if you're too lazy to read the whole thing (or to click the link), here's the scoop: Maxon 9 series pedals produced after early 2004 are True Bypass for real. Pedals produced earlier were not.]

Hey - I bought a Maxon OD-9...

Why? Well, as it happens, just the other day I walked (drove, rather) home from the shop with a brand new Maxon OD-9. I got it fairly cheaply, but aside from that my two main reasons for picking it up were:

  1. to use it as a testbed/mod object (my old '83 TS-9 has done enough of that duty, and just needs to be played), and
  2. because I was curious to see for myself if they really are true bypass, as advertised.

A quick play test showed my OD-9 to sound great when active, but downright awful in bypass mode. When I plugged the guitar straight into the pedal, there was a distinct treble roll-off with the pedal turned off. And it wasn't the true bypass type of treble loss either (the one you get when all the pedals are TB and bypassed, which effectively doubles the cable length). No sir... The treble loss got worse or better, depending on what pedal or input stage that followed the OD-9. The best combination was straight to the amp, and the worst I found was with the OD-9 feeding a Danelectro DanEcho. The treble came back as soon as I stuck a buffered pedal (Boss or Ibanez - in this case it was a vintage TS-9) in front of the OD-9. The Maxon OD-9 has some serious impedance issues, which will be investigated in depth further down the page, and needless to say I highly doubt that Maxon is telling the truth about the bypass system on this particular pedal... According to several sources, pedals produced from early 2004 onwards come with "real" true bypass - Maxon even advertise their use of 4PDT switches, but only with the pedals that have dual/stereo outputs. In any case, the mono/single output pedals built earlier than 2004 definitely seem to be a little dubious... check the bottom of this page for updates on this situation.

Here's what the Maxon site says: "True Bypass Switching — Mechanical true bypass switching allows your signal to pass through a non-electronic bypass line when the effect is disengaged, feeding your amp with direct unaltered signal from your instrument." Now, most of the ad copy is true - even the old-style 'output switching' type of bypass has the signal running through a "non-electronic bypass line" when the effect is off. But for it to be true bypass - as we know it - the guitar signal has to be physically disconnected from the effect input, when the effect is bypassed. I'll explain why this is important a little later in the article, but for now let's just repeat the mantra a few times: true bypass means that the guitar signal is physically disconnected from the effect input... true bypass means that...

For reference, here's what a true bypass circuit looks like. There are variants to this theme, but in its most basic form, this is it. Notice the input to the effects circuit being physically (I just can't say that enough times, can I?) disconnected from the signal line. Now, lets get right on with the investigation, shall we?

 

OD-9 - clues and evidence...

First off, let's open the pedal up. See those two yellow wires coming off the input jack? One goes to the DPDT push/push switch housed where the Ibanez version has its tiny tactile switch, and another goes straight to the effect input. Uh-oh... This, my friends, is not a true bypass. Put simply, the two wires splits the signal evenly between the switch (providing the bypass line) and the effects circuit input. Alas, it's the dreaded half-assed bypass system, once again... Trust me - there's no difference at all between this system and the one you'll find in a standard Dunlop CryBaby, MXR or pre 2002 Electro-Harmonix pedal. Here's what it looks like - look at the diagram below, repeat the mantra ("true bypass means that the..."). Then look at the two yellow wires, and repeat the mantra again...

 

Switching the signal

Briefly - before we move on - let's just review how the Double Pole Single Throw switch works, since having that knowledge fresh will make the next part much easier to follow. The switch has two basic states, or positions, and stomping/pressing/flicking it (whichever way the specific switch works) triggers the switch to change from one to the other. The DPDT is divided into two halves (as seen in the image on the left), each half being mechanically connected, but electrically separate. This means that the two halves switches state at the same time and in the same direction, but there is no connection between them.

 

Now, by carefully peeling off the foam to get at the switch, we can see what looks to be a tiny DPDT switch, with only the left half switching the audio. Ignore the black wire - it's just a ground wire making a loop into the picture. Anyway, the yellow wire comes straight from the input jack (the "bypass" line), and is connected to the top left lug. The white wire in the middle (connecting to the left center lug on the switch) goes to the output jack, and the white wire on the lower lug carries the signal from the effect itself. Now, since we did our homework earlier, we can deduct that as the switch changes state, either the yellow wire straight from the input jack (the "bypass" line) or the white wire coming from the effect output gets routed to the output jack.

 

Switching the LED

The other (right) half switches the LED, and in a rather odd fashion. The switch doesn't actually switch the LED in/out - at least not like you'd normally do (by closing or opening a circuit from 9v+ to ground, with the LED somewhere in the middle). Instead, the normal state for the circuit is with the LED lit. The switch then makes a connection across/around the LED, effectively bypassing it from the 9v+ to ground circuit, to turn it off... Let me explain this: see the two red and two pink wires? [And yes, both wires to the right are pink - it's just the camera playing tricks with the colours.] One of the red wires feeds 9v+ to the LED, and one of the pink ones bring the current from the LED to ground, via a current limiting resistor (to control the brightness of the LED). This far, we have a closed circuit, which would keep the LED lit at all times. Now, to turn the LED off when the pedal is bypassed, the other pair of red/pink wires come into play.

On both sides of the LED, there are wires going to the switch. When the switch is in bypass state (at the same time as the yellow wire is connected to the output wire - er, when the pedal is "bypassed"), the red and pink wires are connected, thus creating an alternate route around the LED. To understand what difference that makes, you need to keep in mind that current is lazy - it will always use the path of least resistance, on its journey from positive to negative/ground. Since an LED (any diode, actually) will inevitably drop a little voltage, to the current it will appear as an obstacle. When the switch opens the path around the LED, the current will simply choose that route instead. The current flow through the LED stops, and the light goes out. When the switch changes state again (turning the effect "on"), the path around the LED is broken, and the current starts to flow through the LED again. An odd side-effect of this wiring style is that the OD-9 actually draws less current when the LED is lit... When the LED is bypassed, its voltage drop is also bypassed, causing more current to flow to ground than if it were lit.

Obviously, the more common way of wiring would be to simply insert the switch somewhere in the chain, and use it to complete or break the circuit. In that case, turning the LED off would mean stopping the flow of current completely. For some reason Maxon chose a slightly more complicated way of doing this - sometimes I wonder if the circuit designers do these things just for the heck of it...

 

Circuit design - a lesson in minimalism

The circuit board used by Maxon is the exact same one they used when they built the reissue TS-9s for Ibanez. For this pedal, though, it has been adapted to work with the new switching system. To put it more simply: Maxon simply skipped all components that had to do with the electronic switching and added a jumper or two to complete the circuit. It's quite interesting to see exactly how few of the electronic gubbins inside a regular TS-9 that were actually used for creating the sound... The group of components on the left are the main circuit, starting with the input buffer in the top left corner. Then there's the the op-amp (which is the JRC4558D - a nice improvement over the TA75558P in the Ibanez reissue TS-9) with clipping and tone control circuit below, and finally the output buffer along the right side. Some of the components in the top left group belong to the voltage divider section, and partly hidden behind the wires are the filter cap and polarity protection diode for the adapter input. Er... that's about it.

Considering the amount of components taken out of the circuit, Maxon could have dropped the pedal's current consumption quite a bit below the 7mA the TS-9 draws. As is, the funky LED wiring keeps the current consumption up, so it's not that much better off than the Ibanez pedal - current draw is 6.03mA when bypassed, and 5.53mA when active. Not that any of these numbers are anything to be excited or alarmed about - a couple of mA isn't much to argue about, really. Not in this day and age, when we have pedals that use well over 100mA...

 

Er... so what's the deal with the "not-so-true bypass", then?

As I said in the beginning, there may well be a direct (passive) connection between input and output in bypass mode, but in my book that's not good enough. The reason is as simple as obvious, when you think about it. All active circuits have an input impedance, which needs to be quite a bit higher than the output impedance of the source driving it. The bigger the difference, the easier the source can drive the input stage. The closer the two get, the more they will start to cancel each other out.

Now, most of us know that two equal impedances drops to half their original value when combined in parallel (two 8 ohm speakers in parallel makes 4 ohms). But few of us realize that the same rule applies to signal impedances, such as the input/output impedances of our guitar/pedals... Let's start by stating one fact and make one assumption:

For starters, 500Kohm is on the low side of safe, but still workable with passive pickups. An input impedance of 1Mohm would have been much better, but you work with what you've got. Anyway:

When the OD-9 is active, the input impedance the pickups have to drive is 500Kohm total. But what happens when you turn the OD-9 off? Remember the split connection, from input jack to the switch/effects circuit, in the OD-9? Since the direct/bypass wire - which is wired straight to the effect input - is now also connected to the output jack, the input stage of pedal A (the OD-9) will suddenly find itself placed in parallel to the input stage of pedal B. Two 500Kohm loads wired in parallel... that should produce 250Kohm, right? So, the combined input impedance your pickups will have to drive is now only 250K, instead of the 500K it had before, and 250K is starting to become dangerously close to the pickups' output impedance. It definitely was too close with my for the pickups in my Tokai strat... ouch. I haven't heard treble loss like that since the last time I plugged the guitar straight into my stock '78 Big Muff...

Actually, if we can't have a proper true bypass [repeat the mantra], the switching style from the TS-9 (with the signal going through the input stage at all times) would be preferable to this. The Ibanez style will always present the pickups with the same 500Kohm input impedance, regardless of the pedal's bypass state. Of course, if you place an active pedal (Boss/Ibanez with electronic switching) before the OD-9, the impedance issue will be much less of a problem. Those pedals have a constant output impedance of 1-10Kohm, which is far apart from even 250Kohm to work properly.

 

to conclude...

First off, a message to Maxon: You should be ashamed of yourselves. Yes... actually. I don't mind you using the crappy half-assed bypass style in your pedals - even though it's not so fantastic when you examine it a little closer. Lots of other manufacturers use it (MXR, for instance), so you're in good company. But what I do mind is you using the term "True Bypass" to describe a switching system that is very far from it. That is a misleading flat-out lie, and since I refuse to believe that you are unaware of this issue, I have no choice but to concede that the lie is an intentional way of misleading us consumers...

There. That felt good... Now, the latest (2004 onwards) 9 series AD-9, FL-9 and CS-9pro seems to come with a 4PDT switch, which would let Maxon run a proper true bypass configuration even with dual outputs. They even made a special little "4PDT mechanical switch" logo, to go with the advertising for those pedals... But Maxon still doesn't say anything new about the switch in the mono pedals (the OD-9, SD-9 and AF-9). I have heard from reliable sources that there are SD-9's and OD-9's out there that came with the 4PDT switch, so there may be hope. Ideally you'd want to check this before you buy, though - look below for comparison pictures. If the switch looks like the one pictured earlier on this page, move on. The pedal I bought (in late april 2004) and used for this article was brand new, but had probably been sitting at the shop for up to a year.

As for the pedal itself, it's pretty good. It feels solid as a brick, and the overall build and component quality is a notch or two above the current Hoshino/Ibanez TS-9 it rivals. The sound is a little different - a little darker and spongier, but still more upfront than its Ibanez counterpart. This is probably due to the lower parts count - the flip-flop switching system in the regular TS-9 sends the signal through lots of components that are absent from the OD-9. Now, it has been deemed pretty hard to wire up a TS-9 or Boss pedal for true bypass, partly due to the hassle of hot-wiring the switching circuit, but mostly due to physical limitations. Maxon has proven that with the right parts, you can get there - without having to drill for a big fat stompswitch in the pedal faceplate. And that's why it's such a shame that they deciced to stop just a little short of the mark...

 

Updates:

Since I first wrote and published this article, several things has been brought to my attention. First off, I got an e-mail from Patrick, who purchased a used OD-9 in november 2003, and didn't feel that the pedal stole any tone at all. After a little investigation, it turned out that the pedal had the 4PDT switch. Thanks to Patrick and his camera, I can now show you what to look for when shopping for a real true bypass Maxon "9" series pedal. If the switch in the pedal you're thinking about buying looks like the one on the left, walk away (or prepare to keep an active effects pedal in front of it at all times). If it looks like the one on the right, it's true bypass "for real".

Note the foam residue on the cables... this is very odd, since Maxon used a plastic sheet between the foam and the switch on this pedal (and all other "nine" series pedals I've seen). Obviously, the pedal on the right has been altered somewhere in time.

Another pointer I got - also from Patrick, by the way - was that the FAQ at the Maxon US site actually covers the true bypass thing. Sort of... Apparently they are trying to smooth over the situation somewhat. I'll let them do the talking...

Q) Are the Maxon 9-Series models actually true bypass?

A) In some ways the answer to this question is a matter of semantics and perhaps we need to clarify a few things before saying "yes or no." First off, the initial two shipments of 9-Series units (AF-9, OD-9, and SD-9) sent to the USA were configured as true bypass switching (TBS) using a DPDT switch. For purists, calling these models TBS was considered a false statement, as many believe that to achieve TBS you must use a 3PDT switch. However, we were more concerned about performance than anything else, and when these units measured lower resistive loads in bypass than pedals that actually used 3PDT switches (drop us an e-mail for the test results), we felt justified in calling them True Bypass, regardless of the Internet gossip.

Well, I appreciate the apology (half-assed as it is), although much of what is said in the first paragraph is complete BS... There's no "gossip" in the article above - it's pure fact. Maxon is obviously trying to cloud the issue - the problem with the early "nine" series pedals isn't that it uses a DPDT switch instead of a 3PDT, it's in the way the thing is wired. If they'd either skipped the LED or wired up a "Millenium" style circuit to run it, they would have gotten away with a DPDT for true bypass. As they decided to use half the switch for the LED, they would have needed a 3PDT. But what they are trying to say is that the DPDT is actually better than a "real" true bypass pedal. Pffft. Nobody in their right mind measures resistive loads - that has nothing whatsoever to do with how the pedal will perform. What matters is the input impedance, and the non-true bypass OD-9 has too little of it, when it's followed by another guitar pedal. That is also a fact. Also, you cannot "feel justified" in calling a circuit something it physically isn't - regardless of your measurements. It's not a judgment call at all - either it is true bypass, or it isnt. And this wasnt. Anyway...

Shortly after this, Maxon decided to re-introduce the AD-9 and CS-9 Pro, which caused a new problem - since these models had dual outputs, a DPDT switch wouldn't work to make them TBS. Therefore, Maxon decided to go with a 4PDT mini PC mount switch for these models in order to assure their transparent operation in bypass, regardless of mono or stereo operation. Since they were using the 4PDT switches anyway, Maxon decided to upgrade all the 9-Series models to TBS using the 4PDT switch in an effort to please even the toughest customers. Now, every 9-Series model that ships uses this switching configuration and the debate over whether they are TBS or not is finally laid to rest.

This is the important part, I'd say. Indeed the "debate" can be put to rest, as the new pedals (2004 onwards) all apparently come with the 4PDT switch, wired for true bypass. That doesn't change the purpose of this article, though, since there are plenty of non-true bypass "nine" series pedals around. But now you know what to look for, at least.

 

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