.: yes, another tuner page :.

Tuners and true bypass - again

The last few years, the words "true bypass" has started turning up in connection to pedal tuners. Apparently, manufacturers have listened to the growing number of players who want to see this feature in their pedals. But have they only changed their marketing, or are the tuners themselves actually true bypass? I have a list on the other page, where I spill the beans. So if you only want to get a yes or no answer, that page should do it. If you also want to see how and why a certain tuner is or isn't true bypass, this is the place. I will post writeups on tuners that I happen to get my paws on, so there's no need to e-mail me with requests.

First off, let's recap (once again) the basics of true bypass. It is a deceptively simple idea - when the the pedal is off, the signal passes straight from input jack to output jack, without touching anything at all except the switch. There can be no path to ground from the input or output "hot", as that means that there's stuff there touching the signal. The pedal circuit needs to be completely disconnected, like it wasn't there. So, for example, if a tuner senses pitch at all times, it simply can not be true bypass.

Planet Waves pedal tuner

This one caught quite a buzz when it was first released, mostly due to the claim that it was true bypass. In fact, the ad copy said "true hard bypass", which immediately aroused my suspiscion. I quickly posted my concerns, also stating clearly that I hadn't seen one in person so I couldn't be 100% sure. I actually got an e-mail from Planet Waves about that one... they basically said that I was wrong, and that the pedal was true bypass. Unfortunately, I lost the e-mail in a minor computer crash before I could respond with my questions. Anyway, fast forward a year or two, when I finally got my hands on one of these tuners. I quickly took it apart, and here's what I found:

The signal enters the pedal at the input jack (to the left in the pic), and splits off in two directions - one to the direct out jack (right side, lower jack), and the other to the switch. So far, so good - the split isn't my bag of tea, but as long as you're only using one of the output jacks at any given time, no damage is done to the signal. The switch then selects one of two paths - one leading to the main/mute output jack (right side, upper jack) and the other to the tuner circuit.

So, the switch actually disconnects the tuner circuit from the main signal path in bypass, which is good. This is one of the prerequisites for true bypass, and so far Planet Waves has done good. But what actually happens at the switch?

Looking closely at the switch, you'll see a bit of dodgy soldering - very untidy, if you ask me. But that's not really what I'm interested in. What caught my eye were the resistors that are connected to various points at the switch. Those could be a problem, if the manufacturer's claims about the pedal being true bypass are to hold up.

In the back row, the center soldering lug (the pole, if you like) seems to be a ground point - all the sleeves/shields end up there in a big blob of solder, and there's also a black wire connected from there to the case. The yellow wire from the right lug (throw) seems to control the LED, while the left lug has two resistors soldered to it - one from there to ground, and another from there to the right lug in the front row.

In the front row, the signal from the input jack enters the switch at the center lug (the pole). The right lug has the above mentioned resistor soldered to it, as well as the signal to the muting output jack. The left lug has the signal to the tuner (going through a 100K resistor) soldered to it.

Now, what does all this mean? Just to recap, a DPDT switch like this consists of two separate SDPT switches operating side by side. Concentrating on the front row, the center lug will alternate between connecting to the left and right soldering lugs, as the switch is clicked. The same goes for the back row, and both rows operate in tandem - as the front row has the center/left combination, so does the back row.

Now, the center/left combination is the "active" mode. The signal enters the switch front row center, jumps over to front row left and to the tuner (through the 100K resistor). The wire to the output jack connects through the 680 ohm resistor to back row left, and from there straight to ground (back row center). The 680K resistor between back row left and back row center is bypassed, as the two soldering lugs are directly connected inside the switch. This all means that the tuner is getting signal, while the output jack is more or less muted (680 ohms resistance to ground is not a 100% short to ground, but fairly close).

Step on the pedal, and it switches to the center/right or "bypass" mode. The signal still enters the switch front row center, but now jumps over to front row right (output jack). The input to the tuner is disconnected (as front row left isn't connected anywhere). So far, so good - this is basically what you need the switch to do for true bypass. But... remember the resistors? The 680 ohm resistor from front row right to back row left is still there, as is the 680K from back row left to ground. The two connects in series, providing a 680.7K resistance from hot to ground. Not good... The second rule of true bypass states that there can not be anything connected to the bypass line, and a path to ground (even if it's as large as 680 Kohms) is definitely something...

So in the end, the Planet Waves tuner is sort of true bypass - the switch does disconnect the tuner circuit from the main signal path, but there's still a path from hot to ground (680Kohm or so) present in the bypass line. So I wouldn't want to call the Planet Waves tuner true bypass. Sorry...

Korg PitchBlack

This one just started shipping, and Korg claims it to be true bypass, using a "soft touch" switch. Naturally, I was curious to see what makes this one tick...

I'll spoil the fun right now and say that the PitchBlack is definitely true bypass. It uses a signal relay (the tan boxy thing below the left jack in the pic) to switch the audio, and the switch you're stomping on is only an actuator, poking on a small tactile switch on the switch/jack circuit board. This arrangement should have a better failure rate than going the 3PDT route. Not that I have had many 3PDT's fail on me (I've had to replace one over the years, out of a few hundred), but anyway... Then again, it has worked so-so in the Line 6 xx-4 series (there are lots of reports of switch failures in those) so I guess time will tell.

The relay lets the circuit do stuff that you'd normally need a 3PDT for, which is nice. Especially since Korg seems to have done their homework - the relay even shorts the output jack to ground when the tuner is activated, to properly mute the signal to the amp. I doubt we'll hear many reports of hum or noise when tuning (stuff that has plagued the Planet Waves from day one). There is a resistor hooked on to the bypass path, which could mean that the thing isn't TB after all (we don't want anything connected to the bypass line). But as the relay disconnects that resistor's path in bypass, it isn't going anywhere. So all is well, thus. Now I just have to figure out if I need another tuner, and if I need it to be true bypass (I already have a DT-10, serving as the main buffer for my pedalboard)...

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