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Tone-sucking?
There are many definitions to this term - it is sometimes described as a loss of high frequencies due to an effect loading the guitar signal (even when the effect is off). Others describe it as a loss of punch and presence. The operative word is "loss" - if an effect makes your sound lose something, then it sucks tone. My own favourite description is pretty simple - an effect sucks tone if it makes your tone suck. But why does that happen? The answer is a bit different depending on the circuit design. In the old days the effect circuit was always connected to the guitar input, and a mechanical SPDT switch was used to select either the straight guitar signal or the effect output. For instance: in an Electro-Harmonix Big Muff (in mine, to be precise) there's a cable connecting the input jack to the "effect in" point on the pcb. From that point there's another cable that goes straight to the switch (the "bypass" line). The input section of a Vox wah pedal (vintage or reissue - except the V848, which has true bypass) looks even closer to the graphic below - there's two cables coming from the input jack, one goes to the effect input and the other to the switch. There is no real difference between the Big Muff and the Vox wah - both have the "bypass" line and the effects circuit connected in parallel. Newer Dunlop wah pedals, as well as MXR, still use this arrangement, but as the input/output jacks are mounted directly to the pcb, the Y-connection is a little harder to see. It's still there, though...
This method of switching has two main characteristics:
- The effect input will always load down the guitar pickups, even when you think you've "bypassed" the circuit. When the effect is active, such losses are easily recouped inside the circuit. But when you bleed part of the signal past the circuit, and send that signal on to the amp, those losses aren't compensated. Also (and more importantly), this bypass arrangement places the input impedance of this effect in parallel with that of the next, causing the total input impedance the pickups "sees" to drop to half what it was. As your pickups most probably are high impedance (unless you use active p/ups like EMGs), the lower input impedance of the effect will load the pickups down even more, causing them to sound weaker than they are. This will be most noticeable in the treble region, making you reach for the treble knob on the amp.
- As the effect is constantly fed the guitar signal, it will constanly try to output whatever sound it's designed to make. It's the job of the switch to choose which signal to pass on - a job it might not be fully capable of. High gain effects (a fuzz or distortion) and pitch effects (a chorus or flanger) can often be heard faintly in the background even when the effect is supposedly off. This is called "crosstalk" and is, for the most part, a fact of life. Different signals this close to each other will result in some leakage. It can become less noticeable with a higher quality switch, but still...
Now, it might be ok for the effect itself to kill some of your guitar's top end, as it is probably designed to restore it anyway (while distorting it or changing it in some other fashion). But in my book it's not ok if this loss also occurs when it's supposed to be out of the chain. And the manufacturers realized this too. So to combat the treble loss associated with this type of switching arrangement, they started adding a buffer circuit before the actual effects circuit, designed to increase the input impedance, and ease the pickup loading. It would have been even better if they added the buffer before the split - to give the guitar signal only one input impedance to look at - but for some reason they decided to do it this way instead:
For instance, Dunlop added a buffer to their GCB-95 wah in 1992, and its only purpose is to control the treble loss. It is not intended to act as a buffer in the proper sense of the word - it doesn't act as a unity gain preamp for the main signal, like the Valvulator or the Klon does. Rather, it is put there to raise the effect's input impedance, so that the combined input impedance of this pedal and the next won't end up being too low. Also, the crosstalk issue is still there - meaning that you might still be able to hear the effect faintly in the background when it's supposed to be off.
So then what?
Naturally, the best way to deal with this issue is to simply unplug the pedal that is stealing your tone. Try to make a habit of connecting your guitar straight to the amp from time to time, just to make sure you aren't missing out on anything. However, unplugging and reconnecting pedals during a live performance isn't really viable, so we'll have to settle for the next best thing - completely bypassing those that aren't in use, as if they weren't there in the first place.
The standard true bypass will take care of the loading issue, but there's still the crosstalk to deal with. A bypass arrangement like the one on the right will leave the effect input wide open when it is bypassed. Granted, this is an improvement from the earlier scenario, where the effect was always running. But... if you've ever accidentally unplugged your guitar while it's still connected to the amp, you know what a wide open input sounds like! What actually happens is that the effect input suddenly sees infinite impedance (instead of whatever output impedance your pickups have) and tries its damndest to amplify that, picking up radio stations and all sorts of interference along the way. When you step on the switch to activate the effect again, chances are good you'll hear the tail end of that noise. This will sound like a loud "pop!" and is not nice. We need to find a way to shut the effect up when it is bypassed.
There's two ways to do this:
- Install pull-down resistors. Try 1meg resistors and solder them from hot to ground on the effect input and output. These resistors will only come in to play when the effect input & output are left open (i.e. not connected to anything). Remember that electricity will always travel the easiest way, so when the effect is engaged, the signal will ignore the resistor. When the effect is bypassed, the 1meg resistor offers the least resistance, sending the signal to ground.
- Wire the DPDT switch to automatically short the effect input to ground in bypass mode. This method is the one I prefer, as it is virtually bomb-proof and doesn't require any added components that might not do the trick anyway.
You'll find the wiring schematic to the left. Note that you'll need to connect a wire to ground - it can be anywhere, as long as it is a valid ground connection. In the gif to the right I've numbered the soldering lugs to make it easier to follow the signal as we go through the two modes. The Double Pole, Double Throw switch has two poles (2 and 5) that either has contact with 1 and 4, respectively, or 3 and 6. To switch between those two modes you simply stomp on the switch. Our bypass mode is when pole 2 has contact with throw 1 (and pole 5 with trow 4 on the other side of the switch). Our active mode is when 2 -> 3 and 5 -> 6.
Bypass mode: The signal enters the switch on 6, hops to 5 and to the output jack. It also jumps to 1 (via the blue jumper), but stops there as 1 isn't connected to anything. Meanwhile, since 3 is connected to 2, the effect input gets shorted to ground.
Active mode: The signal enters the switch on 6, but since 6 isn't connected to anything else (inside the switch) it jumps to 1, from where it moves to 2 and to the effect input. 3 isn't connected to anything, so it's out of the picture. Once the signal has passed through the effect, it comes back to 4, moves to 5 and then to the output jack.
I often use an Apem switch from ELFA (part #: 35-761-47) because it's small and neat, and readily available here in Sweden. Another option is Banzai Effects - Olaf sells DPDT, 3PDT and even 4PDT switches, and for us europeans it can be both easier and quicker to order from within the EU - or Musikding, both in Germany. Also, you can buy both DPDT and 3PDT switches from Andi Allan at MonkeyFX in the UK - a very good chap to deal with. Outside Europe, I shop from Aron Nelson, who will happily sell you 3PDT switches at very decent prices, and Steve at Small Bear Electronics. Again, both are good chaps, and will not overcharge you for international shipping either - props to both of them!
© 2002 - 2007
