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Intro to Effectsblog

March 16, 2014
  • The Power of USB

    The Universal Serial Bus (USB) has been a prevalent standard for connecting accessories to computing devices since its initial release in 1996. The USB interface is increasingly being used in environments we would not traditionally consider directly related to computing, especially audio. The ability to carry power and data, including digital audio, along the same small, low cost and easily available cables makes USB an attractive interconnect for musicians. We are starting to see devices such as MIDI controllers, guitar wireless systems, and even effects pedals with USB interfaces.

    I carry a basic USB toolkit with me in my backpack pretty much everywhere I go. It has all sorts of uses. Here’s what you need to make your own.

    USB Battery Pack

    A portable USB power pack can be used to recharge devices such as phones and tablets and power other devices such as some wireless guitar systems. They recharge from the wall or another USB power source. There are numerous different sizes and types available, many with additional features such as an internal flash light. Lithium Ion types provide the most storage capacity relative to size and weight. It’s wise to pay a little more and be sure to get a good quality battery. Respected manufacturers will ensure that there is plenty of protection against short circuits and over voltage, current and temperature; all of which can result in serious failure such as fire or explosion.

    The battery capacity is normally rated in milliamp hours (mAh) which describes how much current the battery can deliver for how long. Watch out for low cost sellers on eBay, Alibaba etc. that are notorious for overstating battery capacity. Here are some great battery packs to consider:

    • APC M10BK : 10000mAh. Very slim for a 10Ah unit. Looks professional. Lots of safety features. On/off switch. This is the one that’s always in my backpack.
    • Griffin Survivor : 6000-10000mAh. Ruggedized with silicone surround and weatherproofing. Internal flashlight. Very easy to carry around. On/off switch.
    • Anker Powercore+ : 26800mAh. USB C and Power Delivery support. 30W capability for large items like laptop computers.
    • Naztech 13000mAh : Slim and low profile, but still powerful. It even has a USB-C output. This one is verified by Mission for use with our 529 products, and can also charge your mobile devices. You can purchase one from us here.

    USB Adapter kit

    USB-C should eventually simplify things as there is just one type of connector, but its new and there is a huge installed base of devices with different types of USB A and B connector. For the best chance of having the right connectors, you should keep a set of adapters. I carry a JDI Tech Goldx 5 in 1 kit. It includes a 10ft cable and is very robust. I’ve been using the same kit for more than five years without issue.

    Note that some of the low-cost multifunction adapters are power only, which may be all you need, but if you expect to send data (including digital audio) make sure that the adapters you use support it.

    USB Tester

    Plug-in USB testers are easily available online for around $20. Plug one in between your source and load, and the meter will display useful information such as the voltage, current and temperature. For basic function checking I use a Drok USB 3 multi-tester. It is very simple to use and has a nice clear display. If I need to do more detailed testing such as USB C, graphing changes over time, and logging to a laptop, I use a MakerHawk USB Power Tester which can work with higher voltages from USB power delivery and log results to a Windows computer via USB or Bluetooth wireless.

    USB – 9V Pedalboard Power Converter

    The Mission 529 converts any 5V USB power source into 5 isolated 9V power outputs for effects pedals. Whenever I need to power a few pedals, I use one of these with the USB battery pack. I can run a modest size pedalboard for a day or so without having to worry about finding a reliable AC power source and running large power cables. If you travel internationally, you don’t have to mess with wall adapters which is an added bonus. Click here to check it out in our store, and click here to check out the 529i to take your portable power a step further.

    USB Wall charger

    For recharging the battery pack, or just charging my phone I usually carry both a USB A and a USB C Power Delivery wall charger. Some of the devices already on the list such as the Mission 529 and the Anker Powercore+ come with their own wall chargers that you can use. If you need to buy one, I like wall chargers from Phihong because of their small size and extensive regulatory and safety testing.

    You can easily carry all of these with you in a gig bag or backpack. If you are like me, you’ll soon find that they get you out of a tight spot so often that you’ll rarely be without them.

  • Batteries: Which One is the Best?

    I’m not sure of the reason the de-facto standard for effects pedal power became the 9V battery. Many low current pedals such as buffers, boosts, and distortions could easily be designed to run equally well on the more common AA battery type if we so desired.

    I’ll hazard a guess that history has a lot to do with it. If I recall correctly, the Boss, Electro-Harmonix, and other pedals I used in the 80’s pretty much all used the 9V battery. I imagine this same history has a lot to do with why we are also stuck with the evil center pin negative DC power connector on most pedals. I’m sure Roland must have had a good reason for using this back in the day on the iconic Boss effects, but from a product design standpoint, it’s a pain in the ass.

    Anyway, let’s get started. We are going to try to figure out the best choice of battery for effects pedals and how long they will last in each of our devices. To do this, we will need a few bits of information. Roughly in order of significance, these are:

    1. Battery chemistry
    2. Device current draw
    3. Device cut off voltage

    Battery chemistry defines the chemical makeup of the battery. The most common chemistry types for consumer primary cells are Zinc-Carbon (or Carbon-Zinc, or just Zinc; it’s the same thing), Alkaline, and Lithium. Let’s get a bit of terminology out of the way first. A primary cell is a single-use or disposable battery. These are designed to be used once and then disposed of, preferably recycled. A secondary cell is a rechargeable battery, and we’ll get to those later.

    The naming of the chemistry is all rather confusing. Zinc-Carbon cells do contain carbon, but it’s the reaction between zinc and manganese dioxide that forms the basis of the battery. We really should call them Zinc-Manganese batteries, but nobody ever does. Alkaline batteries also use Zinc and Manganese so they could be called the same thing. However, we call them Alkaline because they use a base electrolyte rather than the acid electrolyte used in Zinc batteries. Lithium batteries use a Lithium anode but are not the same as Lithium-Ion, which are secondary batteries. Got it yet? No?

    Zinc-Carbon batteries are the cheap ones you can buy in boxes of 50 for $19.99 on eBay. They are often called Heavy Duty, or Super Heavy Duty, neither of which means anything. They have a lower capacity than alkaline batteries, resulting in a shorter usable life. The body of the battery is made of zinc and forms the anode. The acid electrolyte eats into the zinc over a fairly short time giving these types of batteries a much shorter shelf life, and they are more prone to leaking. This type of battery is OK for something like, say a TV remote, but best avoided for effects pedals. You can use them in a pinch, but don’t leave them in the pedal unused for long periods.

    Alkaline batteries are the most commonly used in effects pedals. These are the Duracell and Energizer batteries that most of us use day to day.

    Lithium batteries are relatively new and quite expensive. We’ll do some calculations later and see if they make sense to use in effects pedals.

    Current draw is a nominal figure that defines how much current will flow through the device during operation. Depending on the pedal design, this can change during use, but most pedal manufacturers will publish a figure for current draw, and we can use this to calculate our battery life.

    If the pedal uses DC-DC converters, which digital devices usually do, it will have a Cutoff Voltage. This is the point at which the voltage from the battery gets low enough that the pedal stops working. These pedals will work the same all the way down to the cut off voltage, and then just stop. Other types of design may not have a hard cutoff voltage as such, they can continue working but the performance will change. It’s unusual to see a cutoff voltage published in the specs. Fortunately, there are some common industry practices around this, so we can get an estimate for our calculations.

    Head over to your favorite search engine and search for a datasheet on your battery; reputable manufacturers will publish these. If you can’t find your exact make, an equivalent will do. I use the Duracell 6LR61. Find the specs on your pedal from the User Guide or manufacturers web site and look for the current draw. For ease of demonstration I picked a few from the Roland Boss product line, and looked up the current draw on the spec sheets.

    • DS-1 Distortion – 4mA
    • OD-3 Overdrive – 9mA
    • DD-7 Digital Delay – 55mA

    There’s no exact cutoff voltage listed for these so we’ll have to estimate. It’s common industry practice for 9v battery operated products to work at least down to about 7v, so we’ll use that for our calculations. On the 6LR61 datasheet we are going to look for the constant current discharge graphs. Let’s start with the OD-3, which has a draw of 9mA. The red line on the graph is close at 10mA so we’ll use that. Draw a line across from the 7v cutoff voltage until it intersects the 10mA line. Then draw a line down to read off the service hours.

    Life of a 9v Alkaline battery in the OD-3 Overdrive

    From this we can see the approximate life of a 9v Alkaline battery in the OD-3 Overdrive is about 50 hours. Pretty neat. Let’s try some more. The DD-7 has a higher current draw of 55mA. We’ll need to go to the second chart from the datasheet for that. The closest line is 50mA, so again we’ll start at 7v cutoff, draw across to the 50mA graph and then read off the service hours.

    Life of a 9v Alkaline battery in the DD-7

    From this we can estimate about 7 hours life from the same battery in our DD-7.

    What if there is no chart for the current draw of our device? Well we can approximate it by drawing our own line. The DS-1 has a pretty low current draw for an effects pedal at 4mA. Let’s draw our own estimated graph based on the information we have.

    Life of a 9v Alkaline battery in the DS-1

    Here we can see a rough estimate of the battery life in the DS-1 would be about 200 hours.
    Modern programmable digital pedals and multi-effects with DSP’s, micro-controllers and digital displays consume quite a bit more power. A Strymon Timeline for example has a recommended minimum power supply current rating of 300mA, which would give us a battery life of less than 30 minutes. That explains why these types of pedals don’t run on primary batteries!
    A few Lithium Alkaline batteries are available billed as offering twice the capacity. Let’s take a quick look and see if they would be a good choice for effects pedals.

    Comparing the life of 9v Lithium battery vs Zinc-Carbon and Alkaline equivalent

    Here’s a chart comparing the life of 9v Lithium battery vs Zinc-Carbon and Alkaline equivalents at 50mA continuous discharge. If you recall, we used 50mA as our number for the Boss DD-7, so let’s do a quick comparison. The graph for the alkaline battery is probably an average, rather than the specific chart we looked at for the 6LR61 so the numbers are a little different, but they are in the same ball-park.
    This chart shows a service life of around 6 hours for 50mA at 6.6v cut out voltage. We got around 7 hours at 7v on the specific battery model, so it’s close enough.

    The Lithium battery is showing around 15 hours vs 6 hours for the alkaline. That’s 2.5 times the service life, which sounds pretty good. So we should start using Lithium batteries in all our effects pedals and get double or more the life, right? Well here’s the problem: Battery Junction has 9v Duralocks (essentially the 6LR61 in our tests) at $1.15, whereas the lowest cost Lithium 9v are $6. So in our DD-7 we’d get 2.5 times the life for 5.75 times the cost.

    There may be some cases where a Lithium battery makes sense. If you needed to run our example DD-7 on battery for a day at a festival with minimal opportunity to change batteries and it was worth the cost to avoid the possibility of failure? Maybe. You can also see that the discharge curve is much flatter; which means if you have a pedal with a very high cutoff voltage, above 7v for example, the Lithium might make sense, but such products are unusual.

    So there we have it, the old favorite alkaline 9v remains the best choice in most cases. The range of service life is quite interesting. Just with the three pedals in our example, we have almost 30 times difference in battery life. If you need to run your effects on batteries, it’s definitely worth making the calculations to figure out how long you should expect in each device.
    Note that we have a margin of error in our examples. If you need to be more precise, factors such as operating temperature and the battery’s internal resistance need to be taken into account. Devices with voltage regulators will draw more current as the voltage in the battery decreases and this will also impact the figures. A manufacturer’s current draw figure is a nominal value that should be used as a guideline. Even so, these details are only going to make a few percentage points difference. Unless you are designing a pedal for sale and are concerned with optimizing it for energy efficiency, using the techniques here should be quite adequate for most.

  • Inside EJ’s Box of Dead Batteries

    I’m sure you’ve all heard the story about how renowned tone magician Eric Johnson keeps around a box of partially discharged 9-volt batteries and can tell the state of charge from the sound of his fuzz pedal. There are plenty of people who are convinced their gear sounds better with different levels of battery charge. Some pedal board power supplies even come with controls that allow you to adjust the voltage range on some outputs so you can simulate a low battery. But does this really work, and if so, how?

    First things first. Many effects pedals, in particular digital effects, include voltage regulators for many parts of the circuit. Digital devices such as micro-controllers, digital signal processors, and others only sometimes run on 9v, and are very sensitive to the voltage variations. 5v or 3.3v are typical supply voltages for micros, so electronics elements such as buck and boost converters are utilized to ensure they receive a stable voltage regardless of fluctuations in the supply. If the supply drops too low for them to function, they simply shut down. If the main audio elements of the circuit in your effects pedal are powered by a regulated voltage, then using a partially discharged battery is going to have no effect whatsoever other than to reduce the run time of the device.

    Some analog devices can also be sensitive to voltage changes, and the designer may choose to regulate their voltage supply. The case here is much the same as for digital pedals; if the voltage is regulated, then using a half-dead battery or reduced voltage power supply is going to have no perceivable effect on the audio. That being said, there are some devices where varying the input voltage might influence the audio. Let’s look at those and see how it might work.

    As a battery discharges, it’s output voltage gradually reduces. If the powered device is unregulated, it will be running with the reduced voltage. This particularly impacts amplifiers such as the op-amp, diode, and transistor-based circuits in effects such as boost, overdrive, and fuzz pedals. These pedals are basically amplifiers, and the load on the output is being controlled by the power supply. The signal from the guitar pickups is modulating the power supply to provide the varying output current, but the eventual output power depends on the gain of the amplifier and the limits of the input power supply.

    As an example, let’s take an amplifier with a gain of 2 and a 3V power supply. If we provide a 1V input signal, the amplifier will try to increase this at the output to 2V. The output is 2V and our power supply can deliver 3V, so all should be well. Now let’s increase our input signal voltage to 2V. Again, we’ll multiply our input signal by our gain which is now 2 x 2, or an output voltage of 4V. Now the amplifier is trying to increase the output voltage to 4V, but the input power supply is only 3V. In this scenario, the amp will begin clipping. So, in these types of circuits, reducing the input voltage can make the effect clip earlier. It’s worth trying your boost or overdrive pedal to see if a lower input voltage has this effect.

    Distortion and fuzz pedals are more likely to be always clipping to some extent, so reducing the voltage will have a different effect. On the traditional transistor-based fuzz pedal, changing the battery voltage causes a response very similar to that of the volume control. Reducing the battery voltage reduces the signal level at the output. In combination with the existing controls and a tube amp on the edge of breakup, it gives you an extra knob to twiddle, but it does not provide a dramatic change in behavior.

    Testing with a Dunlop Fuzz Face shows a proportional reduction in output level as the voltage is reduced. The effect continues to operate down to about 5V at which point the signal from a single coil passive pickup begins dropping out.

    Dunlop Insides
    Inside the Dunlop Eric Johnson Fuzz Face. It’s a simple circuit utilizing a pair of BC 183 NPN transistors. Here, the battery input is connected to an external variable power supply for testing.

    Variable power supply
    A variable power supply allows precise control over the input voltage to the Fuzz Face, simulating a discharging battery. As the input voltage reduces, the signal level at the output reduces. Here, we are setup for 9V. The signal begins to drop out at about 5V.

    1KHz test signal
    Here’s a nice clean 1KHz test signal with the Fuzz Face bypassed.

    9V Output
    Here’s the output from the Fuzz Face at 9V with the volume and fuzz controls turned up around full.

    6V Output
    Here’s the output from the Fuzz Face with the input power reduced to 6V. The output level has reduced by about 50mV.

    As with so many things, the story of the discharged battery improving tone does have elements of truth, but it helps to understand a bit more about how it works to see what benefits may be had. In some effects pedals, this will have no impact at all since the effect regulates its voltage. In others, there is some change to the behavior either in output level, headroom, or both. Try it out with some of your pedals and see if it works for you.

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