Great Reception Of The Birdcord | Product Of The Year

It has been about 7 months now since the release of the Birdcord USB to 9V Converter Cable and many musicians around the world already got one. Most use it to power their pedalboard, but there are also some who use it for powering synthesizers, drum machines, portable amplifiers and more. The feedback that I get is extremely positive. More than half of the sales come from recommendations. Thanks to everybody who bought a Birdcord, to everybody who provides me with feedback and product wishes and of course thanks to everybody who spreads the word online and offline, you are amazing!

Here’s an extract of the online reception of the Birdcord:


New Opto Tremolo In Development

After countless modifications and testing more than a dozen of different resistive optoisolators I am finally at a point, where my new Vactrol-based opto tremolo circuit sounds just awesome. I already sent a first prototype to Styrian guitar player “Sir” Oliver Mally, who confirmed my assessment: this is something big. I’m really looking forward to bringing this little sound monster to market in the next weeks!

scope tremolo prototype waveform rigol ds1054 stompbox amp style vactrol super reverb fender songbirdfx songbird fx

tremolo circuit developement songbird fx songbirdfx stompbox trem amp style opto optical waveform signal sound

Keep on  rocking!

How To Measure The Output Impedance Of Your Guitar

What Is The Output Impedance And Why Do I Even Care About It?

The output impedance or source impedance Ri of a perfect signal source is 0Ω. When talking about DC voltage sources it is also called internal resistance (That’s why I call it Reven though a guitar pickup is an AC signal source). A (passive) guitar pickup is by no means a perfect signal source (Ri > 0). This means that the output voltage will drop when connected to a load (effects pedals, amplifier). This effect will be more significant the higher the output impedance of your guitar pickup and the lower the input impedance of your amplifier/effects pedal is (voltage divider between Ri and RL).

guitar output impedance thevenin internal resistance effects pedal buffer voltage divider
voltage divider between output impedance Ri of the guitar and input impedance RL of the load

Recently I simulated the circuit of a Fuzz Face with LTspiceIV and realized that the output impedance of the guitar affects the final output waveform of the effects pedal.


Fuzz Face Schematic:

Fuzz Face Simulation Sound LTspice circuit impedance


Output Waveform Of A Fuzz Face With Perfect Signal Source (Ri=0Ω) At Input:

Fuzz Face Simulation with Buffer Pedal perfect signal source

Output Waveform Of A Fuzz Face With Realistic Signal Source (Ri=10kΩ) At Input:

Fuzz Face Simulation LTspice Output Impedance Guitar

You have to find out for yourself if you like the sound of those interactions or not. If you don’t like it you should reconsider the order in which your guitar effects are arranged in your signal chain. Buffer and booster/preamp pedals have a high input and a low output impedance. They can be used to preserve the original waveform coming from your guitar pickups when used as the first pedal in your signal chain. Active guitar pickups are even better than buffer pedals because the guitar cable is a (capacitive) load too.


How To Measure The Output Impedance Of Your Guitar Pickup?

For measuring the source impedance of your guitar you will need an oscilloscope. If you don’t have one you can use my results because it won’t differ that much. By the way the exact model name of my guitar pickup is a Seymour Duncan SH-4 JB in bridge position.

  1. Measure The Peak-Peak Voltage With Open Output:
    Turn your guitar up to full volume to make sure that the pots don’t influence your measurement. Then strum a note (I strummed the thicker E string).
    guitar source impedance measurement calculation output impedance

    peak peak voltage vpp guitar output e string signal waveform without load

  2. Measure The Peak-Peak Voltage With A Load (RL=1k):
    Strum the same note with the same intensity as before to get the best results.
    guitar internal resistor calculation measurement impedanceoutput waveform of a guitar maximum typical output with load measurement

  3. Calculate The Output Impedance Of Your Guitar Pickup:
    Finally we can take the voltage divider formulas from above and substitute the variables with our measured values.
    calculation guitar output impedance voltage divider formula
    Result: The output impedance of my guitar is about 10kΩ.

Note: The impedance changes with frequency. This result is only true for the lower E-string, however we can assume that it won’t change dramatically. To get a more detailed result you can repeat this procedure at different frequencies (different notes).


USB Rechargeable Guitar Effects

Are you tired of low 9V batteries in your pedals? This is now over! My company Songbird FX invented the world’s first USB rechargeable Overdrive pedal, the Bluebird Drive. Below you find a video of the Germanium version, produced by the great Mike Hermans.

Interested? Click here for more information!


Keep On Rocking!

How Does The Tone/Volume Control Of A Guitar Work?

Gibson style guitars usually have two humbucking pickups, a tone and a volume potentiometer for each humbucker and a toggle switch to select the pickup. How exactly are these components wired together and how do the pot settings affect your sound? In this little article I will give you an answer to these questions and tell you some advantages and disadvantages of this wiring scheme. I will also show you the frequency response of the different settings.


Wiring Scheme

gibson style wiring scheme tone volume potentiometer pot capacitor cap toggle switch humbucker humbucking pickup les paul sg explorer es
Please note: the middle position of the toggle switch is not correctly drawn. Actually both pickups are connected to the output in the middle position.

In the diagram you can see that each pickup has independent tone and volume controls. The obvious advantage of this wiring scheme is that you can set two independent sounds and easily switch between them via the toggle switch.

Example Settings:
  • Classic Rock
    Neck pickup: Volume 100%, Tone 0% (creamy lead sound)
    Bridge pickup: Volume 70%, Tone 100% (crunchy rhythm sound)
    This is a typical classic rock guitar setting where you can switch between lead and rhythm sound.
  • Kill Switch
    Neck pickup: Volume 0%, Tone 100% (short circuit – no output)
    Bridge pickup: Volume 100%, Tone 100% (high output lead or rhythm sound)
    This setting can be used as a special effect instead of a kill switch: Quickly move the toggle switch up and down to create a tremolo-like effect.

One disadvantage of independent volume control is that the mix position of the toggle switch is only useful, if you match the volume-settings of both pickups. If you don‘t, one pickup outweighs the other and you can‘t hear much of a difference to the single pickup sound.

Another disadvantage of passive volume control in general is that at lower volume settings the output impedance is very high -> Your signal is more sensitive to electromagnetic disturbances and gets noisier. You don’t have this problem with active guitar pickups.


Frequency Response

I simulated the frequency response of different settings with LTspice XVII. The signal source I used has a flat frequency response and a 10k output resistance.

simulating guitar frequency response tone volume control gibson les paul

frequency response guitar gibson style tone volume setting pot potentiometer attenuation curve db
Frequency response: Different volume settings and different tone settings.
  • The tone control is an adjustable lowpass filter
  • The tone setting does not change at different volume settings (the cut-off frequency stays the same)
  • Significant tone change only happens between 0%-10% of the tone pot value -> I recommend using audio taper potentiometers to compensate this unlinearity


I hope this article is useful to you. Please check out the products on this website: My company Songbird FX is a manufacturer of high quality micro-USB rechargeable guitar pedals.


Keep On Rocking!