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Guitar Circuits#

Here you will find some archetypal electric guitar circuits which have featured within the circuitry of some of the most popular and professional stomp boxes (guitar effects) of all time.

Attribution: The above is a true bypass wiring diagram illustrated by the famous Beavis Audio

The above shows how to wire up a guitar pedal

Irrespective of your preference for true-bypass or a buffered system, the above diagram is exemplary, insofar as it totally shows how to wire up a guitar effect pedal.

  1. The box must be metal and usually this means aluminium - this prevents hum, protects against dropping the thing, and goes a long way toward stopping that awful mobile phone (cell phone) log in thing, which sounds terrible on stage!
  2. Always use open style jack sockets as shown as these can be cleaned, fixed and are generally better than their plastic counterparts.
  3. The wire colour is not arbitrary nor random! It is there to show what line carries which type of electric current - this stops you from making a total -f up.

Buffer or true bypass?#

Buffer or true bypass switch? The question is almost as old as some of my -f T-shirts. If you check forums or google this subject, you will find endless debate on buffers vs. true-bypass. Nobody seems to agree on this!

The good news is that it is not a binary decision. Here's what has been found over countless tone and effect setup experiments:

  • A pedal chain of all true-bypass devices is not always the best thing

  • A pedal chain of lots of buffered pedals is not always the best thing

  • A buffer at the beginning of your chain of true-bypass pedals, and perhaps one at the end is a good thing

Your ears, as applied to your setup, are the best guide. Try, experiment, listen, create your own conclusions.

So what is the quickest way to understand the efficacy of buffers in your setup? Easy. Stick any modern Boss pedal at the beginning of your chain, and another at the end. The Boss (or any good buffered pedal: Maxon, Ibanez) etc. have the buffers always on. You should be able to tell pretty quickly what's what.

The caveat here is that: some older design pedals (with very desirable sounds) are famous for their hatred for buffers. The classic example is the Fuzz Face--it simply does't sound the same if you have a buffered pedal in front of it. This pedal really needs good RAW guitar input!

So what about building a buffer? Buffers are some of the simplest DIY projects out there, so let's dive in a look at some examples.

Transistor Buffers#

JFET Buffers#

  • Here is a very simple and effective buffer. It presents high impedance to the incoming signal, but was originally designed to make use of the now unobtainable MPF102 JFET.

  • This circuit could be modified to work with MOSFET transistors. However it probably wont sound the same. Additionally, MOSFET transistors load the input down with capacitance. In other words, they seriously affect the input impedance, which is what we are trying to avoid.

  • You may use 2N3819 or 2N5457 (if you can get hold of these devices), which have similar properties to the MPF102

Drawn by YooFab / CC BY-SA

Using a low-gain JFET transistor, this design is as simple as it gets--input cap, bias resistor, and output cap.

BJT Buffers#

Next up, is the single-transistor buffer as found in the Ibanez Tube Screamer--a bit more complex than the JFET, but your ears will be the guide as to whether or not it sounds better. The transistor here, can be any general purpose type such as:

  • The BC548 family is European, including the BC547A to BC550C, are lower voltage, lower current, general-purpose transistors in TO-92 packages
  • The 2N3904 is a Yankside NPN transistor

Drawn by YooFab / CC BY-SA

Op-amp Buffers#

Op-amps make great buffers. Here is another design that uses a TL071 part. The 9 volts shown will work, but if you jack it up to 12-15v DC you will get more headroom for hotter signals. The key here, is we do NOT want the buffer to be creating distortion, as then it would not be just a buffer.

Drawn by YooFab / CC BY-SA

Here is the op-amp-based buffer section from a famous boutique overdrive that rhymes with "Plon Fentar". The Plon Fentar has a buffer before the distortion section, that is loved by a lot of people, including those who profess not to like buffers! This has a few more parts. Again, let your ear be the ultimate authority.

Drawn by YooFab / CC BY-SA

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