Monthly Archives: May 2014

Guitar Rig

Humfree Guitar Rig Wiring

Humfree guitar rig wiring is not easy. Hum can have many different causes. This article gives you the basic skills for properly wiring a guitar rig and will save you some headaches in your rig building adventure. For more detailed instructions, please download “The ultimate Guitar Rig Building Guide“.

Hum Caused by Ground Loops

Ground loops are certainly the most common reasons responsible for the hum. These are caused by double grounding connections. Thus, they have something to do with earth and cable shield. To understand and to get rid of ground loops, it is important to distinguish between “earth”, “chassis” and “cable shield”. But in a way, “earth”, “chassis” and “cable shield” are the same, because they are somehow connected. And the term “Somehow” is exactly the problem. To avoid ground loops, we need to know where “earth”, “chassis” and “cable shield” are connected. When wiring a guitar rig, we must be aware where we want them to merge.

Earth: (also called “ground”): The earth is, as the name suggests, the connection to the earth. This is the zero potential. In power cables, the connection to earth is called “grounding conductor”.

Chassis: If the chassis (housing) of a device is made of metal and the device is operated with mains voltage (120 / 240V), the housing must be grounded for safety reasons (the chassis is thus connected to earth within the device).

Cable Shield: The shield is used to keep electromagnetic fields from the audio signal. Within guitar cables, this is the outer, mostly braided conductor. In order that the cable shield can fulfill its function, it must be connected to earth.

Conclusion: Earth, Chassis and Cable Shield are always connected somewhere. To prevent hum by ground loops, it is important to know where they are connected.

Star-shaped Wiring
Basically, the connection of “Earth”, “Chassis” and “Cable Shield” must be structured like a star:

Humfree Guitar Rig Wiring requires a Star-shaped ground structure.

Star-shaped wiring

Triangle | Ring Wiring
If the star-shaped structure is not strictly observed and instead wiring is made in a triangle, the classic Ground Loop occurs. The problem is that the instrument is connected via two different paths to earth and the current can, therefore, flow through two different ways, respectively, the current can flow in a circle.

Hum caused by triangle wiring

Triangle wiring

Groundloop Caused by Split Guitar Signal

A typical example of such a triangle wiring is the use of two amplifiers. The following diagram shows a typical ground loop:

The typical ground loop using two Guitar Amps

Two Guitar Amps

In a guitar amp, the earth from the power cable and the shield of the guitar cable are connected both to the chassis. Thus, in our example, the guitar is grounded once through the amplifier on the left and once through the amplifier on the right. It does not matter whether the guitar signal is split by a Y-cable, or if the second amplifier is connected to the first amplifier.
Due to the cable resistances, the potential for the two amplifiers are quite minimally different (we are talking about millivolts). Therefore, along the line marked in red, a small current begins to flow in the circle. This is the Ground Loop!
This is audible as hum because this current flows with the mains frequency (50Hz in Europe, 60Hz in America). In addition, the harmonics (100 Hz, 200 Hz, ….  respectively 120 Hz, 240 Hz, …. ) are also generated. The longer the cables are, the bigger is the potential difference. As a result, the hum increases with the length of the cables.

Isolating Transformers to Prevent Ground Loops
In order to prevent ground loops, the connection of the guitar cable from one to the other amplifier must be separated using an isolating transformer. Inside an isolating transformer, there is no electric connection between input and output. The signal is transmitted magnetically instead. Transformers specifically made for guitars must be used (e.g. Lehle P-Split) so that the guitar signal is transmitted unaltered. Isolating transformers for studio applications are not suited for guitars.

Using an Isolation Transformator

Der Einsatz eines Übertragungs-Transformators

Groundloop over Daisy-Chain Power Supply

Another typical example of groundloops is powering the effects via daisy-chain cables or using a power supply with several outputs without galvanic isolation. Since the cables are usually very short, this hum is often inaudible.

Groundloop over Daisy-Chain Powercables

Groundloop over Daisy-Chain Powercables

Groundloop via Send-Return

Inserting effects in the Send/Return is also a groundloop. The longer the cables, the louder the hum. In order to avoid this hum, two approaches are possible:

  • Use an isolating transformer in either the send or the return line.
  • Do not use the 4-cable method to the pedalboard. Instead, connect the effects directly next to the amp with very short cables. If they must be switchable, use a MIDI controllable looper. The short cables also have the advantage to avoid dynamic and transparency losses.
Groundloop over Send/Return

Groundloop over Send/Return

More Information …

This was just a brief introduction to the main issue of hum. But hum can also be introduced by many other things, e.g. by interferences caused by lighting systems, computer monitors, fluorescent lights, nearby high-voltage lines and many other sources.
If you like to read all you need to know for successfully wiring a guitar rig, including a step-by-step instruction for trouble shooting, you can download “The ultimate Guitar Rig Building Guide” which explains everything in detail on over 30 pages.

MIDI over XLR Microphone Cable

StageWire - Sending MIDI data over XLR microphone cable

StageWire – Sending MIDI data over XLR microphone cable

Why using XLR Microphone cables for MIDI?

I did already retrofit MIDI foot controllers with XLR plugs in the 90’s. It requires just a few electronic components to send MIDI and phantom power over a single XLR microphone cable. But why did I do this? I have been touring with bands like Krokus and many others. For fast and reliable cabeling, I did need a solution that is road proof. XLR cables have many advantages over MIDI cables:

  • Safe and reliable connection between the foot controller and the effect rack
  • Extendable cord
  • Locked plugs
  • Spare cable available any time
  • Power supply and MIDI signal over the microphone cable

MIDI cables are OK for use in the studio and for wiring inside the guitar rack, but in my opinion, they are not suitable for running on stage.

However, the MIDI communication is  only unidirectional. This means, one unit talks (e.g. the foot controller) and the other is listening to it (e.g. the effects unit or the guitar amp). But what if you switch a channel on the amp itself and you like the MIDI foot controller’s state to change as well? That’s why we developed StageWire!


StageWire is a consistent further development to send MIDI data over XLR cables. StageWire is a bus system. This means, every one talks to everyone. A Looper|Switcher can be interconnected with up to 14 MIDI foot controllers in daisy chain. Every unit can simultaneously talk and listen, all over a single microphone cable from device to device. Furthermore, the foot controllers are powered over the microphone cable! All units are in sync all the time. It does not matter on which unit you press a button.

StageWire was developed by Prostage and especially designed for rough use on stage. StageWire is four times faster than MIDI. Cable length may be up to 250m. Thus, you can send MIDI data over multicore-cables, e.g. to connect the FOH with the stage. The XLR connection guarantees, unlike the standard MIDI cables, a safe connection between foot controller and amplifier/effect rack. To connect StageWire with standard MIDI equipment, a MIDI XLR interface, such as the Prostage XTMpro, is required.

Well known manufacturers and rig builders such as Fractal Audio or Bob Bradshaw have applied this approach and now also build their foot controllers with 3-pin XLR connectors.

Interview with Wolf Hoffmann | Accept

Wolf Hoffmann Live

Wolf Hoffmann Live

Wolf, on 15th August, the new Accept album will be released. Tell us a little bit about the new songs.

The new album is called “Blind Rage”. All songs were written as usual by Peter and me with Mark contributing the final lyrics. The song writing process took about 6- 8 months total, starting in the summer of 2013. Recording was done in January and February in the US, mixing in the UK in Andy Sneap’s Backstage Studio.

After a longer break, you have been active again for about four years now. What is different compared to the past?

Well, some things never change , others change all the time. What hasn’t changed is the musical identity and direction. We still sound like Accept – Peter and I have been working together for close to 40 years now as a songwriting team. So we automatically know what the other is thinking without much need for words. To me it feels it getting tighter and tighter and more defined with each album.

What has changed concerning your equipment ?

Back in the ‘old days’ (especially the 80’s) we used to carry so much more gear with us, wherever we played. It was almost ridiculous by today’s standards. I am talking containers full of backline and instruments! Back then it was still affordable, nowadays… forget it. Only when we do longer continuous touring with night liners and truck will we carry our own backline and drums set etc.

For fly dates we travel only with the personal items like guitars and pedals etc. Getting your sound out of rental guitar amps can be really tough though, almost impossible sometimes. So the Kemper amp is perfect for me. I can now take my sound with me wherever I go. My setup is ultra portable and very flexible. I use two Prostage X05 boards to trigger the program changes on the Kemper Amp. One for my guitar tech and the other one is on stage. It worked well for the last 100+ shows and I see no reason to change it for this upcoming tour.

Have you ever used a pedalboard?

I have used a poedalboard for as long as I can remember. I was the guy with the most intricate pedalboard designs you could find. I wanted to have more sound possibilities but without destroying the main sound, that was always the main challenge. Over the years I  went from having pedals on the floor to pedals in a rack to no pedals. Nowadays I have all the effects I need (delay, overdrive and Wah, mostly) built into my presets of the Kemper. With the exception of one pedal: it’s a replica of my old Mutron Octave divider pedal, It;s called a vivider, made by Salvation Mods. Everything else comes right out of the Kemper and is controlled through the X05 foot controller.

Wolf, do you know the situation when you are performing on stage and suddenly the guitar rig fails? What does a guitarist do in this situation?

Heck, yeah, I know that it can be pretty scary! The more gigs you have under your belt though the more you realize it’s something that’s bound to happen once in a while and you learn to deal with it. Luckily it does not happen very often.

What can be done to prevent such a situation?

Have good gear, know you stuff really well and if you can, have a backup plan.

When and where can we see you live on stage again?

We will start touring in August and September, Europe, Japan, Australia and also a few US shows… can’t wait to play the new songs live! I hope to see you on the road !!

Wolf, many thanx for the interview.

You are welcome !