Modify your boss DS-1

gain appreciation for classic distortion…

The Boss DS-1 has been around since 1978 and remains to this day one of the top selling guitar pedals ever. Most players will have owned this orange dirt box at one time or another, with it even gracing the pedalboards of legendary guitarists like Kurt Cobain and Joe Satriani.

There is however a twist to this tale; very few of the greats used the stock model…

With the DS-1 being such a common pedal, modifications for the circuit proved popular, allowing players the ability to tailor this distortion to their own sonic desires.

While there are many well documented modifications out there you could choose from, we present to you the CSGuitars mod: a selection of some of the best ideas from other mods, with a unique spin on the values to dial in a deep, dynamic distortion that’s a bit more user friendly than the stock unit.

Watch the original modification video below:

What does this modification do?

The CSGuitars modification aims to make changes to the following areas:

• Extend the clipping into lower frequencies

• Reduce the overall gain and improve low end response

• Introduce asymmetrical hard clipping

• Redefine limits of the tone control

Lower frequency distortion - The first stage of the DS-1 features a couple of high pass filters designed to attenuate low frequencies and prevent them from travelling further into the circuit and distorting. While this is generally a good idea as distorting low frequencies can make the distortion slow or muddy, we felt that dropping the cut off frequencies for these filters slightly (by increasing the values of C2 and C3) would add some extra body to the distortion, while not compromising its aggression.

Gain reduction - Prior to reaching the opamp the signal travels through a transistor boosting stage where the signal level is increased dramatically, the gain in this stage is so high in fact that it drives the signal into soft clipping before it even reaches the distortion part of the circuit!
Reducing the value of feedback resistor R7 helps to tame this initial amplification, allowing the pedal to be more responsive at lower distortion settings and less like a fuzz with the drive maxed out.
Also since the bass frequencies don’t get amplified quite as much at this initial stage it helps to keep the distortion tighter across its range.
The value of C5 has been increased as a result of this to couple the transistor stage to the opamp gain stage.

Asymmetrical Clipping - The stock DS-1 uses a pair of 1N4148 diodes in a hard clipping arrangement after the opamp. Each diode having the same forward voltage will clip each edge of the signal in the same manner.
By replacing D4 with a 3mm LED and D5 with a pair of 1N4001 diodes in series the differences in forward voltage between the two will mean each side of the waveform will clip by a different amount. This provides more even order harmonics to the distorted sound which is aurally pleasing.
The advantage of using an LED as a clipping diode (other than its unique forward voltage) is that the LED will illuminate as the signal clips. Extending this through the chassis provides us a visual indicator of how much clipping is going on.

Tone Control - The DS-1 features a passive tone control with both high and low pass filters which form a mid frequency notch in the centre position. By reducing the values of C11 and R17 we drastically shift the cut off for the tone control’s high pass filter, creating a flatter response in the neutral setting.
This makes the tone control seem much less severe, only brightening or darkening the sound to suit whatever guitar you happen to be using.

other things to try

Increasing the value of R9 will further reduce the gain of the initial transistor boosting stage, allowing far more range for softer distortions at low drive settings. You may opt to change this rather than the feedback resistor R7. You will also want to leave C5 unchanged in this case.

R13 dictates both the gain increase of the opamp and the frequency cutoff at maximum drive settings. The 1K is pretty severe in having enormous gain at the top setting, while also attenuating the gain applied to frequencies of 300Hz and lower.
Increasing this resistor will reduce the maximum opamp gain while attenuating less gain for lower frequencies. It’s really all about what you want the maximum setting on the drive control to do. Somewhere between 2.2K and 4.7K would provide the best results.

The changes to the tone stack high pass filter in this modification effectively removes the mid frequency scoop of the stock unit when the control is in its mid position. If this flat frequency response is undesirable then reducing the modification values of C11 and R17 (as well as experimenting with C12 and R16 which make up the low pass filter) will shift the scoop frequency at the mid position of the tone control.

Any arrangement of clipping diodes will yield different results. You could opt for two LEDs if you liked, keep them both the same for symmetric clipping, or mix colours for a bit of asymmetry (different colours will have different forward voltages; it’s not just for looks!)
This is a place to experiment and see what you like best.
Perhaps even add a switch to toggle between silicon diodes and LEDs, or between symmetric to asymmetric.