BOSS DS-1: modding my own mod

In my previous post I converted the DS-1 distortion pedal into something very close to an overdrive. One of the things I changed was the clipping section; one of the diodes was replaced by a red led. I tried some other combinations, but not very scientifically, honestly. The final one was chosen by ear, and that’s the one I published. But the doubt about some other combinations remained in my head after that.

Recently I got another DS-1 in ebay, and after modifying it (following my own instructions), I decided to give it another twist: let the user decide what diode to use (or no diode at all) for each side of the clipping section. In the next diagram I show how I connected two rotary selectors for choosing the diodes:

The rotary selectors are these ones:

The actual devices with the diodes connected:

The X and Y terminals from the diagram above have to be connected to one of the removed diodes terminals in the PCB (see the white and blue cables):

It is not necessary to connect anything to the other diode because the two diodes are connected cathode to anode and anode to cathode. Don’t connect one of the terminals to ground, as you could do with some other hard clipping designs (ProCo Rat, for instance) because that is not how they are connected in the DS-1.

The result:

The two selectors act (as I have connected them for my own convenience) as two “taps” for the two sides of the signal (positive and negative), as seen from the supply jack side of the pedal. Open the tap and you have a more open (less clipped) signal, close the tap and you have a more clipped signal. The sequence of clipping goes like this:

  • wide open, left position: no diode for clipping. The clipping comes from the transistor section and the operational
  • second position from the left: blue led, Vf=2V
  • third position from the left: red led, Vf=1.5V
  • fourth position from the left: original diode: Vf=0.5V
  • fifth position from the left: schottky diode: Vf=0.2V

Seen from the front, as you play, you can think about left=less volts / right=more volts.

You could say: there are repeated combinations, because for instance “red led + schottky = schottky + red led”, so I could have chosen a 15 positions (I think) rotary switch for all the valid combinations. Apart from the fact that a 15 positions switch is hard to find and it would have complicated the cabling, that hypothesis (“red led + schottky = schottky + red led”) is not completely true in the real world, because of two reasons:

  • Let’s face the truth: two different diodes with the same name do not have exactly the same Vf, not to mention the rest of the specs.
  • Clipping the positive part of the signal is not the same as clipping the negative part of the signal, because of the non linearities of the circuit design and components.

I think that setting two selectors is (as least for me) more intuitive. This is mostly an experiment that can be used also for gigging.

How does it sound

Yes, an experiment, but also a gigging pedal I am planning to use. In spite of the flexibility given by the two selectors, it doesn’t lose its original character. Selecting the combination: position 2 + position 3 (original diode + red led) it sound almost like the other DS-1 I modified, as expected, given the intrinsic differences of every unit components.

Selecting different positions for each selector, especially if they are very extreme, accentuates the asymmetrical character of the distortion (even harmonics, more on that here:

The blue led combined with any other diode gives a very mid rangy character for my ear.

As you “open” the “tap”, the signal is louder. Selecting the open – open combination creates, as expected, a very loud but distorted signal, not bad given the fact that it is created by the transistor and the operational. Cannot be used as a clean boost pedal, but can crank a tube amp. 

At the other extreme, selecting the two schottky diodes and maxing the distortion control creates an almost fuzzy distortion. If you max the three pedal controls, select a neck humbucker pickup and lower the guitar tone control, the fuzz is there for you to enjoy. That way all the treble harmonics that you hear come from the pedal itself, not from the pickup.

Please let any thoughts in the comments section, and if you try this mod please let me know.

The DS-1 mod I mention above (Turn a BOSS DS-1 into a nice overdrive) has been implemented at least by two friends of mine (thanks Pepe and Juanjo for trying it out), and they are very happy users of it, I think they are even gigging with it. They call it “warrior mod” because of my last name in spanish.




DS-1 vs modded DS-1: frequency response

Let’s compare the original BOSS DS-1 with my modified DS-1, so we check out the difference in tonal character between a distortion pedal and an overdrive pedal (or whatever DS-1 has become after being modified in

I have tested them using a Linux computer, its sound card and qloud software. I know the measurement is not very precise, but the real thing is not going to vary very much, I think. All controls were at noon during the measurement.

Original BOSS DS-1

Original DS-1 frequency response

As expected from a pure distortion effect pedal, frequency response is mid scooped, with a bump at 100Hz.

Modified BOSS DS-1

Modified DS-1 frequency response

As I expected after the modifications in the tone stack, frequency response has much more mids. The maximum is not at 800Hz, just because the circuit is not only the tone stack. By touching the tone control, the curve can be modified (I leave it for a next article).

As you can see also, at aproximately the same “level” value, the overall volume is higher (over -60dB for a wider range in the test), without changing any measurement parameter, even if the perceived distortion is higher in the original unit. The reason, I guess, is the red led in the clipping section instead of a common diode, see the article Since the Vf of the led is higher than that of the diode, it clips at a higher voltage, giving the circuit more headroom. This is very common when doing this kind of modifications. I think the tone stack change alone does not explain that higher volume.

Turn a BOSS DS-1 into a nice overdrive


The fence that separates distortion and overdrive pedals is very thin. Usually pedals based on hard clipping, high amount of distortion and mid scooped response curve are called distortion and those ones based on soft clipping and mid boosted are called overdrive. But some of the more famous overdrive pedals, known for being “transparent”, “clean” or “dynamic” are based on hard clipping (clipping diodes at the output of an operational amplifier or transistor). Think of Klon Centaur, for example (mid boosted, by the way).

Hard clipping seems to have usually a more dynamic overall response to the guitar touch than soft clipping, although it depends on the circuit design. Some soft clipping pedals are very dynamic while others are too compressed, but most of them seem to be compressing and distorting all the time.

Hard clipping, theoretically limits drastically the signal when it reaches a certain level, so it creates those high harmonics that give it its character. Soft clipping limits the signal more gradually, giving that “soft”, characteristic valve-like distortion sound.

Having taken all these considerations into account, let’s review my last pedal modification. I wanted to experiment those concepts with a BOSS DS-1 pedal I purchased broken and then fixed. I liked as it was, but that kind of distortion is not for me, frankly.

BOSS DS-1 is based on classical symmetrical hard clipping, two diodes at the output of an operational, and the tone stack tends to mid scoop the response curve, so it should be considered a distortion pedal. It is orange and is called “Distortion”, so in this case it was easy.

My experiment had these objectives:

  • Reducing distortion (amount of clipping)
  • Give it an asymmetrical clipping character, more pleasant to my ears and more valve-like distortion
  • Mid boost the response curve
DS-1 original schematic

For reducing distortion, I have made these two changes:

  • R9 at the emmiter of Q2 controls the gain of the first stage, previous to the opamp stage. With a value of 22 Ohms, the output is so high that the signal at the output of the operational is almost always clipped. I tried with different values and for me 100 Ohms gave the sweet spot for having the right amount of distortion with the gain control at 12 o’clock, for both single coil and humbucker pickups.
  • LED diodes have a Vf higher than common bipolar diodes. Bipolar diodes have Vf=0.7V and LED have Vf > 1.5V, depending on the color. Vf is what causes the clipping, and the higher Vf is, the higher the signal can be before it starts to clip. Replacing only one of the clipping diodes (D5 for instance) by a red LED yields more headroom and at the same time serves my second purpose of having asymmetrical clipping. By the way, this is one of the changes that the famous Keeley Ultra Mod makes to the DS-1.

For the mid boost thing, I changed several components of the tone stack. DS-1 tone stack is based on the Big Muff tone stack. It is passive and tends to mid scoop the tone. By simulating the circuit with LTSpice, I found the spot where the signal is mid boosted without loosing the ability to control the tone (although it is somewhat reduced compared to the original DS-1 design).

Modified DS-1 tone stack

The bump happens at 800Hz, which for me is the best point to get a nice tone that is capable of cutting through the mix in a band context. It is a simplification because the response curve of the pedal depends on the rest of the circuit as well, but I can tell you that the result is quite acceptable.

The components replaced in the tone stack are C11, C12, R15 and R16. As you can se, only six components have been replaced. I have prefered to keep it as simple as posible, but the change in tone and behavior is drastical. Now the pedal is a very dynamic, mid boosted overdrive, with a wide range of distortion. With gain at max level, it reveals it true distortion spirit. Put a compressor before and an equalizer that boosts the 100Hz frequency after it, and you’ll get the real sound of rock and roll.

As a summary, these are the replacements:

R922 Ohms100 Ohms
D51N4148Red LED

For C12, 82nF is not a very common value, but you can put 47nF and 33nF in parallel to get 80nF, enough given the usual tolerances of capacitors. Use a capacitor tester if possible to get a close value. The board has plenty of space to put the two capacitors in that position. For C11 and C12, any kind of capacitor will do, but the values are very important (test if possible).

I hope you enjoy this mod, please let me know of any improvements or mistakes you may find. If you are a good guitar player, please record a demo and upload it to youtube. If you are rich, please send me a Klon Centaur to compare with my DS-1 modified pedal.

PD: if you make this mod, please comment below, I would like to keep track of people enjoying (or not) my mods.

PPD: JAVIER from Argentina made some changes to this mod, he used a 47nF for C12 and a 15K for R15, getting very similar results. Simulating his circuit, we get a very similar curve but smoother, less prominent at 800Hz, and also seems to attenuate high frequencies more:

C12 = 47nF R15 = 15K

Try this if you find the mod too nasal sounding or get some hiss through your amp.

Convierte el BOSS DS-1 en un buen overdrive

La frontera entre pedales de overdrive y de distorsión es más bien fina. Normalmente los pedales basados en hard clipping, mucha distorsión y una curva de frecuencias “mid-scooped” (frecuencias medias rebajadas) son denominados “distorsión”, y aquellos basados en soft clipping y con resalte de medios son llamados “overdrive”. Pero algunos de los overdrives más famosos, conocidos por ser “transparentes”, “limpios” o dinámicos” están basados en hard clipping (cortar la señal en los extremos mediante diodos puestos a tierra a la salida de un operacional). Pensad en el Klon Centaur, por ejemplo (con los medios resaltados, por cierto).

El hard clipping parece tener una respuesta general más dinámica al toque de la guitarra que el soft clipping, aunque depende mucho del diseño del circuito. Algunos pedales con soft clipping son muy dinámicos mientras que otros comprimen demasiado, y la mayoría parecen comprimir a la vez que distorsionan.

El hard clipping, teóricamente limita la señal cuando alcanza cierto nivel, de manera que crea los armónicos en altas frecuencias que le dan ese carácter. El soft clipping limita la señal más gradualmente aportando ese sonido más suave que generalmente asociamos con la distorsión de válvulas.

Teniendo en cuenta todas estas consideraciones, veamos mi última modificación de pedal. Quería experimentar estos conceptos con un BOSS DS-1 que compré averiado y que arreglé. No me disgustaba tal cual, pero ese tipo de distorsión no es para mí, francamente.El BOSS DS-1 está basado en el clásico hard clipping simétrico, dos diodos a la salida de un operacional, y la sección de tono tiende a dar una respuesta “mid scooped”, así que debe ser considerado como un pedal de distorsión. Es naranja y se llama “distortion”, así que en este caso es fácil de clasificar.

Mi experimento tenía estos objetivos:

  • Reducir la distorsión (cantidad de “clipping”)
  • Darle un carácter asimétrico, más agradable a mis oídos y más parecido a la distorsión de válvulas
  • Resaltar los medios en la curva de respuesta de frecuencias
DS-1 original schematic

Para reducir la distorsión, he hecho estos cambios:

  • R9 en el emisor de Q2 controla la ganancia de la primera etapa, previa al operacional. Con un valor de 22 Ohms, la salida es tan alta que la señal a la salida del operacional es limitada por los diodos prácticamente siempre. Probé con diferentes valores y el de 100 Ohms parecía ser el punto justo para tener la cantidad de distorsión requerida con el control de ganancia a las 12 en punto, tanto para single coils como para humbuckers.
  • Los diodos LED tienen una Vf (corriente directa) más alta que los diodos bipolares comunes. Los diodos bipolares tienen Vf=0.7V y los LED tienen Vf > 1.5V, dependiendo del color. Vf es lo que provoca el clipping, y cuanto más alto es Vf, más alta puede ser la señal antes de que empiece a limitar. Reemplazar solo uno de los diodos (D5 por ejemplo) por un LED rojo deja más espacio para la señal, y al mismo tiempo cumple con el otro propósito de tener clipping asimétrico. Éste es, por cierto, uno de los cambios del famoso Keeley Ultra Mod.

Para el resalte de medios, cambié varios componentes de la sección de tono. La sección de tono está basada en el control de tono del Big Muff. Es pasiva, y tiende a atenuar los medios. Simulando el circuito en LTSpice, encontré el punto en el que se resaltan los medios de la señal sin perder la capacidad de controlar el tono (aunque esta capacidad se ve algo reducida respecto al DS-1 original).

Modified DS-1 tone stack

El resalte se produce a los 800Hz, que para mí es el mejor punto para conseguir un tono agradable y capaz de ser oído en una mezcla en el contexto de una banda. Es una simplificación, ya que la curva de respuesta del pedal depende del conjunto del circuito, pero os aseguro que el resultado es bastante aceptable.

Los componentes reemplazados en la sección de tono son C11, C12, R15 and R16. Como podéis ver, sólo se han reemplazado seis componentes. He preferido mantenerlo lo más simple posible, pero los cambios en el tono y el comportamiento son drásticos. Ahora el pedal es un overdrive dinámico muy rico en medios, con un rango amplio de distorsión. Con la ganancia al máximo, revela su verdadero espíritu de distorsión. Coloca un compresor delante y un ecualizador después que resalte los 100Hz y conseguirás el verdadero sonido del rock and roll.

Como resumen, éstos son los componentes reemplazados:

R922 Ohms100 Ohms
D51N4148Red LED

Para C12, 82nF no es un valor muy común, pero puedes poner 47nF y 33nF en paralelo para tener 80nF, suficiente dada la tolerances habitual de los condensadores. Usad un medidor de capacidad si es posible para obtener un valor lo más cercano posible. La placa tiene sitio de sobra para poner dos condensadores en esa posición. Para C11 y C12, cualquier tipo vale, pero los valores son muy importantes (comprobadlos si es posible).

Espero que disfrutéis esta modificación, por favor hacedme llegar cualquier mejora o error que podáis encontrar. Si sois buenos guitarristas, grabad una demo y subidla a youtube. Si sois ricos, enviadme un Klon Centaur para compararlo con mi DS-1 modificado.

PD: si hacéis ese mod, ponedlo en los comentarios abajo. Me gustaría saber si la gente disfruta (o no) de mis mods.

PPD: JAVIER desde Argentina hizo el mod con algunos cambios, usó 47nF en C12 y 15K en R15, consiguiendo un resultado parecido. Al simular su circuito conseguimos una curva muy similar pero más suave, menos pronunciada en los 800Hz, y también aparentemente más atenuada en las altas frecuencias:

C12 = 47nF R15 = 15K

Probad esto si la modificación suena muy nasal, o si obtenéis algo de “fritanga” en el amplificador.