BOSS: Modded DS-1, Diode Compression Opamp

A somewhat polarising classic - the Boss DS-1, with a slight twist, as this has the Joe Davisson discrete diode-compression opamp onboard instead of an IC.

BOSS DS-1 DIODE COMP OPAMP - VERO LAYOUT

BOSS DS-1 DIODE COMP OPAMP - WAMPLER STYLE JCM MODS

This is what I ended up being happy with on the breadboard - it's basically the Wampler JCM mods, but I used a germanium and silicon diode in series for hard clipping rather than two silicon.  The combined forward voltage brings it up around the same level as the original diodes used in the DS-1.   

I also increased the size of the resistor on the emitter from 22 to 470 ohms to reduce gain in the first stage.  You could happily go a bit smaller than this, as the discrete opamp has less gain than a real opamp.  I may have taken a tad too much away - so maybe have a play with that yourself if you plan on trying this.

The most important change in terms of sound is the replacement of a resistor in the tone section, which really changes the character of the sound (mids return).  

So with all of these changes - it sounds like a nice distortion with some character, but not much like a DS-1.  

BOSS DS-1 DIODE COMP OPAMP SCHEMATIC

Some common mods included - minus diode clipping mods, as I'm sure we all know what this involves.  I've kept mostly stock values on the schematic while I test mods.  The only exception is the clipping diodes, where I have two on each side in series, as I just discovered the original diodes had quite a high forward voltage (0.92v typical, 1.2v max), which is close to 2 x 1N4148 in series.  

ORIGINAL BOSS DS-1 SCHEMATIC

 

ON THE BREADBOARD

Looks like a mess... and no input or output buffers at this stage.  Speaking of buffers, I may even try one between the tone and volume control to stop the interaction between the two.

 

ON THE SCOPE / FFT

Straight from the boost section - this is actually pulled back a bit, using a smaller resistor than the stock one, as it's normally distorted before it even hits the opamp (this is a common mod)

The next shot is the op-amp output and then at the clipping diodes. I need to change the diodes, as the original diodes have a forward voltage of about 0.9v, which is a decent step up from a standard 0.6v.  This certainly explains why the output was a bit lower than expected.

Caution - start with low levels.  Adjust the gain control, then tone - trace taken at the output of the tone section.   440hz sine wave