Boss Ds-1 Tone Stack sims

[WGTP]

I've been playing with/researching the DS-1 tone stack and associated tone shaping components and would like to offer my observations for the purpose of bettering humanity and helping Distortionists worldwide get a better tone.  I have been using the notch filter sims at Falstad.com and thank him for the nice applets.  This info should prove helpful for tweaking.

C7 controls the treble output of the op amp by allowing highs thru the negative feedback loop.  The stock 10pf cap reduces the ultra highs and is a positive design feature to minimize oscillation, but doesn't do much to the audible frequencies.  Increasing it to between 100 and 1000pF will reduce fizz and warm things up.  Set the Distortion control where you normally use it to decide.  The roll off frequency will change at different Distortion knob settings reducing the highs as it is turned up.  Start with 220pF.  The larger the cap the more the treble reduction.

C10 controls the treble at the diodes.  Try a 15 to 22nF to reduce fizz and warm things up.

Try changing C7 or C10 or a little at both places to contour the treble to your taste.

Now to the tone stack.  It is made up of high pass and low pass filters in parallel with the Tone control mixing the output of each.  Most of the mods I have seen change the cap values, but I'm going to focus on the resistor values.  If your really into it, I suggest your replace R16 and R17 with 25k trim pots for maximum tweakability.  

With the tone control in the middle position, there is an approximate 9db notch in comparison to 100Hz located at 745Hz.  Changing a value for R16 or R17 changes both the upper and lower midrange, but I have stated it in a simplified manner to help conceptualize the circuit and EQ changes.

R16 controls the upper midrange along with C11 it acts as a high pass filter.  Increasing R16 increases the upper midrange and lowers the center of the notch filter which lowers the low mids.

R17 controls the lower midrange along with C12 it acts as a low pass filter.  Increasing R17 lowers the lower midrange and lowers the center of the notch filter which raises the upper mids.

Lowering R16 and raising R17 spreads the filters out and deepens the notch.

Reversing the changes reverses the effect.

Changing the EQ or tone stack probably makes the most noticeable difference with the DS-1, but the diodes also make a big difference.  It is a little too compressed for my taste and I suggest a Si/Ge - Si/Si arrangement for a little more dynamics without loosing too much distortion.  I also like a Ge/LED combo.
 
Hope this helps, feel free to ask questions or point out mistakes.   

[gregwbush]

Anyone got a spare DS-1?

I'd give some of these mods a crack mate, but i don't have the gear to do so!

The theory all looks bloody good to me, WGTP

Keeping midrange is something i'm always looking out for... anything that clips @#$%in cuts the mids

[Tone-Analyst]

Wow that is a conpletely awesome post. Most detailed info I've ever seen for the DS-1. I have a 1983 unit and love how it sounds but when I raise the tone, the frequency is just too high. Will definitely try these.. thx!!