Boss DS-1 Distortion Reduction Using Ground leg

[wilsonsk]

Hi,

As crazy as it sounds, I love my DS-1s, but would really like to reduce the distortion some.  I have always used them with the distortion set to the minimum, and found that to be a bit much, I would much prefer to be able to reduce it and almost have that minimum be my max, or close to it.

In looking at the schematic attached, and per the quote from a previous post, I am thinking I could add a 47 k resistor to the ground leg after the pot.  This should reduce the minimum distortion effect some, I'm not sure how much, but it seems like it should work.

I could replace the pot with a 250 k as well, I think.

Thoughts?

Quote:
"When op-amp gain is varied via the "ground leg" resistance, gain increases as that resistance gets smaller.  Changes in resistance at the high end produce negligible changes in gain.  For example, the MXR Distortion+ also uses the ground leg, and a 500k pot.  With a 1M feedback resistor and the gain pot at max, you have a gain of 3x.  Reduce that pot resistance from 500k to 200k and you've only changed gain from 3x to 6x.  At the other end of the scale, dropping the pot resistance from 50k to 10k changes the gain from 21x to 101x.

So, as you can see, when using the ground leg, it is changes at the low end that matter more than changes at the high end.

A reverse log pot will get you "through" the highest resistances quickly so that more of the pot's rotation addresses changes at the low end of resistance."

[wilsonsk]

I'm not sure I know how to attach a picture, so hopefully I was clear in my description.

I would either add a 47K resistor between the distortion pot (leg 3) and R13 (or replace R13 with s 47K I suppose), or replace the distortion pot with a 250K.

Here is a link to the schematic.....

http://www.google.co.uk/imgres?imgurl=http://cdn.tonegeek.com/wp-content/uploads/Boss-DS-1-schematic.png&imgrefurl=http://www.tonegeek.com/musicgear/pedals/boss-ds-1-classic-distortion-effects-pedal-modded.php&h=784&w=1332&sz=183&tbnid=5OWrkbSPzTM3yM:&tbnh=85&tbnw=145&prev=/search%3Fq%3Dds-1%2Bschematic%26tbm%3Disch%26tbo%3Du&zoom=1&q=ds-1+schematic&usg=__IUYsU_iyMz2Q4RdVl5iW_VfKqSQ=&docid=vdKIsoudMOePGM&hl=en&sa=X&ei=Qw5BUf6jB6-X0AWK14HgBQ&sqi=2&ved=0CDgQ9QEwAw&dur=979

[antonis]

DS-1 original gain pot is 100k so if you replace it with a 250k you will INCREASE the gain..

If you change the 4k7 resistor you will alter the cut-off frequency..

Try a 50kB pot...
(but you'll have to recalculate R13 & C8 values...)

or better change the Q2 gain by altering the R8/R9 ratio..

[slacker]

You can't reduce the minimum gain of the stage controlled by the distortion pot, when the pot is turned to zero the gain of that stage is one, which is the lowest a non inverting opamp stage can get. Referring to the schematic when the pot is at zero the pot and R13 and C8 are connected directly to the output of the opamp, so don't play a part in setting the gain. It's not the same configuration as the quote wilsonsk posted is talking about.

Like antonis said  you'll need to look at reducing the gain of Q2, or look at changing the clipping diodes D4 and D5 to LEDs or something else with a higher clipping threshold.

[wilsonsk]

Will any led work for that?

[Ice-9]

Will any led work for that?

Yes, any led will work for that. Leds should give you more of a crunch than a distortion. I would try 3mm red LED's but whatever you have lying around try them out.

[PRR]

> Here is a link to the schematic.....

That link goes to a Google Search, many re-directs away from the actual schematic.

Discussion: http://www.tonegeek.com/musicgear/pedals/boss-ds-1-classic-distortion-effects-pedal-modded.php

Circuit: http://cdn.tonegeek.com/wp-content/uploads/Boss-DS-1-schematic.png

This beast has a LOT of gain. Q2 appears to have gain of 500. While it won't be that much, signal is surely mangled by that point, before the Distortion control.

Increase R9 any sane amount. 1K may be a good starter value. This may be too radical, try 100-220 Ohms. Or if you are a very polite boy, make R9 like 3K. That still leaves a gain of 1-20 at U1B, so you can still clip the crap out of the signal in the diodes, or not.

[wilsonsk]

OK, I found some more info on the web regarding just plain removing D4 and D5.  I tried that first as that was easiest, that was pretty much what I am looking for, I have another DS-1 so I replaced D4 and D5 with LEDs on that one and compared side by side, I still liked no diodes better, then I clipped on LED on that one, still like no diodes better, so I disconnected the LEDs as well on the other one.  I can still get more than enough distortion if I want it, now 9:00 on the distortion knob is less than I had before at 7:00.  I did compare the no-diode version to my stock DS-1 before the LED swap.

I want to gig with these before I make any more changes, but as of now, I'm declaring 90% success.
Thanks!