Buffer removal

[HamishR]

I see from time to time that a circuit might be a TS without buffers - like the Eternity and about a gazillion others out there. I recently built a modded Boss DS-1 out of curiosity and have found that I really like it now that it has a bass pot and better treble response. It's ridiculously good!

So now I'm wondering if it would sound any good without the input buffer. Does the input buffer do much for the sound? I really don't know. It's easy enough to work out which is the buffer and where I could remove it. Has anyone tried this? I like reducing complexity if it doesn't destroy the sound.

 

[swyse]

It's tricky with the boss DS-1 because right after the buffer is the first transistor gain stage, which by the looks of it is going to be under 100k ohms input impedance in the best of cases, which is nice if we're dealing with a fuzz face, but not desirable for most applications. With the tubescreamer you have the benefit of the first stage being an op amp so you can get a good impedance without changing much besides the bias resistor to a higher value. In this case the buffer I think is very necessary unless you reworked the first stage to be very different, in which case you'll likely see a change in sound, but it could be a fun experiment!

 

[swyse]

I decided to run it through LTspice instead of trying to guess. Orange being the DS-1, Green being a bufferless TS-9 give or take.


Here are the two circuits, just to show my work incase I missed something. I dropped off the 470nf cap and 100k resistor to vref on the ds-1 because it's just there for the jfet switching and only stands to make things worse in this case.

 

[HamishR]

I must have misunderstood the circuit, which isn't really all that surprising given my level of knowledge! But I can see by your graphics that there is a significant difference.

 

[swyse]

I must have misunderstood the circuit, which isn't really all that surprising given my level of knowledge! But I can see by your graphics that there is a significant difference.

The transistor stage doesn't look like much at first glance so that's an easy mistake to make. The ibanez/maxon SD9 is very similar to the DS-1 but cuts out the transistor boost. It also cuts some more bass on the op amp stage so it's not 1-1, but It makes it a very different pedal. I'm now wondering if putting the boost on its own switch would be an interesting/worthwhile mod.