This Week on the Breadboard: The Chubby Sammich

[Chuck D. Bones]

This article picks up where the Fat Sandwich article leaves off.
Here's what I have at the moment. It's still a work in progress. The Fat Sandwich is kinda like 4 stacked pedals: Clean Boost -> DS-1 -> EQ -> Red Llama. I mainly attacked the EQ section and made the clipping diodes functional. I moved the CURVE trimpot to the front panel and retuned it to have a better feel. I also moved the DRIVE trimpot to the front panel. R40 & R41 were added to make the clipping more symmetric in the last two stages. Their values are still in flux. I raised the input impedance by increasing R27 and tweaked the biasing on Q4 & Q4. I added a variable freq treble cut at the end and named it PRESENCE. I'm currently experimenting with removing D2 & D5. After that, I'll try some alternate Tone networks between U1 & U2.




L-R: VOLUME - PRESENCE - DRIVE - TONE - SUSTAIN - BOTTOM

 

[cooder]

Love how you look under the hood of things and take the nonsensical stuff apart and do the panel beating. Will be interesting again to see where this goes!

 

[Chuck D. Bones]

I've taken this one as far as I could, or as far as I should anyway. Last things I changed were:

1. Reduced the 2nd stage (Q4) gain by about 8dB.
2. Changed R19 & R22 so that U1's input is not driven to the rails.
3. Increased VR1 so that the 3rd stage has 8dB more gain.
4. Deleted the clipping diodes D2 & D5. This increased the dynamics a bit.
5. Retuned the TONE control for more range and a slight mid dip at noon.
6. Increased R11 since it is part of the tone network, and changed VR5 back to 1M.
7. Deleted R41, it wasn't necessary.
8. Added R40 to bias the last stage for (more-or-less) symmetrical clipping.

I might fiddle C22 and/or C25 a bit, but otherwise, I'm done. It's a fun pedal. Having two gain controls and three tone controls distributed around the circuit allows for many tonal possibilities. I think of the SUSTAIN control as a Preamp Gain and the DRIVE control as a Master Volume. I picked up a few ideas from the Fat Sandwich that I may use in future circuits. U1 can be any rail-to-rail opamp. I have a 150pF compensation cap on U1 (not shown). If anyone else wants to experiment with this circuit, another option would be to replace the TONE control network with a James tone stack, tweaked to work in this circuit.

 

[steviejr92]

Oh im seriously looking forward to breadboarding this up!

I think to challenge myself along the build im going to try and incorporate the James tone stack as you mentioned.

 

[thomasbe86]

How does it sound? got any audio to share? thought the tone stack of the FS reduced the voltage by 40dB or so, is it not too loud when hitting U2 in your configuration? oh and what is R40 for? great work, I will definitely breadboard someday soon!

 

[Chuck D. Bones]

R40 tweaks the bias on the last stage. I added item 8 to the list of mods in the post above.
This version can definitely hit the last two stages harder if we want, but we can also back off on the DRIVE knob to get a smoother tone.

 

[music6000]

R40 tweaks the bias on the last stage. I added item 8 to the list of mods in the post above.
This version can definitely hit the last two stages harder if we want, but we can also back off on the DRIVE knob to get a smoother tone.

I purchased a few Way Huge pedals when he released them back in 2009 thru Dunlop for my Mate & some were Great, some not so much & the biggest turn off was their Size, so the pedal name was correct in the naming!, I don't have any for myself.
I see they are more streamlined now as Guitarist want smaller size pedals so they can fit more on their pedalboard!