Buffer. Just a buffer.

[MattG]

Here's my submission for most boring build of 2026: an always-on unity gain buffer. It's... delightfully unremarkable! The opamp is an opa1678. Since that's a dual opamp, it's basically a double-buffer with a little bit of high-frequency filtering between active stages. (And the opa1678 has some inbuilt RF protections.)

The back side is a fully contiguous ground plane!

The only interesting part was the mechanical aspect: for my first attempt, I just eye-balled the drill holes, and ended up with something that didn't work.

So I took a little time to measure on the second attempt, to ensure I'd end up with something that can actually be assembled.

This is my first 1590A build, and even though the PCB itself is tiny, the mechanical/fitment aspects are really challenging!

The intent is for this to be mounted underneath my pedalboard.

Edit: See post #16 below for an update v1.0 buid.

 

[OD is Glorious]

Looking good

 

[szukalski]

I love these little boards! So cute!

 

[jcpst]

Nice- Tango Green is one of my faves.

 

[anevilspar7an]

Would you be willing to share the schematic? I'm curious about the extra filtering you added.

 

[MichaelW]

Love it. These little utility pedals are sometimes my favorites.

 

[Robert]

"Just a buffer" they said....

 

[jcpst]

EUNA, some people wanna throw a punch, but can’t take a JAB.

 

[MattG]

Would you be willing to share the schematic? I'm curious about the extra filtering you added.

Sure! It's truly just a little bit - it's basically R11 and C15. C19 at the input also provides a little filtering too.

 

[HamishR]

Are you concerned that the green enclosure will lend the sound a vaguely TS sound? I would have used a transparent enclosure.

 

[MattG]

Are you concerned that the green enclosure will lend the sound a vaguely TS sound? I would have used a transparent enclosure.

I hadn’t thought of that… but now I can’t un-hear it!

 

[phi1]

If you have more pcbs handy to make another, I’d recommend fitting a 2pdt toggle for true bypass. I have one and I like it for testing purposes (testing like: does this pedal sound different with a buffer? Can I hear the effect of a buffer at this part of the chain?)

 

[swelchy]

If it fits it ships...

 

[Passinwind]

"Just a buffer" they said....

Nope, it's a double buffer, it's one more.

And I love designing little utilty boards like that, they come in super handy for a lot of the type of stuff I do.

 

[anevilspar7an]

Sure! It's truly just a little bit - it's basically R11 and C15. C19 at the input also provides a little filtering too.

Mosfet polarity protection and a fuse? Very fancy.

 

[MattG]

I made a few small tweaks to the design:

• added more RF filtering
• increased power supply filtering/decoupling capacitance
• used 3x10uF tantalum caps for VREF capacitor
• used a smaller opa1678 package (because it's cheaper)
• ponied up for ENIG surface finish

The original design was perfectly practical I think. Now I'm happily in the deliciously overkill territory.

For this build, I put the I/O jacks on opposing sides, because it works better for my board.

Lesson learned with this build: don't use standard/full-size I/O jacks in 1590A enclosures!

Other than the final assembly headache, everything works great!