Output Buffer with Volume Control for Unity Gain

[Big Monk]

Long story short: My TC Electronic Drip Spring Reverb has an incredibly rich spring reverb tone but falls short, noticeably, from unity gain.

TC Electronic won't give me the schematic and punted me to their service vendors. Service Vendors are of course not going to give it to me either. Anyway, it's all SMD anyway so it would be a paint to modify, even if it was only changing the divider ratio that I am sure exists on the tail end.

So, I was thinking that I could use a simply JFET buffer with gain control after the reverb, built into a little tap tempo box, like the one used on Tonepad's Buffered Wah schematic:

If I am correct, the 2N5457 should only have about 6 dB on tap and could be easily set with a volume control to match unity if put after the reverb.

Any thoughts or suggestions?

As a side note, my Carl Martin Surf Trem has the opposite issue, as it boosts the signal a touch over unity when engaged. That has normal through hole components, however, and East Sound Research sent me the schematic with no issues. Just need to tweak the voltage divider on that one.

 

[mdc]

The EHX LPB-1 is the go-to solution for adding a bit of clean boost at the end of a circuit.
If you want lower output resistance than the LBP-1 offers (but I might be misunderstanding what you mean by buffer?) you could do a 2x BJT common-collector common-emitter cascade.

You can build an LPB-1 daughterboard on a small piece of vero and sneak it into the enclosure; if you've not done vero projects before this would be a really great one to start with.

Electro Harmonix LPB1 with trimmer

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

 

[Big Monk]

The EHX LPB-1 is the go-to solution for adding a bit of clean boost at the end of a circuit.
If you want lower output resistance than the LBP-1 offers (but I might be misunderstanding what you mean by buffer?) you could do a 2x BJT common-collector common-emitter cascade.

You can build an LPB-1 daughterboard on a small piece of vero and sneak it into the enclosure; if you've not done vero projects before this would be a really great one to start with.

Electro Harmonix LPB1 with trimmer

Collection of vero (stripboard) & tagboard layouts for 100s of popular guitar effects, with over 1000 verified designs. DIY your own boutique effects!

tagboardeffects.blogspot.com

You are correct and I was unclear. For an electrical engineer, I use the wrong electronics terms quite frequently.

I after reviewing your post and a few from diystompboxes, I took the gain recovery stage of the BMP and tweak it to only provide about 6 dB of Boost. That should be enough to get my Reverb pedal to unity cleanly.

I had to reorder some stuff from Small Bear because ordered the wrong PCB mount pots so I added one of those mini pedal type enclosures and I’ll send another order off to JLCPCB for a little PCB that will mount on the output pot.

 

[spi]

The EHX LPB-1 is the go-to solution for adding a bit of clean boost at the end of a circuit.

I was thinking the same concept for the EP pre-amp. Although now we're talking a bit more parts than just a transistor and a few other components. But it might be useful in other ways too (I use the Secret Preamp as a tone sweetener)

So, I was thinking that I could use a simply JFET buffer with gain control

Check out the Glory Hole PCB circuit. It also has a jfet gain stage at the end--I built a similar post-boost into a pedal and it has a lot of gain on tap. Same concept as the wah buffer but different layout (output is the drain instead of the source).

 

[Big Monk]

I was thinking the same concept for the EP pre-amp. Although now we're talking a bit more parts than just a transistor and a few other components. But it might be useful in other ways too (I use the Secret Preamp as a tone sweetener)


Check out the Glory Hole PCB circuit. It also has a jfet gain stage at the end--I built a similar post-boost into a pedal and it has a lot of gain on tap. Same concept as the wah buffer but different layout (output is the drain instead of the source).

I’ve actually abandoned the idea because I’m selling the pedal to fund my Strymon Flint purchase.