These FX Loop PCB boards cost me 25 cents each!

[Snicksound]

EDIT: It works! KiCad files added in new post below (Jun 18th).

For real! 2.50$ for 10 boards, delivered to my house! Crazy cheap from JLCPCB using coupons! Yes, shipping included (slow shipping but took less than 2 weeks)

NB: I'm in Canada

So yeah, learning to design PCBs is worth it!

First time doing a loop so hopefully I didn't f anything up! If it works as expected I can share documents with anyone interested. It's based on the high voltage LND150 design that everyone is using these days, with a negative feedback buffer stage so that the overall polarity isn't flipped.

(PS: I did screw up my first batch, used a narrow footprint for the MOSFET that would have failed under high voltage, but at these prices it was not an expensive mistake at least)

received_27486608954263928.jpeg

[Guy77]

These look great! Yes would love to see the documents whenever you get around to it.

Thanks

Guy

[xtian]

And you didn't have to pay six million percent tariff!

[Snicksound]

And you didn't have to pay six million percent tariff!

Not a penny over 2.50$

I'm in Canada

[KaptinKangaru]

Have a schematic? Single sided?

[didit]

Quite cool, and very Canadian. Clearly two-sided though just pads and VIAs. I too look forward to seeing some details. I have a stalled loop PCB project, but built with USSR "pencil" submini valves.

..

[Snicksound]

Quite cool, and very Canadian. Clearly two-sided though just pads and VIAs. I too look forward to seeing some details. I have a stalled loop PCB project, but built with USSR "pencil" submini valves.

..

Good eye! Yes, double sided 2mm 1oz PCBs (the standard at JLCPCB, you're not really saving anything by doing anything less).

The vias are because there's a copper pour on both side connected to ground at a single point. I put all signal traces on top so this should shield them against all the stuff that's happening underneath (these usually get installed above the preamp tubes)

I'll be happy to share the doc once I've tested them. Don't want to send bad designs or schematics into the interwebs! Then people find them through image search and don't check the context...

[Snicksound]

Success! Finally had time to assemble one and use it in an amp and it works as expected!

724128841_1382036773974396_8590089398896927177_n.jpg

Here are the KiCad files for anyone that wants to play with it or get some made. I'm not interested in sharing this as a "paint by number" thing, I'm an amateur and may have made some mistakes
So, sharing this more for educational purposes for anyone interested in making their own loop board. But as it is, it worked for me, and there's enough information in there to figure out the parts you need (I put the part numbers in the description of the capacitors, but just make sure they fit the footprint and have the right voltage... or you can change the footprint to use something else if you want)

LND150 High Voltage FX Loop Prototype - Use at your own risk.zip

Some details:
- R12 can be a different value, whatever gets your around 300VDC on the supply line
- I included pads to connect shields when using shielded wire, if you use them DO NOT connect at the other end or you'll create ground loops
- Some versions of this circuit use 2M2 for R1, I haven't tried both, up to you
- Instead of a Source Follower, this circuit uses a LNFB stage as the buffer, this means you can adjust the gain instead of using attenuation to control the output, keeping the output impedance as low as possible. Adjust the trim to get unity gain compared to the bypassed signal.
- This configuration means each stage inverts the phase, so the overall phase is not flipped (this doesn't really change anything, but it does make switching the loop in and out seem more transparent)
- Not all versions of this circuit have C4, but it can avoid DC issues. It can be very low voltage (I used 63V) and thus very small
- R4 helps fight ground loops with external FX units
- There's no zeners on the first LND150... up to you if you want to add them back. I've had various versions of this circuit with and without, never had any issues.
- There's a copper pour on both side connected to the ground at only one point. This MAY lead to a little loss in high frequencies due to the capacitance it creates, but if you have the loop hanging over preamp tubes or filament wiring, it will shield the signal from it (all signal traces are on the top).

[Snicksound]

For those just curious about the schematic

Screenshot 2026-06-18 111002.png

[Guy77]

This looks great! Thank you for sharing SnickSound.
Maybe I am missing something but is their an adjustable pot for the return side? I see one on the input side, RV1.

Thanks

Guy

[didit]

Hello --

Congratulations on success. It's a real road to get there.

For curiosity sake downloaded the zip and unpacked. Needed to update my apps package, which was way out of date, to current version. Libraries for symbols and footprints in kiCAD are a perennial source of mischief and grief. I pulled some common ones that kiCAD offers and still couldn't get your PCB to render. I've no time today to chase this down.

You maybe want to retrace your steps and provide pointers to the libraries relied on for this. Despite a clear comment about "paint by number" you maybe could share gerbers for fabrication for anyone that hasn't the resources to pull kiCAD up and generate their own?

Best ..

[Snicksound]

This looks great! Thank you for sharing SnickSound.
Maybe I am missing something but is their an adjustable pot for the return side? I see one on the input side, RV1.

Thanks

Guy

There isn't, and I don't find it necessary because this type of loop is typically placed before the Master Volume (though you don't have to). A Return control is effectively a Master Volume so it would just be redundant.

There are fancier loops that are designed to switch between pedal and line levels, this isn't that. This one is optimized for pedals.

The trimpot does effectively act as a send control, but it's really there to tweak the signal reduction on the buffer side to match the gain on the return side (MOSFETs have large tolerances) so that the overall gain is unity. I don't personally care about unity gain since I don't switch it in and out while playing, so I don't mind adjusting the trim if I want more signal or less to be sent to the FX, then use the Master to compensate.

Someone desiring something more complex can use this and modify to suit their desires.

[Snicksound]

Hello --

Congratulations on success. It's a real road to get there.

For curiosity sake downloaded the zip and unpacked. Needed to update my apps package, which was way out of date, to current version. Libraries for symbols and footprints in kiCAD are a perennial source of mischief and grief. I pulled some common ones that kiCAD offers and still couldn't get your PCB to render. I've no time today to chase this down.

You maybe want to retrace your steps and provide pointers to the libraries relied on for this. Despite a clear comment about "paint by number" you maybe could share gerbers for fabrication for anyone that hasn't the resources to pull kiCAD up and generate their own?

Best ..

Good to know, I'll see what I can do. First time sharing KiCad project files. I don't remember using any non standard footprint on that one, but maybe I did...

[didit]

Good to know, I'll see what I can do. First time sharing KiCad project files. I don't remember using any non standard footprint on that one, but maybe I did...

Possible that my configuration needs local tweaking to get fully operational. It's been several years since spending any quality time inside that set of tools and my install was way out of date.

..

[flemingmras]

So y'all are really just going to copy and sell Steve Miller's Zero Loss Loop?

You do realize this is not only HIS design, but also his only source of income?

Steve has been battling long time health issues. This design, which he licensed to MetroAmp/Metropoulos Amplification, Friedman Amplification, and a few others, is his ONLY source of income. The fact that y'all seem to think it's an open source design (it never was) is absolutely appalling.

I bet you'd just love it if someone took your music that you wrote, started plagiarizing and making money off of it. Because this is the exact equivalent of that.

Steve has been linked to this thread as I have emailed it to him. I'm sure we'll hear from him shortly.