Princeton Reverb PCB (+ mods) - KiCAD sources + Gerbers

[tristanc]

I've just designed, fabricated and assembled a Princeton Reverb clone.

I was after a 'cleaner' amp with reverb and the PR was the form factor that seemed best. A known, classic circuit with a sound to match. But it had its flaws. So I set about updating the basic circuit (as supplied by Michael at Modulus Amplification with his Princetown kit) to include various updates people make, as well as sensible engineering updates following Merlin Blencowe's books. The original idea was to be clever and modify the existing turret board. But it was easier to just make a PCB.



All design (KiCAD 10) and fabrication files are at https://github.com/tristancollins/PrincetonReverbUpdate. The v1.0.1 release can be downloaded at this link: https://github.com/tristancollins/Princ ... v1.0.1.zip This set of files is what I have built and tested.



Things I've done:

• moved the reverb to its own node, reducing noise

• moved the LFO to its own spur, reducing thumping

• used an LED to bias the LFO, better / stronger

• added a large stopper to the PI grid, reducing blocking distortion

• reduced the PI coupling caps going to the 6V6s (I could reduce further, but we'll see), to reduce blocking

• adopted a multi-star grounding scheme using ground planes for each node, that daisy chain from the reservoir cap to the input, to reduce noise

• a single earth <-> signal ground connection near the input, reducing noise

• tried to make the off-board connections short, to make assembly easier

• it's all on one board! No need for a bias board.

This has all worked out really well, even if I do say so myself. I've got a lush sounding amp, perfect for playing in pubs and the living room, that is so quiet I can hardly tell it's on.

I've a few boards left over from the PCBway order, should anyone be interested. All you'd need is the kit from Modulus (or similar) and a few additional parts here and there. Or you can always order your own using the files linked above.

[xtian]

Beautiful!

[martin manning]

Nicely done indeed! Thanks for sharing!

[Tohr5150]

Thanks for sharing! I ordered the PCBs last week and got them today. Any tips for a first time amp builder?

[tristanc]

Thanks for sharing! I ordered the PCBs last week and got them today. Any tips for a first time amp builder?

Brilliant. PCBway? Do keep me posted on how you get on. I think that's maybe 5 people who'll be using the design.

Tips?

• Start with a PR kit and swap out the turret / tag board with the PCB. That gets you 80% of the way there.
• Then carefully go through the schematic I've shared and match it to the kit's.
• Make sure you have all the parts ready before assembly - test fit them to both chassis and PCB (including leads - a couple of the coupling caps have leads that are a tight fit in the holes)
• Populate the PCB going small -> big components
• attach flying leads to the PCB (give yourself an inch or 2 spare so you can trim to size once in place).
• then do the hardware and proceed as you would with the kit.

At that point I'd follow one of the excellent guides (e.g., RG's) either at ampgarage or EL34world, in particular the 'turning on' procedure.

I'm in the process of writing a short guide of things I did to get this PCB working amazingly well - e.g., buying shoulder washers to isolate the Switchcraft jacks from the chassis. Also following Merlin's grounding guide everywhere including the reverb connections and tank itself. Then you are sure to have a noise / hum free build. Mine is very quiet - in fact the mechanical hum from the power transformer is the the most audible noise almost to the point of being annoying in a quiet room.

[Tohr5150]

Thanks for sharing! I ordered the PCBs last week and got them today. Any tips for a first time amp builder?

Brilliant. PCBway? Do keep me posted on how you get on. I think that's maybe 5 people who'll be using the design.

Tips?

• Start with a PR kit and swap out the turret / tag board with the PCB. That gets you 80% of the way there.
• Then carefully go through the schematic I've shared and match it to the kit's.
• Make sure you have all the parts ready before assembly - test fit them to both chassis and PCB (including leads - a couple of the coupling caps have leads that are a tight fit in the holes)
• Populate the PCB going small -> big components
• attach flying leads to the PCB (give yourself an inch or 2 spare so you can trim to size once in place).
• then do the hardware and proceed as you would with the kit.

At that point I'd follow one of the excellent guides (e.g., RG's) either at ampgarage or EL34world, in particular the 'turning on' procedure.

I'm in the process of writing a short guide of things I did to get this PCB working amazingly well - e.g., buying shoulder washers to isolate the Switchcraft jacks from the chassis. Also following Merlin's grounding guide everywhere including the reverb connections and tank itself. Then you are sure to have a noise / hum free build. Mine is very quiet - in fact the mechanical hum from the power transformer is the the most audible noise almost to the point of being annoying in a quiet room.

Yeah, I used PCBWAY. I have zero experience building amps, but I’ve built tons of pedals so I should be ok populating the board.

I’d be really interested in the guide, as a lot of what you said at the end of your reply is completely new to me haha. I did a bit of googling on Merlin‘s grounding but it’s still a bit over my head…