I have finally built my reverb on the ground of TT reverb unit. There was some old scrap 1U rack chassis laying in my place, so I decided to use it for this project. Which brought some problems on with the original TT kit, biggest PSU being too high for the box (also I already had half of the components, so it didn't make sense to buy them all) - I just bought few missing components, both trafos and reverb tank. In the beginning I planned a functional rack device, but that would bring serious complications with attaching "the guts" (with my limited ability in metalworking) - so now the screws just protrude out of the chassis and I installed rubber feet. Planning for the 1U environment with p2p style proved quite a challenge! But I nailed it. As my previous p2p projects proved to be messy and difficult to service or troubleshoot, I decided to go half way to the board style, maintaining "true p2p" codex. I tried the concept on "Jupiter", a small homemade effect PSU. With small number of components etching is troublesome and dirty, prone to failures too. But it is good to have some physical support for the components. So instead of etching I use the board (with no copper) only for the "chassis" of the circuit and attach components to it via rivets - the components are attached on tube socket on the other side. Connections are made mostly with component leads, some with wires. There is sort of a "common rail" design for the ground and B+ supply on the board (DC on top, gnd on bottom). Heater wiring also on the top, twisted. I listened to the colleagues on this forum and installed AC heater wiring (to give it a try - it is a big complication less really). Instead of original PSU I used an old multisection capacitor from my scrap components, and paired it with 1uF poly cap, soldering the bridge directly to it, with 22uf caps between its leads. I added some poly caps on the board itself (had some from previous projects). The wiring of jacks and pots is really short, so there is just one piece of shielded wire used. I had some questions as how to wire the ground of the OT / "tank in" jack - I decided to lead two wires from the jack.
The unit runs great and has majestic reverb. There were no beginner mistakes made I guess. Still, there is quite a lot of hum and it gets louder with the mixer pot being turned clockwise (more reverb). For the beginner still quite impressive, still useful for playing, but would like to eliminate hum. Possible solutions:
- DC heater - I confess, that was my first suspect; still, there is no hum on "dry" sound, and maybe I am just too much of a "sceptic"
- trafos too close / wrong orientation of the OT; will try with some metal plate between the trafos
- heater "centering" resistors should be grounded directly to star ground instead to the board rail (but why so much difference between dry and wet signal)
- potential made in ground "common rail" - interrupt it and lead it directly to star GND
- tank output uses cable shield also as a ground lead - do it "by the book" and separate those two
- ?
It sounds like mains noise.
Has anybody else had similar probolems? (Yes, I know, I haven't stuck to the layout so it's difficult to tell)
The second problem is pedal switch, it makes quite a loud click electrically when pressed - it is annoying; it looks like there is quite a potential between gnd and signal wire of tank output. Maybe a decoupling cap would be a solution, or a 1M resistor over the terminals - I was already inquring about similar problem and Dirk suggested the resistor ...
And there is another question, just the beginner stuff, I have. What are 4 22nF caps over the bridge for? Are those "snubbers"? What is their function?
project gallery:
https://www.dropbox.com/sc/xp152rcgjqj4mjc/AAD7h7MQMPjl6O7iAX-GIuyDa