Reverb unit scratch build questions

[tubeswell]

Remember than when you plug the reverb unit in, you are creating a ground loop. In this regard, each amp will have its own ground circuit voltage determined by its own chassis, mains power cord, whereabouts in the chassis you have bolted the ground return etc etc. The way in which this factors into the ground loop created by plugging in the reverb unit may mean that for some amps the unit is quieter than for others.

[Casey4s]

It's just a box for the verb or a head cabinet. Something that small does not really NEED finger or dovetail joints, a simple screw & glue will work fine if you are Tolexing, but if it is fine wood then finger or dovetails are a better choice cosmetically.

Good luck with the cabinet.

[Casey4s]

Nice work Sir.

[Wombaticus]

Remember than when you plug the reverb unit in, you are creating a ground loop. In this regard, each amp will have its own ground circuit voltage determined by its own chassis, mains power cord, whereabouts in the chassis you have bolted the ground return etc etc. The way in which this factors into the ground loop created by plugging in the reverb unit may mean that for some amps the unit is quieter than for others.

TW - take a look at what the '63 reissue does. This unit separates audio ground from chassis ground with a 15R flameproof resistor. If there is a ground fault putting a ton of current through these they won't catch fire, but they will fail open, which is obviously a problem. Therefore, these are paralleled by a pair of silicon diodes in opposite orientation in order to provide a fail-safe path to ground in case of fault.
Anyway, this trick should help with some of the "cross-amp ground loop" issues you describe.

By the way, the reason I know this is that I'm fixin' to make one of these myself..... got the chassis and cab already on the way, and am working on a layout and design.

Why is it that we end up making such similar kit? 5E3 deluxe, 5G9 tremolux, now this? Whatever the I'm really glad that you've done one of these too, because I have a question... I've seen elsewhere users describing a loss of volume when the unit is taken out of circuit. But I'm not completely clear if they mean that volume is diminished specifically when the reverb footswitch is grounded, or whether they mean that volume is somewhat diminished with the unit in between the guitar and the amp, relative to just a guitar->amp signal path?

As is my usual practice, I intend to make a couple of mods. I think, for instance, that I'll implement a vactrol optoisolator to avoid having the grid of reverb recovery running all the way out to the footswitch. But I may also try and address this volume issue, depending on your response.

Cheers,

Paul

[tubeswell]

I've never noticed a loss of volume running my reverb unit through any of my amps. I was aware of the '63 RI ground-lift though. I am curious as to why they use 2 x 15R FP resistors (I guess that means it is only lifting the ground with 7-8R). Either way, I recall that it is also a good idea to put a 1kV or so .01-.1uF cap in parallel with the 6A diodes and the FP resistor

[Wombaticus]

I've never noticed a loss of volume running my reverb unit through any of my amps. I was aware of the '63 RI ground-lift though. I am curious as to why they use 2 x 15R FP resistors (I guess that means it is only lifting the ground with 7-8R). Either way, I recall that it is also a good idea to put a 1kV or so .01-.1uF cap in parallel with the 6A diodes and the FP resistor

Yes, it's curious that they decided to separately connect to the pot brackets. Judging from the circuit description, they for some reason they thought it desirable to have a ground reference on these when the board is out of the chassis...

Anyway, I'm pretty sure I'm gonna incorporate the audio ground lift in addition to the star grounding in mine - poking around I've seen several reports of the old units and clones humming with certain amps.

[mort]

It's just a box for the verb or a head cabinet. Something that small does not really NEED finger or dovetail joints, a simple screw & glue will work fine if you are Tolexing, but if it is fine wood then finger or dovetails are a better choice cosmetically.

Good luck with the cabinet.

After thinking about it a while, I've decided to go at it myself. I've got plenty of scrap wood to practice on so why not. I just need to find the right jig and a little time to play with it. I'll probably finish it with just a plain poly or laquer.

Nice work Sir.

Thanks!

[Rhodesplyr]

The tank in the original mounts with the open face towards the front of the cabinet. This allows for a lever mechanism that is used to clamp the tank down for transport. Like you, I went with a tank that mounts open face down.

I talked with some techs at Accutronics when I was building a power supply/reverb unit for my Farfisa Compact Duo, and they gave me a lot of good advice. Like you, I had planned to mount the reverb tank open side down, but they told me that if it was practical, the BEST mounting orientation was open side of the tank towards the front/back/side (Input/Output jacks up or down). They do, of course, select the internal suspension springs for the mounting you're planning to use, but I don't think they change the orientation of the transducers. I tried it both ways, and damned if it didn't sound best mounted the way they suggested. And this was the way Farfisa did it in the original.

I also found this to be true of an Organ Mate tube reverb unit made for Hammond Organs. For convenience, the instructions tell you to mount it open side up, screwed to the underside of the top of the organ, but it sounds better if you rotate it so that the jacks point up.

Try turning your reverb unit on its side and see if it changes the character.

[Rhodesplyr]

With pots, if you know what you're buying, there is some truth to the "you get what you pay for" maxim. There are lots of cheap pots on the market these days that don't last long and never have good contact integrity. The Precision Electronics pots are pricey, but they are very nicely made.

I have used some of the smaller Sprague Atoms, but, even if they're packaged the same way, I doubt that they're exactly what they were selling 40 years ago. If you're going for sound quality, get something like Nichicon KZ series from Mouser or Elna RFS. They are both better and cheaper. Of course, they don't come in 25uF, but the value of a cathode bypass isn't earth-shakingly critical, especially since reverb units usually do some high-pass filtering. Despite how it looks on the schematic, cathode bypass capacitors are very much in the signal path.

I got Triode Electronics' upgrade power transformer for my Dynaco ST-70, and the quality is great.