PRe-verb - Tube-Driven Digital Reverb

[vigilante397]

With my hand being the way it is I can't solder and I sure as hell can't play guitar, but one thing I can do is push components into a breadboard This was a design I played with months ago but never really got the sound I wanted out of until now. It's essentially a Rub-A-Dub reverb but using 6N16B tube stages instead of the op-amp stages. It doesn't get insanely wet, but it goes from subtle spring reverb emulation to dripping washy reverb. I left a trimpot for the second stage plate resistor so it can be adjusted to unity gain or slightly above for a lovely drive, making it an excellent solo-with-some-extra-reverb effect. I'm using linear regulators for thr 6.3V heater and 5V for the Belton brick and a nixie style PSU for the high-voltage on the plates. Oh, and I almost forgot, it will of course fit in a 1590B, because that's how I roll

Schematic:



Spaghetti mess on the breadboard:



And super rough demo video. I promise I'll record a better one when either my hand gets better or I have someone that plays guitar over at my house to demo it. But hopefully you at least get an idea of what it sounds like.

I just got my latest Elecrow order yesterday, but since I can't solder yet I figured I would just order more boards, so here is the 3D rendering of what this one will look like:

[deadastronaut]

sounds great nathan,  love that psu too...got a closer pic.

[diffeq]

Neat project, those sub-minis make it sound pretty good. "Serious" sound, which I like a lot. 
Couple of (boring) questions:
1. How 6.3V rail is derived? I see a charge pump for 200V (555?) but no regs or anything for 6.3.
2. Is the tube mounted on a main board or to the adaptor PCB, then to the board?

[vigilante397]

1. How 6.3V rail is derived? I see a charge pump for 200V (555?) but no regs or anything for 6.3.
2. Is the tube mounted on a main board or to the adaptor PCB, then to the board?

I suppose I could have just posted a schematic of the power supply too



I use a 7806 regulator with a schottkey diode (1N5817 or similar) between the middle pin and ground, which gets me right about 6.3V. I've also seen people use a 5V regulator with two 1N400* diodes in series on the middle pin which would get you about 6.4V, so same idea. My last tube design used a through hole regulator and diode, but I finally got around to buying some SMD regulators and diodes so I have some beefy D2PAK 5V and 6V regulators (U3 and U4 on the PCB)

As for the tube, it could be mounted directly on the board, but I like the adapter boards because they make it a lot easier to keep pins from shorting. The only problem is the adapter boards add a little bit of height so if you solder them wrong (which I did several times) the assembled tube board is taller than the pots and will hit the enclosure.

sounds great nathan,  love that psu too...got a closer pic.

Thanks That PSU is probably the most useful thing I've ever built. It sure makes breadboarding easier when I don't have to re-build a power supply every time I prototype things.

[Mark Hammer]

That sounds great.  I don't know what the use of tubes adds to it, but they certainly don't take anything away.

If this is what you can do with one hand, I'm in anticipatory aw3e of what you could do with two. 

[vigilante397]

I don't know what the use of tubes adds to it

Basically I'm marketing it to people that are worried their pedalboard doesn't draw enough current I haven't measured it but it should draw about 320-ish mA, the advantage of course being that it will still run on a 9V supply so you can just add it on to your OneSpot

Seriously though, the main logic behind the name is that it's a preamp and a reverb, so it definitely colors the sound. At first I was trying to keep the original level and frequency response, giving a super "transparent" reverb, but then I got a light mid-boosty sound that I really liked, it punched the reverb really nice so I stuck with it.

If this is what you can do with one hand, I'm in anticipatory awe of what you could do with two. 

Uh-oh, I may have set the bar a little too high

[diffeq]

I use a 7806 regulator with a schottkey diode (1N5817 or similar) between the middle pin and ground, which gets me right about 6.3V. I've also seen people use a 5V regulator with two 1N400* diodes in series on the middle pin which would get you about 6.4V, so same idea.

Ah, nice trick, I've never seen a diode there in a fixed-voltage regulator before. I did see some resistor+pot+opamp combination to make it a variable regulator, in one of them datasheets. There's even an example of negative rail use.  *

My last tube design used a through hole regulator and diode, but I finally got around to buying some SMD regulators and diodes so I have some beefy D2PAK 5V and 6V regulators (U3 and U4 on the PCB)

Always surprises me how SMD devices, being smaller, still get higher power ratings than good ol' THD 

As for the tube, it could be mounted directly on the board, but I like the adapter boards because they make it a lot easier to keep pins from shorting. The only problem is the adapter boards add a little bit of height so if you solder them wrong (which I did several times) the assembled tube board is taller than the pots and will hit the enclosure.

If only there were sockets for those. Vertical and right-angled would be ideal.

* I like how some "hacky" example circuits get removed from datasheets over time, leaving only conservative ones.

[bluebunny]

Very nice, Nathan.  Can't have too many reverbs, particularly those that dim the street lights a little.      On the list, fer sure.

[PRR]

> surprises me how SMD devices, being smaller, still get higher power ratings than good ol' THD

The wire-leg device has to shed 90% of its heat from its body. SMD puts most of it to the PCB.

The PCB is typically much bigger than a TO-92 body. Fiber is not a great heat conductor, but much better than air, which is always the final destination. (Until you get to geo-well heat pumps.)

[vigilante397]

I was about to reference this thread in another thread and realized I never updated it since stuffing the board Here's stuffed pics, front and back:





I misread when I ordered my 5V and 6V regulators, and it turns out they're DPAK, not D2PAK, so they have quite a bit of room on the pads It works great, but I think I may play with it a bit as it cuts some lows that I didn't want it to. Probably add some cathode bypass caps and adjust some resistor values to keep the gain at unity. After that's done (if it's ever done ) I'll actually put it in a box.

[vigilante397]

Finally got around to boxing up the first Pre-Verb this weekend. The top graphic was supposed to be a visualization of what reverb is, but it didn't turn out very well, so I probably won't do it again. I also decided to try a super fancy embedded LED 3PDT on this one, because why not?