Spring Reverb Pedal

[vonFrenchie]

I have spring reverb on my main amp. The only problem is on the second channel it doesnt have reverb. I prefer the second over the first because it is much cleaner. I looked online and found a site with detailed instructions on building a spring reverb unit. I was thinking about building it then having the circuit in a box located away from the reverb unit. So in theory its a reverb stomp box.

Here is the diagram and website

sound.westhost.com/project34.htm

I was planning on buying a reverb box from accutronics. If I bought their Type 8 reverb I could have it built into the pedal (the pedal would end up being about 10 inches long.) Im not so sure about that, the reverb might not be long enough and it might get bumped and make that horrible, or lovely depending on the genre, crashing spring sound.
www.accutronicsreverb.com/

What are your thoughts on this?

[sumgai]

vF,

Go for it. ;D


Seriously, just be sure that you get the right reverb tank. Pay particular attention the the Accutronics page linked at the bottom of ESP's page - Rory's Accutronics Page. You don't want to get stuck with a high input impedance unit, and I've seen some of those around. Also, pay attention to the orientation - vertical tanks don't work very well when layed out horizontally, and vice-versa.

In most cases, cheap is an attractor that might get you into trouble, so keep yer eyes peeled, matey.

Can't say as I'm a big fan of this circuit, but then again, I don't have anything as simple to offer, so I'll let you flail away at it..... I know you'll report back with your results.


sumgai

[RJB]

VF
that's about as simple a circuit as you can get. The only changes I might make would be in the way of additions. Just watch the +ve supply. The LM386 tops out at 18V (2-9v cells ok. They're never really 9V).
RJB

[vonFrenchie]

I was told that the circuit required 15 volts. And yes, I am very aware of the tank impedances and that was one of the main things keeping me from doing this. What would you guys recommend for the tank impedances?

[sumgai]

Frenchie,

Low impedance is more common, in fact, it's almost like hooking up a speaker. Are you perchance starting to see a resemblance between this and a normal speaker transformer? You should.

In the original Fender circuit, Leo used a 6K6 and a standard output tranformer, feeding into an 8Ω tank. Worked slicker than snot then, and still works like a charm now. ('Ceptin' the lack of 6K6 tubes, the re-issue unit uses a 6V6 instead.)

In Fender's combo amps with built-in reverb, the tube is a 12AX7, both sides hooked in parallel. This turns it into something of a current amplifier instead of a voltage amp, but it also lowers the output impedance to match that same reverb transformer. Hence, the same parts are interchangeable from combo amp to outboard unit, and vice-versa.

Planned obsolescence? Not on Leo's watch! ;D

The LM386 actually comes in several models. Fortunately, the not-quite-standard versions will have some kind of suffix after the 386 part. Watch out here, because a few models top out at only 12vDC, while others can go clear up to 22vDC, so make double sure of what you're getting. I'd recommend against the lower voltage versions, they probably won't produce the necessary power for the reverb tank itself.

Not quite final note: If'n you don't regulate the power supply properly, you might notice more distortion than you think should be present. Remember, in cases like this, you're not after voltage amplification, the LM386 is a power amplifier - you're increasing the current output. A good (meaning stable) power supply is mandatory. Batteries are the best source of rock-solid power, but they tend to drain pretty quickly. Either make plans for lots of 9v batteries, or install a multi-cell holder that can take 10 C- or D-size cells (10 x 1.5 = ......). That should last you several weeks, if not months.

The alternative to that would be a good quality wall wart - why reinvent the wheel, eh?

Now the final note: Is there a source somewhere for a printed circuit board? If you have to make your own, or perhaps you're gonna use a Quick-Connect breadboard, just be sure that you can arrange and re-arrange your wiring layout. Reverb circuits in general are highly susceptible to self-induced oscillation. Most of the time, that comes from the wiring passing an output signal back to the input, via capacitive coupling. Stirring the wires around will eliminate that problem, should it occur.

But like I said originally, Go For It! ;D



sumgai

p.s. For more data on the LM386, get the straight poop from the original source, National Semiconductor. Try this: www.bricotronique.com/datasheets/ampau/lm386.pdf