How do those Spring Reverbs work in guitar amps?

That is exactly the info I was looking for. The PDF file includes pictures too, and is very useful. Thanks for the link.

Reply to
oldschool
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Any of them ever use push-pull to drive the transducer? That is to say, not push-pull in the way a regular complimentary output amplifier or op-amp is, but say a bridged configuration of two op-amps driven out-of-phase.

I had wanted to drive an inductive load with a varying impedance over frequency with a bridge configuration to put more power into it than what the supply could provide single-ended, but couldn't figure out the proper sense topology so both amps could provide current drive over the whole cycle.

Reply to
bitrex

d
e

o must be driven the same way. Tiny tube magnets are made to twist by the d rive coil assembly while at the far end a near identical transducer convert s the twisting back to an electrical signal.

axis about +/- 30degrees. A torsional wave travels fairly slowly down a sp ring, making for long reverb times.

torsional waves in the springs but only lateral ones and so are largely rej ected by the pick up assembly.

by Fender in the 60s guitar amps.

Accutronics site disappeared.

Cool! This is mostly unrelated, but with the right choice of mass and mome nt of inertia you can make a Wilberforce Pendulum, where the torsional mode is al most the same frequency as the vibrational mode, and you can get them to couple.

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We made these with slinkys and 1 foot rulers (with pennies taped on the end s).

George H.

Reply to
George Herold

Accu-Bell "hides" their website behind Adobe flash. Fortunately, "How Reverb Works" also appears at other more "open" websites:

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"How Reverb Works" contains a spring reverb history mini-history. Here's an excerpt:

The use of coiled springs to delay audio signals was originated by early telecommunications engineers to simulate the effects of long-distance telephone lines. While the prolonged sequence of echoes was undesirable for their purposes, it seemed most useful to an inventor named Laurens Hammond, who promptly appropriated the concept for use with the keyboard instrument which bears his name.

The

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link in my first followup points to "Spring Reverb Tanks Explained and Compared" by Kurt Prange. Prange's tutorial references:

Scott, J. L. - Chief Engineer; Accutronics document 126-00005

That Accutronics document may explain the gadget's wave physics in greater detail. In light of the telecommunications history mentioned at your link, Bell Labs documentation also seems like a good prospect to discover the more mechanical principles of operation.

Thank you,

--
Don Kuenz KB7RPU
Reply to
Don Kuenz

If you look at the schematics, you'll notice that the feedback is taken from the coil current, rather than voltage. For a bridge amplifier, you'd need more complicated way of picking up the feedback signal. Besides, a simple complementary 2n3904/2n3906 would be enough (or a LM386).

--

-TV
Reply to
Tauno Voipio

Indeed, the "more complicated way" was what was giving me the trouble. ;-)

In the application I had in mind I'm driving a square wave through an actual small step-up transformer, not a reverb tank transducer. I can't put feedback from the secondary to the primary, but the output waveform looks like trash when using voltage drive, mostly due to the aforementioned variation in impedance over frequency

Reply to
bitrex

Sweet! I want to make one :)

Reply to
Clifford Heath

Right, the slinky is not as good, lower Q.

You can't make a Wilbur reverb, (just dreaming) unless you were willing to hang one of the magnets. Maybe if you hung some weight in the middle you could couple vibration into angle.. maybe not at the middle. (some harmonic sweet spot?)

I never knew (some) reverb was by the torsional motion of springs. I want one of those.... I wouldn't mind a slightly broken one if it had most of the parts.

George H.

Reply to
George Herold

Not the same thing, but you might look at the PT2399 ic.

Dan

Reply to
dcaster

Fun, thanks.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Not the same thing might be the understatement of the year. To use that IC for an actual reverb, not just echo, you have to do quite a bit.

First of all you have to take the clock speed up quite a bit, and then you have to figure out a feedback circuit with just a hair under unity gain. Th e circuit is not likely to be very stable and that might be why they don't do it.

If you want that IC to sound like a spring reverb the parameters are on the edge to get the sustain. It would be easy to kick the thing into oscillati on. All it takes is one little slight error in design and the right input a nd the thing will probably howl.

I am not sure a PT2399 will clock fast enough to emulate a spring reverb no matter what. And the design, as far as I know about that chip, would proba bly be more trouble than it is worth. Using two of them might help, but onl y if they can clock fast enough. If not you are f***ed.

I heard of one thing that beats a spring reverb. Long time ago. About a rec ording studio that had a well dug accessible in the building, they dropped a mic down there and had a speaker somewhere. Now THAT'S a tank !

The spring job is the next best thing as far as I know, unless you go total ly digital. Even then, some people do not like the sound of the digital, he ll some even play records because they don't like CDs. But once everything is mixed down I have much doubt as to whether they will be able to tell.

But the PT2399 is a cheap chip. I think all it is is a BBD with an oscillat or. Nothing wrong with that, but it is NOT going to sound like a good rever b tank.

Reply to
jurb6006

Oh, (thanks) I have very little interest in the reverb, but the physics of driving magnets on springs and picking up at the other end looks interesting.

George H.

Reply to
George Herold

f

ing.

I programmed on a computer that used mercury as a delay line. It had a tro ugh that was about 5 feet long. A transducer at one end to put sound into the mercury and anther transducer at the other end to pick up the sound. T he pulses were reshaped and retransmitted.

Dan

Reply to
dcaster

You're welcome.

AmplifiedParts personnel kindly sent me Document 126-00005, which was written in 1978. It appears that only the two spring variety of tank was manufactured at that time. Document 126-00005 is now available at:

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Here's what it says about the mechanical physics of the tank:

Accutronics' electromechanical reverberation devices consist of input and output transducers and a set of transmission springs. These components are mounted on an aluminum channel, which is usually supported by four springs to an outer case or channel. Briefly, the device operates as follows: An electrical signal applied to the input transducer is translated by the magnetic circuit to a torsional force on two small cylindrical magnets. The magnets are mechanically coupled to a pair of transmission springs and the torsional motion is propagated slowly along the spring path. At the output, a replica of the original input signal is produced by the action of magnets again coupled to the transmission springs. The signal has now been delayed by some period, determined by the diameter, wire gauge, and length of the transmission springs. Additionally, most of the torsional energy is reflected back to the input transducer. The result is a multitude of reflections each smaller in amplitude than the last. The delay time of each additional reflection is 2T since the torsional motion must travel the spring path twice to reach the output transducer.

Thank you,

--
Don Kuenz KB7RPU
Reply to
Don Kuenz

It works for me.

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Reply to
Michael A. Terrell

** So you like looking at blank pages?

..... Phil

Reply to
Phil Allison

It works for me too.

Dan

Reply to
dcaster

** What do you see??

.... Phil

Reply to
Phil Allison

Bunch of reverbs on a red background. and buttons at the top for products, orderinge, history, How reverb works, application, about us.

Dan

I am using Firefox for a browser.

Reply to
dcaster

No, but I read a lot of you empty posts, anyway.

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Never piss off an Engineer! 

They don't get mad. 
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Reply to
Michael A. Terrell

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