Reverb with reverb tank: any schemmo's?

[smoguzbenjamin]

Hey all!

I have a reverb tank lying there doing nothing and I want to wire it up! It doesn't have any markings so I don't know it's specs. But who can point me in the direction of a good drive circuit?

[Peter Snowberg]

Start by checking the DC resistances of the coils. First check the reading with your meter probes shorted and subtract that value from your coil readings. Once that question is answered, the question of the drive circuit can be answered.

Take care,
-Peter

[sfr]

i know there's a few threads on this back a bit, if you use the search function, you might find it.  I'm pretty sure one of them had some good links.

no help to you, really - but I have a friend with a non-working stand-alone reverb - it's an older Fender, which, albeit solid state, sounds really really nice (I've heard some of his father's recordings with it before it died and he inherited it) I'm going to be trying to get it working again - it's nothing I've been able to find the schematic for online (except pay sites) would anyone be interested in a schematic while I've got the thing open?  The problem pretty much appears to be in the power supply, so I wasn't planning on drawing up a schematic to figure things out like I usually do when I fix things; regardless, at a quick glance it seems like it'd make for a pretty easy build - not an aweful lot going on in there; so if I have the thing in my hands long enough I can make a schemo if anyone's interested.

Don't mean to drag the thread off-topic, it just reminded me.  My buddy's out of town right now, so I don't know when I'll have the things in my hand, so don't go waiting on me, smoguzbenjamin

[Marcos - Munky]

There's a driver at GGG.

[Neutral]

I'm glad this topic has come up because I have two Accutronics spring Reverb tanks, one from a fender twin and one from and old hammond organ, and I want to build a stereo amp for them. They are both identical.
The output resistence accross the coil is 172 ohms.
The Input resistence across the coil is aprox 3 ohms?
Is this right? It's basically a dead short?

This site is very informative:
http://members.tripod.com/~roymal/reverb.htm
albeit the tech info is a bit beyond my knowledge

[Peter Snowberg]

Neutral, I'm guessing by your numbers that your tanks are 1AB or 4AB types.

The low drive impedance of your tanks means that circuits like the Stage Center Reverb will not work as is. You can use the recovery and mixing sections, but the drive amplifier will need to be changed for something like a LM386.

The drive impedance of your tank is about 8 ohms. It looks more like a short circuit when you look at the DC resistance.

http://www.accutronicsreverb.com/ioic.htm

Take care,
-Peter

[Neutral]

Thanks Peter,
One of my tanks is a 4AB301B, the other looks the same but has no markings (except the patent No's, which are the same)

So the Stage center Reverb Circuit would be appropiate for these with a LM386?
Thanks for your help.

[Peter Snowberg]

So the Stage center Reverb Circuit would be appropiate for these with a LM386?

Absolutely. Just add an LM386 to the output of the Stage Center as-is. The only change I would make would be to change R7 into a 500K pot to adjust the drive. This is usually called "dwell". Another way would be to use the Stage Center without modification, wire the reverb drive signal (F) to one end of a 10K pot with the other end grounded and the wiper connected to the input of a 386 (directly to pin 3). A gain of 20 will probably be just fine. See the first example circuit under typical apps. in the datasheet. http://cache.national.com/ds/LM/LM386.pdf

Any differences between the tanks will be mounting position (can easily be changed with pliars), insulation on the jacks (not an issue here), or delay length.

Happy building.
-Peter

[Neutral]

Thanks Peter,

Just add an LM386 to the output of the Stage Center

To do this would I just wire point 'F' to LM386's pin 3, Pin 2 to ground and pin 5 to reverb input?
Or Not?
I'm new at this game so forgive me if I'm a touch confused.
Thanks again.

[smoguzbenjamin]

Right, measuring as I type...

OK,

Probes connected: 0.05 ohms
Probes together with 'gator clip: 2.4 ohms
Coil 1: 4.7 ohms
Coil 2: 295 ohms[/list:u]
That's the measurements, so the real resistance is

Coil 1: 2.3 ohms
Coil 2: 292.6 ohms[/list:u]
Cool. Now what does that tell me? There's 2 springs there, not 4 that are intertwined, and they're about 7" long. Anyone?

[smoguzbenjamin]

I looked at the stage center reverb over at GGG, how do I use that schematic?

[Mark Hammer]

It will work fine, but if you don't have one you don't need to use a 386 necessarily.  The key thing is that the stage driving the tank be able to deliver current to very low impedance loads.  The LM386 or any of the other small "power amp" chips used for personal listening devices, clock/table radios, and small computer speakers will all work fine.  

In some ways, actually, it might be nice to try out one of the little chips like the JRC2073 that uses bridging (BTL) mode.  In these instances, none of the leads going to the speaker is expected to be ground which means you can tinker with switching the polarity of the leads going to the tank just to see if it sounds different when in or out of phase with the guitar signal.

Fortunately, the LM833 and NE5532 dual op-amps are equally at home driving 16-ohms loads and 10k loads, so if you make the Stage Centre Reverb using either of those you should be okay, in theory.  Get a pair of them and they will fit every part of the schematic nicely, without having to change anything.  The problem with the op-amp specified in the original is that it needs to see a load at the input to the tank which may be much higher than what your tank actually has.  Using a more flexible chip like the 5532 or 833 means matching is a non-issue.

I might point out that Forrest Cook has a couple of reverb projects posted here: http://www.solorb.com/elect/musiccirc/
One of them uses a 386 and the other uses a 5532.

Following Dave Barber's suggestion about the virtues of paralleling op-amps, I'm curious about using a pair of 5534's in parallel (i.e., one on top of the other with the pins soldered together so it plugs into one IC socket) to drive a spring tank.  Somebody gave me a fistful of 5534's the other day so I'm eager to waste a few.

[smoguzbenjamin]

I have a 386, but in my headphone amp it distorts at ver low input levels. I used a 10k pot to be able to change it's input level and labelled it 'distortion'.

But I'm worried that I'm gonna get a big-ass distortion/reverb thingy :?