I have a spring reverb tank, now what?

[jmusser]

I've typed this in 3 times now, and it keeps timing out, so I basically want to know if i can make a stomp box out of the reverb Accutronics #4, using their General Purpose Reverb Drive and Recovery unit.

[jmusser]

I'll see if it'll let me add more this time. Their site http://www.accutronicsreverb.com/drive1.pdf, shows this circuit. I pulled this unit out of a ruined Peavy PA. It is a type #4, 1475 ohm input, 2250 output, 1.75  to 3.0 sec decay time, grounded input, insulated output, mounted Horizontal open side up.

[jmusser]

The drive and recovery unit looks easy enough to build, and it looks like i could just hard wire the D&RU, right to the circuit, and then go in and out with standard jacks. It  does require a -15/+15 supply voltage, which I've never dealt with. It also shows for high levels (8 ohms) for low levels(150 to 600 ohms) on there, which I'm guessing is load impedance? Most of the stuff they talk about on that site, is way over my head, so any hand holding would be appreciated. It just looks like a nice unit, and I'd like to get some use out of it.

[petemoore]

  I have a nice tank [I know because] I used to use it in a tube/si [Legend 30] amp that died long ago,  a tank reverb is a nice thing to have.
  I also used it with my sisters little Fender PA...according to the manuals outlined hookup [pick a channel for drive, choose another for recovery], having a separate reverb for more channels does have mostly all advantages except taking up the extra channel. I've not seen this on any other mixer/amp/PA/box. It had a built in tank reverb also.
  Problem I must face is that I think I blew the coil spring driver [word ] unit on one side...
  That schematic looks pretty easily workable, Mark Hammer has mentioned options for reverb units like pre-voicing for eQ or Distortion, IIRC there are alot of them that could be used for reverb. I'd would use a 'hi/low' reverb setting switch.
  15_/15+ PS is something I've avoided messing with, two batteries can do that.
  A preferred? method would be found [oC] at GEO, there's one about getting _/+ 9V from a single battery IIRC..worth a look around.

[Paul Marossy]

I wouldn't try running something like that off of a battery. I would go with the bipolar pwer supply arrangement.

[Mark Hammer]

Will it "work"?  Of course.  Will it work off batteries?  Unlikely, unless they're C-cells or something.  Reverb pans are pretty inefficient units and require lots of current to be pumped in.  I mean you could get it to work, just not for a long.

Does it need to be +/-15v?  Nah.  You can probably do fine with +/-9v or 12v.  Fifteen volts is simply a maximum "cruising speed" for the op-amps used.

You will notethat the circuit shown at the accutronics site is really a circuit fragment.  That is, it assumes the circuit will be inserted into a larger circuit, and is not a standalone unit.  The 100k input pot is great if its coming from something with a low-impedance output, but I wouldn't want to plug my guitar in there straight.  Of course the clincher is that there is no wet/dry balance function.  So the assumption is that you'll tap another stage somewhere else, feed it to the 100k input pot, and then feed the 100k output pot to a mixing stage elsewhere.

[jmusser]

OK then Mark, if this is something you want to tackle, what does it take to make this happen without actually having it tapped into an amp. for a power supply, would a 12 volt wall wart have enough current to drive this tank, or does it really need a true power supply? Would I need some other impedance matching, and this wet/ dry circuitry? If this is too much to get into for you, I certainly understand.  This is something I thought would be neat to do, but I certainly don't know what it takes to get it done. Another thing I don't know, is whether the tank needs to be in an enclosure the size of an amp for resonance purposes, or weather it could be in wooden box the size of a four sleeve cracker box, and do just fine? I have never really listened to reverb stomp boxes to know if it would even be worth the effort to built this spring unit. I've always considered spring reverb to kind of be the gold standard, and I had one, so I though I'd give it a try.

[Mark Hammer]

OK then Mark, if this is something you want to tackle, what does it take to make this happen without actually having it tapped into an amp. for a power supply, would a 12 volt wall wart have enough current to drive this tank, or does it really need a true power supply?

From where I stand, a 12V wallwart IS a "true" power supply, although it might not provide the regulation you want.  The circuits shown here - http://www.solorb.com/elect/musiccirc/reverb/index.html - work off +12Vdc supplies so that might make things easier for you.

Would I need some other impedance matching, and this wet/ dry circuitry?

Well, if you want to make it the sort of thing you can plug your guitar into, yes.  If you have an effects loop on your amp, though, it may not be necessary at all.  I've mentioned it once or twice, but a review of a boutique amp (SMF?) that I read in Guitar Player about 2-3 years ago was raving about having one power amp and speaker dedicated to reverb, and the other dedicated to non-reverb, made for an exquisitely lush sound.  In many respects this is how many players feel about the similar arrangement for chorus in the old JC-120 amps.  *IF* you were to use the circuit you linked to at the accutronics site for conditioning the signal to be sent to a second amp, (taking its input signal from an effects loop send or an active splitter), you would not need to worry about input or output impedance or mixing capabilities much, if at all.  The problem comes when your intent is to make the reverb unit part of your signal chain as you would an analog delay or phaser, etc.  You would need to have a means for keeping some dry signal in and adjusting the proportion of wet and dry.  Forrest Cook's circuit ( http://www.solorb.com/elect/musiccirc/reverb/reverb.gif ) does that for you.

Another thing I don't know, is whether the tank needs to be in an enclosure the size of an amp for resonance purposes, or weather it could be in wooden box the size of a four sleeve cracker box, and do just fine? I have never really listened to reverb stomp boxes to know if it would even be worth the effort to built this spring unit. I've always considered spring reverb to kind of be the gold standard, and I had one, so I though I'd give it a try.

I'm not the expert here, but my own understanding is that the key thing is to have it be relatively immune to mechanical feedback and unintentinal jarring.  Other than that, as long as you have enough room for the pan and the pats, and whatever air circulation you need, you're in business.  By mechanical feedback, I mean vibrations coming through the cabinet (via the floor, etc) and shaking the springs at some resonant frequency.  So, for instance, you might make a cabinet which wedges the pan between some sheets of foam so that the pan is not mechnically coupled to any surface in the cabinet.  In theory, you should be able to wail away without any cow-like braying coming from the springs.

So now, if its in a box stuffed inside foam, how on earth do you bypass it?  If you look at a bunch of reverb-equipped amps, what you'll often find is that bypassing is simply a matter of grounding the reverb pan output.  So, that 0.1uf cap you see after the reverb pan output in the schematic gets grounded.  The cable you run to the stompswitch is shielded (regular guitar cable) so that the post-pan gain stage is not busy amplifying noise you pick up via the cable, and the stompswitch is a simple SPST.

The key thing in reverb driver circuits is that they accommodate the input impedance of the reverb pan.  To the best of my knowledge, the LM386 used in this circuit is quite happy to drive a 1.5k load, so the circuit should work.  I don't know that it is "better" than the one you linked to, but it uses the type of supply you seem to have available.  besides, I'm guessing you have a 386 sitting around but not a 307.

[rfoust]

Spring reverb in a pedal -- check out the Little Lanilei reverb pedal by songworks http://www.songworks.com/pages/3/index.htm
I know it doesn't help with the technical questions (and it looks like the guy's using a smaller reverb tank), but it shows that it can be done. And his runs off a 9v battery or wall adaptor.
It looks like it uses a remote footswitch, probably because stomping on the tank in the middle of a song isn't always a good idea 
Of course, having the tank within stomping/kicking distance could make for some neat effects -- didn't Neil Young do something similar,  mounting it under the stage or somesuch?

[jmusser]

Thanks a lot Mark. From what you're telling me then, this schematic is pretty much all inclusive, correct? It looks like it takes care of the elements that usually the amp would provide. You are correct about the amp chip. I have a whole drawer full of LM386s, and have never heard of a LM307. I sort of figured that I hadn't reinvented the wheel here with wanting to have a stomp box spring reverb. From the looks of the schematic, I should have everything on hand to do this.

[Mark Hammer]

Is kicking a reverb fun and interesting?  You bet. Is NEVER being able to play above a certain volume or situate your reverb within a certain distance of the drums fun and interesting?  Nah.  Reverb units which are acoustically insulated from ambient vibrations are, happily, still susceptible to deliberate jarring.

[Fret Wire]

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