Stage center spring reverb

[Jmsteele187]

So, I've wanted to make a spring reverb pedal since I first saw the sole-mate from van amps.  I was looking around and found this link for Craig andertons center stage reverb. http://www.generalguitargadgets.com/effects-projects/reverb/stage-center-reverb/
It calls for a 310 ohm spring reverb tank.  However, I have a 600ohm tank that I pulled out of an old practice amp I had laying around.  Is it possible to adapt this circuit to work with the tank I alread have, and how would I go about it?  Or, would I have to buy a tank with the proper input impedance to make it work?  If that's the case, I may just try to put together that space and time reverb I was reading about on here earlier today.  The sound clips that I listened to sounded pretty good.

[jsleep]

It should work okay with the 600 ohm tank.  I don't have a 600 ohm tank here to try it, but I'm guessing it will work fine as-is.   It just will not work as-is with an 8 ohm tank.  I've been meaning to try a transformer between the tank-driver and the tank to see if I can get it to work with 8 ohm tanks, but too much to do and haven't had the time yet.

JD

[Jmsteele187]

I only asked because I read something that said you should always make sure you match up the input impedance when replacing a reverb tank.  Otherwise it could sound bad, or not even make sound.

[PRR]

> It calls for a 310 ohm  ...I have a 600ohm

Just do it. Close enuff to work.

> I read something that said you should always make sure you match up the input impedance when replacing a reverb tank.  Otherwise it could sound bad, or not even make sound.

There are few-Ohm, hundreds-Ohm, and thousands-Ohms tanks. Getting WAY off will give low reverb. Maybe so low you can't hear it behind the direct sound. So the 2K tank from an Ampeg, in the 4-Ohm circuit of a Fender, is a Big Mismatch.

But 310 or 600.... bah, these could even be the same coil. (Different series are measured different ways.)

[jsleep]

I'll update the wording.  What I meant to say is that it won't work with the 8 or 10 ohm tanks.  8 ohm tanks are fairly popular, so I just need to make it clear that SCR won't work with those without  some alterations.  I do have an updated version of the SCR in the wings, it has some slight improvements and a charge pump on board. I've tested it, just haven't had a chance to update the project yet.

JD Sleep
General Guitar Gadgets

[Jmsteele187]

@JD It was the charge pump version that I was looking to put together.  If nothing else, when I get it together, if it doesn't work to my liking, I'll just buy another tank.

[jsleep]

I'll post the new stuff as soon as I can.  Probably within this week.  if you are etching yourself and haven't etched it yet, the new layout is better than the old.  There is a trimmer in the feedback loop to adjust gain of the tank driver, dual opamp ICs (suggest 5532 ICs) instead of the quad and charge pump on-board.   But if you've already etched the old PCB, save yourself time and stick with that one, they sound pretty close to the same.   I haven't decided whether or not if we will sell PCBs for it.

JD

[Jmsteele187]

Actually, I haven't even ordered any parts yet.  I'm going to wait until I have my first build done, a red llama, before I start another project.  I was planning on using perfboard for the pcb.  I haven't tried etching boards yet.  It seems fairly easy though.  I'll keep an eye out for the new layout.

[Mark Hammer]

We really need to start up a homebrew reverb pan initiative here.  You can buy suitable springs from many hardware sources, with the right degree of compliance, for somewhere in the neighbourhood of a dollar or two.  Where commercial reverb pans rely on essentially matching springs of identical compliance and length, there is nothing stopping the DIY-er from combining springs of different length and/or compliance to achieve a richer reverberant sound.  Moreover, the different spring lengths could be driven by individually EQ-ed drivers. to complement the length, and more closely mimic natural reverberant spaces (e.g., lots of hi-cut for longer springs, and bass-cut/treble-boost for shorter springs mimicking early reflections).

I keep meaning to finally package my experiments, and take some pics, but sadly it sits way down a rather lengthy list of projects that await finalizing.  HOWEVER, I will confirm that one can use simple headphone amp chips (or chips like the NE5532/LM833 that can sub for headphone chips) to "wiggle" a spring whose end is epoxied to the middle of a small speaker at one end, and epoxied to the middle of a piezo disc at the other.  The sound produced by the speaker can either be "contained" in a more or less soundproof enclosure, or reduced in loudness by surgically cutting away parts of the speaker cone so that it moves the spring when it goes back and forth, but not very much air.

The piezo discs can be pretty much whatever size you want, although I suppose one needs to be finicky about mounting the disc so that it doesn't break or get mounted in a way that damps vibrations too much.  A suitable high input impedance gain stage after the disc "recovers" the sound sent along the spring.  Alternatively, since any speaker coil can also serve as an ersatz dynamic mic, you can epoxy both ends of the springs to speakers, and use one end for driver, and the other for sensor, along with suitable electronics.

That's really all there is to it: make a spring wiggle by treating it like a speaker, and sense the wiggles with something that acts like a mic.  Companies like Accutronics have opted for equal-length springs since it simplifies their production and keeps costs down.  That's not a criticism of them, just a recognition of how manufacturers need to think and operate.  But there is no reason why folks like us have to be content with what's out there.

[jsleep]

Jimmie - Yeah perfboard is do-able, I don't think it's too complicated for that.

Mark -  Your are the DIY MAN!  I love the electronics DIY stuff, but I've never had much success with mechanical DIY things like this.  I guess I need to keep on working on my skills 

[Jmsteele187]

JD, considering I've never worked with perfboard before, I might just find it a PITA when I build my llama.  If that's the case a May just consider etching the board for the stage center reverb.  Soldering to pre-existing traces seems a lot easier than making all the connections, by hand on perfboard.

[Jmsteele187]

Hey JD, I just looked at the new layout.  It looks like you've made a number of changes/improvements to the circuit.  My biggest question now is; what does that 500k trimmer do?

[jsleep]

Hey JD, I just looked at the new layout.  It looks like you've made a number of changes/improvements to the circuit.  My biggest question now is; what does that 500k trimmer do?

It was meant to tune it in to get the best sound out of whatever tank you are using with this circuit.  Whether it works or not, I don't know for sure,  I only have a limited number of various reverb tanks (pans) to work with here.  I think it helps to have it there.  It doesn't have the kind of impact that I thought it might.   If you're using the 600 ohm tank, you can probably just put the resistor in that space and you wouldn't need to get the trimmer.

JD

[thom]

While searching for a spring reverb project I liked, I must have built half a dozen, including the Stage Center, and my favorite one of those is this one http://sound.westhost.com/project34.htm.
You'll need a bipolar PSU, though.

I have a working perfboard layout if you're interested.

[jsleep]

I was listening to the SCR again today and the updated version and I'm just not happy with it yet.  I think I'll pull the updated version off the site until I figure out something better.  There is some distortion on some of the settings and the mix doesn't really work so well even on the original (distorts at the far end of the clean mix).  It sounds good when you tune it in, but I think we can do better.  I'll see what I can come up with.  I'm sorry about the false start. 

JD

[Jmsteele187]

No worried JD, it'll probably be a short while before I start that project anyway.  I'm still debating on how to enclose the entire works, instead of just the circuit, and plugging into the tank.  I'll probably etch my own board as well.  I'm finding that making all the conections on perfboard to be quite tedious.  I may even start over with the llama I'm putting together and etch a board for it as well.