Reverb unit from salvaged pan and computer speaker amp

[monstermovie]

Hey forum --

First post -- so hi to everyone! Wanted to say this looks like a great resource for someone like me who has some fun ideas, but not so much the skill, knowledge and experience to put them into place. It would be kind to say that I am a hack when it come to electronics. I fiddle around with an idea through trial and error until I get (or close to) the results I'm after. Still I have fun with it.

Currently, I am trying to piece together a reverb unit for using with guitar and keyboard. I am using a salvaged 2-spring reverb pan from a Crate combo and a computer speaker amp to drive it.

As it stands, I have the reverb pan hooked through the amp as shown in the (admittedly poor) schematic attached. Instrument goes through the left channel input, out the left channel output (normally to 8 ohm speaker), in the reverb input, out the reverb output, into the righ channel input and outputs to right speaker (8 ohm 3 inch full range speaker).

I am using a keyboard to drive the sound. With everything hooked up as described above the reverb signal is incredibly weak. I need to crank the volume on the amp and keyboard to full in order to hear it. The reverb effect is there but very weak to where I need to hold the speaker up to my ear to hear it clearly. If I run the circuit without the reverb pan, the volume is good (if a little noisy).

Measuring the ohm resistance of the pan out of the circuit with my multi-meter, I get 250ohm on the input and 40ohm on the output. My guess is that the resistance is too high and I need something to drive it. This is where I'm stuck. I don't think I need _another_ amplifier to drive the reverb unit, but I thought maybe a capacitor or...?

Okay, so that's as far as I've been able to get. Any help appreciated.

http://www.aronnelson.com/gallery/main.php?g2_view=core.DownloadItem&g2_itemId=36951&g2_serialNumber=1

[monstermovie]

Work week bump.

If I need to provide more information, including photos of the amplifier or the reverb pan, please reply back. If the diagram is too confusing, please let me know and I'll try to explain it better.

Looking over the circuit board of the Crate combo GX-15r (where the reverb pan was pulled from) there is an IC located between the connections for the reverb pan in/out. The chip is labled:

5532D
JRC
0036G

Googling about, the best I can figure is the chip is an op-amp of some sort. So maybe I DO need an amplifier to drive the reverb unit.

Would like to give this a go, just need some help.

[petemoore]

  The input transducer is like a speaker, coil..mechanical motion..a motor, and like a speaker needs an amplifier capable of driving it, that means appreciable 'current' will be drawn by the speaker, if there's an impedance mismatch, the large current draw will 'mess with' the AC voltage swings.
  So you need an amplifier with an output impedance that won't get 'swamped' by current draw of the input transducers needs during work cycles.
  Not knowing the input impedance of the reverb tank makes it difficult to arrive at a driver amplifier design.
  The rest is a little easier, and small signal components can do the mixing and recovery stages needed to have a reverb 'amount' knob called 'depth' or 'reverb' when labeled, the usual stuff applies...impedance etc.

[monstermovie]

  The input transducer is like a speaker, coil..mechanical motion..a motor, and like a speaker needs an amplifier capable of driving it, that means appreciable 'current' will be drawn by the speaker, if there's an impedance mismatch, the large current draw will 'mess with' the AC voltage swings.

This part I understood a bit when starting the project. My initial thought was that the right channel of the amplifier would be enough to drive the reverb pan.
 

So you need an amplifier with an output impedance that won't get 'swamped' by current draw of the input transducers needs during work cycles.

Let's see if I understand how this works: Power is sent through the amplifier channel (in this case the left stereo channel) into the input of the reveb pan and stimulates the transducer. Because the power draw is so much on the input (and possibly because there is so much resistance traveling through the spring), there is not enough energy to effectively stimulate the output transducer. Correct (or close)?

How do you regulate or help the output transducer? 

Not knowing the input impedance of the reverb tank makes it difficult to arrive at a driver amplifier design.

Sorry. The measurements are buried mid paragraph in the OP. I used my multi-meter and measure in the same way I would get the ohm rating of a speaker -- using the K/OHM setting.

Input: 250
Output: 40

The rest is a little easier, and small signal components can do the mixing and recovery stages needed to have a reverb 'amount' knob called 'depth' or 'reverb' when labeled, the usual stuff applies...impedance etc.

My hope with this project was to reuse the amplifier circuit as much as possible. If it turns out that I will need to have someone help me design a circuit from scratch, I might be better off builder something like the Stage Center Reverb and buy a pan that I know the stats of and save everyone lots of trouble.

Thanks for the help so far. I'm still holding out hope for the hack, but it's looking less so.