Spring reverb driver/recovery impedance matching

Long story short, I'd like to design a spring reverb unit that can be used with the reverb tank in/out of any amp (or at least as wide a variety as possible).

If possible, I'd prefer to use passive components so the unit doesn't require external power. I can start with any type of reverb tank, so long as there's a switching circuit to make it work reasonably well with most major amp types, or at least as many as possible (Fender, Marshall, Vox, Mesa, Peavey, Orange, etc)

Does anyone have any ideas how to do this cheaply and effectively? Thanks!

I presume the originals come in a wide range of impedances, much like on this page of specs for a modern product. You probably want to read some other parts of this site as well as these pages:
http://www.accutronicsreverb.com/main/?skin=sub05_04.html
http://www.accutronicsreverb.com/main/?skin=sub05_05.html

I'm guessing you would need a beefy audio power amp chip like an LM3886 to be able to drive the whole range, giving a high voltage for higher impedance tanks (as used in tube amps) and the gain either greatly reduced and/or going to voltage divider arrangement for low impedance tanks (as used in solid state amps). Resistors may need a couple of watts of power rating to get the voltage down to range and still maintain the needed current.

> use passive

Use the reverb tank which the amp expects?

There's many variations in drive circuits. Less in recovery circuits.

I would suggest a transformer with 4 16 100 600 and 2K impedance taps. Whatever tank you use, connect it to the proper tap. Then try feeding the amp drive circuit to the several taps until it seems happiest.

A 4-8-100-600-2K transformer may be found on some old PA amplifier outputs. It is MUCH too big, but will prove (or refute) the concept.

I'm actually just "prototyping" a spring reverb,
For amps I found cheap ebay lm386-modules
(Like http://www.ebay.com/itm/LM386-Audio-Amplifier-Module-200-Times-Input-10K-Adjustable-Resistance-5-12V-wc/221596848986?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D2%26asc%3D40757%26meid%3D15d2a647d4e847cebd35a91a488fefa1%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D282121374997)


They are really lofi, but seem to work well enough on driver/recovery amp..
(Or You could use some mic preamp for recovery?)

This ain't passive nor the best way to do this,
but I needed something cheap&quick and this seems to do its job

I've been laying out a board for driver/recovery circuit for a tank I want to use. This page http://sound.whsites.net/articles/reverb.htm has a lot of good info about different circuits, nothing passive though I think.

I read on the JLM forum that you can use the DINGO for this:

Yes we have several DIY guys running reverb springs with 1 x dingo or 2 x BA mic pres or 1 x BAD mic pre. In the dingo with a normal OPA2604AP or NE4432AP you can drive 240ohms or higher (using a 99v or Hybird you could go down to 190ohm or 10ohm with a series resistor of 51R and the input to the dingo makeup amp is 20k so will work with any output spring impedance lower than that.

Click to expand...

https://www.jlmaudio.com/forum/viewtopic.php?f=2&t=5&hilit=dingo

The most basic reverb design I have encountered was in a small tube amp. The reverb tank was connected to the speaker, the speaker transformer was also the reverb drive. There was a trim circuit and a pot for intensity where the tank returned near the input tube.  You could connect your passive reverb to an extra speaker jack and return to either effects return or input jack. Add a switch to lower the signal when connecting to input jack.

walter said:

The most basic reverb design I have encountered was in a small tube amp. The reverb tank was connected to the speaker, the speaker transformer was also the reverb drive. There was a trim circuit and a pot for intensity where the tank returned near the input tube.  You could connect your passive reverb to an extra speaker jack and return to either effects return or input jack. Add a switch to lower the signal when connecting to input jack.

Click to expand...

Hey Walter! From one Seattleite to another, thank you! That's a great idea! But obviously, a 100W Marshall I tube head is going to drive the circuit a lot more than a 15w solid state amp. It's seems like you'd need to create a current limiting device, or a "hot plate" type unit, perhaps with different response curve/sensitivity settings  for different amp types (ie low to high volume on a monster tube rig and low to high volume on a little bedroom amp and everything else in between.)

You could do it passively, which is awesome, but seems like it would get very complex and expensive. Also would change the impedance/load on the speaker, which might not be ideal.

But I like the idea....if there was a cheap, effective way to implement it to work with multiple amps that would be awesome! Maybe just a static current limiting device that would have the same sensitivity no matter what power amp is connected? Is such a passive circuit even possible?

Now that I think of it, the 500 series Radial Tank Driver basically does what I need  (buffer that auto-adjusts it's drive/recovery circuit to any reverb tank provided)

Expect in the case of my device, the reverb tank is static and the buffer would need to adjust for different amps driver/recovery needs.

Also, of course this device couldn't be passive with buffer op amps.....but might be a better solution than a complex, expensive, large passive system. Hmmmmmmmmm.....