Thats the one yes……
1 Like
For a plate reverb the secret sauce is matching a speaker driver (the hardware that is) to the plate material. Some are too weak, some too forceful.
I see no reason why the Doepfer circuit wouldn’t work though you will need to up the gain to get the signal moving. The fun part is matching the signal to the combination of the speaker driver and the mass and resonance of the plate. For the return a piezoelectric pickup works almost as well as a stripped down speaker as a microphone.
There are several dedicated drivers (the speaker hardware) out there being punted for flat speaker systems that are just ridiculously over priced. As I’m old school I’ll be down the scrapyard to hustle a few car stereo speakers; remove the paper cone and you have reasonable driver. For the proof of concept set up I mentioned the driver was just hot glued to the sheet. I took a metal frame I was given by a pal which was the transport frame for his new washing machine and tried suspending different sheet materials to see the effect. In some cases I put the metal sheets under surface tension (beating out the surface with a hammer much like a guitar resonator or older cymbals.
The one I’m looking forward to play with is using a pane of double glazing as glass has a number of frequency sweet spots, though some frequency/amplitude combos may shatter the pane which is cool.
One reverb id like to play with is a design using a laser as the pick-up, much like a galvanometer, to add the sheet movement to the original sound. The displacement of the sheet is an analogue to the reverb effect.
A DIY plate reverb won’t ever match the quality of the big studios systems but I guarantee no other musician will have the individual nuance of your own plate. I know many producers that swear by some seriously hinky kit for ‘their sound’ and refuse to use other gear.
I have yet to make a final version for myself but I’ve been part of a few DIY reverb projects for producer friends. I think I mentioned a couple on the forum here.
And the to-do pile it ever grows.
1 Like
From what i’ve read in some articles is that you need at least 1meter by 2meters sheet metal plate of 0.5millimeters thick to get some decent reverb times. The bigger the plate the longer the reverb is. That sounds logical but for a first project i think i might start digging up info about the electronics.
1 Like
I had a similar notion about size and thickness until I spoke to a friend (Murray Campbell, professor of musical acoustics in Edinburgh’s physics department)
He tipped me off as to what happens in a plate reverb sheet. Abbey road has a huge sheet which WAS essential as there were no ic amps or small high quality speaker drivers when it was installed. Size and thickness are relevant and the maths for sound propagation vary with these dimensions but not as much as how you prepare/filter the sound for the reverb. The Abbey road setup has a bunch of pre effect filters and some fx for adding in low to sub audio waves to the mix.
It’ll work regardless.
It’ll sound different with every plate or change but once dialed in (gain, driver placement, pickup etc) it will be a unique reverb. Where a small plate won’t perform like a classic plate reverb is when used on mixdown for every sound at once. For that case use bigger is better.
A small sheet of tin or steel can have the surface ‘case hardened’ which lines up the molecules on the surface making it a superb audio conductor and both signals (wet and dry) can be re combined for a greater effect.
I will post up my findings when I finally build my final model for my own studio.
Oh, and you could also pitch shift up the input and shift the output back down to suck the marrow out of whatever sheet size you use. Fiddly but again it’ll be unique.
1 Like
Nice info!. but what if…………. we could use more than one plate? smaller ones like 60cm by 60cm and place them behind each other in a row so to speak? just like spring reverb tanks. multiple shorter spring that all combined are the same size as one long spring? maybe theoretically this could work on multiple plates too. benefit would be to have a small plate reverb dimensions instead of the size of my livingroom 
don’t know how to connect them or in that scenario if we would need more drivers/pickups/piezo’s installed. but let me see what else I can find.
1 Like
I was thinking of how I could use the reverb out. didn’t test it yet because I’m designing a panel for it. I would like to fit it on a 40mm wide panel. 4 pots, 4 jacks, 2 rca’s and a switch. panel would be so crowded so I was thinking what can I leave out to save space?. Maybe the reverb out?. Its 100% wet signal right? but then I thought, it is nice to have a wet out because you then have the ability to route it to a filter, and change the sound characteristics of the reverb and mix that in with the dry signal. So I think I leave it in .
1 Like
Hmmm, if you have a number of plates in a row you’d have to overcome the inertia each time for each plate like a domino effect which acoustically may be challenging. That said a network of smaller plates with each processing a selective band of the signal might be quite trippy.
If you have the room a tall pendulum cable or even a metal pipe might be fun.
A garage door would be fun with the wind etc adding a unique background noise. I did try little beaters as drivers on a stretched balloon once, it worked better on a floor board.
I like to experiment far more than I like to make ‘proper’ gear. Tuning longish lengths of fence wire as an an Aeolian wind harp morphed into a giant diddly bow and then a drab echo thing; twas a good week!
Did you know that a combination of an electric guitar and a driver plus magnet can not only give you Santana style sustain but can be a wild reverb unit? As can a record needle on glass over a speaker.
Stop me! This is a rabbit hole I know too well.
Crack on!
1 Like
You could also use the signal as a gate or envelope for other sounds and effects.
1 Like
Yeah nice out of the box thinking for applications. Your right! Far more interessting to experiment and accidently bump into something new.
1 Like
I have 1 more question to ask regarding the Doepfer springreverb. The external feedback option. If i turn the pot all the way up i hardly hear any difference. When i connect the 2 wires directly bypassing the pot, i hear some self oscillation starting in the reverb tank springs. So to my ears that sounds like feedback but with the pot and the additional 100k resistor active, it does nothing. When feeding it with a saw wave from my vco, i hear the saw wave far away in the background (full wet sound) So, this means that the so called feedback is working. Without external jack inserted and a little reverb dailed in, when i then turn feedback up it does not really change, enhance or richesness the sound or anything. So how should i use this feedback option in normal operation?
1 Like
The purpose of the “external feedback” input is that you can patch the full wet reverb out through effects and back into the external feeback to give different flavours to the feedback. I agree that it’s pretty weird that R13 removes most of the gain of the internal feedback connection. You could replace R13 with a 1k to fix that.
2 Likes
Hi Sandelinos. Thanks for the update.
Yeah. I mean a 100k resistor from reverb output to feedback jack which then goes to a 100k pot and a 100k to the pcb is a lot of resistance. I will replace the resistor with a 1k. 
or maybe a trimpot so i can set a treshold
2 Likes
.Changed R13 for 1k. Will test it later this evening. Then my eye saw another doubtfull thing. If you backtrace R13, you see that it is connected to R11, a 1k resistor. I know that resistor is meant for protection of the opamp’s output, but why is the wet reverb output behind R11 and not directly at the opamps output? I mean, that R13 should then be connected directly at the output instead of behind R11 (dont know the reason why it should). Basically now you have 2x 1k resistors in series. Does that make any sense? In other schematics i often see that multiple outputs from 1 opamp has its own 1k resistor for example: the audio output has 1k, and if there is a led or something or you need to route that same output to another device, an additional resistor is used. Let me know if my reasoning makes any sense
Fixed it. A lot more feedback now and better controlable via potentiometer. Thanks. Another puzzle solved.
2 Likes