sunday project spring reverb, needs some more work

[SineHacker]

I went through town today suffering abuse and confrontations from skinheads and drunks so I could buy a plastic tub and try this out:



I am using an LM386 to drive the speaker and a cmos 4049 circuit from Nicolas Collins designs for the piezo contacts. I tried a LM386 for the contacts as well but the 4049 was much cleaner and I could use a cap to put a little top-end roll off on the "wet" sound this way as well.

It sounds nice, but the reverb effect only lasts about a second, which is ok - but it would be great if I could make it longer, I was wondering if there is a way i can bleed the wet signal back to the amp side for a feedback effect?

also, I had to separate the chips into two circuits, otherwise a lot of the dry signal seemed to spill through into the output, I guess this is more down to noisey ground from the LM386 - any tips on fixing this so I can run it off one battery?

[Gordonjcp]

Make sure the supply to the 4049 is well decoupled.  I don't recommend using that as an amplifier though since "modern" CMOS chips don't really work well in their linear region.  It was a trick that worked on fragile old CMOS chips that lacked protection diodes.

[SineHacker]

Cool, thanks for the tip, I used a 220uf cap for the 4049 board and a 100uf for the lm386 board and that helped a lot but wasn't perfect. I could only get feedback to work if the two boards were connected to the same battery. Came out ok, but the sound is incredibly bass heavy - sounds good with vocals but not so good with other stuff.



I will build another at some point. thinking next time I will use a number of amps and speakers with each piezo being connected to another amp to a speaker in series to see how that comes out 

[SineHacker]

oh yes and this:

[soundcloud]http://soundcloud.com/aidantaylor/reverb-test[/soundcloud]

[nochtanseenspecht]

i think this reverb sounds quite nice
did you try it on drums, percussion etc  ?

[Gordonjcp]

Sounds pretty good.  Have a look at tone control circuits and see if you can add something to boost the treble a bit on the input.  Most spring reverbs keep the springs fairly tight.  Is the sound from the speaker muffled?

Bear in mind that The Prodigy use a bit of reverb (probably digital, though) low pass filtered above 60Hz or so to get that big bassy *thump* on drum loops.

[SineHacker]

When I was testing it, I thought the sound would be really tinny because of the piezos. So I used a slight adoption of the "bass boost" circuit from the lm386 datasheet. On the breadboatds this sounded good and the recording came from before it was soldered up. The feedback worked much better before I soldered it as well. I have one or two other things to try - I could cut the components of the stripboard in relation to the bass boost for one thing, but saying that, the speaker sound ok (after the boost) so the bass is likely coming from the springs and preamp.

I left the springs pretty loose, because I didn't know any better  I guess design revisions will have to go into a whole new project now.

Working on some PT2399 delay circuits next this month!