diy spring reverb - noob electronics questions!

[mymymetrocard]

hey

i recently brought and asssembled lushproject's atari punk console (following a decent review in SOS), and i'd recommend it, it's a fun afternoon and makes some rather unpleasant noises!

i'm fitting it inside a biscuit tin and using a mini slinky to create a spring reverb effect for it. my plan is to have the slinky glued to the speaker at one end and glued to a piezo at the other. the piezo would be attached to a mono jack socket.

my questions are
1) am i good to just attach the piezo direct to the jack socket? a few things i see online involve having the piezo amped with a tiny mono amp before going to the jack. do i have to do this, or will i just be able to turn up the input when it gets to my soundcard? and what are the chances of damaging the pre-amp on my soundcard (UA-101 if that makes a difference to ya)?

2) the jack socket i have has 3 connectors, 2 little ones and a big one (kinda like this http://www.touchstonetonewoods.co.uk..._800_False.png).
anyone got any clue what i should be connecting to what?

apologies for the noobiness, i've just discovered the joy of solder!
thanks
alan

[DVDdoug]

2) the jack socket i have has 3 connectors, 2 little ones and a big one (kinda like this http://www.touchstonetonewoods.co.uk..._800_False.png).
anyone got any clue what i should be connecting to what?

There are 3 terminals, which means you don't have a mono jack. You have a stereo or TRS connector (Tip, Ring, Sleave).

The big terminal (sleeve) is the ground/shield. The other two are the tip & ring. If you are going to plug-in a mono (TS) plug, you can wire the signal to the tip, and leave the sleeve unconnected.

Since you can't see inside the connector, you may need to plug-in a mating plug and use an ohmmeter (or continuity tester) to find out which solder-pin is the tip. (I would guess the longer one is the tip...)

.. am i good to just attach the piezo direct to the jack socket? a few things i see online involve having the piezo amped with a tiny mono amp before going to the jack. do i have to do this, or will i just be able to turn up the input when it gets to my soundcard? and what are the chances of damaging the pre-amp on my soundcard (UA-101 if that makes a difference to ya)?

There's very little chance of damaging your soundcard or preamp. If your signal is too high, you'll get distortion but you should not do any damage.

I know a tiny bit about piezos... I don't know if you can drive the soundcard directly... Piezos are capable of putting-out relatively high voltage into a very-high impedance.

But, it depends on how much the piezo device is being actuated/moved. And, a soundcard load of ~10k might be low-enough impedance to "drag down" the signal. A microphone preamp will have lower impedance, which will drag-down the signal further, but it will also have higher gain.

I believe a piezo is also a capacitive source, which means that with a (relatively) low impedance load, you might get a signal that's high-frequencies only and no bass.

So my guess is, a peizo pickup works best into a special preamp with an impedance of 1M ohm or more. You can build a high-Z preamp with an op-amp, or a FET op-amp (or a FET or vacuum tube). You shouldn't need much voltage gain, but you need a low impedance output. (i.e. You need current gain... But, you don't generally design for, or calculate, current gain... You just need enough voltage/signal, and any op-amp has enough output current (and low-enough output impedance) to drive any power amp or soundcard...)

FYI - There is a company called PAiA that has been selling a spring reverb kit for many-many years. They used to sell the spring reverb tanks separately, but it looks like they are now only sold along with the kit. It's not cheap but good spring-reverb tanks are not easy to find. (It's easier to find a spring reverb simulator VST plug-in. )

[mymymetrocard]

Thankyou so much for your reply, it's really helped. i ended up emailing audiospares to see which tip was which, and got a really polite and quick reply!

"Hi Alan,

Thank you for contacting AudioSpares.

Actually, of all the questions we get yours is probably one the least stupid since it's not immediately obvious what the contacts are without metering them out, so we've done so and added the information to the description on our web site.

The contacts are:-

Tip = Rounded silver-coloured tab
Ring = Squared copper-coloured tab
Sleeve = Clamp / Shell

So for mono you only need to wire signal to tip (the rounded silver-coloured tab) and the cable shield to the cable clamp.

If you want to adhere strictly to mono wiring you should also "short" the ring (squared copper-coloured tab) either by running or splitting the cable shield between it and the sleeve.

Regards,
AudioSpares"

as i'm pretty confident that my soundcard'll survive, i think i'm going to give it a go direct from piezo -> jack -> mic pre on soundcard, and see what the result is. then if necessary i'll add an op amp.

I've got a number of spring reverb plugins, but where's the fun in that! the atari punk console just makes nasty noises, so getting a paia would be a bit overkill, as i'm installing it all in a self contained unit.

thanks again for your help

[djz]

as an aside...APCS RULE!!!!! you can do so much with those little 555 chips. There's also a 556 which contains them both in one; not sure which one your kit would have come with but... you can actually do a lot with that, 4 synced square oscillators through a delay gets really wacky very fast. If you want to add a little pizazz to it, you could build a filter, overdrive, octave doubler circuit.... mmm

sorry if this was off topic. I just.....love the APC. such a fun circuit!!!!

[mymymetrocard]

Originally Posted by djz

as an aside...APCS RULE!!!!! you can do so much with those little 555 chips. There's also a 556 which contains them both in one; not sure which one your kit would have come with but... you can actually do a lot with that, 4 synced square oscillators through a delay gets really wacky very fast. If you want to add a little pizazz to it, you could build a filter, overdrive, octave doubler circuit.... mmm

sorry if this was off topic. I just.....love the APC. such a fun circuit!!!!

the kit i got was from lushprojects.com (highly recommended, they even sent me a replacement speaker cos mine was bent in transit), and contains a 555 and a 556 chip. it's all alchemy to me at the min, i've no idea what they do, all i know is they make whirrr,cshh,vraapvraap happen!