Spring Reverb - electronics question..

ecc83

jpfamps said:

ecc83 said:

Some years ago when son was home playing and recording I thought of getting a stand alone spring reverb unit. Until I saw the price! I then looked at tanks, not too bad, and I then roughed out a drive/recovery circuit. 

Would have used valve drive back then but now I would go for an 8 Ohm tank send transducer and drive it with a TDA3050 or similar IC amp. Recovery would be the ubiquitous NE5532 or maybe pus the boat out for the even lower noise LM4562.

Nice little project now winter is acoming in?

Dave.

You don't want to drive the tank with a voltage source, ie the TDA3050; this is because the input transducer of the tank is (almost) a pure inductance so you will be have a low pass filter. 

Reverb tanks should be driven, ideally, from a current source.

You could configure a TDA3050 for constant current operation (although this is not recommended with these chips), but this would be overkill. A couple of cheap BJTs would be all that's required to drive a medium impedance tank.

There are plenty of circuits on the web for this. An excellent article on this can be found here:

http://sound.whsites.net/project34.htm

re the recovery amp, an NE5534 is likely to be lowest noise of the usual suspects, however as the output impedance of the tank rises with frequency and is not insignificant, you can't discount current noise, so the LM4562 may in fact be noisier than an NE5532/4. 

Another option would be a low noise discrete JFET (very low current noise) combined with an op-amp in a hybrid configuration.

Oddly I am in the process of prototyping something like this at the moment, but for another application.

Yes, I had considered current source drive (a la tape heads) but then the Fender circui* is a medium ra triode (2 p'lld?) and a step down traff, the ratio of which I know not but I still think the source Z would be pretty low?

Again, 5534/LM4562, pays yer money. Certainly Self shows the 34 to be the quietest of the common chips for a phono cartridge amp, beating the LM just because of the rising Z of the source. However in his treatise he points out that the noise comes about because the cartridge no longer shunts the "noisy" 47K load R which you cannot do without in a phono amp. In a reverb recovery amp the coil could be DC coupled to the chip as the bias feed.

I don't know but the DC resistance of the coil might mitigate the current noise of the 4562? Whatever! both are better than gitamps usually get!

BTW the TDA3050 is probably an overkill/hi fi amp? The TDA 2003 would almost certainly do but this old brain could not remember the number at the time!

*Of course, THEY might have done it wrong all those years ago! Guitar amp design is littered with poor design and copies ad. inf of such design!

Dave.

57Deluxe

I have fancied a Fender Reverb unit for ages but got fed up waiting for a good deal and half measures with other reverb pedals, so I got a  Mosky Spring Reverb and is superb. You get that massive bottom thump when you load up your picking and with my 57 Deluxe sounds killer.

https://i.ebayimg.com/images/g/NF0AAOSw9GhbPxsT/s-l640.jpg