Interesting spring reverb project

[Strategy]

Those are interesting comments, Strategy. What do you think makes the difference between a spring reverb "for guitar" and one "for keyboards"? Levels is the obvious first answer, but is there anything beyond that? Perhaps keyboards need a more open reverb path since they might have more treble end than a guitar...or not, I dunno.

I think EQ is part of it. That's all baked in to Surfybear with some of the bass rolled off I think - what you'd want for guitar and a surf tone. But in this particular case it's mainly a levels thing. It just does not like line level; distorts. Could it cause damage? Not really wanting to experiment there

[Rob Strand]

It just does not like line level; distorts. Could it cause damage? Not really wanting to experiment there

It depends if the drive side or the recovery side is distorting.  In the first case you can reduce the amount of drive then add more gain in the recover.   On the drive side the drive amp can distort or or the drive amp can overdrive the input coil of the spring.  What's happening becomes fairly clear when you look at the waveforms with an Oscilloscope.

[Nasse]

Good spring tank is important I believe

I did read something somewhere how some emulations suck at simulating real "surf" style reverb, while they May Be good for something else

[BluffChill]

Interestingly, it includes a variable feedback path from the recovery stage back to the driver stage to extend the decay of the reverberation.

From my DIY SS spring reverb bookmarks collection:
Another example of a circuit using feedback:
https://kassu2000.blogspot.com/2015/10/spring-reverb.html

Quick question - what's with the C2 and C4 duplicates laid cathode to cathode? I've never seen that before.

[anotherjim]

The back to back caps are to make a non-polar cap. In that position and with bi-polar power, the signal will swing positive and negative about 0v.  It is quite common where a large (uF range) non-polar cap is required.

[Mark Hammer]

+1

If you wanted to find/buy a 10uf NP cap, that might be both tough and expensive, not to mention bulky.

[BluffChill]

The back to back caps are to make a non-polar cap. In that position and with bi-polar power, the signal will swing positive and negative about 0v.  It is quite common where a large (uF range) non-polar cap is required.

Interesting! I still don't fully understand how this works, but thanks for your explanation.