Author Topic: Interesting spring reverb project  (Read 837 times)

Mark Hammer

Interesting spring reverb project
« on: March 15, 2019, 03:35:31 PM »
It took me a while to identify the issue it occurred in, but I finally located it.  A 1983 issue of the Canadian edition of Electronics Today had a spring reverb project that included several useful features, including an optoisolator-based limiter to prevent spring-splat.  Interestingly, it includes a variable feedback path from the recovery stage back to the driver stage to extend the decay of the reverberation.

I imagine a different issue of one of the other international editions of ETI (Australia, UK, India, et al) may have had the same project, but I wasn't going to sift through all of them.  Here is the issue, courtesy of the American Radio History site, and whoever graciously scanned their copy.  Haven't built it myself, but it looks promising.

https://www.americanradiohistory.com/Archive-Electronics-Today/Canada/80s/ETI-1983-07-Canada.pdf

ElectricDruid

Re: Interesting spring reverb project
« Reply #1 on: March 15, 2019, 03:43:03 PM »
Thanks Mark! It just so happens I've been looking at spring reverb circuits the last couple of days, so that's very timely.

Thus far, this is the best page I've found on the topic:

http://roymal.tripod.com/reverb.htm

(linked from here: http://roymal.tripod.com - there's some other useful stuff too).


Mark Hammer

Re: Interesting spring reverb project
« Reply #2 on: March 15, 2019, 04:46:17 PM »
Well thanks, Tom!  Much appreciated.

Rob Strand

Re: Interesting spring reverb project
« Reply #3 on: March 15, 2019, 05:26:54 PM »
Quote
I imagine a different issue of one of the other international editions of ETI (Australia, UK, India, et al) may have had the same project, but I wasn't going to sift through all of them.
I don't remember seeing that one in the au version of ETI.   Interesting how the local variants of ETI have different projects.  That's happened number of times now.

Quote
Interestingly, it includes a variable feedback path from the recovery stage back to the driver stage to extend the decay of the reverberation.
Probably something that hasn't been explored enough for spring reverbs.    (Where's mac?)

A few of the earlier smaller tube amps used the amp output to drive the reverb, then feed the reverb output back to the input.   The motive here was to save a reverb driver more than anything but by default it achieves a natural regenerative feedback loop.   The problem with those is you can't control the amount of feedback separately from the "once through" signal so you were forced to keep the reverb at a low level, making it sound weak.
The mind often distorts without gain.

MaxPower

Re: Interesting spring reverb project
« Reply #4 on: March 15, 2019, 06:49:47 PM »
There's a spring reverb project in a fairly new issue of Everyday Practical Electronics. If anyone's interested I can find which issue. The mag is available as a digital download if it can't be found online.
What lies behind us and what lies before us are tiny matters, compared to what lies within us - Emerson

mth5044

Re: Interesting spring reverb project
« Reply #5 on: March 15, 2019, 10:54:42 PM »
Thanks Mark! It just so happens I've been looking at spring reverb circuits the last couple of days, so that's very timely.

Thus far, this is the best page I've found on the topic:

http://roymal.tripod.com/reverb.htm

(linked from here: http://roymal.tripod.com - there's some other useful stuff too).

You may have come across these articles, but in case not:
http://sound.whsites.net/articles/reverb.htm
http://sound.whsites.net/project34.htm

BluffChill

Re: Interesting spring reverb project
« Reply #6 on: March 16, 2019, 07:49:11 AM »
I recently pulled an old spring tank out of a 70s transistor organ, so I'll be playing with these soon :D
Kits & Pedals! EctoVerb - HyperLight - Shagpile - http://bluffchilldevices.bigcartel.com/

mac

Re: Interesting spring reverb project
« Reply #7 on: March 16, 2019, 12:00:52 PM »
Quote
Interestingly, it includes a variable feedback path from the recovery stage back to the driver stage to extend the decay of the reverberation.

Probably something that hasn't been explored enough for spring reverbs.

(Where's mac?)

 :icon_lol:

I tried feedback, but as the spring was not isolated from speaker, street traffic and flies wings,  small amounts of feedback made it resonate badly.
I did not go further.

This is the first driver for the speaker-piezo,



Thanks to Rob, I changed to coil-to-piezo, and coil-to-coil with a similar all-opamp driver circuit.
Feedback is easy to add.

https://www.diystompboxes.com/smfforum/index.php?topic=120207.0

mac


mac@mac-pc:~$ sudo apt-get install ECC83 EL84

Rob Strand

Re: Interesting spring reverb project
« Reply #8 on: March 16, 2019, 04:44:25 PM »
Quote
I tried feedback, but as the spring was not isolated from speaker, street traffic and flies wings,  small amounts of feedback made it resonate badly.
I did not go further.
Maybe some fly-spray will fix it  ;D.   I guess you can only have feedback in small doses.  Maybe some sort of filter on the feedback can help tame the beast.

Those old amps had the speaker shaking the whole works so the reverb would have to be backed off somewhat.

Quote
This is the first driver for the speaker-piezo,
One cool thing about that circuit is the loading on the piezo levels the response from the voltage drive on the drive side.

Quote
Thanks to Rob, I changed to coil-to-piezo, and coil-to-coil with a similar all-opamp driver circuit.
Feedback is easy to add.
It was all your hard work.
« Last Edit: March 16, 2019, 04:48:35 PM by Rob Strand »
The mind often distorts without gain.

j_flanders

Re: Interesting spring reverb project
« Reply #9 on: March 16, 2019, 08:46:54 PM »
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

Mark Hammer

Re: Interesting spring reverb project
« Reply #10 on: March 16, 2019, 09:16:04 PM »
The absence of any trimming of the low end on that feedback path is, um, questionable.  The "anti-shimmer"?

Phoenix

Re: Interesting spring reverb project
« Reply #11 on: March 17, 2019, 03:43:28 AM »
The absence of any trimming of the low end on that feedback path is, um, questionable.  The "anti-shimmer"?
U1B takes care of that  ;D

noisette

Re: Interesting spring reverb project
« Reply #12 on: March 17, 2019, 06:58:49 AM »
Very interesting thread and links, I think the ETI circuit has been discussed here before some years ago?? (EDIT:here https://www.diystompboxes.com/smfforum/index.php?topic=111671.msg1028607#msg1028607

Another thought is to follow a (long) spring reverb with a vca and trigger an envelope generator with the audio and optionally superimpose that envelope on the reverb. Has anybody experience with something like that?
« Last Edit: March 17, 2019, 07:02:13 AM by noisette »
"I don't like jail, they got the wrong kind of bars in there..."
Bukowski

StephenGiles

Re: Interesting spring reverb project
« Reply #13 on: March 17, 2019, 07:11:15 AM »
There's a spring reverb project in a fairly new issue of Everyday Practical Electronics. If anyone's interested I can find which issue. The mag is available as a digital download if it can't be found online.

Mornin' all, here you go -
https://www.dropbox.com/s/uo0mjeoh3lpqmbg/Everyday%20Practical%20Electronics%20-%20April%202018.pdf?dl=0
"Gods teeth", he muttered, "if these thing bite one will be singing soprano".

Mark Hammer

Re: Interesting spring reverb project
« Reply #14 on: March 17, 2019, 09:30:41 AM »
Your status as "prince of a man" is re-affirmed, Stephen.  Many thanks.

PRR

Re: Interesting spring reverb project
« Reply #15 on: March 17, 2019, 02:29:02 PM »
> absence of any trimming of the low end on that feedback path is, um, questionable.

As Greg says, there's heavy low-cut in the forward path. Bass won't build up.

C6 R10 is 350Hz. R9 C4+5 is also 350Hz. The recovery stage has 35Hz. Feedback gain will peak above 1KHz (where you hear it) and deep rumble is seriously suppressed.

Mark Hammer

Re: Interesting spring reverb project
« Reply #16 on: March 17, 2019, 03:17:38 PM »
You're right.  I should have looked at more than simply the feedback path.

Strategy

Re: Interesting spring reverb project
« Reply #17 on: March 19, 2019, 02:31:01 PM »
Late last year I tried building the Gaussmarkov version of the G. Forrest Cook spring reverb and late in the process encountered a number of inconsistencies between the build docs and the schematics and the original Cook page. The Gaussmarkov page had been revamped and old comments were gone. I had built the Stage Center Reverb as one of my earliest DIY efforts, ten years ago; it was successful but didn't sound good.

I just built a Surfybear spring reverb -- sounds amazing but really only works with guitar, not decent for my many keyboards and line level sources.
Still would love to build something for broader applications.

This ETI one looks do-able!

Strategy

ElectricDruid

Re: Interesting spring reverb project
« Reply #18 on: March 19, 2019, 07:07:33 PM »
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.

The reason I ask is I was studying reverb circuits looking for something suitable for an organ. I had an old Yamaha transistor organ from the Seventies and it did a fantastic Reggae stab sound if you turned the reverb up and played stacatto chords. Bliss. I want to get back there, so I guess I'm looking for something that can get pretty "twangy" when it's turned up too much or driven fairly hard. And that's a clue...I suspect that how hard you drive a reverb spring might affect the sound a bit. Does anyone have any experience to offer having tried different drive levels?

Thanks,
Tom

Rob Strand

Re: Interesting spring reverb project
« Reply #19 on: March 20, 2019, 11:30:17 PM »
Quote
I want to get back there, so I guess I'm looking for something that can get pretty "twangy" when it's turned up too much or driven fairly hard. And that's a clue...I suspect that how hard you drive a reverb spring might affect the sound a bit. Does anyone have any experience to offer having tried different drive levels?
Increased drive level helps with electronic noise and mechanical noise but I don't remember the tone changing much.

You could try a fairly high cut-off high-pass filter with a bit more post boost to push the level up.  Follow that with a small amount of low-pass filtering.
The mind often distorts without gain.