Drunk thoughts: Analog reverb?

[somnif]

Howdy all, I've been drinking!

And as such, I've been thinking. The Belton brick is probably the most popular reverb unit on the market right now, popping up in everything from DIY pedals to commercial modeling amps. It is basically 3 interplaying PT2399s, the most common digital delay chip on the market right now.

So...

Would it be possible to replicate this interplay using bucket brigades? The three chips in the brick run delays at 87.5 ms, 67 ms and 50 ms with a bit of LFO modulation to blend them together (source: https://www.google.com/patents/US8204240), which I imagine are within the realm of possibility of BBDs. Has this been attempted? Is there a reason beyond impracticality that if it hasn't? (Although if my law classes are remembered correctly the language of that patent is vague enough to cover any IC containing reverb unit. That seems unfair)

Inquiring (and inebriated) minds want to know!

[Scruffie]

There were specialty BBD chips intended for this, the MN3011 (long extinct, what few remain as they were doubtful made in as large a numbers as any of the other BBDs should be saved for repairs) being the most well known having 6 'taps' at varying delay times and having tried the few circuits that use them, I can assure you they sound awful as reverbs, for the added complexity you're better off with just a slapback echo with lots of feedback, there's not much difference in the sound.

I don't think any of the commercial pedals at the time that used them were big sellers, while it did offer the benefit of a spring sound in a small package at a (relatively) cheap price before digital was more affordable, it was a poor imitation at best and still expensive as this price list shows for the EHX Solid State Reverb;


Could it be made to sound good? Quite possibly but the circuit would be monstrous and for the sake of using a BBD to call it analog, it's just not worth it.

Going a bit more in depth, you'd need first of all to control noise and still get some bandwidth so you'd need a compander, then each BBD (let's assume three 3208s if you want to achieve 87.5mS as the maximum time) will need its own filtering to imitate natural reverb so that's 4 low pass filters minimum including the input one which you'll have to calculate nicely to sound good, then each BBD needs a different clock frequency to give varying delay times so you'd need a master clock and a 4013 to divide it twice for the other 2 BBDs (which also gives you fixed interval delay times which isn't helpful in imitating the sound) and all the wrap around circuitry, if you wanted to vary the delay intervals each BBD would need its own clock and then you'd have to worry about heterodyning between them.

[thesmokingman]

6g15 reverb or the surfy bear reverb, doesn't much more analog than that.

[midwayfair]

Little spring tanks are cheap. The surfy bear is your best bet. Hardly compact, though.

[somnif]

Yeah, I suppose I was thinking in terms of "discrete circuitry" rather than spring tanks, but the information is interesting. EHX had another BBD based pseudo-reverb in their "Stereo Ambitron" unit (mono-to-stereo emulation) based around the SAD series chips.

http://smg.photobucket.com/user/zero_thehero/media/schematics/AMBITRON.jpg.html

Unfortunately the thing is rare enough that I can't find a demo of it. Fascinating though.

I gotta wonder though. Has some electro-engineering student been desperate enough for a semester project to cook one up at some point over the years. I've seen some seriously goofy pedal designs down the years that came about that way (using the term pedal lightly, most of them would be boards the size of cereal boxes).

[selfdestroyer]

Im working on a couple of these:
http://www.op-electronics.com/en/delay-reverb-and-chorus/292-spring-reverb-8000292716445.html

It uses one of the mini Accutronics Blue Reverb tanks. Its a pretty cool project, I need to finish up my artwork and drill template.

Cody

[Scruffie]

Yeah, I suppose I was thinking in terms of "discrete circuitry" rather than spring tanks, but the information is interesting. EHX had another BBD based pseudo-reverb in their "Stereo Ambitron" unit (mono-to-stereo emulation) based around the SAD series chips.

http://smg.photobucket.com/user/zero_thehero/media/schematics/AMBITRON.jpg.html

Unfortunately the thing is rare enough that I can't find a demo of it. Fascinating though.

I gotta wonder though. Has some electro-engineering student been desperate enough for a semester project to cook one up at some point over the years. I've seen some seriously goofy pedal designs down the years that came about that way (using the term pedal lightly, most of them would be boards the size of cereal boxes).

The ambitron's not really a reverb, paraphrasing the designer it was designed to add a stereo sounding field to his mono records (one schematic version even includes the amp section for this) so it's for separating tracks. I don't think a demo would be very exciting, at best it might sound like a short slap back/double track, but some old hi-fi's included a similar set up (and occasionally even have a MN3008 in them) if you want an idea of it. Also just to note the circuit was later updated to the MN3005.

I'm sure it has been done many times, it wouldn't be hard to do, I could probably do it on the breadboard in a day if I wanted but, there's better uses of time for a better sound. Reading in to the theory behind reverb might help explain why BBDs make a poor choice for it, besides as you say, cereal box sized circuit boards.

[somnif]

Ah, I just noticed in the EHX catalog page you listed earlier it said "With reverb" so I used the term. Thanks for the info!

[gordo]

Excellent prices.  I ordered one of each :-)