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Spring reverbs (AKG BX20)


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Hey all,

 

When I think of "spring reverb", I think of cheap, tinny sounds from guitar amps. I recently checked out the UAD plugin version of the AKG BX20, and I was pretty blown away. I put it on a drum track with an EQ in front of it (I rolled off 300 Hz and below, and shelved the highs by -3dB above 5 KHz), and it sounded fantastic. I also put another instance on an EP solo and it sounded equally great.

 

I'm going to try it on a guitar track today. It's on sale and I have a coupon, so I think I'll spring for it (no pun intended). It definitely has a different sound than my EMT-140 plate emulation, the EMT-250, and the Lexicon 224 (my standard go-to's).

 

Fun stuff.

 

 

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The actual BX-20 was a very good reverb for its day. The satandard (when you didn't have a live chamber) was the EMT 140 plate, the approximate sound of which is famous by its proliferation. The BX-20 was what small but pro studios and broadcast facilities used.

 

It doesn't have coil springs like the Hammond spring reverb, it uses torsion bars like the fine sports cars of its day.

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It doesn't have coil springs like the Hammond spring reverb, it uses torsion bars like the fine sports cars of its day.

 

Very interesting, I never knew that. But given that we've just started spring, this seems like a really salient discussion.

 

FWIW here's my contribution to the world of coil spring reverbs. I created a circuit that used two tanks. The input coils were connected in parallel and out of phase, while the outputs were connected in series, in phase. The out of phase input greatly reduced the "sproings" and "boings" at the onset of reverb, while the reverb "bloomed" as the signals became more different during the decay. Meanwhile, the series outputs increased the level, so there was less noise. It sounded quite "plate-like" but also sounded somewhat like reverb sounds like onstage, where you don't hear a loud initial impulse but you hear the reflections.

 

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The actual BX-20 was a very good reverb for its day. The satandard (when you didn't have a live chamber) was the EMT 140 plate, the approximate sound of which is famous by its proliferation. The BX-20 was what small but pro studios and broadcast facilities used.

 

It doesn't have coil springs like the Hammond spring reverb, it uses torsion bars like the fine sports cars of its day.

 

 

 

That's not true. I bought a Bx20E new in 1978 and had it for years. There are springs in that wooden box. What akg sillily (is that a word) called torsional transmission something or other...ie... springs!!

 

You open the wooden door, there's a cardboard tube hanging in the center of the box, the box has various glued in foam-type (like auralex) wedges here and there and within the cardboard tube (and I do mean cardboard.... it actually comes apart after a number of years, are two sets of coiled..... springs. Big-uns compared to a reverb tank in a Fender twin but nonetheless.... springs.

 

You know what those springs always kinda reminded me of? The springs on a screen door to the front door of your house in the 1950s. Anyone remember those? I do. They'd cut your fingers off if you were a stupid kid, opened the front door wide, and stuck your fingers in between the springs to see what happens.

 

I had my entire bx20 completely apart at various times for various reasons and would often glance at my $2500 set of front door springs :)

 

The springs loop at the top and bottom of their path around a metal choke-hold router thingee that keeps the entire contraption intact. That then fits snugly into the cardboard tube and then that is suspended by these springy rubbbery strings that attach to the top of the wooden case inside. I always figured that if someone took the two springs off the upper/lower contraption and just laid them out on the floor, you'd have about fifteen feet of spring...x two. Not that I was about to try it just to get a measurment.

 

The door itself has the circuit panel on it and that, at various times over the years, caused all sorts of gremlin pops that I never tracked down. That was okay, you get to live with gremlins with this stuff.

 

My bx20 was basically a nice hall but not good for anything other than sparse ballads... no matter what the time setting, even down to 1.5 seconds. I would often gate and compress sends and returns to try to get other sounds but the bx20e was basically a one-trick pony for me... not a complaint.... but i DID spend $2500 cash for it new so it would've been cool for it to be more variable for me. Alas, it was a nice match for my plate and then beginning in 1985 or so, my WONDERFUL pcm60. I then owned what I considered a nice array of reverbs.

 

I had the bx20e in a small room about 40 feet from the control room most of the time and darn if it STILL wouldn't pick up noise from large trucks. Although the BOING of a bx20 is a pleasant boing.... not like thwapping the reverb in a Twin for fun.

 

I don't miss my bx20 and often solo printed reverb tracks I have on my old multitracks that used it.

 

I may get a UAD version at some point. I dunno. I have impulses of bx20s but don't really try them. Guess I've got to catch up with Craig's Apollo review to get re-enthused towards going UAD at some point.

 

But the bx20........... pure springs. don't let anyone try to fool you on that. By the way, I was going to add a bx10 a few years later and in auditioning it, it didn't sound anywhere as deep and ...okay....creamy... as my 20. So, I don't consider the 10s as a viable alternative. Like it matters out here in the 21st century anyway.

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I used the demo again today, and it really sounds great on drums. I roll off 300 Hz, and it gives a nice depth to snares and hi hats without clouding the mix.

 

The one thing about this plugin, is that it's hungry. You can run a dozen stereo EMT140's on a duo card, but only four stereo instances of the BX20. Lately I've been using the Waves versions of the 1176 and LA2A/LA3A, so my UAD has become more of a reverb card for me. I also use it for it's fantastic emulation of the SSL G-series bus compressor. But if you have an older system, the BX will tax it a bit.

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I bought a Bx20E new in 1978 and had it for years. There are springs in that wooden box. What akg sillily (is that a word) called torsional transmission something or other...ie... springs!!

 

You open the wooden door, there's a cardboard tube hanging in the center of the box, the box has various glued in foam-type (like auralex) wedges here and there and within the cardboard tube (and I do mean cardboard.... it actually comes apart after a number of years, are two sets of coiled..... springs. Big-uns compared to a reverb tank in a Fender twin but nonetheless.... springs.

 

Well, darn! 40 years of fantasy shot to hell. I've never taken one apart, only seen drawings in the marketing literature that clearly shows vertical rods. Maybe that was the artist's conception. But they were very clear about the "torsion" thing. I wonder if perhaps rather than the springs being pulled and pushed laterally (along its length) by the transducers, the spring is suspended from its end and the there's a perpendicualr rod attached to the end of the string that's pulled and pushed by the transducer, inducing a twisting motion in the spring. Did you see anything inside that looked sort of like that?

 

AKG did make a smaller, rack-mount sized reverb, the BX-10, that used an ordinary spring drive unit.

 

There were a few other "pro" spring units back in the late 1970s and '80s. I have a Great British Spring (which I don't think had anything British about it) that was a long PVC tube that used four Hammond spring units. I never pulled it apart to look at the wiring, but that might have been a good opportunity for playing with the polarity of the reverbs like Craig's design. It didn't boing too badly (that was its selling feature) except when you hit it. I had it in my mobile recording truck, and when $1000 digital reverbs became available, I replaced it with a Roland SRV-2000, which I still have, and still use.

 

The MicMix Master Room spring reverbs were somewhat popular, too. They had one model that had three springs that just hung free on the wall, as well as several rack mount self-contained models. Orban had one, too.

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I've never taken one apart, only seen drawings in the marketing literature that clearly shows vertical rods.

 

 

On brochure pics, the little pics of the internal mechanism do look like vertical rod-like elements from a nuclear reactor or Delorean time machine. But those outer area verticals are indeed the big, honkin' springs suspended between the top and bottom choke-hold pieces.

 

"Torsional Transmission System" was just a silly akg term for "springs". Sort of like tv commercials in the 50's for medicines for "post nasal drip" (ie... runny nose)

 

Whenever I'd be looking closely at the mechanism inside my bx20 (in true dissect it now and ask questions later routines), I was often tempted to touch the springs but never did as I could just see myself screwing them up. As big as they were/are, they were etched in random funny ways and I thought I'd squash a section if I dared touch it.

 

There was nothing mechanically moving to change r time between the 4sec-1.5sec etc settings. No motors of ANY type... and I know cuz I was lookin for them when my crated up Bx20e arrived that first day and I was monkeying around inside the box.

 

No transducers on the springs either. They were wound....looped.... around the top and bottom pieces (the choke holds I mentioned) and the ONLY electrical connections were from the ends of the springs.... at the bottom, running out of the cardboard tube, along the bottom of the wood box, slightly up the right side, around the door bottom door hinge...and into the circuit panel mounted on the door. When you'd open the door, there was a bit of play in the wiring to facilitate opening the door all the way up,

 

Basically..... and not to blow fantasies but.... the wiring was exactly like what you have on a guitar amp reverb tank,,, input to the springs (xlrs at the door fed to the circuit panel inside.....and then to the springs at one end....output of the springs at the other end to the amplifying circuitry/r-time control.... and onward.

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Basically..... and not to blow fantasies but.... the wiring was exactly like what you have on a guitar amp reverb tank,,, input to the springs (xlrs at the door fed to the circuit panel inside.....and then to the springs at one end....output of the springs at the other end to the amplifying circuitry/r-time control.... and onward.

 

The inputs and outputs aren't to the springs. There's no electrical current flowing through the spring. There's a transducer at either end of the spring. The transducer at the input end acts like a little loudspeaker that shakes the end of the string. The mechanical energy travels down the spring and the transducer at the other end acts like a microphone to pick it up and send it on to the amplifier.

 

It's indeed kind of mysterious inside the BX-20. Is this what yours looked ilke inside? IS there anything in those brick-sized metal things at each end? Or are that just there for a lot of inertia so the spring attachments will be very stable?

 

152454d1263185413-spring-reverb-guidance-bx20-1.jpg152456d1263185413-spring-reverb-guidance-bx20-4.jpg

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The inputs and outputs aren't to the springs. There's no electrical current flowing through the spring. There's a transducer at either end of the spring. The transducer at the input end acts like a little loudspeaker that shakes the end of the string. The mechanical energy travels down the spring and the transducer at the other end acts like a microphone to pick it up and send it on to the amplifier.

 

It's indeed kind of mysterious inside the BX-20. Is this what yours looked ilke inside? IS there anything in those brick-sized metal things at each end? Or are that just there for a lot of inertia so the spring attachments will be very stable?

 

152454d1263185413-spring-reverb-guidance-bx20-1.jpg152456d1263185413-spring-reverb-guidance-bx20-4.jpg

 

Looks exactly like mine except any framework was black, not blue like in your pic. You can see the silver springs path and.... see those every-so-often etchings on the springs? My springs were like that too. You can also see how the springs loop over the top piece... which they do the same way at the bottom. The entire frame in the pic slides out of the cardboard tube. Your input/output note may or may not be saying what I feel... which is that the entire unit is more or less the same principal as a guitar amp reverb tank.... on a bigger scale.

 

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