#big device

AKG - BX-15

two channel spring reverb

“ The BX-15 is designed for use in small studios. Two mechanically and electrically separate and isolated channels make it possible to handle two independent signal sources with different decay times (1.5 - 3.5 seconds), treble and bass settings and reverb intensity. “

Screwed Circuitz - The Tower

“ The Tower is a 36″ tall real spring reverb with several other built-in effects! Screwed Circuitz has experience building weird and unique effect pedals that interface with synths and other instruments, so The Tower is right in their ballpark (although it is much bigger than a pedal!). “

Well, especially for reverbs it might be useful to introduce a “big device” category, as “desktop unit” doesn’t exactly / exactly doesn’t nail it.

PHILIPS - el6910 ray delayer echo machine

“made in zurich ... early 1960s. ... the removable amplifier modules are all tube - recapped and with special  A class multi multi layer output transformers. ... the echo is made  from a revolving (600 or 300 RPM) precision turbine wheel with a magnetic edge coating. there are 6 shift-able heads mounted around the wheel  . erase - record - and 4 playback . they are all set a paper thickness off the magnetic surface. the record amp explodes a super amped signal across the air gap onto the mag and the play heads pick a tiny signal back off . the 4 play amps super-amp it back up and mix it together in the output amp . the controller unit feeds some of that mixture back to the record input to achieve echoing regeneration effects. the controller has all manner of adjustable ness and push button more go  action. all in all - a fabulous and fun machine to stand up against and play with.  of course it has a fat mic input. and an onboard self monitoring amp with 8" speaker. weighs 216 KG and is 2.03 meters tall. comes with service - instruction manual.”

AKG - BX25 spring reverb

“1981 ... Made in Austria * RARER THAN MERMAID TEARS *

The father of all springs, "The AKG BX25". This model was an improvement on the AKG BX20. They were able to increase the spring length by 25% while reducing the size by 1/3 ...

AKG BX-25 was the next step in true studio and transportable two-channel reverberation. Replacing the BX-20, the BX-25 continues to provide both the quality and operating features required in studio applications. The BX-25 is based on the patented and extremely successful Tortional Transmission Line principle used in all AKG reverb units. The TTL-SYSTEM has been improved by extending the overall length of the spring by about 25% over the BX-20 yet at the same time reducing the overall size of the BX25 dramatically by about one-third. The two Tortional Spring Systems are physically separated and isolated providing a dramatic increase in channel separation resulting in greater than 60 dB crosstalk. Independent decay-time adjustment (via R25 remote control, included). High and low frequency equalization, external input and output level adjustments and dry/reverb signal mixing are provided for each of the two electronically and acoustically separate channels. Decay time is adjusted silently through the use of motional feedback. In addition to the shelving type frequency equalization, AKG has incorporated a high-cut filter at the input/reverb drive amplifier. This enables the selection of a bright, more aggressive sound or a more mellow natural reverberation sound. Plug-in PC boards are used for the electronics within the control module. This module may be removed from the main housing and operated remotely via an optional extension cable up to 30 feet away from the reverb section. The exciting news is the new M-250 Digital Delay module that may be added to a BX-25 at any later time or ordered within the BX-25. As a complete unit (reverb and delay). The BX-25ED incorporates all the reverb features mentioned above plus digital delay. The new digital delay module provides: remote mix control between reverb signal and reverb plus individual reflections. Individually adjustable level for each of the discrete reflections in 2dB steps from original level down to 20dB below the original level, descrete reflections are available as reflections only or mixed with reverb; initial delay for the reverb signal is switchable to 0, +30ms and +60ms; two discrete reflections for each channel may be adjusted in 6ms steps from 6ms to 60ms; bandwidth reflections: 12kHz. At the rear of the digital delay module are six XLRconnectors - two input and four output. Two of the output connections allow for fixed echoes only. The second set of output connections allows for mixing between reverb only and reverb plus echoes (using R25 remote). REVERB SECTION: • Decay time: 1.5 to 3.5 seconds continuously and in ­dependently adjustable for each channel on remote control • Nominal input level: adjustable to -22, -6, 0, +6 and + 12 dBm (0 dBm ~0 775 volts) • Maximum permissible input level: 35 dB above selected input level • Input limiters: Threshold = 6 dB above selected nominal level Range = approx. 30 dB • Input impedance: ~ 10 k ohms per channel, transformer balanced • Nominal output level: adjustable to -6, +6 and +12 dBm • Maximum output level: Associated equipment should have input headroom of at least 20 dB over selected nominal output level to accommodate instantaneous peaks in reverb signal • Output impedance: 300 ohms (+12 dBm); 100 ohms (+6 dBm) transformer; 15 ohms (-6 dBm) balanced • Recommended load impedance: 600 ohms (+12 dBm); 200 ohms (+6 dBm); 50 ohms (-6 dBm) • Frequency range: 50-4,000 Hz in position 50-8,000 Hz in position • Signal to noise ratio: ~ 76 dB r. m. s. weighted ~ 75 dB r. m. s. unweighted • Bass control range: +/-10dB at 150 Hz • Treble control range: +/-5 dB at 5,000 Hz • Crosstalk between channels: ~ 60 dB • Level difference between the channels: adjustable compensation • Acoustical feedback safety: ~ 120 dB • Operating temperature range: - 10° to +60° C • Power requirements: 115/230 volts, 50-60 Hz, 80 VA • Max permissible inclination during operation: 10° (20%)“

wardrobe-reverberation

AKG - BX20 reverberation unit

(BX10 and BX5 in the middle and on the right)

“... produced in the late 1960s ... is a 2-channel unit that has a separate remote for controlling decay time ... One interesting characteristic is the fact that it can be used in either mono or stereo. The inputs in the unit can be paralleled or used separately. Another feature that makes this piece of gear so special is that it is in a league of its own. It is not your common plate or chamber reverb even though it has characteristics of each.”

“Im prä-digitalen Zeitalter beschränkten sich die Möglichkeiten der künstlichen Hall Erzeugung auf Hallkammern und Platten, beides vor allem für transportable Anwendungen denkbar ungeeignet. Als man gegen Ende der 60er-Jahre im Hause AKG über mögliche Alternativen − vor allem für den Rundfunkbereich − nachdachte, verwarf man den Gedanken an ein Federhallgerät zunächst wieder. Die klanglichen und technischen Eigenschaften wurden als durchweg ungeeignet bewertet. Stattdessen ersannen die AKG-Cheftechniker Werner Fidi und Dr. Görike einige bisweilen fast bizarr anmutende Konzepte, wie etwa eine aus Glas bestehende Hallplatte sowie komplexe Anordnungen von Resonatoren aus perforierten und mit Walzenkörpern versehenen Messing- und Alustangen. Da die gesteckten Ziele − ausreichend lange Hallzeiten bei hoher Resonanzfrequenzdichte − so nicht erreicht wurden, verfiel man schließlich doch wieder auf Experimente mit Spiralfedern.Die Hallfeder wird studiotauglichLangwierige Bemühungen führten schließlich zu einem Weg, lange Hallfedern durch mehrfache Faltung in einem recht kompakten Gehäuse unterzubringen. Der »Antrieb« der Federn geschah mittels aufwendig entwickelter Magnetsysteme. Aber selbst Federn von bis zu 2,5 m Länge lieferten keine befriedigenden Klangergebnisse. Der Zufall soll Werner Fidi schließlich zu einer Lösung geführt haben, welche die Höhenwiedergabe des Systems entscheidend verbesserte: Durch kontrolliertes Erhitzen (Tempern) ließ sich der Frequenzgang deutlich erweitern. Um die Diffusität bzw. Dichte des Hallsignals zu erhöhen, behandelte Fidi die Federn zudem mit gezielten Verätzungen. Den Klang in tiefen Lagen optimierte er mittels eingedellter Federwindungen in unterschiedlichen Abständen. Den letzten klanglichen Schliff lieferten speziellen Dämpfer-Elemente, die man über den Federweg verteilte. Nun musste das System »nur noch« transportsicher »verpackt« werden. Auch hier entwickelten Fidi und seine Kollegen eine aufwendige, aber funktionale Lösung, die schließlich ab 1971 in Form des 46 kg schweren »Kleiderschrankes« namens BX 20 zur Legende wurde.“