LIABILITIES, INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE, SHALL BE LIMITED IN DURATION TO THE DURATION OF THIS WRITTEN LIMITED WARRANTY. Some
states do not allow limitations on how long an implied warranty lasts, so the above limitations may not apply to you. IN NO EVENT
SHALL WE BE LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES FOR BREACH OF THIS OR ANY OTHER
WARRANTY, EXPRESS OR IMPLIED, WHATSOEVER. Some states do not allow the exclusion or limitation of special, incidental or
consequential damages, so the above limitation may not apply to you. This warranty gives you specific legal rights, and you may
also have other rights which vary from state to state.
METASONIX shall not be held liable for any incidental, consequential, or direct damages or expenses associated with the use or
misuse of its products. The audio output of this product is capable of damaging some types of solid-state audio equipment; such
use is entirely at the risk of the user. METASONIX does not guarantee that any of its products are designed for any particular use
or purpose. The entire risk of suitability and performance of this product lies with the user. Products manufactured and/or sold by
METASONIX are not authorized for use as critical components in devices used in life support and other systems whose failure or
performance could result in compromised safety or danger to life or property.
NOTE: All sales are FINAL, especially custom designs. Only a Metasonix authorized dealer is permitted to return products to
Metasonix for a refund or exchange.
What it does:
The RK5 is the world’s first lowpass gate in the style of the original Buchla 292 LPG—except using a vacuum tube instead of op-amps. It
implements the simple “Sallen-Key” lowpass filter of the 292 with a single triode as a cathode follower, plus CV control via a pair of Silonex
linear optocouplers. Unless the tube is deliberately clipped, signal distortion will be less than 0.1% and there will be no possibility of
crossover or slew distortion, since the circuit is pure Class A cathode follower.
The audio inputs have 500k ohm impedance. The CV inputs are about 3k ohms impedance and need to produce at least 3 mA to fully open
the optocouplers. The audio output is able to drive a 10k-ohm load (do not load it down with 600 ohms or you will lose a lot of signal volume).
USAGE
Connect the RK5 to an adequate Euro cabinet power supply. Connect an audio source to one channel’s INPUT, and connect its OUTPUT to
a monitor speaker or headphone amplifier.
For use as a VCA, connect an envelope generator or other CV source to the channel’s CV input. It should produce full volume when the EG
is triggered. The gate will be fully closed with 2.0v CV input or less, and opens fully when the CV reaches 5.0v. Between these points, the CV
will make the RK5 channel act like a simple low-pass filter with two poles. When closed there will be at least 40-50 dB of signal rejection;
when fully open, the output signal will be close to 95% of the input signal level (no, the RK5 does NOT provide any signal gain). It’s tubes,
and it’s BRUTE FORCE, so an RK5 might not completely cut off the signal or balance from channel to channel. If you expect total muting
when not triggered, use a VCA or a noise gate on the output of the RK5; or cascade the output of one channel to the input of the other.
The two channels are completely independent and should have no audible crosstalk. Note that the 17JK8 tube in the RK5 is a “dissimilar
dual triode” with high perveance, originally intended as a cascode amplifier in television and radio circuits. This makes it a good cathode
follower on a low-voltage power supply. Because the two triodes are different and the optocouplers vary from unit to unit, the two channels of
the RK5 will NOT sound exactly identical in operation. Do NOT assume the RK5 is “broken” if the two channels sound different when the
gate is opening or closing. This is normal.
Note: The RK5 can NOT be damaged by signal overdrive. In fact, it is doubtful if even a lightning strike or electrostatic shock will damage it.
There are no integrated circuits or transistors in the signal path. There is no high-voltage power supply in the RK5 as the tube operates
directly from the +12 and -12 rails.
MAINTENANCE
The RK5 requires a power supply pro12v and -12v DC at 100 mA. When first powered on, the RK5 briefly draws greater current, so
be aware of this when using a power supply to run it plus other modules. You MUST assure the power supply is able to handle the RK5 load
plus the load of other modules. Most power supplies on the market should be able to handle this load (although it depends on how many
other modules are being powered from the same supply)
The tube in the RK5 is being run VERY conservatively. It should last for tens of thousands of hours of normal use. Still, the RK5 tube
produces a lot of waste heat,
so we recommend shutting it off when not in use.
UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING, DO NOT REPLACE OR SUBSTITUTE THE TUBE YOURSELF!
Please note: not all tubes have easily visible heaters. They were not designed to offer pretty cosmetics. If you can't see a heater glowing, DO
NOT assume that tube is bad. If you hear an output signal, the RK5 tube is working. We get many foolish complaints of this type!
TUBE REPLACEMENT: despite its expected long lifetime, the tube might be damaged or develop faulty internal wiring connections, requiring
replacement. This particular RK5 was shipped, and wired for, a 17JK8 dual dissimilar triode. It is possible to use a few other tube types in the
RK5 without modification; types with low plate resistance, a heater of 12.6v to 20v, and pinout 9A will work. We would recommend 12AT7s,
12AU7s, 12AV7/5965, or a few similar types. Be warned that other types will draw more current from the power supply than the 17JK8 and
may not behave the same way.
Experiment at your own risk.
We recommend sticking with the original tube type;
t
here is no worry about
finding them, as 17JK8s are still quite easy to find and are available from distributors such as Radio Electric Supply (
vacuumtubes.net
) or
Antique Electronic Supply
(tubesandmore.com).
If you are confused or have ANY technical questions, feel free to contact us. Please DO NOT ASSUME and
if you are not an
experienced technician,
DO NOT TRY RANDOM TUBES OR MODIFY THE CIRCUIT IN ANY WAY!
495 N. Main #109, LAKEPORT CA 95453 USA
[email protected], www.metasonix.com
