METASONIX RK6 User manual

RK6 RESONANT
LOWPASS FILTER
user's manual
Copyright 2018 Metasonix. All rights reserved.
Please read all of this before using it!
RETAIN INSTRUCTIONS: The safety and operating instructions should be retained for future reference.
EED WARNINGS: All warnings on the RK6 and in the operating instructions should be adhered to.
FOLLOW INSTRUCTIONS: All operating instructions should be followed.
WATER AND MOISTURE: The RK6 should not be used near water (e.g. near a bathtub, washbowl, kitchen sink, laundry tub, in a wet
basement, near a swimming pool etc.). Care should be taken so that liquids are not spilled onto or near the enclosure.
VENTILATION AND COOLING: The RK6 normally operates warm to the touch. The tube generates considerable heat. It MUST be
situated so that its location or position does not interfere with convective cooling. The RK6 MUST NOT be used on a bed, sofa rug
or similar surface which may prevent proper cooling. It is NOT a toy. If the RK6 is mounted in a synthesizer rack or other built-in
installation, space must be left around it to allow convection cooling. Use great caution if handling the RK6 when it is powered up.
EAT: The RK6 MUST be situated away from heat sources such as radiators, heat registers, stoves, or other devices (including
power amps) that produce heat.
POWER SOURCE: The RK6 should be connected to a power supply ONLY of the type described in the operating manual or as
marked on the RK6. WARNING: Each RK6 requires +12v at 100mA and -12v at 5 mA, with a brief transient consumption of 200 mA
at first power-on. The cabinet power supply must be able to deliver this current. Most available switch-mode power supplies
should be able to handle this load. WARNING: The tube becomes hot in normal operation and should not be touched after 10
minutes with power applied.
CLEANING: The RK6 should only be cleaned with a soft cloth moistened with water. Disconnect all possible power supplies before
attempting to clean or handle.
NON-USE PERIODS: The RK6 should be shut off when left unused for a long period of time.
MEC ANICAL: protect the RK6’s tube from damage. Use of a Eurorack cabinet with a removable lid tall enough to protect the tube
is recommended, if the synthesizer is to be moved or transported. Remove the tube from the socket if the cabinet's lid will not
clear it.
DAMAGE OR TUBE REPLACEMENT REQUIRING SERVICE:
The RK6 should be serviced by qualified service personnel when:
--The power supply has been damaged;
--The RK6 has been dropped, physically damaged, or subjected to force;
--Liquid has been spilled onto the RK6 or it has been exposed to rain;
--The RK6 does not appear to operate normally or exhibits a marked change in performance.
SERVICING: The user should not attempt to service the RK6. All servicing should be referred to qualified service personnel.
METASONIX LIMITED WARRANTY and standard legal disclaimer
Thank you for purchasing this Metasonix product. The following terms and conditions apply:
1. Warranty period is for ONE YEAR from date of purchase with proof of purchase submitted. Warranty covers electrical failure of
vacuum tubes and gas-filled tubes, except in cases explained in 3 below.
2. Operating instructions must be followed. This device was intended ONLY for use by AUDIO AND MUSIC PROFESSIONALS.
IT IS NOT INTENDED FOR USE BY ORDINARY ONSUMERS!!
Product must not have been damaged as a result of defacement, misuse, abuse, neglect, accident, destruction or alteration of the
serial number, improper electrical voltages or currents, repair, alteration or maintenance by any person or party other than our own
service facility or an authorized service center, use or installation of non-Metasonix replacement parts in the product, or the use of
this product outside of the U.S.A. or Canada (except as a product distributed by an authorized Metasonix dealer), or modification
of the product in any way, or incorporation of the product into any other products, or damage to the product caused by accident,
fire, floods, lightning, or acts of God, or any use violative of instructions furnished by Metasonix.
3. Obligations of Metasonix shall be limited to repair or replacement with same or similar unit, at our option. To obtain repairs
under this warranty, present the product and proof of purchase (e.g. bill or invoice) to the authorized Metasonix service center,
transportation charges prepaid. When returning the product for repair, please pack it very carefully, preferably using the original
packaging materials. Please also include an explanatory note.
IMPORTANT:
To save yourself unnecessary cost and inconvenience, please check carefully that you have fully read and followed the
instructions in this instruction manual.
This warranty is in lieu of all other expressed warranties, obligations or liabilities. ANY IMPLIED WARRANTIES, OBLIGATIONS, OR
LIABILITIES, INCLUDING BUT NOT LIMITED TO T E IMPLIED WARRANTIES OF MERC ANTABILITY AND FITNESS FOR A

PARTICULAR PURPOSE, S ALL BE LIMITED IN DURATION TO T E DURATION OF T IS 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
S ALL WE BE LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES FOR BREAC OF T IS OR ANY OT ER
WARRANTY, EXPRESS OR IMPLIED, W ATSOEVER. 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 RK6 is a TOTALL UNIQUE product, one that never existed before. It is a Sallen-Key lowpass filter with a feedback loop, to allow it to
resonate. There are no integrated circuits or transistors in the signal path. It is a PURE TUBE design, the sort of design that might have been
invented in the 1950s if anyone had dared to create a tunable lowpass filter for musical uses before Moog and Buchla. It even uses a
coupling transformer to provide the proper phase of feedback signal --- purely a “classic good old days” approach, and one rarely seen in the
21st century. Two “vactrol” optocouplers tune the filter, and another coupler allows CV control of the filter’s resonance.
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. Signal gain with the filter fully open is about 0.9. 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 RK6 to an adequate Euro cabinet power supply. Connect an audio source to the INPUT, and connect its OUTPUT to a monitor
speaker or headphone amplifier. The RK6 is quite easy to overdrive with a Euro-level audio signal so attenuation might be needed for best
filtering effect. Adjust IN LEVEL as needed.
Connect an envelope generator or other CV source to the TUNING CV input. It should open the filter fully when the EG is triggered. The filter
will be fully closed with 0v CV input, and opens fully when the CV reaches 3.0v, when the TUNE control is properly adjusted (it acts as an
offset control). Between these points, the CV will make the RK6 channel act like a low-pass filter with two poles. It follows a more-or-less Hz/
v tuning curve, and might be adjustable to track with a Hz/V VCO if desired; a CV attenuator and careful adjustment might be needed to get
this effect.
The RESON CV input works in parallel with the RESONance control. Full variation of resonance is had from 0v to 2v when the control is
adjusted properly. Note that full resonance oscillation will only occur at frequencies above 700-800 Hz and not in the bass region; this is
normal and expected. Each RK6 is slightly different from each other one in behaviour and sound effects, so if you buy two of them, don’t be
surprised if they vary slightly.
If you want to use it as a lowpass gate and expect total muting when not triggered, use a VCA or a noise gate on the output of the RK6.
Adjust TUNE appropriately and RESON to taste; beware of feedback “howling” when increasing resonance. When fully turned down there
will be at least 40-50 dB of signal rejection; when fully open, the output signal will be close to 90% of the input signal level (no, the RK6 does
NOT provide any signal gain). It’s tubes, and it’s BRUTE FORCE, so it won’t be a “perfect filter”. But it won’t sound like anything else.
Note: The RK6 can NOT be damaged by signal overdrive. In fact, it is doubtful if even a lightning strike or electrostatic shock will damage it.
MAINTENAN E
The RK6 requires a power supply producing +12v at 100 mA and -12v at 5 mA. When first powered on, the RK6 briefly draws greater
current, so be aware of this when using a power supply to run it plus other modules. ou MUST assure the power supply is able to handle
the RK6 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 RK6 is being run VER conservatively. It should last for
tens of thousands of hours of normal use. Still, the tube produces a lot of waste heat, so we recommend shutting power off when not in use.
UNLESS OU KNOW EXACTL WHAT OU ARE DOING, DO NOT REPLACE OR SUBSTITUTE THE TUBE OURSELF!
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 RK6 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 RK6 was shipped, and wired for, a 17JK8 dual dissimilar triode. It is possible to use a few other tube types in the
RK6 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; there 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 T E CIRCUIT IN ANY WAY!
495 N. Main #109, LAKEPORT CA 95453 USA
[email protected], www.metasonix.com