Model 6176 Channel Strip Universal Audio Part Number 65-00053 Universal Audio, Inc. Customer Service & Tech Support: 1-877-MY-AUDIO Business, Sales & Marketing: 1-866-440-1176 www.uaudio.
Notice _____________________________________________________________ This manual provides general information, preparation for use, installation and operating instructions for the Universal Audio 6176. The information contained in this manual is subject to change without notice. Universal Audio, Inc. makes no warranties of any kind with regard to this manual, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Universal Audio, Inc.
A Letter From Bill Putnam, Jr. _____________________________________________________________ Thank you for purchasing the 6176 Channel Strip. The 6176 combines a modified channel of our 2-610 vacuum tube microphone preamplifier with our 1176LN all discrete solid state FET-based limiter / compressor. The 2-610 was inspired by the microphone preamp section of the original 610 console designed by my father, M.T. “Bill” Putnam, in 1960.
Important Safety Instructions _____________________________________________________________ Before using this unit, be sure to carefully read the applicable items of these operating instructions and the safety suggestions. Afterwards, keep them handy for future reference. Take special care to follow the warnings indicated on the unit, as well as in the operating instructions. 1. Water and Moisture - Do not use the unit near any source of water or in excessively moist environments. 2.
Table of Contents _____________________________________________________________ Notice ...................................................................................................................................ii A Letter From Bill Putnam, Jr. .................................................................................................iii Important Safety Instructions ..................................................................................................
The Two Page, Two Minute Guide To Getting Started _____________________________________________________________ No one likes to read owner’s manuals. We know that. We also know that you know what you’re doing—why else would you have bought our product? So we’re going to try to make this as easy on you as possible. Hence this two-page spread, which we estimate will take you approximately two minutes to read.
The Two Page, Two Minute Guide To Getting Started _____________________________________________________________ Step 8: On the right side of the front panel, set the Ratio switch to BP (fully counterclockwise) in order to temporarily bypass the 6176 limiter / compressor section. Set the Meter switch to PRE so that the meter displays the output level of the signal leaving the 6176 preamp section. Step 9: Power on the 6176. The purple LED above the power switch will light up.
Front Panel _____________________________________________________________ NOTE: The left side of the 6176 front panel contains all preamp controls, while the right side contains all limiter / compressor controls. All controls (except the Level, Attack, Release, Input, and Output knobs) are stepped, allowing settings to be easily reproduced. (1) Gain - Adjusts the gain of the input stage in 5 dB increments. Turning the Gain switch clockwise raises the gain.
Front Panel _____________________________________________________________ Hi-Z - Selects the input signal arriving at the front panel unbalanced ¼" jack Hi-Z connection. ( see #5 on page 4) Intended for the direct connection of electric guitar, electric bass, or any instrument with a magnetic or acoustic transducer pickup, this can be set to either 47K ohms or 2.2M ohms. The 47K ohms setting is best suited for the -10 dBv level signals typically provided by active basses and guitars, while the 2.
Front Panel _____________________________________________________________ (8) High Boost/Cut - Selects the amount of cut or boost applied by the high shelving filter. The positive and negative numbers on the front panel denote dB values (-9, -6, -4.5, -3, -1.5, 0, +1.5, +3, +4.5, +6, +9). (9) Low Frequency - Selects the corner frequency for the low shelving filter. Available frequencies are 70 Hz, 100 Hz, and 200 Hz. (10) Low Boost/Cut - Selects the amount of cut or boost applied by the low shelving filter.
Front Panel _____________________________________________________________ (14) Attack - Sets the amount of time it takes the limiter /compressor to respond to an incoming signal and begin gain reduction. The 6176 attack time is adjustable from 20 microseconds (FAST) to 800 microseconds (SLOW). The attack time is fastest when the Attack knob is in its fully clockwise position, and is slowest when it is in its fully counterclockwise position.
Front Panel _____________________________________________________________ (18) Output - Determines the final output level of signal leaving the limiter / compressor section. Once the desired amount of limiting or compression is achieved with the use of the Input control, the Output control can be used to make up any gain lost due to gain reduction. Set the Meter switch to the Compressor (COMP) position while using the Output knob to set the desired output level.
Front Panel _____________________________________________________________ Setting the 6176 to a ratio of ALL causes distortion to increase radically due to a lag time on the attack of initial transients and constant changes in the attack and release times as well as a change in the bias points. Consequently, the meter will go wild, often resting at maximum. Don’t worry, though – you won’t be harming the 6176 by using this mode! Engineers typically use “All” mode on drums or on ambience or room mics.
Rear Panel _____________________________________________________________ (1) Limiter / Compressor LINE OUTPUT - A balanced XLR connector carrying the line-level output signal of the 6176 limiter/compressor section. Pin 2 is wired positive (hot). (2) Limiter / Compressor LINE INPUT - Connect line-level input signal (coming from a device such as a mixer, DAW, tape machine, or signal processor) to the limiter/compressor section via this balanced XLR connector. Pin 2 is wired positive (hot).
Interconnections _____________________________________________________________ When operating in JOIN mode, the rear panel Preamp LINE OUT and the Limiter/Compressor LINE IN jacks are automatically disconnected. For most applications, we recommend keeping the 6176 preamp Level control set between 7 and 10. Adjustments can then be made to the preamp Gain, Impedance, and Filter controls, as well as the various limiter/compressor controls, to achieve the optimum sound for your signal source.
Insider’s Secrets _____________________________________________________________ 6176 Versus 2-610 / 1176LN Why go for the 6176 over a 2-610 and an 1176LN chained together? One factor, of course, is price: the 6176 costs significantly less than a combination of a 2-610 and an 1176LN. Another factor is space: the 6176 combines both signal processors in a single chassis, thus saving potentially valuable real estate space in your rack.
Insider’s Secrets _____________________________________________________________ And reviewer George Shilling, writing for Resolution magazine in their May/June 2003 issue, said, “The [6176 preamp] section is everything I remember about the 2-610—a big warm, clear character, enhancing beautifully.
Insider’s Secrets _____________________________________________________________ things up; maybe a little bottom end gets squeezed out or maybe they are just sort of excitingly solid state... The big thing for me is the clarity, and the improvement in the top end.” Last but not least, if you’re trying to get an extra dose of attitude in a lead vocal, try ALL mode with short attack and release times.
Insider’s Secrets _____________________________________________________________ Remember, the limiter/compressor section in the 6176 is program-dependent. That’s an important feature that allows it to be used in a musical, percussive way. Let’s say you have a medium tempo, 4/4 rock beat—an excellent scenario for using ALL mode. In this application, you’d probably have a lot of input level, a slowish attack (so that the transients sneak through), and a quick release. The sonic result is extraordinary.
Insider’s Secrets _____________________________________________________________ “Treating some electric guitar sounds that had been previously recorded,” Curwin added, “allowed the opportunity of experimenting with the different ratios and the attack and release controls, and with careful positioning it was possible to give the guitar a lot of punch and an apparent sense of urgency in the mix.” The 6176 can serve as a perfect complement for acoustic and electric bass as well.
Insider’s Secrets _____________________________________________________________ Versatility Of course, no preamp or compressor, no matter how well designed, is perfect for all applications or for all microphones. Fortunately, the 6176 is designed to work with a wide variety of microphones and signal sources, and we think you’ll find that it acts as the perfect sonic complement for most of them.
Insider’s Secrets _____________________________________________________________ Mixing Applications The line-level input of the the 6176 allows it to be used in mixing as well as tracking. Even if no equalization is used, and even if the limiter/compressor section is set to Bypass, the signal continues to pass through the transformers, the tubes, and the polarity-reverse circuits, making it extremely useful for coloration of tracks.
The Technical Stuff _____________________________________________________________ History of the 6176 Preamp section The lineage of the 6176 can be traced back to two devices long revered by audio engineers the world over: the 610 preamplifier and the 1176LN limiting amplifier. The preamp section of the 6176 was inspired by the 610 console built by Bill Putnam Sr. in 1960 for his United Recording facility in Hollywood.
The Technical Stuff _____________________________________________________________ At least one 610 module is still in use at Ocean Way Studios, site of the original United Recording facility. Allen Sides, who purchased the studio from Putnam, personally traveled to Hawaii to collect the 610 console that was used to record the live “Hawaii Calls” broadcasts.
The Technical Stuff _____________________________________________________________ Numerous design improvements followed, resulting in at least 13 revisions of the 1176. Plunkett’s LN circuitry was originally encased within an epoxy module, but a subsequent redesign fully integrated these improvements with the main circuit board, resulting in revision D.
The Technical Stuff _____________________________________________________________ We here at Universal Audio, have two goals in mind: to reproduce classic analog recording equipment designed by Bill Putnam Sr. and his colleagues, and to design new recording tools in the spirit of vintage analog technology.
The Technical Stuff _____________________________________________________________ Compressor / Limiter Basics The function of a compressor is to automatically reduce the level of peaks in an audio signal so that the overall dynamic range—that is, the difference between the loudest sections and the softest ones—is reduced, or compressed, thus making it easier to hear every nuance of the music.
The Technical Stuff _____________________________________________________________ Input Signal and Threshold The first and perhaps most significant factor in compression is the level of the input signal. Large (loud) input signals result in more gain reduction, while smaller (softer) input signals result in less gain reduction. Threshold is another important factor. It is a term used to describe the level at which a compressor starts to work.
The Technical Stuff _____________________________________________________________ great, results in virtually no increase in output level. Note that the 6176 has been designed so that selecting higher ratios also raises the threshold level. As an aside, an expander is the opposite of a compressor: a device which increases the dynamic range of a signal. For example, a 10 dB change in the input signal might result in a 20 dB change in the output signal, thus “expanding” the dynamic range.
The Technical Stuff _____________________________________________________________ Output (Makeup Gain) Finally, an output control is employed to make up for the gain reduction applied by the gain reduction circuitry; on the 6176, this is the function of the Output knob.
The Technical Stuff _____________________________________________________________ Impedance Matching Depending upon their design, different microphones provide different output impedances. Typical mic impedances range from as low as 50 ohms (the symbol for ohms is ) to thousands of ohms (K ohms). The 6176 Mic input can be set to either 500 ohms or 2.0K ohms, allowing it to accommodate virtually every kind of microphone.
The Technical Stuff _____________________________________________________________ Maintenance Information Meter Calibration The 6176 meter may occasionally need to be calibrated. This is accomplished by adjusting the GR Zero Set pot, located through a small hole on the front panel between the Input and Output knobs. The procedure for adjusting the meter is as follows: 1) Power on the 6176 and allow it to warm up for five minutes. 2) Set the Meter switch to the GR (Gain Reduction) position.
The Technical Stuff _____________________________________________________________ Stereo Operation With the use of an external 1176 Stereo Adapter (1176SA), available from Universal Audio, two 6176s can be connected for stereo operation. Note: When used in stereo operation, the Attack and Release controls on the two 6176s will interact so that changing the Attack or Release times on either device changes that of both devices.
The Technical Stuff _____________________________________________________________ Changing the Internal Voltage Selector The 6176 can operate at 115V or 230V. To change the internal voltage selector, wait five minutes after power down, then unplug the AC power cord from the rear chassis and remove the top cover. As shown in the photograph below, there is a connector that can be plugged into one location or another to configure the unit for 115V or 230V operation.
The Technical Stuff _____________________________________________________________ 6176 Circuit Details The fundamental problem facing Bill Putnam Sr. when he began designing the 1176 limiter was how to keep its FET operating within its linear region in order to keep distortion sufficiently low.
The Technical Stuff _____________________________________________________________ Input Section Figure 2 - Input Section As shown in Figure 2, the 1176 input section is comprised of an adjustable passive attenuator followed by a transformer. The purpose of this section is to reduce the signal level so as not to overdrive the FET based gain reduction stage. Additionally, the adjustable input level is used to control the amount of compression. This input circuit was used in Revisions A-F.
The Technical Stuff _____________________________________________________________ Figure 4 - Using an FET as a voltage-variable resistor. The combination of R5 and Q1 acts as a voltage divider which controls the gain. Figure 4 shows how the FET’s resistance determines the gain of this section. Resistor R5 and the FET essentially comprise a voltage divider circuit. The lower the FET’s resistance, the less gain this stage will have.
The Technical Stuff _____________________________________________________________ Output Amplifier The output amplifier is a Darlington pair followed by a class A stage based on a 2N3053 transistor. The 1176 output stage was essentially the same as the Universal Audio 1108 pre-amplifier. The output transformer is a custom transformer designed by Bill Putnam Sr. Aside from offering output impedance matching, the transformer forms an integral part of the feedback network used to stabilize the output stage.
The Technical Stuff _____________________________________________________________ A bias level is applied to the diodes by the Compression Ratio pushbutton switches. This controls the threshold of limiting, and is adjusted for the correct value as determined by the currently selected compression ratio selection. R55 controls the compressor’s attack time by regulating how fast C22 is charged. Likewise, R56 determines the compressor’s release time by controlling the rate at which C22 discharges.
Glossary of Terms _____________________________________________________________ Ambient noise - Low-level noise created by environmental factors such as fans, air conditioners, heaters, wind noise, etc. Attack time - Describes the amount of time it takes compressor circuitry to react to and reduce the gain of incoming signal. A compressor set to a fast attack time kicks in almost immediately and catches transient signals of very brief duration, reducing their level and thus "softening" the sound.
Glossary of Terms _____________________________________________________________ dBV - Short for “decibels as referenced to voltage,” without regard for impedance; thus, one volt equals one dBV. DI - Short for “Direct Inject,” a recording technique whereby the signal from a high-impedance instrument such as electric guitar or bass is routed to a mixer or tape recorder input by means of a “DI box,” which raises the signal to the correct voltage level at the right impedance.
Glossary of Terms _____________________________________________________________ Low shelving filter - An equalizer circuit that cuts or boosts signal below a specified frequency, as opposed to boosting or cutting on both sides of the frequency. Makeup gain - A control that allows the overall output signal to be increased in order to compensate (“make up”) for the gain reduction applied by the compressor.
Glossary of Terms _____________________________________________________________ Ribbon microphone - A type of microphone that works by loosely suspending a small element (usually a corrugated strip of metal) in a strong magnetic field. This "ribbon" is moved by the motion of air molecules and in doing so it cuts across the magnetic lines of flux, causing an electrical signal to be generated. Ribbon microphones tend to be delicate and somewhat expensive, but often have very flat frequency response.
Recall Sheet _____________________________________________________________ 39
Specifications _____________________________________________________________ Preamp: Microphone Input Impedance Balanced Line Input Impedance Hi-Z Input Impedance Maximum Microphone Input Level Maximum Output Level Internal Output Impedance Recommended Minimum Load Frequency Response Maximum Gain Signal-to-Noise Ratio Selectable, 500 (ohms) or 2k 20k Selectable between 2.
Additional Resources/Product Registration/Warranty/Service & Support _____________________________________________________________ Additional Resources We’ve got a pretty cool website, if we may say so ourselves. Check us out at http://www.uaudio.com.
