Model LA-610 Channel Strip Universal Audio Manual Number 65-0901 Revision 1.1 Universal Audio, Inc. www.uaudio.
The LA-610 Channel Strip Thank you for purchasing the LA-610 Channel Strip. This unit combines a modified channel of our 2-610 Mic Pre with an LA2A style T4 Optical Compressor. Our 610 was inspired by the microphone preamp section of the 610 tube console designed by my father, M.T. “Bill” Putnam, in the 1950s. The 610 was a rotary-control console and was the first console of the modular design.
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. 2. 3. 4. 5. 6. 7. 8. Water and Moisture – Do not use the unit near any source of water or in excessively moist environments.
Notice This manual provides general information, preparation for use, installation and operating instructions for the Universal Audio LA-610 Channel Strip. 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.
Table Of Contents LA-610 Specifications....................................................................................1 LA-610 Operating Instructions.......................................................................2 610 Front Panel ................................................................................2 Input Select.............................................................................2 Gain ........................................................................................
LA-610 Specifications Microphone Input Impedance Selectable, 500 or 2k Balanced Line Input Impedance 20k Hi-Z Input Impedance Selectable, 2.2M or 47k Maximum Microphone Input Level -8 dBu (2K input Imp. & 15 dB Pad in) Maximum Output Level +20 dBu (120Vac line) Internal Output Impedance 80 Recommended Minimum Load 600 Frequency Response 20 Hz to 20 kHz +/- 0.
LA-610 Operating Instructions The LA-610 is a vacuum-tube microphone/instrument/line preamplifier with basic EQ and an optical program dependent compressor. The main preamp circuit has two gain stages that utilize a dual-triode tube operating in a class A single-ended configuration. Variable negative feedback is applied to both of these stages to control gain, distortion, and frequency response. Balanced inputs and outputs are transformer coupled.
level output, such as keyboards, sound modules and drum machines. The LA-610 may be used as a “tone box” in this configuration, offering a variety of sonic colors based on the front panel control settings. • Hi-Z: Selects the signal from the front panel, unbalanced Hi-Z 1/4”connector. This input can have an input impedance of 47K or 2.2M and is intended for bass, guitar or any instrument with a magnetic or acoustic transducer pickup.
• Frequency: This toggle switch selects the corner frequency (Hz). High: 4.5K, 7K, 10K; Low: 70, 100, 200 • Boost/Cut: This rotary switch selects the amount of boost or cut applied to the frequency “shelf.” The positive and negative numbers on the front panel denote dB values.
T4 Optical Compressor Front Panel (right side) This panel has the Peak Reduction, Gain, Meter Function and Compressor Mode controls. Each control is discussed in the following sections.
Meter Calibration The 0dB gain reduction reading may need to be calibrated using the GR Zero Set pot. The GR Zero Set pot is located through a small hole on the front panel below the UA diamond logo. 1) Turn the LA-610 on and warm up for 5 minutes. 2) Set the meter knob to the GR position. 3) With the Compressor section (right side) Peal Reduction control full off (CCW) adjust the GR Zero Set trim pot so the meter reads 0 dB. Turn pot slowly and watch how meter settles.
Voltage Select The LA-610 can operate at 115 V or 230 V. To change the mode, wait 5 minutes after power down, unplug the AC power cord from the rear chassis. Remove the top cover. As shown below, the Voltage Select Cable can be plugged into one location for 115V operation or moved to the 230V Connector for 230V operation. This figure shows the unit configured for 115V operation.
Expansion Perfect amplifier +10 Compression 0 Output Level (dB B) -10 -20 -30 -30 -20 -10 0 +10 Input Level (dB B) Figure 4- Input/output characteristics of a compressor, an expander and a perfect amplifier. In contrast to an amplifier, whose job is to present a constant gain, a compressor varies its gain in response to the level of the input signal. Large input signals result in less gain, thus reducing or “compressing” the dynamic range of the signal.
As mentioned previously, the compression ratio is defined as the ratio of the increase of the level of the input signal to the increase in the level of the output signal. In this example, the input level is increased by 10 dB while the output level only increases 5 dB. This would be a compression ratio of 2:1. Lower ratios such as 2:1 result in more gentle compression. (Note that a compression ratio of 1:1 is no compression at all). Typically, compressors let you choose a threshold.
electro-luminescent panel. This signal controls the gain of the compressor. After the gain reduction circuit, the signal is sent through an Output Gain control and a two-stage output amplifier, followed by the output transformer. As mentioned previously, compressors are devices that vary their gain in a manner which is dependent upon the level of the input signal.
photo-cell resistance can not go completely to zero and hence there will always be some signal present. The T4 electro-optical device is the heart of the compressor and its gain reduction characteristics. Its unique characteristics affect the overall sound and character of the LA-610. In addition to the compression curve, the combination of the EL panel and the photo-cell determine the attack and release characteristics of the LA-610.
does not control the input level, but rather controls the amount of side chain gain applied to the input signal. Side-Chain Circuit The previously described gain reduction circuit is controlled by the control voltage which is supplied by the side-chain circuit. The LA-610 is a feed-back style compressor. This is due to the fact that the signal that is used to drive the side-chain circuit is affected by the gain reduced signal.
console was dismantled. Putnam’s solution was to build a mic-pre with gain control, echo send and adjustable EQ on one modular chassis using a printed circuit board. While modular consoles are commonplace today, the 610 was quite a breakthrough at the time. While the 610 was designed for practical reasons, it was aesthetic appeal that made it popular with the recording artists who frequented United and Western in the 60’s.
in response to the input signal level. A compressor/limiter "rides gain" like a recording engineer does by hand with the fader of a console: it keeps the volume up during softer sections and brings it down when the signal gets louder. The dynamic processing that occurs at ratios below 10 or 12 to one is generally referred to as compression; above that it's known as limiting.
The LA-2A The LA-2A leveling amplifier, a tube unit with hand wired components and three simple controls, was introduced in the mid 1960s. It utilized a system of electro-luminescent optical gain control that was quite revolutionary; gain reduction was controlled by applying the audio voltage to a luminescent driver amplifier, with a second matched photoconductive cell used to control the metering section. With its 0 to 40 dB of gain limiting, a balanced stereo interconnection, flat frequency response of 0.
