Universal Audio Model 6176 Channel Strip
By Barry Rudolph
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Mix Magazine "Compression And Compressors"
Universal Audio's Model 6176 Channel Strip is a two-rackspace unit containing one channel from UA's Class-A 2-610 tube mic preamp and a UA 1176LN peak limiter. This natural combination gets even better when you realize that both the 610 and 1176LN inside are enhanced over current stand-alone units. Besides featuring refined versions of UA's two stalwarts that date back to the '60s, the 6176 provides the remarkable sonic synergy of a classic tube mic pre followed by one of the most popular transistor compressors ever made.
Preamp enhancements on the 6176 (not found on the 2-610) include a -15dB mic pad and an enhanced +300-volt power supply with high-voltage MOSFET regulation said to improve bass response and the noise floor. The 6176's right half has a complete 1176LN with three new features: a Bypass switch that hard-wires the preamp output directly to the 1176LN output jack; a 1:1 ratio position to use the compressor only for its "color" (a redundant feature, because just like the stand-alone 1176LN, the 6176's attack knob has a CCW Compressor Off position); and an All Ratio switch position that duplicates pressing all four ratio buttons at once; an old engineer trick that wreaks havoc on the ratio button assembly of the 1176LN but produces a wild and chaotic compressor action with increased distortion.
Behind the thick aluminum front panel is a steel cabinet containing three main circuit boards: mic pre on the left, PS in the middle and 1176LN on the right. Four of its five transformers are firmly bolted to either the cabinet's floor or walls. Cinemag transformers for both the mic pre and 1176LN inputs are used, and all connections to the circuit boards are hand-soldered (for audio paths) or use special, high-reliability Molex Trifurcon connectors for easy field maintenance. The preamp section uses 12AX7 and 6072A tubes. There are high-quality Electroswitches, polypropylene capacitors and metal-film resistors galore. Construction is good: You'll never have problems with mechanical ruggedness.
The preamp has three inputs: rear-panel XLR mic and line inputs, and a front-panel, unbalanced 1/4-inch jack for direct recordings. Controls include -15dB pad and phase-invert switches. There is a rotary impedance switch for both the XLR mic (2k-ohm and 500 ohms) and the instrument (47kohm and 2.2 meg) inputs. Gain setting is via a rotary switch with -10/-5/0/+5/+10 "ballpark" positions that set the amount of negative feedback (and therefore gain) for the 12AX7 and 6072 tube amplifier stages. After you have set this switch, there is a large knob that sets final output level. Dominating the front panel's left side, this '50s-style radio knob is impressive-feeling and perfectly sized to "ride" recording levels. The preamp has up to 61 dB of gain---plenty for 99% of all recording chores---and the 1176LN section has up to 40 dB of gain if needed. Because the preamp also has a separate line input, the 610 double-duties as a line-level processor. Increasing the gain switch to +10 offers a pleasant-sounding overload (especially noticeable in the low frequencies) that will warm up the coldest tracks.
The 6176 uses the same equalizer as the 2-610: It's a simple high/low-shelving EQ that works best when you want to brush up a mic's sound rather than seriously carve. A three-position switch toggles between 4.5/7/10 kHz for HF and 70/100/200 Hz for the lows. This very smooth equalizer's boost/cut is in 1.5dB steps for up to +/- 9 dB. The EQ is wonderful for opening up the top end (10 kHz) on a vocal mic or adding a 4.5kHz edge to a direct bass guitar recording. The 70Hz LF shelf was smooth and fine for rolling off mic proximity effects or subsonic noise.1176LN
An 1176LN in a half-rack...hmmm? Maybe UA should build a dual-channel 1176LN with two of these jewels side-by-side! All of the stand-alone 1176LN's usual controls are there; its operation is the same. Controls include: attack, release, ratio (with 1:1, 4:1, 8:1, 12:1, 20:1 and All settings); the input control (to set the amount of compression); and the output level control. There's a three-position rotary meter switch to select gain reduction; Pre shows the output level from the 610 and is useful to get a proper, (or improper) gain structure; and the Comp position reads the 1176LN's output level on the small but lighted VU meter. I'd like to see a larger meter from across the control room, but front-panel real estate is scarce.
There's also a phantom power-on/off, an oversized power switch with an old-style (incandescent) blue-jewel power indicator, and the important Join/Split switch that connects the 610 output to the 1176LN input or separates them for independent operation. There's a pushbutton to select between 15k-ohm or 600-ohm input impedance; otherwise, in Join mode, the impedance is 600 ohms to match the 610 output.
First on the list of jobs was recording bass guitar. The 610 and 1176LN proved a great combo. The 2.2-meg input impedance didn't put a load on the P-Bass offering a thick and creamy tube coloration with loads of sustain. Recording a five-string Fender bass with active pickups, I switched the impedance to 47kohm. The gain setting was different, but I used the same limiter settings, matching levels using the Pre meter switch position to get the same amount of compression. In general, I put the bass sound somewhere between a pristine "direct sound" and a miked bass amp sound. If you crank up the gain (and cut back the Input control on the 1176LN for the same amount of compression), then you'll go dirtier and crankier-sounding. There are many options here for direct recording.
For vocal recording, I adjusted the unit for the cleanest sound by backing down the gain selector and keeping the 610's output-level knob nearly full-up. The 1176LN input control also decreases, as I was looking for about only 2 to 6 dB of 4:1 compression of vocal peaks on vocalist Eloise Laws, whose album I've been recording. Using a vintage Neumann M49 mic, I found that by boosting 1.5 dB at both 10 kHz and 100 Hz, the EQ corrected that mic's occasional tendency to sound nasal. I got a big vocal sound with very good dynamic range and a warmth that helped out when my female singer sang at full voice and near the top of her range.
Recording any instrument or vocal with the 6176 immediately places that sound source on a proper and wide stage. The 6176's "personality" includes tight and clean low frequencies (if you run the unit clean) with a very forward and thick-sounding midrange coloration that's augmented by the bright sound of the 1176LN section. Percussion instruments benefit from slight preamp overload, reducing "spikes," while electric guitars fatten up very well even without the 1176LN switched in. Using an external EQ and/or compressor after the 610 stage will get you anywhere else you'd like, but it is hard to resist not using the unit as is for all recordings!
The UA 6176 Channel Strip retails at $2,495. With all of the choices now in the crowded channel strip market, I found it incredible that there was room for yet another entry, but here it is. The 6176 is a true original with deep retro roots in an updated and modern form and capable of a huge, impressive sound.
Universal Audio, 831/466-3737, www.uaudio.com.
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