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Volume 3, Number 4, June 2005
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Analog Obsession: UA and UREI Equalizers
By Will Shanks

Looking at some of the UA and UREI filters last month got me thinking about some of the other EQ and filter designs that have come and gone through the UA and UREI bygone years. UREI has designed and built many graphic EQs for sound reinforcement and studio applications. This month, we'll focus on some that were designed for the studio.
UA 500-A Program Equalizer

The UA 500-A Program Equalizer is a passive EQ that sustains a 10dB insertion loss (passive, baby!) and is of the L,C,R, Bridged T passive network design. (It also looks identical to the 550-A filter mentioned in last month's issue.) A high-frequency boost or cut in 2dB increments ranging from -10 to +10 dB can be switched between 3, 5, 7, 10 and 15 kHz. A low-frequency boost or cut in 2dB increments with the same range can be switched between 40 and 100 Hz. The 500-A offered true reciprocal boosts and cuts. Like the 550-A filters, the units were available racked as a single unit, or in pairs. Hard to find.

“There were two versions of the UREI 546: black and silver. Expect to pay more for black. Why? Because it’s black.”

UA 500-A Program Equalizer racked
UA 500-A Program Equalizer
UA 508 Envelopmental Equalizer

The UA 508 Envelopmental Equalizer is another of UA's earlier commercially available EQs. It is a no-loss, high- and low-frequency passive EQ designed to be used with modular amps like the 1008 tube amplifier or the 1108 solid-state amplifier. The term "envelopmental" refers to the manner in which 508 becomes electronically enclosed within an active feedback loop of its associated amplifier (much like the EQ of the original and current 610 line). A high-frequency boost or cut in 3dB increments ranging from -6 to +9 dB can be switched between 5 or 10 kHz. A low-frequency boost or cut in 3dB increments with the same range is fixed at 50 Hz. Horizontal or vertical mounted units were available. Also hard to find!

UREI 545 Parametric Equalizer (from original cut sheet)

The UREI 545 Parametric Equalizer is the one I'm looking for...not nearly as famous as a Pultec, or as obscure as an ITI, the UREI 545 has a functionality and feel that just work well. I ran across a pair at Ocean Way last week. With the classic black-anodized UREI front panel and clear skirt 1176 style knobs, the 545 feels familiar--and it was built for heavy use. The 545 implements four bands of overlapping parametric Low, Mid and High EQ bands, plus a versatile Multi-Band with a multiplier range switch, tunable over the entire range from15 Hz to 20 kHz. All bands offer +/-15dB reciprocal boost or cut, with a 1/4- to 2-octave Q/ bandwidth. Concentric controls for each band provide the cut/boost and frequency selection, while a control for Q adjustment remains separate; the Q adjustment controls double as a pull-out control for band bypass. I love it! The 545 also sports high and lowpass filters of the 12dB-per-octave Butterworth type, with a range of 16 to 800 Hz, and 25 kHz to 800 Hz respectively. An overall Bypass switch, Power switch and Overload light are also featured on the front panel. The 545 utilizes an output transformer, and is probably Class AB. A bit hard to find, and usually a little bit pricey.

UREI 545 Parametric Equalizer
UREI 546 Dual Parametric Equalizer (in silver)

The UREI 546 Dual Parametric Equalizer is a 2-channel unit based on the 545. It's not much different in terms of functionality, although the 546 has four overlapping bands: Low, Mid Low, Mid High and High (rather than the High, Mid, Low and Multi-Band of the 545). One unique feature of the 546 is that the eight bands can be combined with a rear panel switch to make the 546 a mono eight-band parametric EQ. The main drawback of the 546 is that the smaller controls of the 546 mean it is not as easy to navigate. I actually acquired a UREI 546 a few years back (thanks, Chris) and found it very useful, mostly for EQ'ing kicks and toms "on the way in" (perfect for super-carved, hard-rock drum sounds), so I bought a second unit on eBay. These are fairly common and can be found at reasonable prices. There were two versions of the 546: black and silver. Expect to pay more for black. Why? Because it's black. I don't believe there is any design difference.

UREI 546 Dual Parametric Equalizer (in black)
UREI 545 Parametric Equalizer

The UREI 555 and 556 Bandpass Filters are a couple of obscure gems that I've perhaps only seen twice on eBay. There's not much information out there or in-house. There must have been a pretty short run with these! The low-down: High and low cut filters at 18 dB per octave (Butterworth); low cut 20 to 200 Hz, high cut 20 to 2 kHz. I'm not even sure what the difference between the 555 and 556 is. If anyone out there has any more info on these, please contact me!

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