1176 and LA-2A Hardware Revision History

June 16, 2011 11:11:11 AM PDT
Reissue 1176LN and LA-2A Hardware
UA Classic Reissues: 1176LN Limiting Amplifier & LA-2A Leveling Ampifier

We get occasional calls here at Universal Audio from people wanting to know what era some Universal Audio, UREI or Teletronix piece they bought on the vintage market dates from. So in this post, we're offering a complete revision history of the world's two most popular compressors, the 1176 Limiting Amplifier and the Teletronix LA-2A Leveling Amplifier. We also get calls wondering if we do repairs on vintage equipment; sorry, we don’t. However, we do highly recommend David Kulka at studioelectronics.biz for all 1176 and LA-2A repairs, or any other vintage UA/UREI or Teletronix equipment you may have. David is the best in the business.

1176 Classic Limiting Amplifier

While the 1176 has seen a huge number of revisions in its history, the most significant revision to the 1176 circuit was designed by UREI engineer Brad Plunkett in an effort to reduce noise — hence the birth of the 1176LN (LN stands for low noise) at revision C. Numerous design changes followed, resulting in at least 13 revisions and variations on the 1176. Most units include the revision letter with the serial number. Revisions C, D and E (the first three with the LN circuit) are all very similar, and are historically the most beloved. The current Universal Audio’s 1176LN reissue is built from that circuit, as are the 1176 limiter in our 6176 Vintage Channel Strip and our 2-1176 Twin Vintage Limiting Amplifier.

  • Revision A (AKA “Bluestripe”)
    • Design Date: 6/20/67
    • Serial Numbers: 101-125
      • Faceplate is brushed aluminum with blue paint and red power light
      • Original 1176 designed by Bill Putnam for broadcast use, class A design
      • Signal Preamp: Used FET (field effect transistor) in a voltage divider configuration for gain reduction, a technological first
      • Used FET as voltage variable resistor to control the gain
      • Used ‘T-pad’ resistive attenuator to drop the input voltage
      • Input Stage used a 600 ohm input transformer
      • Used FET followed by bipolar transistor as preamp
      • Output amp used essentially the same circuit as in the preamp, but followed it with a 2N3053 operating in class A
      • Output transformer was the UA-5002; this transformer has split secondary, tertiary winding for negative feedback, emitter winding; the design was basically that of the 1108 preamp
      • A Weston meter is used


  • Revision AB (AKA “Bluestripe”)
    • Design Date: 11/20/67
    • Serial Numbers: 125-216
      • Changed several resistor values in signal pre-amp stages; this improved stability as well as noise
      • Circuit added bypass cap around the resistor feeding the gain reduction FET to improve stability


  • Revision B (AKA “Bluestripe”)
    • Design Date: Not indicated
    • Serial Numbers: 217-1078
      • Replaced FETs in the signal pre-amp with bipolar transistor (2N3391A)
      • Tapped off of the emitter of the first transistor in the input stage; this provides a replica of the input voltage to the voltage variable resistor
Bluestripe 1176

  • Revision C (1176 LN) (AKA “Blackface”)
    • Design Date: 1/9/70
    • Serial Numbers: 1079-1238
      • Faceplate is anodized black
      • Low noise ‘LN’ circuitry was added in the signal preamp; this reduces DS voltage on the gain reduction FET and keeps the FET within its linear range
      • Modification to program dependency tuning
      • Trimpot added to feedback circuit of audio FET, to minimize distortion
      • The LN circuitry was built in a module that was encased in epoxy to protect the circuit
      • A Modutec VU meter is used, with two lamps mounted above


  • Revision D (AKA “Blackface”)
    • Design Date: Not indicated
    • Serial Numbers: 1239-2331
      • Adds "UREI" branding to existing Universal Audio branding
      • The LN module was no longer used and the circuit board was redesigned to accommodate the LN circuitry on the main board
UA 'Golden' blackface 1176

  • Revision E (AKA “Blackface”)
    • Design Date: Not indicated
    • Serial Numbers: 2332-2611
      • A switch was added to change between voltages


  • Revision F (AKA “Blackface”)
    • Design Date: 3/15/73
    • Serial Numbers: 2611-7052
      • Output amplifier changed to a push-pull (class-AB) configuration from the original class-A design
      • Output transformer is changed to the B11148 type with 12 dB of gain (same transformer as the LA-3A)
      • Push-pull design provided more output drive, and was based on the 1109 preamp
      • Changed the metering circuit to an op-amp following the meter FET, instead of balanced bridge transistors


  • Revision G (AKA “Blackface”)
    • Design Date: Not indicated
    • Serial Numbers: 7053-7651
      • Removed the input transformer, and replaced it with a differential input op amp stage
      • Removal of program dependency


  • Revision H (AKA “Silverface”)
    • Design Date: Not indicated
    • Serial Numbers: 7652- 8000+
      • Faceplate is brushed aluminum with red “Off’ button; this is the only revision with a blue UREI logo
      • Removes Universal Audio branding
      • VUi meter is changed to Modutec "light box" type, with two internal lamps
Blue Logo UREI Rev. H 1176

  • Universal Audio Reissue 1176LN
    • Design Date: 4/1/2000
    • Serial Numbers: 101-1959
      • The new Universal Audio’s first product release
      • Based on the most beloved revisions C, D and E — most similar to E, due to 110/220 switchable power transformer
    • Serial Numbers: 1960-2946
      • When Clarostat T-pad input attenuator became unavailable:
        • Changed from 600ohm T-pad to 1Kohm log taper input attenuator (same configuration in 6176 and 2-1176)
        • Changed 012 Magnetika to Cinemag input transformer (same configuration in 6176 and 2-1176)
    • Serial Numbers: 2947-present
      • When original 600ohm T-pad input attenuator became available again under Precision Electronics:
        • Resumed production with T-pad attenuator
        • Resumed production with 012 Magnetika input transformer
1176LN Classic Limiting Amplifier

  • Revision AE "Anniversary Edition"
    • Design Date: 6/04/08
    • Serial Numbers: 001-500
      • Faceplate is black anodized with blue paint
      • Unique Rev. A/E “hot-rod-mod" features, cosmetics and sonic signature
      • Return to program dependency of legendary “Bluestripe” Rev. A 1176
      • New, gentler compression ratio with 2:1, 4:1, 8:1 and classic 20:1 for hard limiting
      • Expanded range of “multi-button” compression and classic “all-button” mode with 2:1 ratio
      • Click-stop “Slo” 10 ms Attack setting adds increased versatility for new uses
      • Limited-Edition of only 500 units worldwide
1176AE Anniversary Edition

Note: Other variations of the 1176 exist, such as the 1178 stereo limiter and the 1176/LA-3A FET/optical dual-detector hybrid UREI Modulimiter.

LA-2A Classic Leveling Amplifier

Patented by Jim Lawrence, the LA-2A optical Leveling Amplifier was first produced by Teletronix in Pasadena, California. Earlier variations such as the very rare LA-1 and LA-2 still exist in private collections, but the LA-2A was the improved design that caught on. Teletronix later became a division of Babcock Electronics Corp. in 1965. In 1967 Babcock's broadcast division was acquired by Bill Putnam's company, Studio Electronics Corporation, shortly before he changed the company’s name to UREI®. Three different versions were produced under the auspices of these different companies before production was discontinued around 1969-70. In addition to these iterations of the LA-2A, two “re-issues” were put out, one while still under UREI, and one under UREI after being purchased by Harman/JBL.

  • Revision 1 (AKA “Greyface”)
    • Faceplate is painted grey
    • First compressor to use of photo resistors and luminescent panels to achieve gain reduction - the T4A
    • Produced by Teletronix in Pasadena, CA (sometimes labeled Los Angeles, sometimes labeled Sunnyvale)
    • Octal jumper socket located before the UTC HA-100X input transformer for pad/pre-emphasis modules
    • Later units included a variable pre-emphasis filter, R37
    • All rear panel graphics are hand stenciled or stamped
    • Some units offer a fixed Limit function while others feature a Limit/Compress switch on the back 
Jim Putnam's Rev 1 LA-2A

  • Revision 2 (AKA “Silverface”)
    • Faceplate is brushed aluminum
    • Teletronix patent acquired by Putnam's Studio Electronics Corp. of North Hollywood
    • This iteration had an added a compress/limit switch on the back
    • Input transformer changed to UTC A-10
    • Limit/Compress switch on the back
    • This revision starts with unit #384
Silverface LA-2A Rev. 2

  • Reissue 1
    • In the late 70's, UREI brought back the LA-2A for a run of around 200 units 
    • Return of the greyface front panel
    • The T4A is replaced with a T4B
    • A safety switch is added so power shuts off when front panel is opened


  • Reissue 2
    • In 1985, 235 units were re-issued by UREI while under Harmon/JBL
    • This brought the unit once again back to the aluminum silverface look, but this time with the UREI name on the front
Silverface LA-2A Re-Issue 2

  • Universal Audio Reissue Teletronix® LA-2A
    • Based on Revision 1
    • Released in May of 2000
    • Moved the Limit/Compress switch to front panel
    • Removal of user accessibility via front panel thumbscrews
Teletronic LA-2A Classic Leveling Amplifier

— Will Shanks