Universal Audio La-2a_manual

8/6/2019 Universal Audio La-2a_manual

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M od e l LA-2 A

Le v e ling Am p lif ie r

Universal Audio, Inc.

www.uaudio.com

PO Box 38 18

Santa Cruz, CA 95 06 3-38 18


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ii

Te le tron ix LA -2 A by Unive rsal Au dio

Tha nk you for p urcha sing this reprod uction of the Teletronix LA-2 A. The LA-2 A wa s

originally produced in the early 1960s by Teletronix, which was later acquired byBa bcock Electronics Corpo ra tion. My fa ther purchased the pro duct rights a nd the na me

Teletronix from Babcock Engineering in 1967, folding it into his Studio Electronics

Corporation, shortly before he changed the name to UREI. There were three different

variations of the LA-2A during this period before production was discontinued around

1 9 6 9 .

Straightforwa rd in its de sign, a nd initia lly intended for b roa dca st a pp lica tions, the LA-2 A

quickly be came sta nda rd e quipment in studios worldwide. Ma ny have be en p a insta kingly

maintained for the 30 years that they have remained in use since production stopped. A

tube-ba sed co mpressor, the LA-2 A fea tures hand-wired co mpone nts a nd two simple

controls. At the time, its electro-luminescent op tica l ga in re duction wa s quite re volutiona ry:

applying the audio signal to an electro-luminescent light panel which shines on a photo-

electric cell which in turn controls the g a in. In contra st to the electro-op tica l devices which

preceded it, the electro-luminescent light source provided the fast attack necessary for

bro a dca st a pp lica tions. Additiona lly, the cad mium-sulfide p hoto-cells pro vide d a very

natural two-stage release which resulted in a compression characteristic more

transpa rent than the o ther compre ssors of its da y. To this da y the LA-2 A delivers a

trademark sound treasured by engineers worldwide.

Here a t Universal Audio, we have go ne to grea t leng ths to recre a te the LA-2 A with

complete a uthenticity. Its be en no sma ll fea t to loca te obscure pa rts, put qua lity control

programs in place that didnt exist 30 years ago and find personnel capable of the

handwork that go es into e a ch unit. Every step wa s necessa ry to ensure tha t ea ch LA-2 Ade livers the sound you e xpe ct.

As for the future, we a re wo rking on a dd itiona l rep rod uctions be yond the LA-2 A and

1 1 7 6 LN. To that end, we a re interested in your opinions ab out your fa vorite pieces of

vintag e ge a r. Wha t ca nt you live without? Wha t would you love to own, but ca nt find

a ny longe r? In add ition, Universal Audio is working on new p roducts designed to meet

the de mands o f the mod ern d igita l recording studio, yet reta ining the cha ra cter of cla ssic

vinta ge eq uipment.

Develop ing these pro ducts ha s be en quite a n ad venture, enjoyed by a ll involved . We

thank you for your suppo rt and we thank my fa ther, Bill Putna m.

Thank you,

Bill Putna m


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iii

IMPO RTAN T SAFETY INSTRUCTION S

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

wa rnings indicated on the unit itself, as we ll a s in the op e rating instructions.

1 . W at er and M oi st ure Do not use the unitnear any source of water or in excessively moist

environments.

2 . Object and Liquid Entry Care should betaken so that objects do not fall, and liquids are

not spilled, into the enclosure through openings.

3 . Venti lat ion When installing the unit in a rackor any other location, be sure there is adequate

ventilation. Improp er ventilation will ca use

overheating, and can damage the unit.

4 . Heat The unit should be situated away fromheat sources, or other equipment that produces

heat.

5 . Power So urces The unit should be connectedto a power supply only of the type described in

the operating instructions, or as marked on the

unit.

6 . Powe r Cord Protect ion AC power supplycords should be routed so that they are not likely

to be walked on or pinched by items placed upon

or against them. Pay particular attention to cords

at plugs, convenience receptacles, and the point

where they exit from the unit. Never take hold of

the plug or cord if your hand is wet. Always grasp

the plug body when connecting or disconnecting

it.

7 . Grounding of the Plug This unit isequipped with a 3-wire grounding type plug, a

plug ha ving a third (g round ing) pin. This plug will

only fit into a gro unding-type po wer outlet. This is

a safety feature. If you are unable to insert the

plug into the outlet, contact your electrician to

replace your obsolete outlet. Do not defeat the

purpose of the grounding-type p lug.

8 . Carts and Stand s The unit should be usedonly with a cart or stand that is recommended by

the manufacturer. The unit and cart combination

should be moved with care. Quick stops,

excessive force and uneven surfaces may cause

the unit and cart combination to overturn.

9 . W all Or Ceil ing Mo unt The unit should bemounted to a wall or ceiling only as

recommended by the manufacturer.

1 0 . Cleaning The unit should be cleaned only asrecommended by the manufacturer.

1 1 . Nonuse Periods The AC power supply cordof the unit should be unplugged from the AC

outlet when left unused for a long period of time.

1 2 . Damage Requir ing Serv ice The unitshould be serviced by qualified service personnel

when:

a ) The AC power supply cord or the plug has

been damaged; or

b) Objects have fallen or liquid has been spilledinto the unit; or

c) The unit has b een e xposed to rain; or

d) The unit does not operate normally orexhibits a marked change in performance; or

e) The unit has been dropped, or the enclosuredamaged.

1 3 . Servicing The user should not attempt toservice the unit beyond that described in the

operating instructions. All other servicing should

be referred to qua lified service p ersonnel.


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LA -2 A Use rs Guide

Universal Audio, Inc.

PO Box 38 18Santa Cruz, CA 95 06 3-38 18

(831 ) 454 -06 30 voice

(831 ) 45 4-06 89 fax

www.uaudio.com

Universa l Audio Part N umber LA2A-M0 1 .

Revision 1.3

Notice

This manual provides general information, preparation for use, installation and operating instructions for the

Universa l Audio LA-2 A Leveling Amp lifier.

The informa tion contained in this ma nua l is subject to cha nge without notice. Unive rsal 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. shall not be liable for errors

contained herein or direct, indirect, special, incidental, or consequential damages in connection with the

furnishing, pe rforma nce, o r use of this ma terial.

Copyright

2 00 0 Universal Audio, Inc. All rights reserved .

This manual and any associated software, artwork, product designs, and design concepts are subject to

copyright protection. No part of this document may be reproduced, in any form, without prior written

pe rmission of Universa l Aud io, Inc.

Trademarks

LA-2 A, 11 76 a nd the Universa l Audio, Inc. log o a re tra de marks of Universa l Audio, Inc. Othe r compa ny

a nd pro duct names mentioned herein are trade marks of their respective compa nies.


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Ta ble of Con te nts

Teletronix LA-2 A by Universa l Audio ..................................... ....................................... ....... ii

Spe cifications ........................................... ............................................ ................................ 1

O pe ra tion of the LA-2 A .................................... .......................................... ......................... 2

Input a nd O utput Connections ............................................................................... 2

Peak Reduction Control ........................................................................................ 2

Gain Control ....................................................................................................... 2

VU Meter O pera tion ............................................................................................ 3

Limit / Comp ress Switch........................................................................................ 3Ca libra tion .......................................... ............................................. .................................... 4

Me ter Zero Adjust ............................................................................................... 4

Side-Chain Pre-Emphasis (R37).............................................................................. 4

Stereo Balance Adjust (R3) ................................................................................... 4

Theo ry of O pe ra tion ............................................................................................................5

Compre ssor Ba sics ............................................................................................... 5

Gain Reduction Circuit.......................................................................................... 8

Side-Cha in Circuit .............................................................................................. 11

O utput Circuit.................................................................................................... 11

Me tering Circuit................................................................................................. 11

Appe ndix .......................................................................................................................... 1 2

Crea tive Classics: The 1 1 7 6 Solid State Limiting Amplifie r a nd the LA-2 A

Leveling Amplifier .............................................................................................. 12

The LA-2A ..................................................................................................... 12

Developing the 1 17 6 ..................................................................................... 13More Than a Vintage Fad: Classic Sound .......................................................... 13


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Specifications

! Ga in Red uction: up to 40 dB

! Distortion: less tha n 0 .35 % total harmonics at +10 dBm, and less tha n 0 .75 % total

ha rmonics a t +1 6 dBm output

! Response: +/ - 0 .1 d B, 30 cycles to 1 5 kilocycles

! No ise: 75 dB be low +10 dBm output level

! Ga in: 40 +/ - 1d B

! O utput Leve l: +10 dBm nomina l, +16 dBm pea ks

! Input Level: +16 dBm ma ximum

! Very fast attack time

! Release Time: approximately 0.06 seconds for 50% release, 0.5 to 5 seconds for

complete re lea se de pe nding upo n the a mount of previous red uction

! Input Impeda nce: 6 00 ohms ba la nced

! O utput Impeda nce: 60 0 ohms balanced

! Pa nel Size: 19 x 5

! Depth Behind Pa nel: 7

! Panel Controls: Gain (Output level), Peak Reduction, and Meter Selector Switch

! Meter: dB Ga in Red uction a nd d B O utput

! Tube Complement: (2) 1 2 AX7 A, (1 ) 12 BH7A, (1) 6 AQ5


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Ope rat ion o f the LA -2 A

Inp ut a nd Outpu t Con ne ct ion s

Input and O utput conne ctions are made using standa rd XLR style connectors. Terminalstrips a re a lso provide d.

O utput connections Input connections

6 ) Stereo Link 1 ) + 6 0 0 ohms

7 ) Ground 2 ) + 2 5 0 ohms

8 ) + 6 0 0 ohms 3 ) Center ta p

9 ) Center ta p 4 ) - 2 5 0 ohms

1 0 ) - 6 0 0 ohms 5 ) - 6 0 0 ohms

Ba rrie r Strip Co nn e ction s

If you wish to use the b a rrier strip instea d of the XLR conne ctors, connect as follows:

INPUT: Connect + 6 0 0 (1 ) to HO T a nd 60 0 (5 ) to NEUTRAL.

O UTPUT: Connect + 60 0 (8 ) to HOT a nd 6 0 0 (10 ) to NEUTRAL.

Connect Ground (7 ) to the ca ble shield.

Pea k Re du ction Con trol

O pe ra tion of the LA-2 A is very stra ightforwa rd. There a re o nly two controls that one must

dea l with. The first is the Peak Reduction control. This control should be set so that the

compre ssor exhibits the de sired amount of compre ssion. This control should be setindepe ndently o f the Ga in Control.

Ga in Con trol

This control doe s not a ffect the compression. The ga in control should be set a fter the

de sired a mount of compre ssion is de termined using the Pea k Reduction control. O nce the

Peak Reduction control is set, adjust the Gain Control to achieve the desired output level.

Power

Transformer

12 AX7

6AQ5

12AX712BH7

R3

R37HA-10 0X

T4A-24

IEC

10 9 8 6 5 4 3 2 17 O utp ut Inp ut


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Calibration

Me ter Zero Adjust

The zero-adjust of the meter is set by the screw-adjust potentiometer located next to theLimit / Compre ss Switch. To a djust this, put the meter into G a in Reduction mod e. Ma ke

sure that there is no signa l pre sent. Loo sen the locking nut a nd use a screwd river to a djust

this potentiometer until the meter reads zero.

Side -Cha in Pre -Em p ha sis (R3 7 )

The LA-2 A was de signe d for use in bro a dca st a pp lica tions. The a udio signa l in FM

broa dca sting undergo es pre -empha sis and re sults in a 1 7 d B boo st a t 15 KHz. Due to this

increa se in signa l leve l, tra nsmitters a re subject to ove r-modula tion. The LA-2 A pro vide s a

control (R3 7 ) which controls the a mount of high-freque ncy compre ssion.

This potentiometer is fa ctory set for a fla t side -cha in response (clockwise). Increa singthe resistance of this potentiometer by turning it counter clockwise will result in

compre ssion which is increa singly more sensitive to the highe r frequencies.

Stereo Balan ce Adjust (R3 )

For stereo ope ra tion, two LA-2 A units are interco nnected in ord er to a chieve the same

a mount of ga in reduction from ea ch of the two units to ma inta in stere o ima ging. In order

to accomplish this, terminals 6 from ea ch unit should be co nnected together. Add itiona lly,

their grounds (termina l 7) should b e connected tog ether.

The interco nnecting wire should be less tha n 2 fee t in length and should be shielde d. The

shield should be used to connect terminals 7 from each of the units together.

To calibrate the units for stereo operation:

! Connect the units together as described previously.

! Turn the Pea k Red uction knob counterclockwise (no compre ssion).

! Set R3 on e a ch unit to a clockwise p osition.

! Set ea ch meter to rea d G a in Red uction.

! Adjust the Peak Reduction control on the left channel until approximately 5dB of

ga in red uction is achieved.

! Adjust R3 on the unit that shows the greatest amount of gain reduction until thega in red uction indica tions a re e qua l.

! When operating, set the Peak Reduction controls to the same setting on both

channels.


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5

The ory o f Ope rat ion

Com p resso r Basics

Before we dig in to a description of the LA-2A circuit, it is useful to examine the generalcha ra cteristics of compre ssors a nd review some terminology. Figure 1 d ep icts the

input/ output chara cteristics of a compressor, an exp a nde r and a pe rfect amplifier. When

operated within its specified range, an amplifier provides a constant amount of gain

rega rdless of the leve l of the input signa l. In Figure 1 , the midd le line depicts a p erfect

a mplifier with a ga in of 10 dB. To see this, notice tha t a signa l with a n input leve l of 30

dB will result in a n output level of 2 0 dB, which is an increa se o f 10 dB. Similarly, an

input level of 0 dB will result in an output level of 10 dB, hence the gain stays fixed at 10

dB rega rdless of the input level.

-30

-20

-10

0

+10

-30 -20 -10 0 +10

Input Level (d B)

Output

Level (dB)

Compression

Expansion

Perfect

amplifier

Figure 1 - Input / ou tpu t character i st ics o f a comp ressor, an ex pand er and a p er fec t

ampl i f i er .

In contrast to an amplifier, whose job is to present a constant gain, a compressor varies its

ga in in resp onse to the level of the input signa l. La rge input signa ls result in less ga in, thus

red ucing or co mpressing the d ynamic ra nge of the signa l. Referring a ga in to the line

marked compression in Figure 1, we see that an input level of 30 dB results in anoutput leve l of 20 dB, indicating a ga in of 10 dB. Repe a ting this for input leve ls of 20

dB a nd 1 0 dB, we see tha t the co mpressor exhibits ga ins of 5 d B a nd 0 dB respe ctively.

From this, it is clear that the gain decreases as the input signal increases.

Referring to the diagram, we see that the compressor will increase its output level by 5 dB

for every 10 d B that we increa se the input level. The compression ra tio is de fined a s the

ra tio of these two numbers. In this case the compression ra tio wo uld b e 1 0 :5, which can

be reduced to 2:1.


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7

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Figure 3 - Block diag ram o f the LA-2A com presso r.


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LA-2A Block Diag ram

A functiona l block diagra m of the LA-2 A is pro vide d in Figure 3 . A brief overview o f the

op era tion will be pro vide d he re. The input transformer pro vide s isola tion a nd impe da nce

matching. After this the signa l is fed into bo th the side-cha in circuit a nd the ga in reduction

circuit. The side-cha in is comprised of a volta ge a mplifie r, a pre -empha sis filter, a nd adriver stage which provides the voltage necessary to drive the electro-luminescent panel.

This signa l controls the g a in of the co mpressor. After the g a in reduction circuit, the signa l

is sent through a n O utput Ga in control a nd a two-sta ge output amplifier, followe d by the

output transformer.

Electro-luminescent

PanelPhoto-Electric Cell

Figure 4 - Diag ram of th e T4 e lectro-op tical ce ll .

Ga in Re d u ction Circuit

As mentioned pre viously, compressors a re de vices that va ry their ga in in a manne r which

is de pe nde nt upo n the level of the input signa l. In orde r to do this, the compre ssor must

first have some method of determining the level of the signal, and must then be able to use

this to control the ga in. There a re ma ny diffe rent schemes to acco mplish these ta sks. In

the ca se o f the LA-2 A, both of these functions are pe rformed b y the T4 , which is a n e lectro -

optical element.

A T4 is comprised of an electro-luminescent (EL) pa ne l a nd a p hoto -electric ce ll. The EL

pa nel is essentia lly a night-light. As you wo uld e xpe ct, the larg er the signa l that is app liedto it, the b righter the light that is gene ra ted . This light shines up on the pho to-electric cell.

A photo-electric cell is a light sensitive device whose resistance changes depending upon

the intensity of light to which it is subjected; the brighter the light, the less resistance the

photo-ce ll will have.

As depicted in Figure 5 , the p hoto-cell is used to contro l the ga in o f the circuit. Essentia lly,

the pho to-cell a cts a s the b ottom leg in a voltage divider circuit. The lowe r the resista nce

of the photo-cell, the lower the signal voltage will be at the output of the gain reduction


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sta ge . To see why this is true, we can loo k a t the extreme ca ses. If the resistance is

extremely high (this is the case when there is a small input signal and the light is off) then

the photo -cell do es not a ffect the circuit a nd there is no ga in reduction. The seco nd ca se

we ca n loo k a t is when there is a la rge signa l pre sent. In this cond ition, the light shines

brightly a nd the p hoto-cell exhibits very low resista nce. If the re sista nce o f the photo-cell

becomes zero (a dea d short), then the signa l would be grounded a nd there would be nooutput. In rea lity, the p hoto-cell resista nce ca n not go completely to z ero a nd he nce there

will always be some signal present.

7

R5 6 8 K

R6

68 K

R7

2 .7 K

8

9

10

TO V O LTA G E

A M PLIFIER

TO G A IN

R ED U C TIO N

C O N TRO L

TO A TTEN U A T O R

D RIVE A M PLIFIER

G A IN R 1

1 0 0 K

PH O TO C O N D U C TIV E C E LL

E LEC TR O LU M IN ESC EN T

E LEM E N T

H A -1 0 0 X

.0

0

4

7

u

F

Figure 5 - Sche ma tic of the LA-2 A inpu t and ga in redu ct ion circui t .

The T4 electro-optical device is the heart of the compressor and its gain reduction

cha ra cteristics. Its unique cha ra cteristics affect the overa ll sound a nd cha ra cter of the LA-

2 A.

In a dd ition to the co mpression curve , the combina tion o f the EL pa nel a nd the p hoto-cell

de termine the a tta ck a nd re lea se cha ra cteristics of the LA-2 A. This is one o f the most

importa nt contributors to the sound of the LA-2 A. Unlike othe r compre ssors which a llow

the user to a djust these p a ra meters, the a tta ck a nd relea se of the LA-2 A a re co mpletely

de termined by the T4 .

There a re severa l importa nt cha ra cteristics of the T4 which play crucial roles in the soundof the LA-2 A. The first is the a ttack. The LA-2 A wa s the first electro -op tica l comp ressor to

use a n electro-luminescent pa nel for the light source. Previous a ttempts a t electro-op tica l

compre ssion employed either neo n or inca nde scent lights. Both of these took time to light

up, a nd this de lay resulted in slow a tta cks. The e lectro -luminesce nt pa nel resulted in a

fa ster a tta ck than e xhibited by other contempora ry devices.


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10

The next impo rtant a spect is tha t of the relea se of the co mpressor. This is de termined

a lmost entirely by the cha ra cteristics of the photo-cell. The LA-2 A uses ca dmium-sulfide

photo -cells. The first impo rta nt a spe ct of the ce ll is its two -stage de ca y. After the light is

removed from the cell, it releases quickly (40-80 milliseconds) to approximately half of its

off resista nce. The rema inde r of its relea se can take place over a s much as severa l

seconds.The ne xt aspect is the memory o f the cell. This results in two impo rtant asp ects of the

cha ra cter of the LA-2 A. The a mount of time it takes for the cell to recover a fter the light is

removed d ep ends on how long light had be en shining o n it and ho w bright the light. In

the ca se o f the LA-2 A this results in beha vior where the re lea se time is slowe r if the unit has

either be en in compre ssion for a while, o r the amount of compre ssion is la rge . This signa l

dependent release characteristic is critical to the sound of the unit.

The amount of compression, as well as the compression threshold, is controlled by the

Pea k Red uction p otentiometer. This potentiometer controls the ga in of the side -cha in

circuit. The gre a ter the ga in of this circuit, the lowe r the threshold a nd the gre a ter the

a mount of compre ssion will be . Ma ny mod ern limiters and co mpressors a llow for thedirect ad justment of the threshold. O ther units such a s the 11 7 6 LN use a fixed threshold

and provide an input level control, which adjusts the signal level before it is applied to the

compre ssion circuit. In contrast, the LA-2 A, while a lso ha ving a fixed threshold,

does not control the input level, but rather controls the amount

of side chain gain applied to the input signal.

C 8

.0 3

R3 1 1 K

R2

100K

C 9

.02

R3 3

220K

1 MegLIMRESP

R37

R3

1 M

STEREO

A D J

O U T PU T

R3 6

1K

C 1 0

50 uF

C 7D

30 uF

R3 5

220K

R3 4

2 2 K 2 W

V4

6 AQ 5 A

IN PUT

R3 0

47 K

.0 1

A TT EN U A T O R

D RIVE-A M PLIFIER

C12

.001

STEREO

PARA LLEL

PO W ER

SU PPLY

R3 2

1 K

C 6

12AX7A

V3 B V3 A

C 11

.1

Figure 6 - Sche ma tic diagram of the LA-2A side-cha in circui t .


16/21


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12

pre viously, the ga in red uction is controlled by the p hoto-cell in the T4 el-op . In ord er to

track the operation of this cell and determine the gain reduction, a second photo-cell is

a lso illumina ted b y the sa me EL pa nel. This pho to-cell is ha nd-selected to match the ga in

red uction p hotocell a nd he nce gives an a ccura te indica tion o f the a mount of compression.

Appendix

Cre ative Classics: The 1 1 7 6 Solid State Limit ing Am plif ie r an d

the LA-2 A Le ve l ing Am plif ie r

The LA-2 A and 1 1 7 6 co mpressor/ limiters long a go a chieved classic sta tus. They're a

given in almost any studio in the world relied upon daily by engineers whose stylesrange from rock to rap, classical to country and everything in between. With so many

newe r pro ducts on the market to choose from, it's worth looking a t the rea sons why these

classics remain a necessary part of any professional studio's outboard equipment

collection.

The b a sic concept of a compre ssor/ limiter, is of course, rela tively simple. It's a de vice in

which the gain of a circuit is automatically adjusted using a predetermined ratio that acts

in response to the input signa l leve l. A compre ssor/ limiter "rides ga in" like a reco rding

engineer does by hand with the fader of a console: it keeps the volume up during softer

sections and brings it do wn when the signa l ge ts loude r. The dyna mic proce ssing that

occurs at ratios below 10 or 12 to one is generally referred to as compression; above that

it's known as limiting.

Modern day compressors offer a great degree of programmability and flexibility while

older d evices such a s the 1 1 7 6 a nd the LA-2 A a re more stra ightforwa rd in their design.

Perhaps it is this fact that has contributed to their appealing sound and the longevity of

their popularity.

The LA-2 A

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 0.1 dB from 30-

1 5 ,00 0 hz a nd a low noise level (be tter than 70 dB be low p lus 10 dBm output,) the LA-

2 A quickly be came a studio sta nda rd. O rigina lly pa tented by Jim La wrence, it was

produced by Teletronix in Pasadena, California, which became a division of Babcock

Electronics Corp. in 1965. In 1967 Babcock's broadcast division was acquired by the


18/21

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legendary Bill Putnam's company, Studio Electronics Corp shortly before he changed the

compa nys na me to UREI. Three different versions of the LA-2 A were pro duce d unde r the

a uspices of these d iffere nt compa nies be fore p roduction wa s discontinued a round 1 9 6 9 .

De v e l o p in g t h e 1 1 7 6

It was Bill Putnam himself who, in 1966, was responsible for the initial design of the 1176.

Its circuit was rooted in the 1108 preamplifier which was also designed by Putnam. As is

evident from entries and schematics in his design notebook, he experimented with the

recently developed Field Effect Transistor (F.E.T.) in various configurations to control the

gain reduction in the circuit. He began using F.E.T.s as voltage variable resistors, in which

the resistance between the drain and the source terminals is controlled by a voltage

a pp lied to the g a te. His grea test challeng e wa s to e nsure tha t distortion wa s minimize d b y

op era ting the F.E.T.s within a linea r region o f ope ra tion.

After several unsuccessful attempts at using F.E.T.s in gain reduction circuits, Putnam settled

upon the straightforward approach of using the F.E.T. as the bottom leg in a voltage

divide r circuit, which is pla ced a hea d o f a pre a mp sta ge .

The output stage of the 1176 is a carefully crafted class A line level amplifier, designed to

work with the (then) sta nda rd loa d o f 6 0 0 ohms. The he a rt of this stag e is the o utput

transformer, who se d esign a nd p er forma nce is critica l. Its primary function is to co nvert the

unbalanced nature of the 1176 circuit to a balanced line output, and to provide the

prop er impe da nce matching to drive the line impe da nce of 6 0 0 o hms. These two job s are

accomplished by the primary and secondary windings whose turns' ratio defines the

impeda nce ra tio.

This transformer is critical due to the fact that it uses several additional sets of windings to

provide feedback, which makes it an integral component in the operation of the output

amplifier. Putnam spent a great deal of time perfecting the design of this tricky transformera nd ca refully qua lified the few vendors ca pa ble of pro ducing it.

The first major modification to the 1176 circuit was designed by Brad Plunkett in an effort

to red uce no ise--hence the birth of the 1 1 7 6 LN, whose LN sta nds for low noise. Numerous

design improvements followed, resulting in at least 13 revisions of the 1176.

Leg end ha s it tha t the D a nd E blackfa ce re visions sound the most "a uthentic".

M ore Tha n a Vinta ge Fad : Classic So un d

Both the 1 1 7 6 a nd the LA-2 A rema in in da ily use. Busy engineers a nd prod ucers

comments abo ut both the 1 1 7 6 a nd the LA-2 A de monstra te their impact on the industry:

Mik e Sh ip ley

Mike Shipley (Def Lep pa rd, Shania Twa in, Blond ie ): "I gre w up using 1 1 7 6 s --- in Engla nd

they were the compressor of choice. They're especially good for vocals, which is also what

I primar ily use the LA-2 for. Most a nything e lse I can do without, but I ca n't be without a t

lea st a pa ir of 1 1 7 6 s a nd a n LA-2 A. For e xa mple, o n the Enrique Iglesia s project I'm


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currently mixing, I'm using b oth a n 11 7 6 a nd a n LA2 o n his voice, which is not unusual for

me.

"The 1 1 76 a bsolutely add s a bright chara cter to a sound, a nd you ca n set the a tta ck so

it's got a nice b ite to it. I usually use them on four to o ne, with quite a lot of ga in re duction.

I like how variable the attack and release is; there's a sound on the attack and release

which I don't think you can get with any other compressor. I listen for how it affects thevocal, and depending on the song I set the attack or release--faster attack if I want a bit

more bite. My preference is for the black face model, the 4000 series--I think the top end

is especially clean.

"The LA-2 A is not a s versa tile, b ut it also ha s a sound that I rea lly like. O n certa in voices

you can crank it heavily, to where you almost want to put a piece of tape over the meter

because there's so much gain reduction that you don't want anyone else to see it! I'm not

particularly into over-compression, but when you use it that way there's something about it

that just sounds really great. It does depend how it's set on the back, where there's a flat

control that can be set to roll off certain frequencies when you reduce more gain. If you

have a singer with an intensely piercing voice I find that compressor a good one,incredibly useful. It makes things warmer, especially when you crank it, and for thinner

voices tha t ca n be just the ticket."

Al le n Side s

Allen Sides ha s a lwa ys bee n known for ha ving g olden e a rs when it comes to the sound of

eq uipment. The owne r of O cea n Wa y Studios in Los Ange les a nd N a shville, he 's a lso a

speaker designer and engineer who is especially respected for his work with live

musicians, including orchestra and string dates. Among his recent credits are work with the

Goo Goo Dolls, Alanis Morissette and Green Day. Sides brings his different perspectives

into pla y when he talks ab out using the 1 1 7 6 .

"The 1176 is standard equipment for my sessions. I just used them last night, as a matter of

fa ct, on a pro ject for singe r Lisa Bone t tha t Rob Cavallo wa s prod ucing a t O cea n Wa y.

We were record ing d rums and I used them on the left/ right overhea ds a s effects limiters.

It's something I lea rned from (enginee r) Don La ndy, who wo rked with Ra ndy N ewma n a

lot. I mult the left and right overheads and bring them back on the console, then insert a

pair of 1176s into a pair of the mults. Push in 20 to one and four to one simultaneously

a nd it puts the unit into overdrive crea ting a very impre ssive sound ."

M urray Alle n

Murray Allen is a veteran engineer and Director of Post Production for the San FrancisoBay Area company Electronic Arts. He has a fascination for gear both old and new and

he explains why he thinks the 1176 has been so popular for so long. "It has a unique

sound to it tha t peo ple like, it's very ea sy to o pe ra te, a nd it do es a grea t job . You ha ve just

two controls relative to the ratio of compression. You have input and output and you have

attack and release. That's all there is. It's still my favorite limiter for Fender basses and

string basses, because you don't know it's working. It doesn't change the way the bass

sounds, it just keeps the level at a more controllable place.


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inconsistent piece to piece than the 1176s, because of the tubes and the difference in

fatigue of the tubes.

"My big mentors were Andy Johns a nd Lee DeCarlo a nd Ron N evision b eca use they were

all Record Plant guys. I learned how to make a rock and roll record from them. Although

over the years it's become my own thing, my style still tends to be that Record Plant style,

U87s, 1176s, LA-2As, 47 F.E.T.s...it's what I like."

M ik e Clink

Produce r/ Enginee r Mike Clink (Guns N' Roses, Sa mmy Hag a r, Pushmonkey) a lso comes

from the Record Plant school of recording. "I find that I actually use 1176s more now than

I ever did," he comments. "I like them because they bring out the brightness and presence

of a sound--they give it an energy. It seems like when I'm mixing I end up using an 1176

on the vocals every time. And if I want to compress a room sound I'll take a mono room

mic, put an 1 1 7 6 a cross it and push in a ll the b uttons."

Bruce Sw e de in

Bruce Swedien is a master engineer who needs no introduction. He also is a die-hard

1 1 7 6 fa n. "I ha ve two silverfa ce 1 1 7 6 LNs in my ra ck that Bill Putna m persona lly picked

out for me," he says. "I remember sitting at Bill's place in the Channel Islands, and talking

about the 1176 and how I wanted a pair . The next time we went over he'd picked this

pair out and they were sitting in his garage waiting for me. I love them on vocals. All of

the Michael Jackson and James Ingram vocals that everyone has heard so much were

done with at least one of those 1176s. I couldn't part with them for anything. They sound

fabulous."

Universal Audio La-2a_manual

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