1
UsersManual
TUBE-TECH LCA 2B
compressor and limiter
DESCRIPTION:
The TUBE-TECH LCA 2B is a two-channel unit with an independent compressor and
limiter per channel. The unit is all tubebased (except for the power supply and sidechain circuit). Output gaincontrol is placed be tween the VCA and output stage. The
VCA (1 dual triode) is placed between the input transformer and the output stage (2
dual triodes). The audio signal is picked up after the VCA and fed to the sidechain
circuit. The control signal from the compressor and from the l imiter is combined and
sent to the link switch and to the control amp, which feeds the VCA. The bi-directional
link busses are accessible at two 1/4" stere o jack sockets on the rear panel. The
channels can be linked together f or stereo applications and also linked to other LCA
2B's via the two link busses and a standard stereo jack/jack cord.
The co mpressor has six attack/release pr esets as well as manual control.Thelimiter
attack/release is fixed and equipped with an on/off switch.
The L ED display is fed from the control amp. The l imiter LED is fed from the li miter
buffer.
The a udio path is fully symmetrical from input to output.
Input and outpu t have fully floating transformers.
All DC voltages are stabilise d, except the anode voltage for the output stage, which is
only fi ltered.
COMPRESSOR INTERCONNECTION:
The sidechain sockets for interconnection of several compressors are located on the
rear panel.
A switch (LINK 1, LINK 2) on the front se lects which compressors are interconnected,
and on which bus they are connect ed. If you select LINK 1 on both channels, t hey will
perform exact t he same gainreduction.
Having several connected co mpressors in a rack, you can select which compressors
you will have working together.
By select ing e.g. LCA 2B no 1, ch. 1 on link 1, LCA 2B no 2, ch. 2 on link 1 and LCA
2B no 3, ch. 1 on link 1, they are now interconnected and all three will perform the
exact same compression.
The interconnection implies, that the unit, which performs the most compression , is
controll ing the others.
To cho ose which one you want to control, select the attack/release time, the threshold
and the ratio on that unit, and turn the threshold fully counter clockwise on the
reminding compressors.
It is of course possible to have all the interconnected compressors control each other
simultaneously.
(150205)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
2
CONTROLS:
GAIN:
DISPLAY:
LINK SWITCH:
IN/BYPASS:
COMPRESSOR:
The
control is used to "adjust" for the gain l oss, which takes
gain
place when the unit is compressin g. It is placed between VCA and
output st age. The
-control is continuously variable from -6dB to
gain
+10dB.
The g reen LED display shows the gainreduction for both the
compressor and for the limiter. A red LED shows if the limiter is
active.
The d isplay is fro m the factory supplied in dot mode. This can be
altered to a bar by placing a strap on U6 (U106) from
pin 3 to pin 9
Interconnects several compressors on link 1 or link 2.
If the compressor is left in the off p osition, it works entirely
independently.
This switch switches the compressor in and out of the signal path.
In the bypass po sition the entire u nit is switch out.
RATIO:
The
control varies the ratio by which the input signal is
ratio
compressed.
If the ratio selected is to 2:1, and the input signal increases 10dB,
the output signal is only increased by 5dB. The
ratio
control is
continuously variable from 1,6:1 to 20:1.
THRESHOLD:
The threshold is the point where the compressor begins its
action. It is defined as the point where the gain is red uced
by 1dB.
The threshold is related to the output le vel and is continuously
variable from off to -10dBU.
NOTE: If both the RATIO control and the T HRESHOLD control are at
their extreme (> 15:1 and < -5dB), overreaction can be
expected.
ATTACK:
The
attack
control chooses how fast/slow the compressor
responds to an increase in the input signal.
The a ttack control is continuously variable from 0.3 to 70
milliseconds.
RELEASE:
The
release
control chooses how fast/slow the compressor
responds to a decrease in the input signal.
The release control is continuously variable from 0,07 to 2
seconds.
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
3
ATTACK/RELEASE SELECT:
This switch selects how the compressor reacts to an increase
(
attack
) or decrease (
There are two settings of the switch:
1. Manual.
Attack ti me: from 0.3 mS to 10 mS
Release time: from 0.07 sec to 2 sec
2. Preset.
pos 1. 1,5 mS 0,25 S
pos 2. 1,5 mS 0,8 S
pos 3. 3mS 2,2 S
pos 4. 6mS 5,0 S
pos 5. 3mS 0,5/4 S
pos 6. 1,5 mS 0,5/4/20 S
release
) of the input signal.
Attack Release
The release time in position 5 and 6 is program dependent, that is:
pos 5, 6 for sho rt peaks: 0,5 S
pos 5, 6 for long peaks: 4S
pos 6 for continuously high levels: 20 S
LIMITER:
ON/OFF
THRESHOLD:
This switch defeats the limiter when in the
The threshold is related to the output le vel and is continuously
variable from off to 0dBU.
Ratio: 20:1
Attack: 0,6 mS
Release: 0,5 S
off
position
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
4
ADJUSTMENT PROCEDURE:
CAUTION:
Before making any adjustment let the unit heat-up at least 30 min.
Always check the DC voltages at the power supply.
When the VCA tube has been replaced, adjustment of:
BASIC GAIN
GAIN REDUCTION
BALANCE
shall be carried out
.
The a djustment procedure refers to channel 1. The trim pots in brackets are for
channel 2.
At the sidechain jack sockets at the rear of the unit, the tip is link 1 and the
ring is link 2.
ADJUSTMENT OF BASIC GAIN:
1) Turn the
THRESHOLD
-control for the compressor and limiter fully
counter-clockwise.
2) Apply a signal of 1 kHz, 0,0dBU to the input of the compressor.
3) Turn the
GAIN-
4) Adjust the preset
control fully clockwise (+10).
GAIN
P3 (P103) (located on amp/psuPCB)toanout-
put-reading of +10,0dBU.
ADJUSTMENT OF GAINREDUCTION
1) Turn the
THRESHOLD
-control for the compressor and limiter fully
:
counter-clockwise.
2) Apply a signal of 0,0dBU, 1 kHz to the input of the compressor.
3) Adjust the
-control to an output-reading of 0,0dBU.
GAIN
4) Apply a DC-voltage of +5,000 V into the sidechain jack socket (tip).
5) Set the
-switch at LINK 1 a nd observe that the output level has dropped to
LINK
-20,0dBU. If this is not the case, adjust the level with P7 (P107) at the
sidechain PCB, to obtain a drop of -20,0dB.
The level might increase a little (+0.5 to +1dB)fromtheinstantaneously value
(within 5-10 sec.). This is quite normal.
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
5
ADJUSTMENT OF DISPLAY
:
1) Turn the
THRESHOLD
-control for the compressor and limiter fully
counter-clockwise.
2) Apply a DC-voltage of +5,000 V into the sidechain jack socket (tip).
3) Set the
-switch at LINK 1 a nd observe that the -15 LED just turns off and
LINK
the -20 LED is on.
4) If this is not the case, adjust P8 (P108) at the sidechain PCB.
TEST OF TRACKING:
1) Turn the
THRESHOLD
-control for the compressor and limiter fully
counter-clockwise.
2) Apply a signal of 0,0dBU, 1 kHz to the input of the compressor.
3) Adjust the
-control to an output-reading of 0,0dBU.
GAIN
4) Apply a DC-voltage of +1.750 V into the sidechain jack socket (tip).
5) Set the
within -7,0dBUand-9,0dBU. If this is not the ca se, the VCA tube shall be
rejected and replaced with a new one.
-switch at LINK 1 a nd observe that the output level has dropped to
LINK
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
6
ADJUSTMENT OF BALANCE IN THE VCA TUBE (V1, V101):
As a quick check of the balance of the VCA tube, adjust the o utput to a level of 0
dBU
and turn the LIMITER THRESHOLD slow CW until the LIM led turns slightly on.
If the led turn on abruptly or starts oscillating, the balance should be read justed.
1) Turn the
clockwise, and the
2) Switch the
THRESHOLD
-switch to LINK 2.
LINK
-control for the compressor and limiter fully counter
-control fully clockwise.
GAIN
3) Apply a sine wave of 1 kHz, +15dBU via a 1Kresistor into the sidechain jack
socket (ring).
(The +15dBU shall be measured before the 1Kresistor.) *
4) Adjust trim pot P2 (P102) (located on amp/psu PCB) to a minimum reading at
the output.
5) Reduce the level of the sine wave to -5dBU.
6) Adjust trim pot P1 (P101) (located on amp/psu PCB) to a minimum reading at
the output.
7) Repeat step 3 - 6.
8) When both adjustments are at minimum, the level at the output shall be:
+15dBU less than -13dBU
+5dBU less than -14dBU
-5dBU less than -21dBU
If this cannot be obtained, the VCA tube shall be rejected and replaced with
new one.
* If the sine wave from the oscillator is observed on oscilloscope after the
1Kstor, the negative part of the sine wave has been clamped to ground.
We recommend that the balance adjustment of the VCA should be carried out
every 6 month.
NOTE: 0 dBU=0,775V
(941010)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
7
SPECIFICATIONS FOR LCA 2B
Input impedance:
Output impedance:
Distortion
(THD+n @ 40 Hz):
>2k
<60
0 dBU: <0,15%
10 dBU: <0,15%
Max output (1% THD+n): >+26dBU
Noise
(Rg=200):
Gain: 0 dB 10 dB
22 Hz-22 kHz: < -85 dBU < -80 dBU
CCIR-468-3: < -75 dBU < -70 dBU
Frequency response
Gain:
Crosstalk
CMRR
Tracking
(20 Hz-22 kHz): < -70 dB
(@ 10 kHz): < -60 dB
(0 to -20 dB gain reduction ): +/-1dB
(-3 dB): 5Hz- 40 kHz
-6 dB - +10 dB
LED display for gain reduction: 0dBto20dB
Compressor:
Ratio: 1,6:1 to 20:1
Threshold: off to -10 dBU
Attack (manual): 0,2 to 70 mS
Release (manual): 0,1 to 2 S
Preset attack/release:
Attack Release
pos 1. 1,5 mS 0,25 S
pos 2. 1,5 mS 0,8 S
pos 3. 3mS 2,2 S
pos 4. 6mS 5,0 S
pos 5. 3mS 0,5/4 S
pos 6. 1,5 mS 0,5/4/20 S
The release time in position 5 and 6 is program dependent , that is:
pos 5, 6 for short peaks: 0,5 S
pos 5, 6 for long p eaks: 4S
pos 6 for continuously hig h levels: 20 S
Limiter:
Threshold: off to 0 dBU
Attack: 0,6 mS
Release: 0,5 S
Ratio: 20:1
LED indicating limiting
Tubes:
Dimensions:
Weight:
2xECC81, 2xECC82, 2xECC83
H: 2 units, W: 19", D: 205 mm
6.5 kg
Power requirements:
(115V/230 V, 50-60 Hz): 30-45 W
All specifications at RL=600
Lydkraft reserves the right to alter specifications without prior notice (150130 JGP)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rø dovre
Denmark
8
SERVICE HINTS
:
SYMPTOM CAUSE ACTION
Noise Unbalance in VCA tube Adjust balance
Noise Noisy VCA tube (V1,V101) Replace and adjust
Noise Control amp IC 4 (IC 104) Replace. Check gain reduction and readjust
Hum +12V, +110V, +15V PSU Repair
Overshoot when compressing Unbalance in VCA tube Adjust balance
Oscill ations with no signal and
max ratio and low threshold Unbalance in VCA tube Adjust balance (replace tube)
(940530)
LYDKRAFT ApS
Mose Allé 20, DK-2610 Rødovre
Denmark
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