eq one assembly manual

eq one assembly manual
ASSEMBLY MANUAL
500 Series
17 Park Terrace Lane, Glasgow, G3 6BQ, United Kingdom
info@totalaudiocontrol.com www.totalaudiocontrol.com
INTRODUCTION
Thank you for purchasing EQ ONE in kit form. You will have a lot of fun in building and using it.
EQ ONE is one of the first in our flagship “Designed by Langley” series of pro-audio products. Yes, as the name reveals it is designed
by Mr Graham Langley, a name that requires no introduction. The premium quality components are used without any exception to
provide the highest performance and most reliable operational life. The PCBs are fully gold plated. Nothing is compromised.
EQ ONE follows the topology of the four band parametric equaliser that Graham first used in the Amek M3000 mixing console in
1979. This was later adapted for use in M1000 and M2500 consoles and formed the basis of the equaliser design in many other
Amek and Total Audio Concepts consoles.
As with the original design, 12dB/octave swept high and low pass filters are included. The frequency bands have been revised to be
more suitable for a stand-alone equaliser and noise performance has been improved.
The topology differs from many other state variable filter designs in that each band is composed of a 6dB/octave high pass and a
6dB/octave low pass filters with different turnover frequencies. This enables the bandwidth to be varied over a wide range and also
facilitates the Bell/Shelf switching on the High and Low frequency ranges. The Q control is disabled when in Shelf mode.
The parametric section and the filters section may be individually inserted in the signal path.
A single LED provides indication of signal level. This has quasi-PPM ballistics and illuminates green for signal present (-18dBu), yellow
for signals above +4dBu and red for signals above +18dBu.
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Figure 1: Block Diagram
Typical specification:
High pass filter:
Low pass filter:
High frequency:
High mid frequency:
Low mid frequency:
Low frequency:
20Hz to 400Hz @ 12dB/octave.
800Hz to 20kHz @ 12dB/octave.
660Hz to 20kHz, +/-15dB, Q: 0.25 to 1.5 with shelf mode.
320Hz to 10kHz, +/-15dB, Q: 0.5 to 3.2.
100Hz to 3.2kHz, +/-15dB, Q: 0.5 to 3.2.
32Hz to 1kHz, +/-15dB, Q: 0.25 to 1.5 with shelf mode.
Frequency response (EQ out):
Phase response (EQ out):
Maximum input and output (100k load):
Internal operating level/headroom:
THD&N (EQ in or out, +10dBu input signal):
Noise (no EQ in), 22Hz-22kHz, RMS, 40 ohm source:
Noise (typical EQ setup), 22Hz-22kHz, RMS, 40 ohm source:
Input/output impedance:
+/- 0.5dB, 20Hz-80kHz.
+/-20 degrees, 20Hz-80kHz.
+27dBu.
-6dBu/+27dBu.
better than 0.05%, 20Hz-80kHz.
-103dBu.
-90dBu.
20k ohms/75 ohms
ALL SPECIFICATIONS ARE SUBJECT TO CHANGE
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FEW WORDS ON ASSEMBLY
Before rushing into building your EQ ONE you should study this manual from front to back and familiarise yourself with the design
before starting to solder the first component. As the expression says “one picture tells a thousand words” each sequence is
photographically presented in detail.
The components are packed and numbered in the correct order. The numbers correspond to the bill of materials. Open them one at
a time. Do not open the next package before completing the assembly of the previous one. There is a reason behind each stage.
Populating a PCB always starts with the smallest components. Resistors and/or small signal diodes being the first. If you solder the
larger components first you’ll have a hard time in soldering the resistors or the small signal diodes.
Before soldering a component visually check its value and designation. Although normally it is not required, testing them would also
be a good practice (excluding integrated circuits) before they go on the board. We are extremely lucky to be living at a time when a
reasonably well performing digital multimeter with semiconductor testing capability or a capacitance meter can be picked up from ebay for the cost of literally a burger meal. Therefore, investing into a few handheld meters would pay dividends in the long run.
A good quality soldering iron and a set of hand tools are a must. Component leads are not trimmed using a Black Smith’s pliers. A
miniature close cutting side cutter will have to be a part of your tool kit. Equally fixing an M2 screw will not be possible with a screw
driver normally used for M10 bolt. A simple spring action desoldering pump will do fine for single sided boards. But for double
sided/plated through boards such as this a proper (electric motor pump action) de-soldering tool will be essential. However, you do
not have to get the ones that require re-mortgaging your house. There are affordable ones that will also do a good job.
Most faults will arise due to incorrect components being inserted or solder bridges. It is particularly important to closely examine
the soldering of components with close pads such as transistors. Therefore, unless you have eagle eyes having a good quality hand
held magnifier in your tool kit will save you a lot of time and trouble. A next step up is a table mount, illuminated magnifier.
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Do not stay on the components with the soldering iron for too long as there can be a possibility of causing damage. You should be
able to get in and out of a solder node within few seconds.
There is no need to crop connectors, potentiometers or switches unless specified.
In general do not rush. Work methodically and have fun.
Total Audio Control
March 2013
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LD020 MAIN EQUALISER PCB (ZOOM IN TO ENLARGE).
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COMPONENT DESIGNATIONS WITH VALUES
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LD020B MAIN EQUALISER PCB ASSEMBLED.
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LD034B I/O SUB CARD (ZOOM IN TO ENLARGE).
COMPONENT DESIGNATIONS WITH VALUES
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LD034B I/O SUB CARD RIBBON CABLE ASSEMBLY
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SUB CARD ASSEMBLIES:
TOP LEFT LD021B FILTERS SUB CARD
TOP RIGHT LD026 SWITCH SUB CARD (MATES WITH LD025B).
BOTTOM FROM LEFT TO RIGHT;
LD022 HIGH FREQUENCY SUB CARD.
LD023 HIGH MID FREQUENCY SUB CARD
LD024 LOW MID FREQUENCY SUB CARD
LD025 LOW FREQUENCY SUB CARD (MATES WITH LD026)
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LD021B FILTERS SUB CARD ASSEMBLY
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LD022B HIGH FREQUENCY SUB CARD ASSEMBLY (REPEAT FOR LD023B, LD024B and LD025B)
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LD023 HIGH MID FREQUENCY SUB CARD
LD024 LOW MID FREQUENCY SUB CARD
LD025 LOW FREQUENCY SUB CARD (MATES WITH LD026).
LD026 SWITCH SUB CARD (MATES WITH LD025B).
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LD025B AND LD026B COMBINATION SUB CARD ASSEMBLY. THEY ARE KEPT APART BY THE TWO SPACERS SUPPLIED.
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PLACE SUB CARD ASSEMBLIES INTO THEIR POSITIONS AND CONNECT THE RIBBON CABLES INTO THE BOX HEADERS
RESPECTIVELY.
EACH SUB CARD ASSEMBLY POSITION IS CLEARLY MARKED ON THE MAIN BOARD
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MAIN BOARD SITS INSIDE THE BACK PLATE AND IS FIXED BY FOUR M2 SCREWS INTO THREADED INSERTS.
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MAIN BOARD IS FIXED TO THE LEFT HAND SIDE PLATE BY TWO M3 SCREWS ON
THE LEFT (FIX1-FIX11) AND TWO HEX PILLARS ON THE RIGHT (FIX2-FIX 12). ONE END OF THE HEX PILLAR IS
THREADED MALE WHICH SCREWS INTO THE SELF CLINCHING NUT.
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FACEPLATE IS FIXED ONTO THE BACKPLATE BY FIVE M3 SCREWS FROM THE INSIDE.
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CONNECT THE RIBBON CABLE TO THE BOX HEADER ON THE MAIN BOARD AND FIX THE IN/OUT CARD USING FOUR
M3 SCREWS INTO HEX PILLARS.
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RIGHT HAND SIDE SCREEN PLATE IS FIXED USING TWO M3 SCREWS INTO HEX PILLARS, AND TWO M2 SCREWS INTO
THE BACK PLATE.
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LED AND KNOB COLOUR CODING.
LF BELL
HF BELL
EQ IN
FILTERS IN
GREEN
GREEN
BLUE
BLUE
HIGH PASS
LOW PASS
FREQUENCY
LEVEL
Q
GREEN
GREEN
GREEN
RED
BLUE
APPLICATIONS.
EQ IN
FREQUENCY
LEVEL
Q
HF BELL
LF BELL
FILTERS IN
HIGH PASS
LOW PASS
SIG
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APPLYING POWER
Before applying power visually check and inspect the module one last time.
Check that no ICs are inserted the wrong way round.
After switching the module on do the following checks.
Do all the illuminated switches light up on pressing them?
Does anything smell of burning or feel excessively warm. If so switch off. Wait a short time then switch on power
again and try to locate the component that is warm.
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INITIAL MEASUREMENTS
If all seems well, using a DC voltmeter measure each of the test points referenced to GND (TP13).
All these figures are nominal and can vary due to component tolerances, particularly with output offset voltages.
However, large deviations may indicate a fault.
1). Measure the supply voltages. Note that approx. 250mV is dropped across the PTCs at the quiescent current of
about 120-130mA.
TP11
TP12
TP13
+15.75V
-15.75V
0V
+VDc
-VDc
GROUND
2).Measure current consumption if possible.
The positive rail draws slightly more current due to reference for the level indicator.
Quiescent, no signal = +130mA/-111m
+4dBu through all sections into 200k = +130mA/-111mA
+23.5dBu through all sections into 200k =+145mA, -126mA
+23.5dBu through all sections into 600R =+163mA, -144mA
The additional current in the +rail is largely due to the reference for the LED “meter”
Since this module occupies two “API” slots the current consumption is within the specification of 160mA/module
position.
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3) Set input to 0dBu and observe/measure output signal – it should be 0dBu +/-0.5dB
4) If possible do sweep
5) If all seems well, using a DC voltmeter measure each of the test points:
Below off-set voltages should be close to zero under no-signal conditions.
TP1 Output of input stage.
TP2 Output of filters stage.
TP3 Lo input to peak detector.
TP6 Hi input to peak detector.
Below voltages could be up to +/- several hundred mV and will vary with the settings of the EQ controls.
TP7 HF stage output.
TP8 HMF stage output.
TP9 LMF stage output.
TP10 LF stage output DC input to meter
TP11 +15.8V +VDC
TP12 -15.8V -VDC
TP13 0V GND
TP14 +858mV +4dB meter reference
TP15 +4.34V +18dB meter reference
TP16 +69.7mV Signal present meter reference
TP17 + Meter input (DC)
TP18 +12V 12V meter reference
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Below voltages will have to be confirmed after Output Symmetry Trimming.
TP4 -2.24mV Main output Lo
TP5 -1.69mV Main output Hi
If you do not have the facility to carry out this operation skip the OUTPUT SYMMETRY section and
follow the below procedure.
 Manually adjust the wiper of VR2 to mid position by measuring both sides with your multimeter
before fitting it onto the board.
However, due to component tolerances the null point could end up being at any position, so we have to
assume that SYMMETRY will only end up being "reasonable" if not trimmed.
DC OUTPUT:
Many output stages are DC coupled in order to minimise the number of electrolytic capacitors in the signal path.
Capacitors on the inputs and outputs of equipment can fail when accidental connections are made to voltages
that exceed their working voltage – such as phantom power.
The typical DC output that one might find on each leg is +/-5mV. It will not necessarily be the same on each leg.
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OUTPUT SYMMETRY:
Symmetry is a measure of how much the device can suppress common-mode signals at its output
Symmetry is ideally measured with a balanced output level of +20dBu.
The gain of the signal path should remain as close to unity gain as possible to minimise noise contribution at the
output.
Symmetry is measured at the junction of two closely matched 300R resistors (600R load) and trimmed to
achieve a null at 20kHz.
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PROCEDURE:
Make a normal balanced connection to the device under test as shown above.
Connect the measuring instrument using two 300R closely matched resistors as shown above.
Release FILTERS IN and EQ IN switches (FILTERS and EQ by-passed).
On the signal generator, select low output impedance and a frequency of 20kHz.
Adjust the signal generator level to obtain an output from the device under test of +20dBu.
Adjust the input SYMMETRY trimmer for minimum output and note the level if required.
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TYPICAL AP PLOT OF OUTPUT SYMMETRY FOR DISCRETE CROSS-COUPLED OUTPUT
The top curve is the normal output feeding 600R.
The bottom curve is the trimmed symmetry signal.
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SIGNAL PATH TESTS:
These tests should be carried out using balanced input and output signals.
Input signals should be from a low impedance source and the output load should be greater than10k ohms.
1) Test with neither FILTERS nor EQ switched IN.
2) Test with just FILTERS IN. Set frequency controls so that HP is fully anticlockwise & LP is fully clockwise.
There should be no noticeable level change in mid band signals when FILTERS are IN or OUT.
Sweep each control and notice tonal change corresponding to the filtered frequency band.
When HP is fully clockwise & LP is fully anticlockwise the sound will be attenuated and telephone-like.
3) Test with just EQ IN.
Set all parametric control pots to 12.00 o'clock.
Test one band at a time.
Turn boost/cut knob to fully boost and sweep frequency.
Test operation of Q control.
Repeat with boost/cut knob to fully cut.
Ensure sound is as expected for given frequency range.
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4) For HF and LF the Q control is not active unless BELL is selected.
Operating the BELL/SHELF switch may cause small clicks. This is normal.
5) If there are loud clicks when operating any switches, or if there are thumps or significant noise when
operating any of the controls there is a fault.
Check section output test points for any DC to locate the source.
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CURVES.
BOOST/CUT LINEARITY
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PHASE
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FILTERS LEVEL
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HF BELL LEVEL
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HF SHELF LEVEL
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HF SHELF / BELL FREQUENCY LEVEL COMPARISON
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HMF BELL LEVEL
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LMF BELL LEVEL
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LF BELL LEVEL
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LF SHELF LEVEL
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