Klark-Teknik DN300 Graphic Equaliser
Operating and Service Information
This document provides comprehensive operating and service information for the Klark-Teknik DN300 Graphic Equaliser, a 30-band unit designed for professional audio applications.
Introduction
The graphic equaliser is a crucial component in audio systems, influencing the overall sound quality. The Klark-Teknik DN300 offers high performance and reliability, utilizing proprietary 'MELT' (Micro-Electronic) filter circuits, which are warranted for 5 years. While graphic equalisation can correct many response issues, it cannot fix fundamental acoustic problems like standing waves or excessive reverberation. For complex acoustic environments or specific needs, parametric equalisers may offer greater control. When using an equaliser, significant boost or cut may indicate underlying system or room acoustic issues that require separate attention.
Instrument Familiarisation
Front Panel Functions
The front panel features 30 faders, each corresponding to a specific frequency band (25Hz to 20kHz) for precise adjustment. Controls include:
- Power Switch: A two-pole switch that illuminates a red status LED when the unit is powered on.
- Output Level Control: Adjusts system gain from full attenuation to +20dB.
- Bypass Switch: Silently removes the equaliser and high/low-pass filters from the signal path.
- Slope Switch: Selects the low-pass filter slope between 6dB/octave and 12dB/octave.
- Overload LED: Illuminates when signal levels exceed a threshold set 3dB below clipping (+19dB), indicating potential signal distortion.
- Low Frequency Filter (High Pass): Continuously variable turnover frequency from 15Hz to 300Hz.
- High Frequency Filter (Low Pass): Continuously variable turnover frequency from 2.5kHz to 30kHz.
- Faders: Oil-damped for smooth operation with a centre detent for accurate 'flat' settings.
Rear Panel Functions
The rear panel provides connection and configuration options:
- Mains Input: IEC standard 3-pin connector for power supply.
- Voltage Selector Switch: Allows switching between 110V and 220V nominal supply voltages. The unit must be disconnected from the mains before changing this setting.
- Fuse Holder: Houses the mains fuse, which must be replaced with the correct type and rating.
- Earth-Lift Switch: Disconnects the signal ground from the mains and chassis earth to resolve earth-loop hum issues.
- Input/Output Connections: Complementary XLR sockets for balanced or unbalanced signals.
- Serial Number: Located for reference in correspondence.
Audio Connections
Input
The input circuitry is transformerless and electronically balanced, offering high symmetry. Transformer balancing is available as a factory-specified option only.
Output
The standard output is unbalanced. Balancing transformers can be retrofitted. The output circuitry can drive a 600-ohm load at a level of +22dBm.
Connection Details
Input/Output XLR Pinouts:
- Unbalanced: Pin 1 (Ground), Pin 2 (Signal), Pin 3 (No connection or Ground).
- Balanced: Pin 1 (Ground), Pin 2 (Hot/Positive Signal), Pin 3 (Cold/Negative Signal).
In a balanced system, either pin 2 or pin 3 can be designated as the 'HOT' terminal.
Balanced Circuits
Balanced connections provide 'common mode rejection', reducing interference from external sources like mains hum. This is particularly beneficial for long cable runs. Transformer-balanced circuits offer an additional advantage of being 'fully floating', isolating the signal ground from the chassis ground, which helps prevent grounding problems.
Specifications
| Parameter | Specification |
|---|---|
| Input Type | Electronically balanced |
| Input Impedance | Balanced: 20k ohm, Unbalanced: 10k ohm |
| Output Type | Unbalanced |
| Min. Load Impedance | 600 ohms |
| Source Impedance | <60 ohms |
| Max. Level | +22dBm |
| Frequency Response (Eq Out) | ±0.5dB (20Hz - 20kHz) |
| Frequency Response (Eq In) | User defined |
| Distortion (@ +4dBm) | <0.01% @ 1kHz |
| Equivalent Input Noise | <-90dBm (20Hz - 20kHz unweighted) |
| Overload Indicator Threshold | +19dBu |
| Level Control | +6dB to ∞ (infinity) |
| Filter Type | *MELT (Proprietary Microcircuit) |
| Number of Filters | 30 |
| Centre Frequencies | 25Hz - 20kHz (1/3 octave steps) |
| ISO Tolerance | ±5% |
| Maximum Boost/Cut | ±12dB |
| High Pass Filter Slope | 15Hz - 300Hz (12dB/octave) |
| Low Pass Filter Slope | 2.5kHz - 30kHz (6dB/12dB/octave) |
| Power Requirements Voltage | 110/120/220/240V, 50/60Hz |
| Power Consumption | <15 VA |
| Weight (Nett) | 3.5kg |
| Weight (Shipping) | 6kg |
| Dimensions (Width) | 482mm (19 inch) |
| Dimensions (Depth) | 205mm (8 inch) |
| Dimensions (Height) | 89mm (3½ inch) |
| Terminations (Input) | 3 pin XLR |
| Terminations (Output) | 3 pin XLR |
| Terminations (Power) | 3 pin CEE |
Circuit Description
Input Section
The input signal enters via an XLR connector and is processed through a relay (RL1) and R.F. filter networks (R7/C20, R12/C22) to a differential input amplifier (IC1). Common mode rejection is factory set for maximum effectiveness. This is followed by an input level control and a non-inverting amplifier (IC2B) providing 3dB gain.
H.F. and L.F. Cut Filters
The signal then passes through 12dB/octave second-order Butterworth filters for High Frequency (HF) and Low Frequency (LF) cut. The HF cut filter can also be switched to a 6dB/octave slope. Turnover frequencies are continuously variable: 15Hz-300Hz for LF cut and 2.5kHz-30kHz for HF cut. These filters are implemented using active circuits, replacing traditional inductors to avoid distortion and hum.
Equaliser Section
The 30 equaliser filters are divided into two sections, with odd-numbered filters connected to IC4 and even-numbered filters to IC5. Each filter circuit functions similarly to a passive LCR network, but uses an active circuit (incorporating a proprietary KTR008 device) in place of the inductor. Faders control the gain at each filter's centre frequency, providing boost or cut. The frequency is determined by a capacitor (Ca), and the maximum boost/cut by resistor (Ra).
Output Section
The output amplifier (IC6) is a non-inverting stage with 4dB gain and high current drive. It is AC-coupled and connected to an output transformer socket (SKT8). For unbalanced units, links connect the signal to the output XLR connector via a bypass relay (RL1). For balanced outputs, the transformer is connected.
Bypass Relay and Delay
A failsafe relay (RL1) is incorporated to automatically bypass the equaliser in case of power supply failure. A delay circuit ensures the relay engages 2 seconds after power-on to prevent 'clicks' and disengages instantly on power-off.
Relay Delay Circuit
When power is applied, a capacitor (C15) charges, triggering a transistor (Q3) via a diode (D10) and resistor (R3) to activate the bypass relay (RL1). Powering off causes the capacitor to discharge, instantly switching off the relay.
Overload Detect Circuit
An overload detection circuit uses an amplifier (IC7) and diodes to monitor signal levels at multiple points. If a signal exceeds +19dB, an LED (D1) illuminates, indicating potential overload. Components R40 and C41 extend the 'on' time of this circuit for better transient display.
Power Supply
The unit uses a +/-18V power supply derived from a toroidal transformer. A voltage selector switch (SW2) allows operation at 110V or 220V. The supply includes a full-wave bridge rectifier, smoothing capacitors, and integrated regulators. An LED (D2) indicates power 'on'.
The Use of Graphic Equalisers
Graphic equalisers serve both corrective and creative purposes in live sound and studio applications. In studios, they can compensate for control room acoustic deficiencies, with the DN300's 30 bands offering precision. For live sound, they are often used on stage monitors or foldback systems to reduce feedback caused by speaker response peaks or stage reflections. While equalisation can mitigate acoustic problems, it cannot eliminate fundamental issues like standing waves or excessive reverberation. For challenging acoustic environments, careful system setup and analysis are crucial. It is generally recommended to attenuate peaks rather than boost dips, as excessive boosting can consume amplifier power and cause distortion. Creative uses include filtering voices for telephone effects or modifying instrument tones.
Equalising a Sound System
The primary goals of sound system equalisation are to increase potential gain before feedback and to improve the naturalness or intelligibility of the sound. A systematic approach involves listening to the raw system, performing sine-sweep tests, and checking frequency coverage. Gradual adjustments are preferred, especially in critical listening environments. Using a real-time analyser with averaging capabilities can help smooth out local fluctuations and highlight problematic peaks and dips. Patience and careful listening are essential throughout the process.
Inserting the Equaliser in the Signal Chain
The placement of an equaliser in the signal chain depends on the application, such as mixer channel input, group insert, or auxiliary send. For systems with digital delay lines used for synchronisation, the equaliser can be placed before or after the delay line. In complex systems with multiple loudspeaker types or varying acoustic environments, individual equalisers may be needed for each delay channel to address specific loudspeaker responses or room effects. Equalisers are best viewed as a final tuning measure to enhance intelligibility and perceived sound quality, rather than a solution for fundamentally flawed system design.
Warranty
Klark-Teknik warrants the DN300 against defects in components and factory workmanship for one year from the date of purchase. The proprietary 'MELT' filter circuits are warranted for five years. The warranty covers repair or replacement at Klark-Teknik's option, provided the unit is returned shipping pre-paid to an authorized service facility. The warranty is void if the product is subjected to unauthorized repairs, misuse, negligence, accident, or improper connection/operation. This warranty does not affect statutory customer rights.
Service Request Form
A Service Request Form is provided for users to detail malfunction symptoms, affected channels, operating conditions, fault nature (permanent/intermittent), and troubleshooting steps taken. This form should be completed and sent to Klark-Teknik before returning the unit, with a duplicate attached to the returned product.
Important Note
Users are advised to contact their dealer or the factory to explain any problems, as many issues can be resolved without returning the unit. If return is necessary, original packing should be used. Factory-authorized service facilities are located globally.
Fader Setting Record Chart
A Fader Setting Record Chart is included to allow users to document the specific fader positions for their equaliser settings, useful for recalling or replicating specific sound configurations.
Frequency Range Chart
A Frequency Range Chart is provided, correlating musical notes and octaves with their frequencies. It also cross-references these frequencies with the ranges covered by Klark-Teknik's Graphic Equalisers (DN22, DN27A, DN30/30) and the typical frequency ranges of various musical instruments and vocal types.
