EQ is available everywhere. EQ is on everything we buy in pro audio. EQ is perhaps the most common audio tool in the market. EQ is used in every aspect of the recording process; and any studio engineer has his/her favorites… Ted Fletcher is not new to EQ. From his console designing days, he has produced many designs, and has heard a great many more… His favorite design of all time has now become the TDE; Ted’s Definitive Equaliser!
- Wide bandwidth
- High Quality Transformer inputs
- Uniquely warm glossy sound
- High capacity output stage
- NO POTS!! All controls are switched.
What Makes the TDE?
The TDE is a two channel, four band EQ. 2 bands are high and low shelving, 2 bands are parametric mids. There are high and low pass filters on each channel. The first major difference with the TDE from other EQs from the outside is that none of the controls are potentiometers (pots), they are all switches. This is a major feature of older equipment, that enables precise control over every parameter, and repeatability of results. Over the years, with things like EQ, pots have replaced switches to save on manufacturing costs, however, for the purist, pots can be very inaccurate and failure prone. On the inside, the TDE features a classic design of EG using inductors and vintage amplifiers. This design is an adaptation of Barry Porter’s classic that oozes musicality and richness. The amplifiers are pure class A, discrete that in themselves add a quality that is hard to define, yet unmistakable.
The P9’s inductor driven EQ does more than simply cut and boost frequency. Gentle phase transitions make the EQ applied sound completely natural and warm. Even with the most gentle EQ setting, music sounds warmer and more complete. As a mastering tool, the P9 can subtly enhance the mix in ways that you can hardly measure, but are unmistakable to the ear. The P9’s switched settings give the engineer confidence in the basics of what the P9 is doing to the mix, but the subtleties will remain a mystery, leaving plugin EQs sounding brittle and dull in comparison. Because of the P9’s extreme smoothness, you can apply heavy EQ to a sound before losing any musical qualities. That’s not to say that the EQ goes unnoticed though, under heavy EQ, sounds take on a completely new character that is unmistakably the classic design of this EQ working hard. When used to extremes, the P9 is an awesome musical tool, shaping sound to amazing effect.
Each P9 channel comes with high and low pass Sallen and Key filters on 4 way switches for 3 frequency settings and an off position. In use, these filters are as smooth as it gets. Useful for tracking and the mix.
The P9 is not a cheap equaliser. It is designed to be everything that Ted Fletcher could possibly want from an EQ, and each unit is hand made to his exacting standards in England. It is a product exclusively for people who can hear the difference, and want the best for their sounds and mixes.
The P9 features, 2 channels of…
- 4 bands of Inductor based EQ
- All switched settings (rotary and toggle)
- 12 EQ gain stages
- boost/cut per band (24 gain positions in total)
- Mid Q shaping (2 bands)
- 11 input and output gain settings
- 3 way high pass filter
- 3 way low pass filter
- input clip meter
- post EQ 9 LED meter
- EQ bypass switch
All rotary controls are multi-position switches with the gain or equalisation set by fixed 1% resistors. It’s a 2-channel unit with a common built-in power supply, separately screened to eliminate any interference between the mains transformer and the sensitive inductors used in the mid frequency circuits.
The Input stage
The line level Input stage uses a completely new circuit incorporating a precision input transformer (giving 5KV fully floating isolation) followed by a balanced gain-correcting amplifier formed from dual silicon (not J-Fet) operational amplifiers arranged so that gain is shared and kept to a minimum. The op-amps are types with minimal 3rd order distortion and extremely low noise.
Operating level is chosen so that from a noise floor of around 118dB below input, and a maximum level within the stage of +26dBu, we can achieve a stage signal/noise ratio of 112dB and at the same time, an overload margin of 32dB. This input stage performance is achieved across a bandwidth of 1OHz to 2SKHz (although these figures may be modified later in the circuit) and THD is not sensibly measurable, even at low frequencies. (Normal transformer input stages would exhibit non-linearity below 30Hz at levels above OdBu, and conventional transformerless inputs are prone to hum and balance problems and would not meet these noise criteria).
Both High-pass and low-pass filters are optimised Sallen and Key designs using specialist op-amps operating at unity gain to provide the buffering. The filter slopes are at 12dB per octave.
The HF and LF Filters
The design achieves lift or cut by applying frequency selective feedback around an amplifier. A single amplifier is used for both HF and LF. The amplifier uses discrete transistors and operates from a single rail 45-volt power supply in true class A mode.
The equaliser gives shelving curves with gentle phase transitions and a maximum slope of 6dB per octave. Turnover frequencies are selectable.
The MF Equalisers
Tuned circuits with controlled damping, made up of hand-wound iron-core Inductors and high-stability capacitors, are used in feedback circuits around a second discrete transistor amplifier to produce the mid frequency controls. The frequencies are switch selectable, and the ‘Q’ value is also selectable on each circuit with a 2-way toggle switch. The proposed ‘Q’ values are 0.7 and 1.2 but this value Is still open to development.
The Output Stages
Low noise, low gain op-amps with resistor ladder gain setting provide the output level set, and the line output is provided by a balanced, auto correcting output arrangement capable of driving +26dBu into any (sensible) load.
Where op-amps are used, they are selected to be low noise silicon types, and gain is restricted to ensure rigid stability (complete transparency) even during overload conditions. The class A discrete amplifiers are designed with active current source loads to maintain gain margins under adverse conditions. Coupling capacitors used in the audio path are all high stability types Electrolytic capacitors are only used for power supply purposes.
An input clip LED flashes on when the signal following the input stage reaches 2OdB below clip. (12dB above operating level). An LED array shows the peak audio level immediately before the output gain control.
Although I maintain that published performance figures mean very little nowadays, I do expect this equaliser to meet the following real and practical specifications.
- Input 2OKohm predominantly resistive impedance. -ISdBu to * ISdBu nominal level. Floating earth free balanced.
- Output 1SO ohm source impedance balanced. Max level +26dBu
- Filters, frequencies to be defined. 12dB per octave. Equaliser, see front panel drawing for specified parameters. Noise, approx. 1OOdB below input RMS 20Hz to 20KHz.
- Distortion, 3rd order less than 0.002% at any level up to +20dBu out.
- 2nd order may rise to 0.1% under some conditions, but normally within O.O2%.
- Amplitude Frequency Response, 3dB down points at 8Hz and 30KHz. With EQ switched flat’, within 0.4dB 20Hz to 16KHz.
- Switch accuracies, aiming for 0.1dB where gain is specified in O.SdB steps, and generally to within 5% of specified level measured in AC volts.