The preamplifier functions as the control center of your component music system. It is the interface between the audio sources and the basic power amplifier. It provides appropriate switching, and adjustment of the volume, balance and tonal correction, as well as the additional amplification and frequency compensation required for magnetic phono cartridges. Given the wide choice of preamplifier designs, a price range of ten times or more, some laden with features, and others burdened with notable complexity, there is a natural tendency for you to expect that the highest performance will necessarily be achieved with the most costly designs. This need not be true. The David Hafler Company has a tradition of maintaining a very high level of quality while achieving substantial cost reductions in our products. In the DH-100 we have state of the art. Performance in a handsome unit which is very modest in cost.
Our philosophy has always been to produce maximum performance at minimum cost, offering exceptional value in every one of our designs. The ability to achieve this is based on our expectation that the merits of each product will be so well recognized that demand will enable us to produce it in substantial volume, with the attendant economies in purchasing and manufacturing. Some of the design features which contribute to this value factor are:
Elimination of frills, such as unnecessary inputs, loudness controls, and the like, while we provide all the important features
Careful component selection and painstaking distillation of each circuit to its essentials delivers unsurpassed performance.
We develop a physical arrangement which enables reliable, reproducible performance with easy low cost assembly techniques.
We expend a large amount of engineering time to make our designs conform to close standards, without the need for time-consuming adjustments.
A further benefit of these factors is that our designs can be supplied as kits with ease of assembly and assurance of success for the builder, with additional savings.
While the DH-100 exemplifies the "no-frills" path to ultimate economy, it is replete with subtle features which are not apparent at first, but which make a significant contribution to its superior performance:
Low impedance power supply maintains that characteristic out to the highest audio frequencies.
A delay circuit provides muting to eliminate surges and "pops" at turn-on
Unused inputs are isolated to prevent feedthrough and consequent distortion from unselected sources
Precision RIAA phono equalization and a balanced tone control circuit assure flat response.
Sufficient line output enables the use of high impedance headphones for direct listening, as an alternate to the power amplifier connection.
A goal of the lowest possible distortion is axiomatic. The conventional harmonic and intermodulation distortion of the DH-100 are almost unmeasurable. But further, we determined to make some of the more obscure forms of distortion equally inoffensive. Outside of conventional audio band it is possible for signals to intermodulate, producing distortion products inside the listening range. This ultrasonic intermodulation is an insidious form of distortion that is not shown in conventional specifications. Some engineers try to reduce it by rolling off the response of the unit so that out-of-band signals are not being reproduced. Our method is to make a very wide band design which can handle high frequency signals cleanly, so that they will not create intermodulation or transient distortion which might be audible.
We have paid special attention to maintaining stereo separation out to the highest frequencies so that phase information remains accurate between the two stereo channels. This provides a stable and sharply defined stereo image.
In selection circuit components, we used special listening tests based on amplified bridge comparisons, so that we could identify those items which adversely affected sonic quality. This LED to the exclusive use of polypropylene and polycarbonate capacitors in the signal path, because their superior quality justified the higher cost. Like the circuit design, the parts which comprise it were selected for the most accurate sound quality attainable.
Specifications
Phono preamp Section
Rated Output: 3 V rms
Max. Output: 8 V rms
Total Harmonic Distortion : less than 0,005%
RIAA Frequency Response :±0,25 dB (20 Hz - 20 kHz); ±0,1 dB (40 Hz - 20 kHz)
Sensitivity: 10 mV (for 1/2 volt at Rec Out)
Max. Input: 180 mV at 1 kHz
Gain: 34 dB at 1 kHz
Input Impedance: 47,5 k Ω in parallel with 130 pF
Signal-to-Noise Ratio better than 100 dB (A-weighted)
Line Amplifier Section
Rated Output: 3 V rms
Max. Output: 8 V rms
Total Harmonic Distortion : less than 0,005%
Frequency Response: ±0,25 dB (20 Hz - 20 kHz)
Gain: 20 dB
Input Impedance: better than 35 k Ω
Signal-to-Noise Ratio : better than 100 dB (A-weighted)
Crosstalk: down 80 dB
Separation: better than 70 dB (at 1 kHz); 55 dB (at 10 kHz)
Controls
Bass ; ±10 dB at 20 Hz (Moving inflection type)
Treble : ±10 dB at 20 kHz (shelving type)
General Specifications
Semiconductors: 7 ICs; 5 Diodes; 1 LED
Inputs: Phono, Tuner, Aux, Tape
'outputs: Record, Line
Power Requirements: AC Supply Voltage 95 - 130 V or 190 - 260 V 50/60 Hz
Power Consumption: less than 5 watts
AC Outlets: 2 switched
Dimensions (W x H x D): 13-9/16" x 3 " x 10"
Weight: 7 lbs net
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