Well, at the moment when the eye catches brand logo, an advance respect to the gold unit is growing rapidly. We have a lot talked about the products of the brand in recent years, and Ground Zero (in regard to the amplifier), the beginning of his change of nationality from the US to the German, was associated with a fairly brutal models and model series, the tops of which are intended for the repair of hearing aids in the Competition for the maximum sound pressure.
However, in recent years a wide, to be sure, the model number of the brand emerged another trend — the release of the automotive High End, with the models presented in this category, once again confirm the prevailing view of Ground Zero — its developers around comes almost to the extent possible. On the other hand, when the lineup is as personable as at Ground Zero, it recommended indexes more closely to understand. For example, the same GZPA Reference 2 is different from said at the outset, not only technical specifications, but also the design up to the size, and all because you and I miss no important detail — the letter «T» at the end of the name …
Extruded aluminum body with patina «under the gold» a matter of respect — it is massive as befits a member, to act as a chassis, and as a cooler. Positive attitude adds the presence of traces of processing on a milling machine — in our times cheaper technologies such operations in mass production, as a rule, try to avoid. However, to say that the body is completely passive cooling provides the viscera, it is not necessary — the ends are provided fans ensure a constant flow of cooling air, it is also possible, and additional cooling.
It is interesting to consider that all of this is possible due to one important detail: the bottom cover is made of transparent plastic — at the expense of the associative design of the amplifier-ating the aquarium. And it should be noted, «fish» in the aquarium can please any radio engineer. First of all, editing and layout is — well, nothing superfluous, everything is done very carefully — «beautiful inside than outside.» Circuitry can be partially tracked with the naked eye. After input potentiometers, providing, by the way, the adjustment range of the amplifier sensitivity of about 40 dB, the analog signal is fed to an operational amplifier ORA2604 working as a newly Tory telya. Next ORA2604 has been used as a second-order high-pass filter with a cutoff frequency regulator Four-running scheme Butterworth filter with a cutoff frequency, adjustable from 41 to 5700 Hz. Switchable high-pass filter is made after him and found «something for which» — gain stage with a dynamic load (SRPP) on dual triode vacuum tube Milliard CV491. As already mentioned. Ground Zero, their designs pohoroshemu vehement and uncompromising. Lamps Mullard CV491, development 1957, can easily be replaced, say, or ESS82 12AU7, but it would be wrong to Ground Zero — selected the most audiophile option. Circuitry final amplifier laconic — a complementary pair of transistors in the output. Plus, such a solution — a high quality in a wide range of volume. Less also has a — very high power should be expected. Uncompromising circuit design, which consists also in the fact that both channels are identical, this deprives the device functions as a bridge switch. It seems that there is no need to get upset use of this class of amplifier in this mode — full profanity … This device is made on a «partial dual mono» — each «okonechnik» is equipped with its own power supply to the toroidal transformer. Schemes preamplifiers are fed separately from a common source, which is when the amplifier supplies power to the filament lamps for fifteen seconds before turning on the final amplifier — have to wait, but not for long.
The sound of the machine tested content on a wide variety of areas, ranging from full symphony orchestra with a range of up to a maximum absolute piano fortissimo to contemporary ambience. First of all, the machine pleases her microdynamics. The effect of masking the quiet loud parties is completely absent. Especially good middle of the range, to recoup with a transparent tube shade — female vocals, horns, especially in jazz recordings are very good. This percussion sounds absolutely clear, from the bass drum to a small triangle.
This time, start with the filter, as it is the simplest and the least intriguing. Filters very low, in line g the appointment of the amplifier, has said that its inclusion in a bridge circuit is not provided, it is the relationship to the subwoofer can not be and should not be, and therefore on the spine board only HPF. However, we note HPF exclusive broadband, in fact rebuilt ot41 cutoff frequency to 5700 Hz, and the perfectly executed: the amplitude at any frequency cutoff — Bessel filter 2nd order privechali hayendschikami for the best transient response.
SOI dependence on the power output characteristic of the hybrid amplifiers.
If you have a minimum signal «transistor» recession with growth of power, which is replaced by a monotonic increase in border after a few watts, which is typical for tube circuitry. In this zone, a reduction of the load resistance leads to reduction of distortion. Naturally, in the «tube» of the region is dominated by even harmonics, and a transistor — on the contrary.
Where as more reasons for their conclusions and / or guesswork give curves distortion of the output power. Here, the hybrid nature of the amplifier shows itself in all its glory. Look, at the lowest levels of the signal curve — purely «transistor» Dropping-schaya with increasing power. Here distortion at low impedance load naturally higher than in the low-resistance. One, going overseas units of Watts, the curve becomes a monotonically ascending character as tube devices. Here distortion at 2 ohm load are lower than 4 ohms at equal power, and it is said that they did not occur in the mind of the output stage, and stage voltage gain.
There is an assumption that if it were not for the tube stage, curves continued to go down until the early klip- ping is of a fine for a transistor amplifier. There is another assumption, or rather, already concluded, it concerns the nature of the regulator BIAS (bias in our opinion). It is still the regulator quiescent current, while increasing its curves start to go lower and continued to be, if the baton of responsibility for non-linearity interceptions room lamp, and it is no control action is not.
Now interesting to see whether the composition of the different harmonics in the «transistor» and «tube» zone. To do this, we took the spectrum of the output signal to the power of 50 MVT and 10W where CED exactly the same. In the first case we see: the spectrum is not just prevalent, and if appropriate reigns so expressed about the level of non-linearity of 0.04%), the third harmonic. Second hardly guessed, high, note, there is little that the «gut.»
The output signal at a power 10W picture is fundamentally different: tare becomes the second harmonic, which is famous for lamp technology, the third amplitude is less than 10 dB, that is, roughly — three times. It is clear who is in charge, the transistor output or lamp at the entrance. Rather, in the middle between input and output.