Three-channel multimedia UMZCh (there is a printed-circuit board)

Despite a set of models multimedia the EXPERT of industrial production, interest of radio fans to independent manufacturing of similar designs does not decrease. The particular interest is caused by systems with the general low-frequency channel. A low-frequency loudspeaker — a subwoofer — thus place in the separate case that the EXPERT of the left and right channels allows to reduce considerably dimensions. The amplifier described here also is intended for this sort of designs with the general rated power about 20 W.

can carry rather small sizes of a video monitor and dimensions of the speaker system placed, as a rule, in close proximity to the listener corresponding to them To features of a multimedia complex. In this regard the maximum capacity of amplifiers for such EXPERT usually does not exceed 10... 20 W. The proximity of an arrangement of the multimedia speaker system quite often limits its admissible sizes therefore placement of a low-frequency head here is widespread in one general case — a subwoofer, and stereophonic loudspeakers act here as "satellites".

For formation of a signal of the LF channel (subwoofer) are usually used by p the adder and the active filter. As an example on fig. 1 the circuit of this knot is provided.

of the Fig. 1. The shaper of a signal of LF (subwoofer)

On OU DA1.1 is executed by p the inverting adder combined with the filter of the first order, on OU DA1.2 — Battervort's active filter of the second order. Frequency of a cut of the third order which has turned out as a result of the filter makes about 180 Hz. The divider of R1R2 sets an OU mode on a direct current. The strip of frequencies of loudspeakers of SCh — éù (satellites) is limited to filters of the first order on an entrance of stereophonic UMZCh.

However for allocation of a strip of frequencies of a subwoofer is not so obligatory to use active filters. On pages of the magazine two options of UMZCh for the computer [1] in which the original way of formation of a signal is applied to a subwoofer, not demanding the separate filter were published. Unfortunately, in the first option of a design two different versions of a chip TDA1519 which not always are available on sale are used. In the second option — hopelessly out-of-date TDA2005, on level of distortions and noise not meeting modern requirements; this chip needs many external elements. Having applied the modern chips of UMZCh intended for automobile radio equipment, it is possible to simplify a little the circuit and considerably to raise operational characteristics of UMZCh.

the Amplifier of capacity is convenient for executing

on the basis of a widespread chip of TDA1554Q (Philips). Two inverting and two not inverting amplifiers enter into it with strengthening on 20 dB, their entrance resistance — 60 kiloohms. Two options of their inclusion are possible. The first — standard, as four-channel UMZCh with the maximum target capacity of 4x6 W (4x11 W) on loading of 4 (2) Ohm. The second option — as two-channel UMZCh in bridge inclusion with the maximum target capacity of 2x22 W on loading of 4 Ohm.

In an offered design two inverting channels are used by p in usual inclusion, and two not inverting, thanks to the original decision — in bridge inclusion.

Parameters of the amplifier

Sensitivity, мВ	500
Nominal resistance of loading, Ohm	4
Rated target power, W, SCh — éù channels the LF channel />/>	2x3,5 12 />/>
the Maximum target capacity, W, SCh — éù channels the LF channel />/>	2x6 22 />/>
the Maximum consumed current, And	3,5
Frequency of a cut of SCh — éù channels, Hz	180
Frequency of a cut of the LF channel, Hz	50... 170

the Supply voltage of the amplifier can be within +10. . 16 V.Tok, consumed by the device in the absence of a signal — no more than 0,1 And. In the Standby mode on duty (a mode of remote switching off) — 0,1 мА. The rated power is specified at the supply voltage equal 15 In, and harmonious distortions about 0,5 %. The maximum capacity as it is accepted, is defined at distortions of 10 %.

the Circuit of the amplifier is provided by p on fig. 2. The device is most simplified, and face values of the majority of elements are unified.

of the Fig. 2. The schematic diagram of the amplifier

Loudness and a timbre are regulated by the doubled variable VR1 and VR2 resistors respectively. In order to avoid an overload of the amplifier depth of adjustment of a timbre depends on the provision of a cursor of a regulator of loudness. At the maximum loudness lifting of VCh does not exceed 2... 3 dB (and that — at the expense of a LF and SCh blockage), but increases to 5. . 6 dB at small loudness [2]. Adjustment of a timbre of VCh on "blockage" is not provided, as as practice shows, in it there is no need. Besides, operated regulators of a timbre and balance have the majority of sound cards of the personal computer programmno. In case of need the range of adjustment of a timbre in the amplifier can be finished to 12... 14 dB, having established the variable VR2 resistor resistance of 10 kiloohms. Possibility of installation of a regulator of stereobalance (VR4) though its need is even more doubtful is provided also.

For installation reasons for satellites are used by p inverting channels of strengthening therefore for preservation of an initial phase of a signal dynamic heads of BA1, BA2 are connected in return polarity. The total signal for a subwoofer is formed on the general for two channels dividing a game-densatores13, каки in [1]. Frequency of a cut of this filter makes 170... 180 Hz. The capacity of the C13 condenser is specified for dynamic heads with full resistance of 4 Ohm. For heads with full resistance of 8 Ohm needs to be reduced its capacity to 220 мкФ.

In relation to signals of satellites the signal of a subwoofer is formed by p as additional function therefore at performance of some conditions (about it later) on a resultant of AChH emergence of "hump" on frequency of the section in size to 3 dB is possible. For elimination of this shortcoming the reconstructed proportional integrating VR3R1R2C3 filter which frequency of a cut changes in a range 50 is entered into the sabvuferny canal... 150 Hz. At frequency reorganization also signal level that allows to refuse a usual regulator of level in the subwoofer channel at the same time changes. On fig. 3 theoretical AChH of filters on electric tension are given; the family of curves of the LF channel for convenience is displaced down on 6 dB.

of the Fig. 3. Theoretical AChH of filters on tension

For ensuring operation of two identical amplifiers in bridge inclusion is necessary to submit to p on their entrances antiphase signals. In this design the cascade with the divided loading is used. From a collector of the VT1 transistor the inverted signal, and from a part of emitterny loading — not inverted acts in film. The factor of transfer of the cascade on both exits makes about-16 dB therefore tension on a LF channel entrance in a mode of the widest strip approximately on 4 dB is higher, than in channels of satellites. It compensates a difference in sensitivity of broadband and low-frequency heads and provides a stock of adjustment of level in the subwoofer channel.

Besides, this measure automatically excludes a cascade overload on the VT1 transistor on an entrance: at the expense of a difference in strengthening signal restriction on an exit of the bridge amplifier will begin earlier, than on usual exits (the signal for VT1 from where undertakes). Thanks to deep OOS via resistors R4, R5 linearity of the cascade is satisfactory and at big signals. The cascade mode on a direct current is provided at the expense of connection of a chain of VR3R1 to the C13 condenser. On this condenser there is the constant tension approximately equal to a half of supply voltage.

One more, while unusual knot for similar amplifiers — the switch of a phase of a signal of a subwoofer of SA2. However in systems of private theatricals and automobile subwoofers it is obligatory to eat such cascade. Need of its application is caused by the following: at prostranstvenno carried speaker system AChH resultant in a point of listening will be defined by a ratio of phases of coming signals. Shift of phases, in turn, is defined by distance to dynamic heads.

On fig. 4 theoretical AChH in a near field of radiation for cases of inphase and antiphase inclusion of heads are shown at their compact installation. Real AChH on sound pressure depending on distances and characteristics of heads can accept even more freakish forms. It is obvious that introduction of the switch of a phase allows to operate AChH resultant more flexibly.

of the Fig. 4. Theoretical AChH in a near field of radiation

the Switch of a food of SA1 operates a chip condition, through it the supply voltage on the cascade of a fa-zorasshchepitel moves. In the switched-off condition exits are transferred to a high-impedance-noye a condition, and the current of consumption does not exceed 100 мкА. Purpose of other details obviously. The capacity of the filter is divided into two parts as to establish the high-capacity condenser directly near conclusions of a food of a chip inconveniently.

About details and a design. Oksidnye K50-35 condensers or similar import, condensers C1, С2, SYu — ceramic any type, the others — K73-17. All constant resistors - МЛТ0.125. The variable resistor of volume control should be with indicative dependence of resistance on an angle of rotation (type B), the others — with linear (type A). The KT315B transistor it is possible to replace with any transistor of structure of n - p-p with factor of transfer of a current of base not less than 50. The choice of other details is not critical.

the Rectifier is executed by p on pulse KD213A diodes, it will allow to increase considerably if necessary filter capacity without risk of emergence of multiplicate hindrances. The network transformer it is possible to use any with dimensional capacity not less than 80 W (better more), an admissible current of a secondary winding not less than 5 Ai target tension 9... 11 Century.

In view of relative simplicity the amplifier can be collected

on a model payment (in such option it worked for the author). The printed-circuit board was developed for the journal publication (fig. 5) on which the majority of details takes place. The payment is calculated on installation of P2K switches on two directions and mentioned above details. The SZ condenser in capacity 0,15 мкФ in case of need can be made of condensers in capacity 0,1 мкФ and 0,047 мкФ for what on a payment additional contact platforms are provided.

of the Fig. 5. The printed-circuit board of the amplifier

Variable resistors, sockets and the network transformer place p out of a payment. Crossing points in a chain of a signal are executed by a thin assembly wire, for installation of power-supply circuits and speaker systems it is necessary to use a wire section not less than 0,75 mm ² . The heat-conducting path can be made of a dural corner of 30x50 mm or to use ready from an autoradio tape recorder (the such is applied in author's option).

Correctly assembled amplifier of adjustment does not demand p. At inclusion it is enough to be convinced tension available specified on the circuit (a tolerance ±10 by %). In case of aimings from the power unit of the computer it is necessary to turn on two ceramic condensers in capacity 220... 470 пФ on a chip entrance (between points 6, the 7th payments and the general wire). They can be placed from printing conductors.

For reproduction of low frequencies need to use a specialized low-frequency dynamic head in acoustic registration. — to use the simplest way the EXPERT from domestic household equipment, having removed superfluous details. The author applied to tests AC S-30B ("Radio engineering"). Acoustic registration of satellites can be the elementary, including open.

Sources

1. of Shoemakers of M. Two simple UMZCh for the computer. — Radio, 2002, No. 4, page 15.
2. Shikhatov A. Passive regulators of a timbre. — Radio, 1999, No. 1, page 14, 15.

Author: А.ШИХАТОВ, Moscow

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