MJ11015 & MJ11016 Guitar Amplifier 60W

Guitar Amplifier general description:

     This design adopts a well established circuit topology for the power amplifier, using a single-rail supply of about 60V and capacitor-coupling for the speaker(s). The advantages for a guitar amplifier are the very simple circuitry, even for comparatively high power outputs, and a certain built-in degree of loudspeaker protection, due to capacitor C8, preventing the voltage supply to be conveyed into loudspeakers in case of output transistors' failure.

The preamp is powered by the same 60V rails as the power amplifier, allowing to implement a two-transistors gain-block capable of delivering about 20V RMS output. This provides a very high input overload capability.

Guitar Amplifier features: 

Sensitivity: 35mV input for 40W 8 Ohm output42mV input for 60W 4 Ohm output
Frequency response: 50Hz to 20KHz -0.5dB; -1.5dB  40Hz; -3.5dB  30Hz
Total harmonic distortion 1KHz and 8 Ohm load: Below 0.1% up to 10W; 0.2%  30W
Total harmonic distortion 10KHz and 8 Ohm load: Below 0.15% up to 10W; 0.3%  30W
Total harmonic distortion 1KHz and 4 Ohm load: Below 0.18% up to 10W; 0.4%  60W
Total harmonic distortion  10KHz and 4 Ohm load: Below 0.3% up to 10W; 0.6%  60W
Treble control:+9/-16dB 1KHz;  +12/-24dB 10KHz
Brightness control:+6.5dB 500Hz;  +7dB  1KHz; +8.5dB @ 10KHz
Bass control:-17.5dB 100Hz ; -26dB 50Hz; -28dB @ 40Hz

Guitar Amplifier circuit diagram:

Guitar Amplifier circuit diagram

Guitar PreAmplifier circuit diagram:

Guitar Amplifier notes:

• The value listed for C8 is the minimum suggested value. A 3300µF capacitor or two 2200µF capacitors wired in parallel would be a better choice.
• The Darlington transistor types listed could be too oversized for such a design. You can substitute them with MJ11014 (Q3) and MJ11013 (Q4) or TIP142 (Q3) and TIP147 (Q4).
• T1 transformer can be also a 24 + 24V or 25 + 25V type (i.e. 48V or 50V center tapped). Obviously, the center-tap must be left unconnected.
• D1 and D2 can be any Schottky-barrier diode types. With these devices, the harmonic modifier operation will be hard. Using for D1 and D2 two common 1N4148 silicon diodes, the harmonic modifier operation will be softer.
• In all cases where Darlington transistors are used as the output devices it is essential that the sensing transistor (Q2) should be in as close thermal contact with the output transistors as possible. Therefore a TO126-case transistor type was chosen for easy bolting on the heatsink, very close to the output pair.
• R9 must be trimmed in order to measure about half the voltage supply across the positive lead of C7 and ground. A better setting can be done using an oscilloscope, in order to obtain a symmetrical clipping of the output wave form at maximum output power.
• To set quiescent current, remove temporarily the Fuse F1 and insert the probes of an Avo-meter in the two leads of the fuse holder.
• Set the volume control to the minimum and Trimmer R3 to its minimum resistance.
• Power-on the circuit and adjust R3 to read a current drawing of about 30 to 35mA.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.

Guitar Amplifier partlist:

R1__________________6K8 1W Resistor 

R2,R4_____________470R 1/4W Resistors 

R3__________________2K 1/2W Trimmer Cermet 

R5,R6_______________4K7 1/2W Resistors 

R7________________220R 1/2W Resistor

R8__________________2K2 1/2W Resistor

R9_________________50K 1/2W Trimmer Cermet 

R10________________68K 1/4W Resistor 

R11,R12______________R47 4W Wirewound Resistors 

C1,C2,C4,C5________47µF 63V Electrolytic Capacitors 

C3________________100µF 25V Electrolytic Capacitor 

C6_________________33pF 63V Ceramic Capacitor 

C7_______________1000µF 50V Electrolytic Capacitor 

C8_______________2200µF 63V Electrolytic Capacitor (See Notes) 

D1_________________LED Any type and color

D2________Diode bridge 200V 6A 

Q1,Q2____________BD139 80V 1.5A NPN Transistors 

Q3_____________MJ11016 120V 30A NPN Darlington Transistor (See Notes) Q4_____________MJ11015 120V 30A PNP Darlington Transistor (See Notes) SW1_______________SPST Mains switch 

F1__________________4A Fuse with socket 

T1________________220V Primary, 48-50V Secondary 75 to 150VA Mains transformer (See Notes) PL1_______________Male Mains plug 

SPKR______________One or more speakers wired in series or in parallel Total resulting impedance: 8 or 4 Ohm Minimum power handling: 75W

Guitar PreAmplifier partlist:

P1,P2______________10K Linear Potentiometers 

P3_________________10K Log. Potentiometer 

R1,R2______________68K 1/4W Resistors 

R3________________680K 1/4W Resistor 

R4________________220K 1/4W Resistor 

R5_________________33K 1/4W Resistor 

R6,R16______________2K2 1/4W Resistors

 R7__________________5K6 1/4W Resistor 

R8,R21____________330R 1/4W Resistors 

R9_________________47K 1/4W Resistor

 R10_______________470R 1/4W Resistor 

R11_________________4K7 1/4W Resistor 

R12,R20____________10K 1/4W Resistors 

R13_______________100R 1/4W Resistor 

R14,R15____________47R 1/4W Resistors

 R17,R18,R19_______100K 1/4W Resistors 

C1,C4,C5,C6________10µF 63V Electrolytic Capacitors

 C2_________________47µF 63V Electrolytic Capacitor 

C3_________________47pF 63V Ceramic Capacitor

 C7_________________15nF 63V Polyester Capacitor

 C8_________________22nF 63V Polyester Capacitor 

C9________________470nF 63V Polyester Capacitor

 C10,C11,C12________10µF 63V Electrolytic Capacitors 

C13_______________220µF 63V Electrolytic Capacitor

 D1,D2____________BAT46 100V 150mA Schottky-barrier Diodes (see Notes) Q1,Q3____________BC546 65V 100mA NPN Transistors 

Q2_______________BC556 65V 100mA PNP Transistor 

J1,J2___________6.3mm. Mono Jack sockets 

SW1,SW2___________SPST Switches

Mixed connection to combined acoustic amplifiers

Amplifier these recorder can be used in two ways - as a two-channel bridge with a maximum power of 2x25 W or as with a conventional four-load connection and "virtual ground". Power in this case is 4h7Vt. The most famous member of this family - Sony 1253/1853. To work with a subwoofer also need to use a dual-channel configuration.

Fig.1.

Selecting the connection type, as in the previous case, be subject to the sensitivity of heads. A variant for capacitors C1, C2 act as HPF. They may be waived if the application heads provide undistorted reproduction of lower frequencies. Branch constant component produced internal capacitors radio. However, for option B necessarily the presence of two high-pass and low-pass filter for the stereo for the total channel. Their mission - to eliminate the parallel operation of heads at low frequencies. Since the impedance at low frequencies is almost equal to their heads DC resistance, lack of filters can lead to overload the amplifier, designed for a 4 ohm load. For stereo used first order filters (C1, C2), for the total - the second (C3L1R1). 

Another variant of the mixed load connection, but within one amplifier channel. It is convenient to connect two or three-way speaker system. LF-head bridging is used, and for the MF / HF or HF - the usual. Mode switch is set to the position for four-configuration. 

Fig.2.

Dependence of the power supplied to the heads of fader position is shown in ris.2.b. In the process of regulatory power to the pavement maximum load decreases by 6 dB (4 times), because in the end positions fader scheme reduces to the usual ("left without a signal" shoulder amplifier acts as a "virtual ground"). Note that in the zone of the joint action of the heads, they are parallel-connected, but because these frequencies are affected by the growth of the load impedance due to the inductance of the voice coil, the amplifier is not really an overload occurs.

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Mixed connection acoustics bi-amplifier and the output fader

     In the operation is still a lot of these "dinosaurs" of the mid 90s. A characteristic feature of built-in amplifiers such devices - they are designed for load 2 ohms and have a good supply of power. This is due to the fact that in the middle position fader front and surround speakers are connected in parallel. However, to use them in conjunction with acoustic component is impossible. The reason is simple - the introduction of the fader increases the output impedance of the amplifier, which leads to a change in crossover. Therefore, the only option enhancers such devices with modern acoustics - dual channel configuration, with the fader excluded from work.

     In this version, you can add a subwoofer to include it in a "mixed-mono". Since the relationship between the levels regulate front speaker and subwoofer impossible, depending on the sensitivity applied to select one of the heads of connectivity options.

     Option A is used in the case where the sensitivity of the front speakers 3-5 dB higher than that of the subwoofer. In this embodiment, they are connected to the amplifiers are not bridged, and the usual way, and the power supplied to them is not more than 7 w / 4 ohms. To obtain sufficient volume of the front acoustic desirable to use high-sensitivity head about 91-93 dB. Pay attention to their phasing - one of the "poluusiliteley" inverting the second - non-inverting. HPF cut formed by the capacitors C1 and C2 can be chosen arbitrarily, but the presence of capacitors is crucial - they do not miss out on the dynamics of the DC component from the output amplifiers. Front head shown conventionally broadband, but they may be coaxial or component.

     Option B is used in nearly all heads of sensitivity. The presence of capacitors C1, C2 for the normal functioning is not necessarily because it is used in a bridge connection. In the absence of capacitors in the passband head subwoofer filter work in parallel. This reduces the load impedance to 2 ohms, but the amplifier is designed. Subwoofer in both cases the second-order filter (C3L1R1).

Mixed acoustic connection to an amplifier with two bridge output channels

Consider the circuit connection to the AC amplifier with two bridge output channels. Dynamic head BA1, BA2 speakers form the left and right stereo channels. They are shown conventionally broadband. Low-frequency head BA3 is connected between the output of the amplifier left and right channels, the signals are summed and head reproduces a mono signal.

This connection will be sure to have two high-pass and low-pass filter for the stereo for the total channel. Their mission - to eliminate the parallel operation and overload amplifier heads. Usually used for stereo first order filters (C1, C2), for the total - the second (C3L1) or third.Their payment is made in the usual way. Crossover frequency of the LPF and the order chosen in the range 80 ... 200 Hz, depending on the location of the low-frequency head. If it is placed in the rear compartment, the crossover frequency should be selected as low as possible, and the order - up to avoid reproducing the subwoofer "voice" of the range. However, this requires the manufacture of relatively large inductors.Used in their construction ferromagnetic yokes undesirable because the distortion caused by the inevitable core magnetization significantly degrade sound quality.

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FAQ on the speakers and subwoofer

Introduction

Recently could hear a lot of questions about speakers and subwoofers. The vast majority of responses can be found on the first three pages of any book written by professionals. Material is addressed primarily to beginners, lazy ;) and rural Homebrew, prepared on the basis of books I.A.Aldoschinoy, V.K.Ioffe partly Ephrussi, journal publications in Wireless Worrld, AM and (some) personal experience. NOT used information from the Internet and Fidonet. The material is in no way purport to lighting problems, and is an attempt to explain the basics of acoustics on the fingers.

Most often, the question goes something like this: "the speaker found that to do with it?" Or "tovarischch and say such subwoofers are>." Here we consider only one solution to this problem: For existing dynamics to make a box, with the optimal settings for HCH as possible. This option differs from the task factory designer-pull system to lower the frequency of the required quantity of TU

[Q] Hashel large speaker on the occasion unmarked. How to know whether you can make him a subwoofer?

[A] Hujno measure its T / S parameters. Ha Based on these data to decide on the form of HCH clearance.

[Q] What is the T / S parameters?

[A] The minimum set of parameters for the calculation of HCH design proposed by Till and Small.

Fs-resonant frequency of the speaker without registration

Q factor Qts-full dynamics

Vas-equivalent volume of the speaker.

[Q] How to measure the T / S parameters?

[A] To do this, you need to collect from the generator circuit, a voltmeter, a resistor, and the test speaker. The speaker is connected to the output of the generator with an output voltage of several volts across the resistor of about 1 kOhm.

1. Remove V (F) = AFC resistance dynamics in the resonance region. The speaker must during this measurement to be in the free space (the distance from the reflecting surfaces). Hahodim speaker impedance on the current fasting person (useful), write in the air resonance frequency Fs (this is the frequency at which the voltmeter maximal :), the voltmeter Uo at minimum frequency (well, for example 10 Hz) and Um at the resonance frequency Fs.

2. Hahodim frequencies F1 and F2, in which the curve V (F) intersects the level of V = SQRT (Vo * Vm).

3. Hahodim Qts = SQRT (F1 * F2) * SQRT (Uo / Um) / (F2-F1) is the total quality factor of the dynamics, we can say, the most important value.

4. To find Vas need to take a small indoor Boxes volume Vc, with a hole a little smaller than the diameter of the diffuser. Tightly to lean to the speaker hole and repeat the measurements. From these measurements, you will need a resonant frequency dynamics in the housing Fc.Hahodim Vas = Vc * ((Fc / Fs) ^ 2-1).

This procedure is written in the audio shop • 4 for 99 year. I had checked it out .. There are others, when measured mechanical properties of the head, weight, flexibility, etc.

[Q] I now have options speaker, what to do?

[A] Each speaker in the design sharpen a certain kind of acoustic design. To find out under what is, look at the quality factor.

Qts> 1,2 it heads for the open boxes, optimally 2.4

Qts <0.8-1.0 - head for closed boxes, optimally 0.7

Qts <0.6 - for bass reflex, optimum - 0.39

Qts <0.4 - for horns

Wise to sort head is not on good quality and value for Fs / Qts. Cite from memory, the reluctance of the formula to calculate.

Fs / Qts> 30 (?) Screen and open housing

Fs / Qts> 50 closed body

Fs / Qts> 85 Tubes

Fs / Qts> 105 Bandpassy (bandpass resonators)

Elasticity, meatiness, dryness and other similar characteristics of the sound emitted by Bass speakers, are largely determined by the transient response of the system formed by the speaker, woofer design and the environment. To this system was not to release the impulse response, its quality factor should be less than 0.7 for systems with one side of the radiation dynamics (closed and phase inverter) and 1.93 for two-way systems (design type screen and open box)

[Q] Where to read about the open design?

[A] Open boxes and screens is the simplest type of decoration. Pros: ease of calculation, no increase in the resonant frequency (the size of the screen depends only view of the frequency response), almost constant quality factor. Disadvantages: large size of the front panel. Sufficiently competent and simple calculations of this type of design can be found in VK Joffe M.V.Lizunkov. Household speakers, M., Radio and Telecom.1984. And in the old Radio certainly have primitive amateur calculations.

[Q] How to calculate the closed box?

[A] Making "closed box" is of two types, infinite baffle and suspension compression. Getting into a particular category depends on the ratio of suspension dynamics and flexibilities in the air box, denoted alpha (by the way, you can try on the first and second count and change by filling).For an infinite screen ratio is less than 3 flexibilities for suspension compression more than 3-4. Can be considered as a first approximation that the heads with high Q sharpened by an infinite baffle, with less-under suspension compression. Taken to advance the speaker enclosure is closed infinite baffle has a larger volume than the compression box. (Generally speaking, when there is a speaker, the optimal body under it is clearly a certain amount. Errors encountered when measuring the parameters and calculations, can be slightly corrected by filling).Speakers for closed shells have powerful magnets and soft suspensions unlike heads for the open boxes. The formula for the resonant frequency of the dynamics in the design of volume V Fc = Fs * SQRT (1 + Vas / V), and an approximate formula relating the resonant frequency and quality of the head in the body (the subscript "c") and open space (subscript "s") Fc / Qtc = Fs / Qts

In other words, it is possible to implement the required quality factor only way speaker system, namely the choice of the volume of a closed box. What is the quality factor to choose? People who have not heard the sound of natural musical instruments, usually choose speakers with Q bolee1 0. In columns with a quality factor (= 1.0) the smallest uneven frequency response in the lower frequencies (and what does that sound?) Achieved at the cost of a small release on the transient response. Maximally smooth frequency response is obtained when Q = 0.7, and fully aperiodicity impulse response with Q = 0.5. Homogrammy for calculations can be taken in the above book.

[Q] Articles about speakers often words like "approximation of Chebyshev, Butterworth," etc. How does this relate to the speakers?

[A] The speaker system is a high-pass filter. The filter can be described by the transfer function. Transfer characteristic is always possible to fit a known function. In the theory of filters use several types of power functions, named for mathematicians first licked a particular function.Function determined by the order (maximum exponent, ie H (s) = a * S ^ 2 / (b2 * S ^ 2 + b1 * S + b0) has the second order) and the set of coefficients a and b (from these coefficients You can then move on to the values ​​of the real elements of the electric filter, or electro-mechanical parameters.) Next, when it will go on the approximation of the transfer characteristic polynomial Butterworth or Chebyshev or something else, it should be understood so that the combination of the properties and dynamics of the body (or containers and inductance in an electric filter) turned so that most accurately the frequency and phase characteristics can be adjusted to a particular polynomial. Most smooth frequency response is obtained if it can be approximated by a polynomial Butterworth. Chebyshev approximation is characterized by the wave-frequency response and a large stretch of the working area (according to GOST to -14 dB) in the region of lower frequencies.

[Q] What kind of approximation to select the phase inverter?

[A] So before the construction of a simple bass reflex need to know the volume of the box and reflex tuning frequency (pipes, holes, passive radiator). If as a criterion to select the most smooth response (and this is not the only possible criterion), we get the following label A) Qts <0,3-most smooth curve will kvazitretego order B) Qts = 0,4 - better described battervortovskimi curves in) Qts > 0.5 - will allow the waves on the AFC, Chebyshev. In case A) bass reflex tuned to 40-80% higher than the resonance frequency in case b), the frequency of resonance, in case B) below the resonance frequency. Also in these cases will be a variable volume enclosure .. In order to find the exact frequency tuning, we must take the original formula, rather cumbersome to bring them here. Therefore, I refer interested in AudioMagazin 1999, then there is an educational program can be sorted out, or book Aldoshina. And even in the article Ephrussi Radio for '69 amiss.

Conclusion

If after reading all this, you still have the desire to rivet something yourself, you can take online nifty program type WinspeakerZ and calculate it all myself, remembering that of G.. candy not do. Not to be carried away by a decrease of the cutoff frequency, in any case, do not try to compensate for the roll off the amplifier. AFC can be leveled and a little bit, but the sound is enriched harmonics and subharmonics weight.On the contrary, the best results, in terms of pleasantness to the ear can be achieved forcibly ruining inlet UM very lowest frequencies, iefrequencies below the cutoff frequency HCH column. Another remark concerning the phase inverter configuration error in the resonance frequency of the phase inverter 20% leads to a surge or decline in response at 3 dB.

Oh, I almost forgot to say about subwoofers that actually strip resonators. Q-factor of the speakers for them should be even lower. The simplest bandpass too incalculable, but this ends my courtesy.

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UM protection unit and acoustics overcurrent

It is based in protection circuit Audio Analogue Aida - from the site of its designer Federico Paoletti . I developed it a little bit and used in his new mobile amplifier - also borrowing from Paoletti. The scheme is applicable to any PA whose output - compound emitter follower (2 stages or more, or a Darlington Naturally - silicon, or a cascade of CMOS).

In the original scheme in the traditional circuit protection (voltage drop across the emitter resistor opens key bypass transition BE composite output transistor) added two optocoupler (circuit shunt base for the upper and lower arm). Current drawn from the shunt base flows through the LED of optocoupler and opens galvanically isolated key. Fine, but the same node can not just arbitrarily turn off power, but doing it on the pitch outside. Need another pair of optocouplers, shunt BE transitions output transistors:

Threshold set divider R1-R2 based on the current limit for each transistor and the emitter resistance in the circuit output. The total resistance R1 + R2 must be in the range 10 .. 100 ohms. Thanks circuit R3-C1-R4-D1, R8-C2-R9-D2 (LPF) threshold DC is much higher than the AF.Furthermore, the threshold decreases with increasing temperature T1, T2.

The first and fourth (vertical) optocouplers - security sensors (closed = alarm), second and third - the keys controlled by an external signal (sink current = off UM). In the chain of forced shutdown necessarily provide current-limiting resistor. Resistors R9-10 - I put instead of jumpers on the board, whether they are as such - probably not.

Despite the additional voltage drop across the LED, the scheme is guaranteed off the PA with a repeater on single and dual Darlington (0.33 ohms under the emitter). The main thing that current drawn T1, T2 in the "triangle" - the voltage amplifier - was sufficient to guarantee the inclusion of optocouplers (not less than 1 mA for TLP521). Optocouplers - any except Darlington (well, they go to hell, and do not need much gain here). Requires current transfer ratio is determined by currents and levels of automatic protection, as well as current shunt which will select from the "triangle". T1, T2 - any thin with low saturation voltage.

Incidentally, memorized by heart half volt LED on - not quite right. The LED TLP521 in this scheme falls at room temperature not more than 0.9V.

When designing the board first, "the mind" is placed own mind and protection circuit - second. In this "ground" defense to hold separate and connect with other "lands" at a common point "star." If a car amplifier analog ground unleashed current board of land and automation unit usually sits on the board, the circuit R4D1 R9D2 connect with analog power and ground otpronov - with on-board.

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Protection device speakers

In life, frequent situations where, for whatever reason speakers connected to an audio amplifier, the power of which exceeds the maximum allowed for a system that, on the one hand, often produce the best sound quality, increase the dynamic range, with another - increases the risk of damage due to overload dynamic heads. This is especially true when using the speaker on school, student, youth parties, where the acoustics are often connected to the first that fell known good amplifier that is "powerful." To prevent damage to the speakers when applying for her power, exceeding the nominal, it is necessary to equip the unit overload protection, built-in speakers and requires no additional power supply. Schematic diagram of such a device designed to protect the AC power 10 ... 35 W is shown in below

Protection device speakers circuits

Also in case of overload tripping SS, this device also protects it from damage by the dynamic head in the event of failure of the transistor amplifier and its output appears on the DC voltage. The device is connected to the output of the power amplifier audio frequency. The AC voltage is rectified by a bridge diode VD1. Resistor R1 eliminates the influence of a job amplifier. The rectified voltage is smoothed oxide capacitors NW, C2. While the output power of the amplifier does not exceed the maximum allowable for the AU, the voltage at the capacitor C2 is small, the zener diode VD3 closed, hence also closed and SCR VS1. In the micro-current SCRs of this type are controllable, ie, they can close the control voltage. Since VS1 is closed and will be closed transistor VT2. K1 relay contacts are closed, dynamic head at AU will do 100% of capacity. As soon as the output power of the amplifier exceeds permissible for AC voltage on C2 increases so that opens zener VD1, open SCR VS1 and the transistor VT2, K1 relay contacts open, the power supplied to the speakers will be limited by resistors R11-R13. These load resistors are a power amplifier, which improves stability of the amplifier in case of disconnection of speaker system, moreover, these resistors reduces arcing between the relay contacts when closing and opening. When protection against overload LED lights HL1. Transistor VT1, emitter junction which operates as a diode with a micropower voltage stabilization 7 ... 12 V protects the FET from the breakdown of a gate insulator. Once the voltage at the amplifier output is reduced, zener VD3 closes closed VS1, VT2, relay K1 is closed, on the AU will come back full power. Resistor R8 introduces small hysteresis to prevent cyclic circuit-opening relay contacts at a constant power output, slightly higher than the threshold. R9 resistor reduces the current through the relay coil by opening its contacts, capacitor C6 accumulates enough energy required for reliable operation of the relay.

When placing the speaker structure within the housing structure elements operate in a fairly strong vibrations in a wide range of sound frequencies produced by the dynamic head, moreover, in some cases, should also be considered an alternating magnetic field from the dynamic head. PCB should be located at a maximum distance from the open magnetic systems dynamic heads.

The device used fixed resistors MLT, Cl-4, C2-23 or imported analogues. Trimmer R3 is desirable to use a sealed enclosure, for example, SP4-1, GPA-16c, SP5-16A, SDR-19a-3 SP4. After setting up the rotation axis of the resistor must be assigned a drop of paint. Capacitor C1 terephthalate film ethyl K73-17, K73-9 or similar. C4 - ceramic K10-17, CM-5, oxide capacitors - K50-35 or imported analogues. NW capacitor can be formed from two 470 uF (provided on the circuit board). If necessary, the capacitor C6 also be used for the operating voltage of 100 V. In the case when the device is applied with amplifiers having a supply voltage output stages more than ± 50 V electrolytic capacitors need to be at the voltage of 160 V, the power and the resistance of resistors Rl, R2 , R9 also need to increase. Capacitors NW, C6 set parallel to the PCB, and further secured with wire clamps on it. Diode bridge can be replaced by a similar low-power, for example, DB103-DB107, RB153-RB157 or make up of four rectifier diodes with a working voltage of at least 100 V. Instead KD243A can install any of a series of KD243, KD247, KD208, KD105, 1N4002-1N4007. 1N4738A Zener diode can be replaced by KS175A, KS175ZH, KS126K LED - any other. Instead trinistor KU112A can apply CG 112 AM in the TO-92. N-channel field effect transistor in this embodiment IRF9540 can operate without the heat sink. Its maximum drain-source voltage of 100 V, the domestic counterpart - KP785A. Instead, the transistor can be used IRF9634, KP796A having UCH MAX> 250 V. Instead KT315A can apply any of the series KT312, KT315, SS9014. Relay K1 - REC-29, passport DUSCH4.501.56.Resistance of the coil of the relay about 950 ohm stable switching contacts occurs at a voltage of 15 V, the minimum voltage retention - 7 V. This type of relay modules used in the control of domestic TV USTST. For replacements, consider the fact that the contacts of the relay must commute significant current.

PCB protection device speakers 

The apparatus may be mounted on a printed circuit board size 140x50 mm, wherein all the elements are installed than the LED. On Figure 2shows the circuit board from the conductors. 

From the installation fee is desirable to cover three or four thin layers of epoxy glue. Each subsequent layer is applied after setting the previous one. Fee is attached to the body with five screws inside AU MOH or screws. If possible it is desirable to close deaf thick-walled (> 0.5 mm) casing, which also reduce the probability of failure of the device due to vibrations in the powerful speakers, as well as reduce the likelihood of contact bounce relay. 

Manufactured author two instances these devices are used in conjunction with speakers 15AS-220, which uses dynamic head 25GDN-3-4.These systems start to wheeze and rattle when the input power more than 40 watts. Protection threshold set to 25 watts. These speakers are powered by an amplifier "Orbit UM-002 stereo", 

which is able to develop power above 50 watts at 4 ohms. Other two copies installed in homemade sealed AC collected on broadband heads 10GDSH-1 powered by an amplifier "Corvette 50U-068 C". On threshold of protection is also installed at the rate of 25 watts of amplifier at 4 ohms. If you are working with powerful speakers (> 35 ... 5O W) and a powerful amplifier SCR will close at too low power for this case, the resistance of the resistors R4 and R7 can be doubled. 

This device can be modified by setting instead of fixed resistor R2 thermistor NTC resistance of 3.3 ... 4.7 ohms at 25 ° C, which, through a pad of heat conductive rubber should be rigidly secured to the magnetic system, a powerful low frequency driver. In this case, strong heating of the magnetic system will include device protection with less output power amplifier.

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