Here the circuit design for DIY guitar transistor preamp. It consists of a circuit of two transistors and four controls that can be vary the level of the treble, bass, gain, and total salidad circuit (volume). It can be used as buffer at the beginning of a chain of effects. Or combine it with the Marshal Guvernor and a power to put together a cute amplifier.

The circuit working with 9v dc power supply or battery.

Guitar Preamp Components list:

Nonpolar Capacitors

• 0.01uF
• 0.1uf
• 4700pF
• 0.047pf

Electrolytic Capacitors

• 1uf x 2
• 1uf x 2 (Tantalum)

Semiconductors

• 2N5089 (NPN or other) x 2

Resistors

• 1M x 2
• 47k x 2
• 2.2k x 2
• 100k x 2
• 4.7k
• 22k
• 1k

Potentiometers

• 250 Kohm linear x 2
• 250 Kohm log
• 10 Kohm linear

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This is the circuit diagram of stereo pre-amp with volume and tone control. When using one of our amplifiers (big or small), you always need a volume control and preferably also a tone control. This circuit available in kit. This circuit operated with 12V symmetrical/dual polarity power supply.

Circuit Features:

• Stereo volume control
• Stereo Baxandall bass and treble control
• Low noise en = 15 nV/√ Hz (typ)
• Output short-circuit protection
• Low harmonic distortion: 0.01% (typical)

Circuit Specifications:

• Supply voltage: 2 x 12VAC / 100mA
• Frequency response: 3Hz – 500kHz (-3dB)
• Standard amplification: x1
• Signal to noise ratio: 98dB
• Harmonic distortion: < 0.005% (@1KHz)
• Maximum output: 5V RMS
• Tone control:
  + and -15dB @ 20Hz
  + and -15dB @ 15kHz
• Input impedance: 50k ohms

To build this circuit, please download the kit manual document from Velleman. It contains schematic diagram and partlist and the guide to build this preamp circuit.

Download Stereo Preamp Circuit Manual Kit

1 file(s) 920.00 KB

Download

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We can say that this Multidirectional microphone circuit consists one side of electret four modules, each of them provide power to the capsule through 10K resistor, DC blocked through 1μF capacitor and the resulting AF signal is received at the end of the potentiometer which serves as a reception setting. 100K resistors and transistors form a network FET preamp and summing several signals, which can be applied without any problems on the line input as the microphone channel of the console.

The circuit is powered by a 9V and consumption is very low, so it can be safely operated by a power source or standard 9V battery. In the latter case, remember that proper filtering is the key to good audio quality.

Output cables must be shielded types (mesh) to prevent interference or noise from the sound produced.

It is recommended to mount it in a cabinet or in a circular or pyramidal. Although the first is what gives best results and has a nice aesthetic.

Another recommendation that is not in the scheme is to put a 100nF capacitor between + V and mass within the printed circuit of the apparatus.

The potentiometer allows to adjust the sensitivity of each microphone. This is useful when there are more people on one side than another, or when someone is talking too loudly than others.

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Amplification of this low impedance input pre amp is therefore very high, whether to reduce, there should be a trimmer R3 series to 100 ohms. The system can be powered by a voltage of between 9 and 18Volts. for its realization, follow the diagram layout.

LIST OF ELECTRONIC COMPONENTS :
All resistors are 1/4 watt unless otherwise specified.
R1, R2 = 1Kohm
R3, R4, R5, R6 = 10Kohms
R7 = 100Kohms
R8 = 100Kohms
Cl = 100uF 16V elec.
C2 = 10uF 16V elec.
C3 = 4.7 uF 16V elec.
C4, C5 = 47uF 16V elec.
T1, T2 = BC237
A 9 volt battery clip.

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When recording gramophone records, the frequency characteristic is lifted at the high end. This lift must be countered in the playback (pre)amplifier. The corrections to the frequency response characteristic are according to a norm set by the Record Industries Association of America (RIAA) and also by the IEC.

The corrective curve provided by the amplifier is shown in the graph (bold line). The thin line shows the ideal corrective curve. The sharp bends in this at 50 and 500 Hz are nearly obtained in the practical curve by network R3/C2; just above 2 kHz is approached in practice by filter R5/R6/C3. The arrangement of R3/C2 in the feedback loop of IC1 gives noticeably better results than the usual (passive) filter approach.

IC1 provides a do amplification of 40 dB, which drops to about 20 dB when the frequency rises above 500 Hz. To minimize the (resistor) noise and the load of the op amp at higher frequencies, the value of R3 is a compromise. The associated polystyrene capacitor, C2, should have a tolerance of 1 to 2%.

To raise the 2-mV output of the dynamic pick-up to line level at 1 kHz, linear amplifier IC2 has been added. This stage has a gain of 22 dB, so a signal of 250 mV is available at its output.

Capacitors C4/C5 at the output, in conjunction with the input impedance of the following preamplifier, form a high-pass filter with a cut-off frequency of 20 Hz; this serves to suppress any rumble or other low frequency noise. The value of C1 is normally given in the instruction booklet of the dynamic pick-up.

The power supply for the amplifier must be of good quality. Particularly, the transformer should be class Al with a small stray magnetic field.

When the amplifier is built into the record player (best), the power supply should not be included unless it is very well screened; otherwise, hum is unavoidable.

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This is Hydrophone preamplifier circuit diagram, designed to be used with a transducer type EDO6166, and is taken from an application note of OPA27/37 of Burr-Brown.

As you can see, it’s really very simple and uses only conventional components. The transducer used, is piezo type and has a relatively high output impedance, which requires a preamp with a high input impedance. The input impedance of this circuit is mainly determined by the value of the resistor R3, 1 MOhms here. The value of other components determines the frequency range used, it ranges here between 1 kHz and 50 kHz.

Hydrophone preamplifier Parts list :

R1 : 1K ohm
R2 : 200 ohm
R3 : 1 M ohm
R4 : 2K ohm
C1 : 470pF
C2 : 100 nF
U1 : OPA37

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Using logic gates to amplify the signal?
But how on earth this possible! Well to find out, just looking for ways to make pre-amp, using the gate of the logic circuit type CD4069. Look at the diagram above.

The diagram shows the schematic of the center of one of the six internal gates is contained in the CD4069, which consists of two field-effect transistors. The diagram on the right represents a kind of equivalent to a conventional bipolar transistor. The four resistances of the two schemes have a very high value of several hundred Mega ohms.

Input
Inputs made via a of 22 nF coupling capacitor, this value is enough to get the lower sound spectrum at a value as low as 10 Hz the input impedance is very high indeed, it being related to the technology for CMOS gates.

Why three logic gates and not one?
For low distortion, which is fixed by a maximum of 0.1%, the rate of reaction-cons must be at least 1000. With only one gate is a little too tight, and two is more than enough. But as it is entitled to a reverse phase (180 degrees) with each logic gate, the use of two gates leads to a rephasing of the output from the input. Which is not suitable for mounting against feedback. Therefore a third gate was added to operate a new phase inversion. The value given to the resistor R5 to left channel (and R9 to the right channel) is low for this reason: no need to have a high gain for the third driver.

Power must be single, and may be between 3 V and 15 V. In practice, a voltage of 2V is also sufficient for the voltage drop of logic gates is much lower than that of the op amp.

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Impedance matching : The left and right inputs are performed both on a 100kOhm resistor (R4 and R11) which acts as load resistance for the turntable. The value of this resistance can be lowered, but not below 47K.

Amplification and RIAA correction : Amplification and RIAA correction is provided by two amplifiers, operational, slightly better than the NE5534 and NE5532 is also known for low noise levels. Frequency Corrections follow the curve which forms depends on the value of the resistors and capacitors that are used around the op amp: R5 to R8 and C6 to C9 for the left channel (upper circuit), R12 to R15 and C12 to C15 for the right channel (bottom circuit). Amplification (gain) is defined by the voltage on the resistor value. Resistors R5 and R12 standardize the frequency response to a value slightly greater than 35KHz. Two op amp frequency compensation is not necessary, thus improving their dynamic performance (better rise time ).

The power supply must be a symmetrical + / 9V to + /-15V (max + /-18V). Local decoupling is provided by the RC network consisting of R1, C1 and C2 for the positive branch of power, and R2, C3, C4 for the negative branch.

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Impedance matching
Left and right inputs performed well on a 47kohm resistor (R2 and R7) that acts as a load resistance for the turntable.

Amplification and RIAA correction
Amplification and RIAA are provided by the NE5532 dual operational amplifier, known for low noise, and related components. There are other integrated circuits perform better than NE5532. Correction frequency following the curve whose shape depends on the value of the resistors and capacitors that are used around the op amp: R3 R5 and C2-C4 for the left channel (upper assembly), R8-R10 and C6-C8 for the right channel (the bottom of the assembly). Amplification (gain) is defined by the voltage on the resistor value.

The supply
The power supply must be symmetrical + / 9V to + /-15V (max + /-18V). Local decoupling is provided by the RC network consisting of R11, C7 and C8 positive for power lines, and R12 C9, C10 to the negative line. For this coupling to be effective, four decoupling capacitors should be placed closest to the pin of the power IC NE5532 (terminals 4 and 8).

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It is designed for a dynamic microphone which output impedance is between 50 and 200 ohms. It is possible to connect a microphone which the output impedance is higher, but at the cost of a slight decrease in gain. Use with an electret microphone will be discussed in other article. The -3 dB bandwidth is 30 Hz to 100 kHz. With the above  scheme, the gain is about 35 dB to 40 dB (40 dB = amplification by a factor of 100).

This transistor microphone preamp circuit is a classic, implementing an NPN common emitter (common emitter simply means that the emitter of the transistor is common to input and output of the preamplifier stage, the base forming the entry and collector delivers the output signal). The gain is mainly determined by the value of the resistors R3 and R4. R3 contributes to the temperature stability of the assembly, and its value fairly high given the location of the component, reduces the gain significantly. Therefore there branch parallel capacitor C2, which “bypasses” the resistance from the moment or is this a sound input (if no audio signal input, the capacitor sees only one component continuous and performs as an insulator of high value – it acts here in the presence of AC signals). By removing this capacitor C2, the preamp still works, but with a gain of about 15 dB below. The capacitor C4 mounted between collector and base of the transistor allows to limit the bandwidth up to a reasonable value (around 100 KHz), and limits the risk of developing an unwanted parasitic oscillation.

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