Preamplifiers

This preamplifier is requirement result of many friends to give a high quality preamplifier, capable to drive high quality power amplifiers with good sound, it's not however difficult to making, it combines simplicity and handiness. It does not allocate a lot of facilities and various filters, but is drawn so the acoustic signal follows the smaller course without it's influenced by stages they do not need, with result the coloration of reproduced sound. It follows the modular philosophy that gives the possibility of changing each module and adapted in yours acoustic taste. Thus it will constitute the base for long-standing listening and experimentations. Use relay in the input selection ensures the smaller way and the better possible quality, because the relay contacts are not influenced easily by temperature changes and environment, offer smaller ohmage and parasitic resistance in the signal course. This of course depends also from the relay quality that you will select; I propose choice of relay small size and very high quality.

The circuit use one simple, but good power supply, is enough its armor-clad by the remainder circuit, if it needs, with a aluminium, so that we avoid the noises. All the circuit can be placed in a small box, from which will only come out the RCA jack, the main power cable, in the back box part and the Diode Led D1, in front part. Good its are placed a Fuse and a good small switch. The signal from the circuit outputs, with a good cable, is led to a free LINE input of amplifier or preamplifier. If the output signal level, is not that we want, we can change the resistors R9-22, with other value so that we adapt the level.

This circuit is mainly intended to provide common home stereo amplifiers with a microphone input. The battery supply is a good compromise: in this manner the input circuit is free from mains low frequency hum pick-up and connection to the amplifier is more simple, due to the absence of mains cable and power supply. The circuit is based on a low noise, high gain two stage PNP and NPN transistor amplifier, using DC negative feedback through R6 to stabilize the working conditions quite precisely.

The headphone amplifier with the natural crossfeed filter published on HeadWize in fact was my first DIY-project. I built this device because I was unsatisfied with the sound reproduction via the headphone-socket of my CD-player. But, as things go, I started to like constructing and decided to design and build some power amplifiers also. Having finished these, they sounded so good that I also made a new matching preamplifier with integrated headphone-amp.

The circuit needs to bring the signal from an electret microphone up to a level suitable for a line input. Based on measurement of the microphone output under a range of conditions, I have chosen two gain levels - 2 & 23. 23 is suitable for everyday general recording. 2 is suitable for live music such as a rock concert. There is a output pot to allow fine-tuning of the level if necessary, but it is intended that usually the wiper will be on the land.

An application, which is considered, of very good quality sound since the entrance transistors are working at Class A. The quality of sound depends to a large extent on IC1, which must be of good quality. It can be chosen from several IC with the best from the point of cost efficiency the proposed NE 5534 (NE 5532 for stereo construction) and the series TL071 (TL072) for greater input impedance. This particular application can be used with very good results and as driver headphone with higher 47R impedance. The amplification can be changed and adapted to the amount we want, if changing the feedback resistors R6/R7.

The circuit is a preamplifier with digital regulation intensity of sound. He is separated in three departments. In first schematic (Fig.1), is found the circuit of control of electronic potesometer. The control become from two pressing switches. The S1 (UP), that put up the intensity of sound and the S2 (DOWN), on the contrary, that lower the intensity, checking them two oscillator follow a bistable multivibrator R-S (ICIC-D), with that determined the direction of counter IC3.. The gate IC2B ensure deactivate the counter in the limits of region of regulation. With the S4 we have the possibility selecting the level of sound, in which it will come back after RESET or when we give supply in the circuit. This operation is very useful when we select null level of sound, then with switch S3 we have the possibility of going to situation MUTE, to rapid nihilism of sound.

A preamp designed for the minimalist, and having no frills at all is the design goal for this project. It is designed as a preamp for the Death of Zen (DoZ) Class-A power amp (Project 36), and has very low levels of noise and distortion, in a minimum component count, fully discrete circuit. This gain module can be used as the basis for any preamp - performance is exemplary, with low noise, wide bandwidth, and it sounds extremely good indeed.

In this circuit exists a second designing proposal of preamplifier RIAA. The first stage uses discernible components and in second exist a opamp. [IC1]. In the negative feedback exist the correction RIAA filters. Certain points need certain discriminators: 1] capacitors C2 and C15, will be supposed to suit with the cartridge characteristics that you will use. 2] Transistors Q1-2 and Q8-9, good is they have matched in their characteristics and they are found very near so that they have the same thermic behavior. This can become with choice from a lot of transistors so that we find certain pairs with same characteristics, measuring with a hfe meter. 3] the trjmmer TR1-2 regulate the characteristics of differential amplifiers in the input, for null of DC voltage in the exit of stage. 4] the capacitors C4-17 and C11-24 should matched between them with capacitance meter, so that they have the same values, avoiding in this way the purchase of precise capacitors. 5] All the resistors should be metal film 1%. the circuit supply become from power supply, that exist already in amplifier or from external good stabilised supply ± 15V 100mA.

The preamplifier that appears in the figure is a completely symmetrical preamplifier, from the input as the exit and it works in Class A. It does not have somebody innovation, simply it uses good solutions, in order the result is what should. Such proposal is the use transistors matched [Q1, 2], that finds in the same chip with result the thermic and other characteristics are ''perfect''. It can they are replaced by simple transistors as the BC550C and BC560C it's enough you enter in the fatigue to matched you pairs with similar characteristics. With the TR1 we can if it needs we regulate the Offset voltage in the exit of unit. It can however be suppressed and it's replaced with two resistances 82 ohm in the place of R6 -7. A point that it should I accent it's that diodes D1 and D2 it should they are placed very near in transistors Q3 and Q4 respectively, so that they have common thermic behavior. The himself should become also with transistors Q8 - Q10 and Q9 - Q11 respectively.

This circuit was submitted by Graham Maynard from Newtownabbey, Northern Ireland. It has an exceptionally good high frequency response, as demonstrated by applying an 100kHz squarewave to the input. I have produced some response graphs using Tina Pro to highlight these characteristics.

This riaa Pre-Amp is the perfect solution to getting a signal off of your old turntable and into your mixing board. Whether you want to grab a couple of loops from a 70’s LP record or just archive your record collection you need an riaa compensated pre-amp to do it. When grooves are cut in the vinyl of a record pre-emphasis is used to even out the size of the high and low frequency grooves. To restore the recovered signals frequency response, de-emphasis is required and this is the function of the PAiA riaa pre-amp.

This circuit was submitted by Graham Maynard from Newtownabbey, Northern Ireland. It has an exceptionally fast high frequency response, as demonstrated by applying an 100kHz squarewave to the input. All graphs were produced using Tina Pro.

This preamplifier has a low output impedance, and is designed to drive long cables, allowing you to listen to a remote music source without having to buy expensive screened cables. The very low output impedance of around 16 ohms at 1KHz, makes it possible to use ordinary bell wire,loudspeaker or alarm cable for connection. The preamplifier must be placed near the remote music source, for example a CD player. The cable is then run to a remote location where you want to listen. The output of this preamp has a gain of slightly less than one, so an external amplifier must be used to drive loudspeakers.

This circuit is mainly intended to provide common home stereo amplifiers with a microphone input. The battery supply is a good compromise: in this manner the input circuit is free from mains low frequency hum pick-up and connection to the amplifier is more simple, due to the absence of mains cable and power supply. Using a stereo microphone the circuit must be doubled. In this case, two separate level controls are better than a dual-ganged stereo potentiometer.

This preamplifier was designed to cope with CD players, tuners, tape recorders etc., providing a gain of 4, in order to drive less sensitive power amplifiers. As modern Hi-Fi home equipment is frequently fitted with small loudspeaker cabinets, the bass frequency range is rather sacrificed. This circuit features also a bass-boost, in order to overcome this problem. You can use a variable resistor to set the bass-boost from 0 to a maximum of +16dB @ 30Hz. If a fixed, maximum boost value is needed, the variable resistor can be omitted and substituted by a switch.

This preamplifier was designed to cope with CD players, tuners, tape recorders etc., providing a gain of 4, in order to drive less sensitive power amplifiers. As modern Hi-Fi home equipment is frequently fitted with small loudspeaker cabinets, the bass frequency range is rather sacrificed. This circuit features also a bass-boost, in order to overcome this problem. You can use a variable resistor to set the bass-boost from 0 to a maximum of +16dB @ 30Hz.

A low noise pre-amplifier suitable for amplifying dynamic microphones with 200 to 600 ohm output impedance. This is a 3 stage discrete amplifier with gain control. Alternative transistors such as BC109C, BC548, BC549, BC549C may be used with little change in performance. The first stage built around Q1 operates in common base configuration. This is unusuable in audio stages, but in this case, it allows Q1 to operate at low noise levels and improves overall signal to noise ratio. Q2 and Q3 form a direct coupled amplifier, similar to my earlier mic preamp.

In recent years, following CD's introduction, vinyl recordings are almost disappeared. Nevertheless, a phono preamplifier is still useful for listening old vinyl discs from a well preserved collection. This simple but efficient circuit devised for cheap moving-magnet cartridges, can be used in connection with both audio power amplifiers shown in preceding pages, featuring low noise, good RIAA frequency response curve, low distortion and good high frequency transients behaviour due to passive equalization in the 1 to 20KHz range. Transistors and associated components provide ± 18V supply to the op-amp, improving headroom and maximum output voltage.

The interest for circuits of tubes, remains big. Thus I will give completed in enough big degree, circuit of preamplifier. It is mainly constituted by the department of main preamplifier, the department of input selector, delay of application voltage and connection output of preamplifier with the final amplifiers and the department power supply. The department of mainly preamplifier appears in the Fig.1. Deliberately it does not have something revolutionary in the designing. In the entry exists a simple circuit constituted from relay that is drive from input selector [S2]. The signal afterwards drive to the next stage that is constituted by a circuit cascade S.R.P.P (shunt regulated pushpull) and a circuit cathode repeater, in the exit.