Phono Preamps For All

This is a collection of phono (black vinyl for the youngsters) preamps and equalisation circuits, one of which is sure to meet your requirements. These are not my circuits, but were contributed by a reader (see above), so I am not really in a position to make any specific recommendations. They are provided as a service to the experimenters out there, and may be found useful for other applications as well.

Source: http://sound.westhost.com/project25.htm

Intercom preamp - Universal high quality preamp

The circuit is so simple that there is little to say about it, but it gives very good results. Tr1 is operated in grounded base mode with input to its emitter to give low impedance input. The values shown give correct operation from 9v. If operating from other voltages you may wish to alter the 1K8 resistor to give symmetrical clipping at high levels. The third circuit is one I was working on as I left the audio company but is seems to be potentially very useful. It should be simple to use it as a low impedance mic amp or as a high input impedance preamp for mic or, with a suitable RIAA equalization, for phono pickup or similar. It can even be used as a balanced input mic preamp.

Source:http://www.4qdtec.com/preamp.html

Audio Preamplifier with Digital Volume

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.

Source : http://users.otenet.gr/~athsam/audio_preamplifier_with_digital_volume.htm

Graphic Equaliser

This equaliser is designed as a preamp suitable for musical instruments - guitar, bass and keyboard in particular. Unlike most conventional graphic equalisers, each slider ranges from fully off to fully on, and not the more conventional +/-12dB or so that is normally available. As a result, there is no flat setting (other than all off!). This graphic is designed to be used to create a sound, and is not suitable for hi-fi. It may be used as an add-on unit to existing instrument amp preamps, tone controls, etc. The flexibility is extraordinary, allowing a hollow "single frequency" type sound, right through to almost any tonal variant imaginable. This is the first of several projects based on the multiple-feedback bandpass filter described in Project 63, it can be made with as many (or as few) filter sections as you want.

Source Circuit:

5 band graphic equalizer using a single IC/chip

This circuit uses a single chip, IC BA3812L for realizing a 5 band graphic equalizer for use in hi-fi audio systems.The BA3812L is a five-point graphic equalizer that has all the required functions integrated onto one IC. The IC is comprised of the five tone control circuits and input and output buffer amplifiers. The BA3812L features low distortion, low noise, and wide dynamic range, and is an ideal choice for Hi-Fi stereo applica-tions. It also has a wide operating voltage range (3.5V to 16V), which means that it can be adapted for use with most types of stereo equipment.

Source circuit

Microphone pre-amp

This is an image Schematic. No Description available.

Link : http://www.ee.washington.edu/circuit_archive/circuits/Micro.GIF

All transistor microphone pre-amplifier

The microphone has high sensitivity in the audio range, but in the ultrasonic range, the sensitivity decreases rapidly. The receiver is very sensitive. To prevent overdriving and feedback due to the high sensitivity of the microphone in the audio range, the gain of the amplifier should be low in the audio range and increase with frequency in the ultrasonic range.

Read More Source: http://bertrik.sikken.nl/bat/preamps.htm