Automatic Level Control Circuit

Description 

The rectifier input is tied to the input. This makes gain inversely proportional to input level so that a 20-dB drop in input level will produce a 20-dB increase in gain. The output will remain fixed at a constant level. The circuit will maintain an output level of 1 dB for an input range of +14 to -43 dB at 1 kHz.

Circuit Diagram 

Circuit Description

An audio source, like a mixer, preamp, EQ, or a recorder, is fed to the input of the Electronic Crossover Circuit. This signal is either AC or coupling, depending on the setting of switch 51, the non-inverting input of buffer amplifier Ul-a, a section of a quad BIFET, low amp TL074 noise made by Texas Instruments op. This stage has a gain of 2, and its output is distributed to both a low pass filter made by R4, R5, C2, C3, and Uld op-amp, and a high-pass filter made by R6, R7, C4, C5, and op amp ULC. These are12 dB / octave Butterworth filters. The response of the Butterworth filter was chosen because it gives the best compromise between the damping and phase.

Active crossover circuit with TL074

Guitar Effect Circuit

Description

This is a circuit I have designed for guitar effect builders, I was very unsatisfied with the way everyone was using just a plain old double pole double throw click switch for the bypassing. Most of the time it was very scratchy sounding using that method and I experienced loud pops in my amplifier when switching from straight through to effect. Observing my "Boss" pedals and how they were switched on and off I figured there must be more to it. It took me only about 4 hours to design and test this circuit, It works very well and I'm really satisfied with it so I'll be using it in all the effect pedals I build. It's a very clean bypass both electronically and mechanically.

How it works: the first stage in the schematic is a 4011 nand gate chip set up as a debounced switch to give the logic pulses from the switch to the flip flop. The second stage is the flip flop, this is a 4027 JK flip flop set up in toggle mode, this controls the switching of the 4016 which is an analog switch, this part controls the bypass. That's about all there is to it. The effect which I have used this in so far is a home built "MXR hot tubes distortion" effect. Feel free to put this up on your site and mail it around to friends. The only credit I ask of this is that my name remains on the schematic. Original artile sourse ee.washington.edu

High Voltage Solid-State Circuits for Tube Guitar Amplifiers

Circuit Description

The IRF820  MOSFET has a  voltage rating of  500v, it should  work well in  preamp stages of  most tube amps. The 100 ohm  resistor is there  to suppress H.F.  oscillations. If  IRF820 is  physically close  to the 12AX7  plate, you  probably won't  need it. You can see how the MOSFET is equivalent to a triode: Source/Cathode; Gate/Grid; Drain/Plate

You cannot use the MOSFET as a direct replacement for a typical tube gain stage. The MOSFET will not "self bias" like a typical cathode-biased tube stage.The MOSFET is an "enhancement device" while a triode is a "depletion" device. In this circuit, it is not necessary to use a heatsink on the IRF820. You can if you want.

High voltage solid state guitar amplifier

High voltage solid state pream stage guitar amplifier

High voltage solid state reverb driver guitar amplifier

Guitar Reverb Effect

Description

The guitar input stage is a class A amplifier with adjustable bias. A 2N3906 PNP tranistor is used for a low noise design on this stage. The output of the preamp stage is sent to three places: the output mixer amp, the reverb driver amp, and the input clipping detector.

The reverb driver amp consists of a phase inverting push-pull circuit made from dual sections of a 5532 high quality audio op-amp. This provides a voltage swing of approximate twice the supply voltage to the reverb impedance matching transformer, allowing higher power transfer. The 100 ohm resistor is critical for insuring a clean drive signal, without it, the op-amps can saturate when driving the transformer, producing unwanted distortion.

The transformer matches the impedance of the driver amplifer to the reverb driver coil and allows a dual phase driving signal to power a reverb coil with one grounded side. The transformer is a standard "70 volt" audio line transformer that is often found on PA systems. One reader reported having good results using a Mouser 42TU013 (1K to 8 ohm) transformer. If you can find a reverb tank with a high impedance driver coil, the transformer may be eliminated, the driver coil will require isolation from ground.

The output of the reverb tank is sent to the reverb recovery amp, it is also a 2N3906 class A low noise stage.

The mixer amplifier is a 2N3904 transistor biased for class A operation. It mixes the dry signal from the input preamplifer with the wet signal from the reverb recovery amp through two 10K resistors. The wet signal level is adjusted by a 10K potentiometer.

The clipping detector stages receive inputs from the guitar preamp and the reverb recovery amp, they act in an identical manner. The 1458 op-amp is wired as a comparator with a threshold that is near the high side of the allowable voltage swing on the associated 2N3906 preamp stage. If the transistor output exceeds this voltage, the 1458 output turns on, causing the 4011 one-shot pulse stretcher circuit to fire. The one-shot circuit activates the LED, and stays on long enough that even minor clipping on the amplifier causes visible blinking.

The power supply filter involves an RC filter between the DC input and the VF1 power bus. VF1 drives the reverb driver, the output amp, and the clipping circuit. VF2 and VF3 are further filtered with their own RC filters, they provide isolated DC for powering the input preamp and reverb recovery amplifier stages.

Guitar Reverb Effect Circuit

Original article sourse solorb.com

Subwoofer amplifier TDA7293

Features

Multipower BCD technology
Very high operating voltage range (±50 V)
DMOS power stage
High output power (100 W into 8 Ω
THD =10%, with VS = ±40 V)
Muting and stand-by functions
No switch on/off noise
Very low distortion
Very low noise
Short-circuit protected (with no input signal applied)
Thermal shutdown
Clip detector
Modularity (several devices can easily be connected in parallel to drive very low impedances)

Description

The TDA7293 is a monolithic integrated circuit in Multiwatt15 package, intended for use as audio class AB amplifier in Hi-Fi field applications, such as home stereo, self powered loudspeakers and Topclass TV. Thanks to the wide voltage range and to the high output current capability it is able to supply the highest power into both 4-Ω and 8-Ω loads. The built-in muting function with turn-on delay  simplifies the remote operation avoiding on-off switching noises. Parallel mode is possible by connecting several  devices and using pin11. High output power can  be delivered to very low impedance loads, so optimizing the thermal dissipation of the system.

Circuit Diagram

Audio amplifier circuit TDA7293

Layout

Layout for audio circuit TDA7293

 PCB

PCB for audio circuit TDA7293

Amplifier Circuit Diagram Class D