Analog Audio Delay Line(3d Sound)

It is fun to make a variable space in your small room, but it’s hard to make the actuator to move your wall or room partition. Using analog audio line delay, you can adjust your room virtually. Just turn a knob in your audio set and you can adjust your room size. The circuit described here will make your dream come true, giving a feel that your speaker is located 15 meters behind you, even though your room is actually 3 meters wide. Here is the circuit’s schematic diagram.The core of this circuit is SAD512D integrated circuit, an analog audio delay. The chip uses 512 capacitors memory to hold 512 sampled analog signal. The delay can be adjusted from about 5,1 ms to 51 ms by R12 pot. Feed the input of this analog delay circuit with a mixed right and left audio signals from your stereo system. The output of this circuit then fed to a small power amplifier and place the output speaker behind you. Now you can perceive like your speaker is 15 m away behind (with maximum delay setting). If you build two unit the cascading the circuit will result in 30 meter expansion of your virtual room.

The circuit consist three main block. The first block (U1A, U1B) is a fourth order low pass filter (-24dB roll-off per octave) with 2.5kHz cut off frequency. The second block is the adjustable analog delay integrated circuit (IC SAD512D). The delay is controlled by the oscillator around U2 which is adjustable from 5KHz to 50Khz. The last block is similar to the first block, a low-pass filter with 2.5KHz cut off frequency.

A variable resistor R9 is provided to adjust the input offset, avoiding signal clipping and maximizing the audio range. For easy adjustment, feed the input with high level audio signal until the output is distorted, then adjust R9 until the distortion is minimum, or if an oscilloscope is available, adjust the R9 until the clipping is equal for both positive and negative cycle. Finally, adjust R28 to give minimum sampling clock noise.

PARTS LIST

Reference Part
C1,C4,C10,C12 10n
C11,C2 1n5
C3 4.7uF/50V
C13,C5 1n9
C6 390p
C8,C7 1u/25V
C9 1uF/25V
C14,C15,C16 100n
J1 input connector
J2 out connector
R1,R2,R3,R5,R6,R7,R11,R20,R21,R22,R24,R25,R26 10k
R4,R23,R27 4k7
R8,R15 15k
R9 2k2 POT
R10 2k7
R12 220k POT
R13 10R
R18,R14 1k
R17,R16 330R
R19 100k
R28 250R trimpot
U1 TL084
U2 4011

Quadraphonic Amplifier

Quadraphonic Amplifier


Description:

This is a four channel amplifier ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card. There is no volume control,audio levels being directly controlled from the sound card itself.

circuit:


Parts List:
D1-D4: 1N4001 (4)
C1,C20: 1000u CAP (2)
C2,C11: 47u CAP (2)
C3,C5,C7,C8,C12,C14,C16,C17,C21,C22: 0.1u CAP (10)
C4,C6,C13,C15: 10u CAP (4)
C9,C10,C18,C19: 2200u CAP (4)
R1,R4,R9,R12: 1M RESISTOR (4)
R2,R6,R10,R14: 100k RESISTOR (4)
R3,R5,R11,R13: 1k RESISTOR (4)
R7,R8,R15,R16: 2R7 RESISTOR (4)
IC1: 7812 (1)
IC2,IC3: LM1778N (2)
SPK1,SPK2,SPK3,SPK4: 8R 2 Watt speakers (4)

Notes:

Construction is straight forward and is suitable for Verobaord. Overall gain is controlled by the ratio R14/R13 and R6/R5. Used with small hi-fi speakers the volume was too loud for my room so I reduced R14 and R6 to 33k. The zobel network formed by R7,C7,R8,C8,R15,C16,R16,C17 prevents instability which can happen with long speaker wires. The input impedance is high, 1M and if very long input cables are present could pick up noise. Screened cable should be used, in my case I used 10k resistors between points A & C, B & C, D & F, E & F. This provides a DC path to ground and higher noise immunity. If instability does occur, then you will notice sound distortion and the LM1877N will become hot to touch.

Connections:

The back of a sound blaster live card has color coded 3.5mm stereo jacks. The image below shows a close up of the rear of my Sound Blaster Live card. As well as color coding, each connector has an appropriate marking, for easy connectivity.

The normal output connector is green and the rear speaker connector is black. Creative provide utilities and sound mixer for use with Windows. Under Linux the utility Gamix can be used, which allows independent volume control for all channels.

Allpass network shifts signals 90°

Allpass network shifts signals 90°

Unlike lowpass, bandpass, and other magnitude-altering filters, allpass filters can shift the phase of a signal without affecting its amplitude. For a first-order allpass circuit, the transfer function is
As you sweep the variables from zero (dc) to infinity, the sign of H(s) changes from plus to minus, indicating a change in phase from 0 to 180°. You can realize this transfer function in two wideband transconductance amplifiers (WTAs). The circuitry inside the dashed lines in Fig 1 is one allpass network.

A WTA's transfer function is IOUT8VIN/Z, where 8 is simply an internal constant and Z is an external gain-setting component connecting the WTA's Z+ and Z- pins. The transfer function for voltage amplification is VOUT/VINIOUTxZOUT. Most applications require a resistive Z. But the WTA also accepts an inductor, a capacitor, or any other impedance network for Z.

The allpass circuit combines a resistive-Z WTA (IC1) with a capacitive-Z WTA (IC2). At low frequencies, IC1 dominates the circuit's output because the capacitor's high impedance allows only a low IOUT from IC2. Rising frequencies lowers this impedance, causing the current from IC2 to dominate at high frequencies. Moreover, IC2 inverts, and IC1 does not, producing the desired noninverting unity gain at dc and inverting unity gain at high frequencies.

Communications and signal-processing applications use allpass networks widely. An example is a 90°-phase-shift network, which, with appropriate mixers, produces a single-sideband signal. In Fig 1, the two allpass circuits have corner frequencies that differ by a factor of 7.5. The output RC networks determine these corner frequencies. The result is an output-phase difference that remains close to 90° over a wide frequency range. Measurements show 0.2-dB amplitude variations and a phase difference of 90°±7° from 180 to 740 kHz-a 4:1 range. (DI #1696)

Two wideband transconductance amplifiers (WTAs) form an allpass network (within dashed lines). Combining two such networks produces two outputs having a constant 90° phase shift versus frequency between them.