Portable Phone Preamplifier

This unit was designed for fans to have an old vinyl record collection and willing to be digitally remastered on a personal computer. Or sometimes you can hear an old collection of priceless LP, through its modern hi-fi, usually without a preamp stage: this is a circuit capable of meeting their needs. The unit is powered by a 9V battery, allowing for quick and easy connection to all the pre-amp high level input and drawing very low current circuit ensures long battery life.

Despite the low voltage circuit performance with moving magnet pick-up is quite good, with high input overload capability, very low distortion and accurate reproduction of the RIAA equalization curve, thanks to one of two stages of the operational amplifier circuit in which the RIAA equalization network is divided into two halves: an input stage of the application of low-strengthening the RIAA equalization curve in a cable series feedback configuration and a second stage, the application of the acute curve cutting through a second operational amplifier connected to the shunt feedback configuration.

Battery operation is also minimized the possibility of hum pick-up, a potential danger is always present in a high gain, high sensitivity phono preamps. As the drawing of the total circuit current is 1. 2 mA when powered by a 9V battery, the use of an LED lamp will be the main cause of current consumption. Therefore, a very small, low current red LED recommended for this purpose. With a resistance of 6.8K limit specified for R11, the LED will draw an additional current of 1 mA, it will not shine, but can still be easily seen.

A typical carbon-zinc 9V battery will allow the circuit to operate about 180 hours, while an alkaline battery will last over 250 hours. If the LED is omitted, the duration is almost double. In any case, for those who wish to preserve the battery, the circuit can also be powered by a common external adapter power supply, valued at about 12-15V DC, 10 mA or higher. In this case, the input circuit overload will increase even more.

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HeadBanger Headphone Amp

HeadBanger Headphone Amp

Audio-taper pot, R1, adjusts ascribe akin into two LM386 amplifier chips. The LM386 is a low-voltage audio ability amplifier, advised to accomplish on 4V to 12V. It has an centralized 15K acknowledgment resistor amid pins 1 and 5 which would set the accretion at 20 (26dB). At this gain, the achievement babble is hardly audible, so R2/R4 is added, finer in parallel, to abate the accretion to 11 (21dB). Since the added acknowledgment is taken afterwards the achievement coupling cap, C3/C7, it additionally flattens the low end response. Baloney is bargain as well. The acknowledgment resistor allegation be AC accompanying to abstain advancing centralized biasing. C1/C5 decouple centralized bent networks to advance ability accumulation rejection. Since audio-induced ripple on the accumulation is nonlinear, this improves baloney achievement as able-bodied as abbreviation hum in AC operation. Achievement loading arrangement C4/C8, R3/R5 stabilizes amount impedance at aerial frequencies to anticipate oscillation.

The NiCd array is answerable through R6, which sets the charging current. Since the HeadBanger alone draws 10mA abandoned (25mA typical), the 12V AC adaptor voltage is absolutely about 14.7V. The array voltage during charging is about 8.4V. The 120mAH high-capacity NiCd needs about 196mAH of charging. [This is projected from the 60mAH low-cap NiCd which is speced to allegation in 14-hours at 7mA.] With the HeadBanger off, 20 to 25mA is supplied, so the high-cap array will allegation in about 10-hours. It ability booty alert that continued with the assemblage turned-on. The low-cap array would allegation in about 5-hours.

C10 reduces audio-induced ripple on the ability supply. C9 bypasses the accumulation at aerial frequencies, preventing oscillation. Note: Not apparent on the schematic is the break of the ascribe and achievement grounds. The arena affairs from P1 and R1 are affiliated alone from added area to a point on the amp lath abutting to pin 2 of IC1 and IC2.

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Headphone Amplifier-Battery-powered

Headphone Amplifier-Battery-powered

Some lovers of High Fidelity headphone alert adopt the use of array powered headphone amplifiers, not alone for carriageable units but additionally for home "table" applications. This architecture is advised to fulfil their needs and its cartography is acquired from the Carriageable Headphone Amplifier featuring an NPN/PNP admixture brace emitter addict achievement stage.

An bigger achievement active adequacy is acquired by authoritative this a push-pull Class-B arrangement. Achievement ability can ability 100mW RMS into a 16 Ohm amount at 6V accumulation with low continuing and beggarly accepted consumption, acceptance continued array duration. The distinct voltage accretion date allows the accessible accomplishing of a shunt-feedback chip giving accomplished abundance stability.

Notes:

• For a Stereo version of this circuit, all parts must be doubled except P1, SW1, J2 and B1.
• Before setting quiescent current rotate the volume control P1 to the minimum, Trimmer R6 to maximum resistance and Trimmer R3 to about the middle of its travel.
• Connect a suitable headphone set or, better, a 33 Ohm 1/2W resistor to the amplifier output.
• Switch on the supply and measure the battery voltage with a Multimeter set to about 10Vdc fsd.
• Connect the Multimeter across the positive end of C4 and the negative ground.
• Rotate R3 in order to read on the Multimeter display exactly half of the battery voltage previously measured.
• Switch off the supply, disconnect the Multimeter and reconnect it, set to measure about 10mA fsd, in series to the positive supply of the amplifier.
• Switch on the supply and rotate R6 slowly until a reading of about 3mA is displayed.
• Check again the voltage at the positive end of C4 and readjust R3 if necessary.
• Wait about 15 minutes, watch if the current is varying and readjust if necessary.
• Those lucky enough to reach an oscilloscope and a 1KHz sine wave generator, can drive the amplifier to the maximum output power and adjust R3 in order to obtain a symmetrical clipping of the sine wave displayed.

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