Circuit diagram:

Parts:

Device purpose:

This amplifier was designed to be self-contained in a small loudspeaker box. It can be feed by Walkman, Mini-Disc and CD players, computers and similar devices having line or headphone output. Of course, in most cases you’ll have to make two boxes to obtain stereo.
The circuit was deliberately designed using no ICs and in a rather old-fashioned manner in order to obtain good harmonic distortion behaviour and to avoid hard to find components. The amplifier(s) can be conveniently supplied by a 12V wall plug-in transformer. Closing SW1 a bass-boost is provided but, at the same time, volume control must be increased to compensate for power loss at higher frequencies.
In use, R9 should be carefully adjusted to provide minimal audible signal cross-over distortion consistent with minimal measured quiescent current consumption; a good compromise is to set the quiescent current at about 10-15 mA.
To measure this current, wire a DC current meter temporarily in series with the collector of Q3.

Technical data:

Output power: 1.5 Watt RMS @ 8 Ohm, 2.5 Watt @ 4 Ohm, 3.5 Watt @ 2 Ohm (1KHz sinewave)

Sensitivity: 100mV input for 1.5W output @ 8 Ohm

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz & 10KHz: Below 0.2% @ 8 Ohm 1W, below 0.3% @ 4 Ohm 2W, below 0.5% @ 2 Ohm 2W.

Note: The text is AUTO translated from Greek version

Cross-over they are netting usually with passive materials that have aim to separate a region of frequencies in smaller. Cross-over the manufacture that to you we offer it separates the acoustic region in two sub areas in order to we lead two loudspeakers for the high frequencies and for low.

Cross-over they are essentially for the operation of combination of loudspeakers. Without them, two things happen: on one side are led all the frequencies simultaneously to different loudspeakers and otherwise is consumed pointlessly force in loudspeakers that cannot him attribute rightly. Cross-over depending on the number of loudspeakers that leads they are distinguished in two streets and three streets, even if they can result also complexes. The each region is figuratively named street, through which will pass the corresponding region of frequencies in order to it leads the corresponding loudspeaker.

The simpler system is that of two streets. In that acoustic region it is separated in two sub areas with two filters: one of low passage and one high. The filter of low passage leads the loudspeaker for the low frequencies and the filter of high frequencies the loudspeaker for the high frequencies. The loudspeaker for the low frequencies is known as woofer and the loudspeaker for the high frequencies as tweeter.

The loudspeakers are distinguished by various characteristics that him make distinguish between them. That characteristics that us interest for the manufacture that we make, are their complex or more simply resistance and diagram that us gives the relation of attribution of sound as for frequency (sensitivity).

The resistance of loudspeakers is characterized in a frequency depending on the destination and their press.  Loudspeakers are distinguished, as for the destination, in loudspeakers of low frequencies, woofer intermediate, mid-range and high tweeter. Their resistance in W is 4W, 8W and 16W. Cross-over that we present it is intended for loudspeakers 8W.

Theoretical Circuit

The theoretical circuit appears in form 1. The manufacture uses passive materials of mediocre dimensions. In order to you make a cross-over you need printed circuit. Observing theoretical circuit we see that it has a entry and two exits, In the entry connect the exit of amplifier and in the exits the loudspeakers. In the one the loudspeaker of high frequencies and in the other the loudspeaker of low frequencies.  The way from the entry to the loudspeaker of high frequencies is not anything other, despite a filter of high frequencies. Respectively, the way to the loudspeaker of low frequencies is a filter of low passage. The filter of low passage consists by inductor L2 and the capacitor C2. The inductor is en line with the circuit and the capacitor at the same time with the loudspeaker.

The complex resistance of this elements changes, associates the price of   frequency. The price of complex resistance of inductor of is proportional frequency and capacitor of reversely proportional frequency. As long as increase the frequency, the self-induction acquires bigger complex resistance and the capacitor smaller. This, in combination with their provision, prevents the high frequencies to reach in the loudspeaker. In the way of high pass filter to the loudspeaker of high frequencies the provision of elements is reversed. En line we place capacitor, a C1 and at the same time inductor L1. In this provision as long as is increased the frequency, is decreased the complex resistance of capacitor while his inductor that is at the same time with the loudspeaker is increased. As long as it increases the frequency, so much facilitates the capacitor the passage of frequencies and so much least it absorbs the inductor force from them.

Apart from the elements of filter in the circuit, existence resistances and capacitors that stabilise the behaviour of loudspeakers. An additional resistance, R3, offers a particular operation. This resistance is always shorts from a safety. If for some reason it passes big current, then is in danger is burned loudspeaker of the high frequencies. Rather the loudspeaker is burned the safety. Then is presented en line the resistance and is decreased the sound level.

Manufacture

In order to you make the manufacture you will need the PCB that appears in form. In this mount materially that exists in the theoretical circuit, according to form.  The montage of materials will begin from the resistances and flowingly will place the capacitors and finally the self-induction. The inductors for the cross-over, if him you find in trade you cans him order from us. In order to you try the cross – over   apply in the exit for the each loudspeaker a resistance 8W. In the entry you will connect a small amplifier with which you will strengthen the signal of acoustic generator. The generator him you will put it produces sine’ signal. Altering the frequency we observe the each expense in an oscillograph. If all have well, then when is increased the frequency and approaches the price 3,5kHz, the tendency in the exit for the loudspeaker of low frequencies falls and the other increases.

Parts

Circuit diagram:

Parts:

Power supply circuit diagram: 

Parts:

Notes:

• Can be directly connected to CD players, tuners and tape recorders. Simply add a 10K Log potentiometer (dual gang for stereo) and a switch to cope with the various sources you need.

• Q6 & Q7 must have a small U-shaped heatsink.

• Q8 & Q9 must be mounted on heatsink.

• Adjust R11 to set quiescent current at 100mA (best measured with an Avo-meter in series with Q8 Drain) with no input signal.

• A correct grounding is very important to eliminate hum and ground loops. Connect in the same point the ground sides of R1, R4, R9, C3 to C8. Connect C11 at output ground. Then connect separately the input and output grounds at power supply ground.

Technical data:

Output power: well in excess of 25Watt RMS @ 8 Ohm (1KHz sinewave)

Sensitivity: 200mV input for 25W output

Frequency response: 30Hz to 20KHz -1dB

Total harmonic distortion @ 1KHz: 0.1W 0.014% 1W 0.006% 10W 0.006% 20W 0.007% 25W 0.01%
Total harmonic distortion @10KHz: 0.1W 0.024% 1W 0.016% 10W 0.02% 20W 0.045% 25W 0.07%

Unconditionally stable on capacitive loads

Make a sound card is no more a complex issue. If you use great IC PCM2702 from BURR BROWN / Texas Instruments you can create a fully functional USB sound card. This sound card can be powered from USB port and has one stereo output. You don�t need to install any driver for Windows XP and Vista, because they are already inside. This is really plug and play.

Few months ago I have seen USB sound card called Alien DAC. The construction on the project web page inspired me to build this thing also.

The core of this construction is 16-Bit Stereo Digital-To-Analog Convertor with USB interface PCM2702.

PCM2702 needs only few additional parts to work. The schematic is not complex. Sound card can be powered directly from USB port (jumper W1) or from external power supply (jumper W3). PCM2702 needs two power supply 3.3V (3V-3.6V) and 5V (4.5V-5.5V). I used fixed output voltage LDO TPS76733Q for 3.3V (IO2) and adjustable output voltage LDO TPS76701Q for 5V (IO3). Both LDO are produced by TI, I used this because I had it in my drawer. Any similar LDO can be used. Output voltage of IO3 should be set to little bit lower than input voltage to allow LDO good stabilization, in my case output voltage is set to 4.8V. Output voltage can be set by adjustable resistor R33. In case of low power supply, IO3 can be shorted by jumper W3. LED D3 signalizes power on.

Assembled top side

Small ferrite beads are placed before all power pins of PCM2702 and in Vbus and GND of USB. These small beads reduce high frequency hum. I had a problem find this small SMD ferrite beads in local stores but finally I acquire few of them from old hard drive. They are not absolutely necessary, you can use zero ohm resistors instead of them.

Low-pass filter is placed in output signal path to reduce sampling frequency. An OPA2353UA dual op amp is configured as a stereo 2nd-order low-pass filter. Led diode D1 is illuminated when PCM2702 plays audio data received from the USB bus. Led diode D2 is illuminated when USB bus suspends audio data transmission to the PCM2702.

Schematic of sound card with PCM2702

PCB assembly diagram

PCB – Download PCB in [EPS format] or [PDF format]

Bottom side of PCB (single side PCB, made by standard etching method)

Assembled bottom side

This circuit works very well. I only shorted crystal during soldering so the circuit didn�t work, but after removing the short the sound card started to work. I have tested in Windows 2000, XP and Vista. It works in all mentioned systems. Drivers are present in operation system so the sound card is ready in few seconds after you connect it.

During writing this article I have found that PCM2702 is now not recommended for new design, but TI offer even better solution. PCM2704, PCM2705 have same functionality as PCM2702, but they include output filter. They are able to drive directly headphones. Volume and Mute can be controlled through SPI bus in PCM2705 or with pushbuttons in case of PCM2704. PCM2704 and PCM2705 are in TSSOP28 package. PCM2706 is similar to PCM2704 and PCM2707 to PCM2705 but in addition they have I2S bus. PCM2706 and PCM2707 are in TQFP32 package. I recommend using these new chips for new design (look at the TI web page).

Pulse Generator kit will generate a frequency in KHz which can form a good test gear project.  This kit is based on the classic LM555 timer IC.

• Input – 12 VDC Max @ 40 mA

• Range – jumper selectable and preset tunable range of 1 Hz to 180 KHz

• Power-On LED indicator

• Terminal pins for easy connection

• Four mounting holes of 3.2 mm each

• PCB dimensions 40 mm x 47 mm

This circuit controls resistive and inductive loads up to 2,500W. Its main functional device is an integrated phase control circuit – Siemens TLE3103. It contains its own power supply, a zero voltage crossing detector circuit and a logic driver. An additional feature is the low voltage input to enable/disable triac firing enabling/disabling the logic driver. The function is as follows: pin13 TLE3103 open (floating), trigger output active, tied to ground trigger output disabled.