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Most of the problems were due to under-rated power supplies. You have to remember that in the 1980's consumer electronics boom, the markets were flooded with very low quality equipment that boasted specifications that were impossible to reach. There were no consumer protection laws in those days so a "Hi Fi" unit might have superb specifications but in reality be an under rated, badly designed, badly built cardboard PCB with 50mm bass speakers! If I remember correctly, one "20W per channel" system that passed through my repair workshop had a 1A rated mains transformer in it that also powered the receiver, cassette deck and record deck motors.
With 'noise' you have to be careful how you measure it. For example, 50mV of noise on a supply line might mean 50mV of noise across the loudspeaker but the same noise at the amplifier input would drive it into full power. Generally, the hiss kind of noise that increases with the volume control is generated in the pre-amplifier stages where the gain is normally much higher. It rarely originates in the power output stage. I have never seen any 'noise reduction' circuits in a power amplifier and usually by careful choice of components and gain distribution, it can be minimized in the earlier stages.
The LM1875 is almost a drop in replacement for the TD2030A but has much higher specifications. It is still in production and easily available. It's distortion specification is typically 50 times lower than the TDA.
Brian.
My point was that 12V at 1A means a power consumption of 12W (Watts = Volts * Amps) but it claimed 20W output power - so where did the extra 10W come from...Seems product class d with germanium transistors was liquidating on hand old stock with the advent of silicon parts they become obsolete.
Hi,
The schematic of post#29 has some issues.
* 200 Ohms may be too low for a standard signal input
* the pot misses the GND connection
* the capacitor in combination with the pot forms an LPF. But the LPF cut off frequency depends on source impedance and pot position. Usually one wants a stable cutoff frequency.
Klaus
The non-inverting input level of your TDA2030 amplifier depends on its output level divided by your gain of 1 + (100k/4.7k)= 22.3 times. but since you are using the minimum supply of 12V the datasheet does not show the puny output level.
Their graph of output power vs supply voltage starts with a 16V supply producing an output of 2.2W into 8 ohms.
Then 2.2W into 8 ohms is 4.2V RMS which is 11.9V p-p. Then the total output voltage loss is 16V - 11.9V= 4.1V.
Your 12VDC - 4.1V= 7.9V p-p which is 2.8V RMS output just before clipping. So the input voltage is 2.8V/22.3= 126mV RMS. your output power into 8 ohms just before clipping is only (2.8V squared)/8= 0.98W.
The datasheet shows an input noise level of only 10uV and with your gain of 22.3 times then the output noise level is 223uV then the signal almost at clipping level to noise level is 12,600 which is about 82dB. But that is at full blast. Your average output level will be about 0.8V RMS then the signal to noise level is only 3400 times which is about - 72dB which might be audible.
So your noise problem is caused by using a low output power supply voltage which causes the low output power level of only 1W to be close to the noise level.
It was mostly due to the electron emission from the cathode electrode falling as the tube got older. The reason for that was partly because of long term chemical changes in the cathode coating and partly because of slow release of oxygen molecules from the construction materials causing oxidization. Bear in mind the cathode would run continuously at several hundred degrees temperature in normal operation. Used within ratings they usually lasted for many years.Were tubes detrimenting quality caused from vacuum pressure loss, electrode deterioration or was it from another issue?
My point was that 12V at 1A means a power consumption of 12W (Watts = Volts * Amps) but it claimed 20W output power - so where did the extra 10W come from...
The audio frequencies you are interested in range from about 30Hz up to about 20KHz, a ferrite bead will have no audible effect at those frequencies. In fact they would have virtually no effect at 10 times audio frequencies.
Noise is something we have to tolerate but we design to make it as small as possible. There is no magic circuit that removes noise after it has been created. Human hearing is more sensitive to noise as the frequency increases (within audible range) but deliberately attenuating higher frequencies to make it less noticeable also reduces the wanted high notes as well. If you have a music system with bass and treble controls, turn the treble down and you will notice background noise also drops but so does the sharpness of the music. The treble control is basically a high frequency attenuation device, working like the capacitors you added to the TDA2030 circuit.
Brian.
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