Yeah, I see that now that you point it out...stupid question. From what I have read, preamps have a high impedance output because they are not intended to drive speakers. I am planning to use a stereo version of this preamp between an MP3 player output and a circuit something like this. The objective is to reduce drain on the MP3 player battery by lowering output volume. However, I am not sure exactly how much gain to expect from the preamp.Do you mean R4?
R4 is a load resistor. You can measure the output without R4 being connected.
As for what value it should be, it depends. What standard that requires a certain load are you trying to comply with?
I haven't done any measurements, but my experience is that I have to run the MP3 player at maximum volume in order to get the volume I want out of the TDA1517. I thought about boosting the power on the TDA1517 amp from 12 to 15 volts. Would that be a better idea?The TDA1517 requires 15.4 microwatts of power at its input. (.96 volts)squared/60,000 ohms.
Are you really trying to save .0000154 watts by building a preamp for a power amplifier that is already designed to work with an MP3 player?
hang on. That was peak voltage. You're trying to save .0000077 watts.
Wow! That's quite a site. Thanks.
Thanks. The maximum output from my MP3 player is (as you say) about 1.6 V, however, I would like to operate it with the volume set at midrange instead of maximum. That setting reduces the output to about 100 mV. Would a preamp not solve that issue? That way, I could increase the play time on the MP3 player by minimizing its battery drain since the preamp and the TDA1517 amp would be powered from a separate power supply.The datasheet for the TDA1517 says that its voltage gain is 20dB which is 10 times.
Its maximum output power is fairly low but much more than an MP3 player that drives 32 ohm headphones with a low level so it doesn't make you deaf.
The output voltage of an MP3 player is probably about 1.8V RMS max. The output of the TDA1517 with a 14.4V supply is about 4.5V RMS (5W into 4 ohms).
Then the TDA1517 has more than enough voltage gain without using a preamp.
It is difficult to predict the voltage gain of a Jfet preamp because of its very wide range of voltage gain (gm). You don't need its very high input impedance used for an electric geetar.
Use a normal transistor or opamp preamp instead.
Maybe you want 100W from the 5W amplifier IC? Impossible.
No, I am using a separate regulated supply and included the diode in the amplifier for just the reason you suggested.I hope you are not powering your amplifier from a transformer. The diode is not a full wave bridge rectifier. The diode probably prevents damage if a battery is connected backwards.
The datasheet shows a single-ended stereo amplifier has an output of only 3.3W with 1% clipping distortion into a 4 ohm speaker with a 12V supply. Its output power is almost halved into an 8 ohm speaker. Your diode in series with the power supply reduces the voltage and reduces the power.I am going to put together a 15 V power supply for the TDA1517 amp and see if that increases its output.
We don't know your speaker impedance.The NXP datasheet for the TDA1517 indicates a maximum operating voltage of 18 V, and a typical of 14.4 V. So, 15 V regulated supply should put 14.4 V on the IC, as opposed to the 11.4 V it's now getting. Should be okay, don't you think?
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