low voltage audio amplifier

[thabart]

Long time-reader and first-time poster. Here's what I'm doing: I am working on a low voltage amplifier using BJT's. Tthe input comes from a PC or mp3 player (around 200mVrms). I want the voltage gain to be higher than 10v/v and 1W should be dissipated to an 8ohm speaker. I tried using a circuit similar to the one attached. It worked great, as long as the input voltage does not exceed 20mV or so. After that point massive clipping occurs. Can somebody explain this phenomenon and maybe hint a solution? Any help is greatly appreciated.

 

[Meridian]

Long time-reader and first-time poster. Here's what I'm doing: I am working on a low voltage amplifier using BJT's. Tthe input comes from a PC or mp3 player (around 200mVrms). I want the voltage gain to be higher than 10v/v and 1W should be dissipated to an 8ohm speaker. I tried using a circuit similar to the one attached. It worked great, as long as the input voltage does not exceed 20mV or so. After that point massive clipping occurs. Can somebody explain this phenomenon and maybe hint a solution? Any help is greatly appreciated.

Check out this link: **broken link removed**

 

[mhtplsh]

got it solved or still need help?

 

[boh]

Download (free) PSpice9.1 to investigate circuit problems. Good fun too, far easier to see what changes will work!

Clipping is caused by excessive gain. Your first stage on its own has gain far greater than 10 V/V, and so does the second. Other complications: the second stage is loading the first; the 2N3904 is rated for only 350mW;the Cs in parallel with 180 and 100 are giving a strange frequency response; the 10k variable looks unlikely to give unsatisfactory volume control; the 8 ohm speaker reacts with the 10 uF to form a high-pass filter.

The 10k and 1.8k at the base of T1 are unnecessarily low, replace with say 100k and 10k. Reduce the high first-stage gain by negative feedback--remove the C across the 180, which should now be about 12 ohms to get a gain of 10 (maybe you vary the 12 as volume control).

The capacitor between C of T1 and B of T2 needs to be bigger, say 47uF, because we're about to make it feed into a rather low impedance.

The second stage should be an emitter follower, based on a power transistor e.g. TIP29. Remove the 1k, replace the 5.1k with 1k, replace the 560 with a short, and the 100 with 10 ohm (or just use the speaker itself instead). If the TIP29 heats up use a heatsink. 1 watt into the speaker is not negligible.

 

[TOMIN333]

Here is low voltage amplifier circuit using TDA2822M IC given in the link. it works on 5v supply can even connected to a Pc usb and produces a decent power output:https://digitdiary.blogspot.com/2010/04/multimedia-pc-speaker-circuit.html

 

[LvW]

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It worked great, as long as the input voltage does not exceed 20mV or so. After that point massive clipping occurs. Can somebody explain this phenomenon and maybe hint a solution? Any help is greatly appreciated.

The clipping "phenomenon" is quite normal for each amplifier. But the main question is: At which level and symmetrical/unsymmetrical?

In particular: If clipping is unsymmetrical, the reason may be an operating point which is not app. in the middle of the available output voltage range. This applies for all stages. Check the operating points (dc voltages). Or is your gain too large?