PC Stereo Chip Amp to Mono Practice Amp

[Nick C.]

I took the amplifier board out of a set of old PC speakers and hooked it up to a small speaker cabinet. The chip is a TEA2025 which should be good for 1.5w at 9v into 8 ohms per channel. The board is set up exactly per the data sheet for stereo with no preamp or even buffer in front. I have the guitar input split going into the 2 stereo inputs and I tied the 2 outputs together.  BTW it needs a preamp/pedal in front of it for decent volume. I altered some components to try to make if more guitar friendly. Sound alright for clean guitar or bass. Louder than a LM386 ruby, but it doesn't distort well.

So could I be getting 3 watts by paralleling the 2 channels?

[Unlikekurt]

The datasheet should provide information on a Bridged setup if applicable.
I've used the TDA2822 as the stereo headphone amplifier in a product and found it to function quite well as a "utility" headphone amp.  It was also able to drive a variety of speakers on the bench without issue.
Not hi-fi by any means, and no replacement for a valve amp, but in a pinch it'd work.

[GibsonGM]

I believe if you tie the outputs together, you should do so thru 2 resistors...just pointing this out, because not doing so could damage the chip, IIRC (?)   Maybe use 2 1K resistors, tied together at the new output....don't quote me, but shorting the outs together doesn't sound good...this chip may be different, but better safe than sorry...

[Nick C.]

    "The datasheet should provide information on a Bridged setup if applicable."

There were too many changes involved to convert it to bridged configuration on the crowded circuit board.

[PRR]

Parallel, 3 Watts in _4_ Ohms.

Bridged would be 3 Watts in _16_ Ohms.

Parallel in 8 Ohms may be 1.6 Watts. The chip already swings most of the 9V, and doubling-up in the same load isn't going to increase the voltage swing enough to matter.

And remember that 1.5W and 3W are much the same, and that speaker changes can be far more change. A good size sensitive for-guitar speaker will BLOW AWAY a couple small "hi-fi" speakers.

Paralleling big amps is bad form, and can be expensive. I suspect all the little chips tolerate it without harm. The distortion could rise (the two channels are not exact match, they fight each other over their small differences) but you are not complaining of that.

[ashcat_lt]

In series, though...   

But seriously, try it.

[Nick C.]

Thanks Paul, I suspected it wasn't so simply additive. The voltage swing I see, but shouldn't there be some increase in current or are the amps "seeing" a different resulting impedance from the speaker? I was thinking it might be akin to seeing a 4 ohm load.

In series, though...   

But seriously, try it.

Watt the..! Do you mean use the 1st amp like a preamp into the 2nd? I'd imagine it would work like a 386 overdrive, which are really loud. Put a master volume on it and some eq and do away with the need for a separate preamp. Possibilities

[ashcat_lt]

Watt the..! Do you mean use the 1st amp like a preamp into the 2nd? I'd imagine it would work like a 386 overdrive, which are really loud. Put a master volume on it and some eq and do away with the need for a separate preamp. Possibilities

Yeah.  It was a while ago when I was playing with something similar, but it was pretty cool in a really nasty kind of way.

[PRR]

> shouldn't there be some increase in current

Same voltage, same load, same current, same power.

There will be some small increase of voltage. The chips are not perfect voltage sources. Say there is 2 Ohms internal loss. Say 9V DC makes 3.18 Vrms sine wave. An 8 Ohm speaker gets 8/10 of 3.18V, 2.5V. With two amps in parallel we would assume 1 Ohm internal loss, 8 Ohm load gets 8/9 of 3.18V, 2.83V. From 2.5V to 2.83V is about 1dB more power, just-barely audible in an A/B test.