1 Watt amplifier from ETI - 6V, 2 speakers, 0 opamps

[duck_arse]

Really simple audio amp

This simple audio amp delivers around one watt output from a 6V supply. But you need two speakers. It's ideal for battery operated gear where small, 50mm transistor radio type speakers can be used.
The BD140 (Q3) should be mounted on a small heatsink. The value of R1 should be adjusted to obtain about a 1.5V drop across each speaker. The full 1 W output is obtained with 4 Ohm speakers, half that with 8 Ohm types.

the above circuit is provided direct from the "Electronics Today Circuit Cook Book, No. 6". I have not tested or built it; please note the "cook book" aspect. and check those transistor pinouts! the BC640 pinout has been know to bring grown men to tears. datasheets for :

http://pdf.datasheetcatalog.com/datasheet/fairchild/BC640.pdf
http://pdf.datasheetcatalog.com/datasheet/fairchild/BD140.pdf

anyone interested in 12 Volting this circuit is advised to wait for a passing adult. they may have some ideas about the viabillity and modding of the circuit, the polarity of, and some trick box-mounting formats for, the speakers, and why the BC640 was used.

as kipper says I say, "I go now".

[tca]

It works nicely, I've tried something similar with a mosfet with source to ground and only one speaker at the drain. You can almost get 50% efficiency out of that small class A amp. Just trust that nothing happens to the speakers!

Cheers.

P.S.
I've used a 6V 400mA cell phone power source.

[blackcorvo]

There are a bunch of similar projects out there, but they usually have only one speaker at the emitter of the power tranny:

[tca]

There are a bunch of similar projects out there...

But there is a difference between "Knowing the path and walking the path."

[duck_arse]

where is the path?

[tca]

Just build one, and try it out!

[PRR]

Any power amp which runs _DC_ through the speaker and has more than 3 parts is a dubious thing.

Running DC through the speaker heats it up (wasting power capacity) and makes the coil sit off-center in the gap (wasting bass excursion).

Back in the 1960s we did do such tricks, but with a lot fewer parts, because parts were eXpensive. (Like 3 hours wages for one power transistor.) Parts are now cheap and you can do a better (less speaker abuse) amp with just a few more parts.

These all have dubious bias arrangements. Even the trimmable one will go-out as it heats. "Simples Alplificador de 3W" could be biased better with fewer parts.

Of course if you just like messing-around, and don't mind occasional smoke, go for it.

[GibsonGM]

I tried that last one, with the TIP31 (used a 2N3055 tho), and it didn't do much to impress...quieter than an LM386 with no gain cap....probably should've used the right transistors, ha ha...I noted the DC at speaker, didn't think that was too cool...

[duck_arse]

I'm afraid I was distracted by the speaker polarity issues and the in-box mounting/phaseing possibilities, and didn't think about the effect of the standing dc until a day or two later. oh, well.

[Seljer]

the question that remains is: does it sound any good when you overdrive it?

[tca]

Yes, it sounds good. I will post the circuit that I used. The most important thing that you shoud know is that you *can burn* the speaker. I mean literaly! It will be a "Burning Speaker Amp".

Cheers.

[tca]

Here is what I've tested (minus the resistor/cap at the source):



It sounded good to me at the time.

Note: This version does not work with batteries.

P.S.
I forgot, it needs a booster before it.

[GibsonGM]

I'm afraid I was distracted by the speaker polarity issues and the in-box mounting/phaseing possibilities, and didn't think about the effect of the standing dc until a day or two later. oh, well.

Hey, they're all worth trying!  I'm going to whip up TCA's new one above with an IRF 510, and see what happens...no 610 handy...

[GibsonGM]

TCA, that's 5.6K at the source, right?  And a 1u bypass cap?

[PRR]

> 5.6K at the source, right?

That does not make sense. It is in series (through the MOSFET) with an 8 Ohm speaker. If 5,600 Ohms, then the speaker gets less than 0.0014 of the DC power as audio output, and voltage gain is less than 0.0014.

5.6 Ohms makes much more sense. The 5.6 wastes less than half the total power (poor, but not atrocious). Voltage gain is less than 1.4, not great, but doesn't suck.

I believe the 5.6 is un-critical and not really needed. I approve of 5 to 10 Ohms here just to limit the damage in an accident. But we can use the speaker's DC resistance as the bias sense. Once non-smoking, you could remove the 5.6 and add a bias resistor to set the Drain near half-supply.

The 1uFd cap makes no sense to me. It improves gain above 30,000 Hz.

[tca]

Hi, R4= 5.6 Ohm and C2=1000uF. R4 just limits the current that goes trough the mosfet (as PRR correctly stated).

> I believe the 5.6 is un-critical and not really needed. I approve of 5 to 10 Ohms here just to limit the damage in an accident.
Exactly so. My first try on this was with R4 and C2 removed.

@GibsonGM The IRF510 will also work.

Let me know your impressions on it.

Cheers.

[duck_arse]

@tca - did I see your "non-burning speaker amplifier" diagram somewhere recently? you know the one, with the audio coupling transformer in place of the loudspeaker.

[Seljer]

Although it takes away from the 'simple' aspect of the circuit, inserting a transformer in there would work at removing the DC right?

edit: doh, should read the post right above mine

But still, might something out of the Xicon 42TM* line work?

[GibsonGM]

OK, using an IRF510 I got this little guy going.  Hey, not bad!  Better than 'the one you always see around the net' that uses a 510.   
I got it going, then just grounded the source.  No bypass cap (altho that has potential...).    Needed no heatsink, running at 6V.

Absolutely HAD to place a booster before it.  I used an AMZ Mosfet Boost, and it sounded pretty cool thru a tiny (2.5"?) 8R speaker.  Very "tube screamerish" - some clean riding on a dirty signal.   

Definitely makes you want to get a transformer and see what more you could squeeze out of such a simple amp.

[tca]

OK, using an IRF510 I got this little guy going.  Hey, not bad!  

Told you so!

Better than 'the one you always see around the net' that uses a 510.

That amp needs some higher voltage and NFB to work properly as a guitar amplifier.

Absolutely HAD to place a booster before it.  I used an AMZ Mosfet Boost, and it sounded pretty cool thru a tiny (2.5"?) 8R speaker.  Very "tube screamerish" - some clean riding on a dirty signal.    

Yes it needs some kind of preamp. You should try and use a big/cheap woofer.

Definitely makes you want to get a transformer and see what more you could squeeze out of such a simple amp.

That sounds simpler that it really is. Transformers are difficult to make good with limited resources.

I would suggest a CCS. Hummm, running this thing at 6V... have to think how to make it. But that will take part of the fun and simplicity of this little amp!

Cheers.