Small laptop TRANSISTOR amplifier

[large_ghostman]

Hi
Can anyone point me in the direction of transistor amplifier circuits to drive both 16ohm and 8ohm speakers, the input is from say a laptop (also a MCU with I2S and sound processing), it HAS to be transistor based NO opamps at all and single source supply unless I can build a split source somehow, I need volume mainly but also I need to be able to add filters.
No much info but this is a early stage project with just a rough outline, I cant explain what I am upto yet because I wont really know until I start building the first amplifier/driver. It will also involve light but not yet and yes its a mad as a box of frogs type project

 

[4pyros]

You could start by looking at something like this but its pretty poor.
What supply voltage are you thinking about?

 

[large_ghostman]

any supply from 5V to 25V is what I have access to. I dont see a link?

 

[4pyros]

Opps;
**broken link removed**
AG would be the best guy to help with this.

 

[Nigel Goodwin]

Such a design is entirely dependent on the power supply available, and the impedance of the speaker - an 8 ohm speaker will have twice the output of a 16 ohm one.

Here's a high quality one from an old radio, a Hacker model (the best radios ever made) - it runs off 18V, and is amazingly loud for a portable radio.

 

[large_ghostman]

No link Nigel, it needs to be able to use both 8 and 16 ohm speakers but not at the same time, I have DC power to around 25V but prefer 22V or under.

 

[large_ghostman]

Opps;
**broken link removed**
AG would be the best guy to help with this.

Thanks for the link, I thin AG is having a lay down after your post on the synth stuff lol

 

[4pyros]

Thanks for the link, I thin AG is having a lay down after your post on the synth stuff lol

He never really got into it.

 

[large_ghostman]

He never really got into it.

No offense but he probably hasnt stopped laughing yet !
Shame you live over there as this is something I would love to design and build!! Not there system but something a bit different, real shame about the bench being a pain to use.

 

[ronv]

Well, color me lazy. Have a look at the 386 schematic. I think it works as drawn.

https://www.ti.com/lit/ds/symlink/lm386.pdf

 

[Nigel Goodwin]

No link Nigel, it needs to be able to use both 8 and 16 ohm speakers but not at the same time, I have DC power to around 25V but prefer 22V or under.

Bummer - I wonder what happened to it?.

No problem using both, an 8 ohm amplifier will feed a 16 ohm speaker perfectly well, just half the power.

Try again

https://www.vintage-radio.com/images/figs/transistor/class-b-output-3b.gif

 

[Nigel Goodwin]

Opps;
**broken link removed**
AG would be the best guy to help with this.

That's a really nasty little circuit

You need a minimum of four transistors to make a decent little amp.

 

[large_ghostman]

Well, color me lazy. Have a look at the 386 schematic. I think it works as drawn.

https://www.ti.com/lit/ds/symlink/lm386.pdf

Why does it NEVER occur to me to use the equivalent circuits in data sheets?? They offer at least a starting point if not an entire solution, but I always forget about them! Its given me something to think about anyway! thanks guy's.
Gives me a chance to mess with different transistors and see what happens, mostly I want transistor because I am following a very old book (1963), I need to be able to take measurements at various points and a chip kind of hides some of the bits I want to measure. One day I am going to be ultra modern and build a valve amplifier!
Dad has a huge stash of valves somewhere he used to collect them as a kid!

 

[4pyros]

That's a really nasty little circuit

You need a minimum of four transistors to make a decent little amp.

I would have to agree. I guess to comes down to how complicated he wants to make it. As we know you don't need too many parts to make noise. LOL

LG why do you want to stay with a discret amp anyway?
For show and tell?
Hope AG is OK have not hard from him lately.

 

[4pyros]

LG you posted just before me.

Why does it NEVER occur to me to use the equivalent circuits in data sheets??

Because there are no part numbers.

Dad has a huge stash of valves somewhere he used to collect them as a kid!

They are probably worth some money.
Its funny when I was growing up tubes just started there way out, so I did get to mess with them.
I fact I think I had more tube theory in school then transistor theory.
We designed ans built amps out of both.
As you eluded to its a lot more interesting then looking at the little black boxes that prevail today.

 

[large_ghostman]

I got a very old book for Christmas it's called something like transistor theory and circuit analysis, or something like that. In the book is a paragraph that basically says what ever comes next the transistor will always be the basic block and everything else will built from them. This book is around 1963 so before much evidence of 'other things' and yet its right in alot of way's.
I have a thing for transistor circuit's, although you can sim them every transistor circuit is a little different, transistors vary a little and it sometimes show's, they fascinate me.
As for part numbers this is true, but that means you cant be wrong or you dont have to feel bad about using a sub, if you have OCD like me that is a big help, it also means I can try different transistors with slightly different properties and measure the difference without actualy being able to say its the wrong transistor!
Dad would never sell his valves, he collected them from around age 5 to roughly 15, he must have 500 valves from many places.
Once he is dead I am going to play with them , but until he is dead I am not allowed near them . I have asked if I can try some circuits with them and he replied " Over my dead body" so be it

 

[audioguru]

Sorry I was busy yesterday and today I just woke up.
I simulated the very simple amplifier with a 9V supply. Its output power is low, its input impedance is also low and its distortion is high.
It will be much better with an added transistor and some bootstrapping.

 

[large_ghostman]

Thanks AG, any chance I can have the LT file please? I know its taking me forever to get to grips with LT spice but I will crack it one day .
What is your opinion on the TI LM386 equivalent circuit? I am sure it is better to start with the simpler circuits and then progress up but they dont take long to build, I dont have great ears for sound although my high frequency hearing is good my judgment on sound quality is pretty poor. Having said that I think it's the circuits that interest me more than the actual sound, I intend to build some with amp chips but first I want to build transistor ones and learn from them.
I have a half decent scope and a frequency analyzer, radio interests me as well. There is alot of stuff on the net but like with the 555 timer when I was playing with that, I learn more from building measuring and tweaking.
I will sim the circuits (where I can) then build,measure and compare.

 

[large_ghostman]

I guess I better explain all this a bit better.
The project isnt exactly defined yet, I am building this on a suck and see basis, the fixed point I know are that there are two speakers that I will be connecting to, one is 8Ohm one is 16. For now the out put is the line out or the headphone socket of my laptop sound card, this will change to a DAC on a micro.
At my school we have a kind of school within a school that is for handicapped children, some are pretty bad some are pretty much like me just not as good looking. The school got a grant or some money thrown at them for a sensory room, they built it and to be honest it is £60,000 of junk! Most of the kids are frightened of it, I know this because one day a week I am taught there for what is called 'social skills'they still think they can make me like people and crowded places! They are convinced that I can become comfortable around groups of people, I go because there is a class of mentally handicapped kids next to my class and I get to go sit in there for a couple of hours each week.
One of the kids lives near me and has been to my house for the day, he got really excited (I assume it was excitement) with the 555 timer toy gun I did for the other kid at Christmas time, I still had the basic circuit I started with on a strip board and messed about with it when this other kid (Gary his name is) was here, normally he sits in his chair dribbles a bit and makes a few noises but not much else, I actually like him alot because he just sits and watches me and dosnt want to (cant anyway) talk, but mainly I get the feeling even if he could talk he wouldnt want to, so this is a perfect friend!
I hooked up one of the 3x3x3 cubes I had to the mic and gary messed with the buttons on the strip board, some of the sounds and flashing made him animated and smiley.
Anyway I have some advanced ARM chips with built in codecs and a couple of DACS etc, I have been playing around with the speek codex but instead of making it sound like a voice I have fed it the output from one of those colour reading chips, I call it listening to colour as I cant think what else it is, I have some RGB Leds that are connected to a simple circuit that is similar to a basic sound to light thing, it has a couple of mics and some filters. The idea is when I play music the Leds glow and flash different colours, this is picked up by the colour chip and passes it to the speek codec the output from that will goto the speakers.
I have no idea why (yet) but it seems the light and noise made by it all is pleasing to Gary (I went to his house with a very basic set up but no amplifier) he went nuts!!! seemed to love it, now he is way up the scale of disabled compared to alot of the kids in that class, so I am using him as my bench mark, he smiles its a go, he turns away and drifts it's crap.
So my plan is to build something that will hook into the water bubble tubes they have in the class, they are large clear cylinders filled with water and a few red and blue leds around the top, it bubbles air into the water and you get a pretty column of water well in theory you do, in reality everyone ignores them as they are boring. But they do have unused speakers in them and enough room to fit some RGB leds into the top.
So I am trying to build a 'SOMETHING' for these kids, I know a bit about the water tubes because each week I volunteer to clean them when I am over that side for the day it helps stop me getting bored and would give me the chance to 'fit some extra's', no one will really notice what I am upto until I am finished that I am sure of.

 

[audioguru]

Here is my LT sim file and I hope it has everything. The last time I posted an asc file it was missing all the other associated files.