Hello,

I just came accross a weird schematic that uses an opamp as driver for power transistor (founs in electuur):

View attachment 157882

They claim an output power of about 6 Watts @ 0.01 %

Bertus

See that's pretty cool. Nooot getting my alertssss. Also do you think it possible to use an lm386 instead? If I have to change it around some that'll be fine with me.

 

See that's pretty cool. Nooot getting my alertssss. Also do you think it possible to use an lm386 instead? If I have to change it around some that'll be fine with me.

Also even to me that is a weird one.

 

I use a Canadian internet provider who uses an United States email company. It takes about 40 minutes for an email to reach me.

A different problem is the clocks on most of these forums is on a different time zone from mine and I don't know the proper setting.
I posted this at 8:52PM Eastern daylight time.
Checking the clock here, of course it says, "A moment ago", no time is shown.

 

I posted this at 8:52PM Eastern daylight time.

Showed up at 8:52 here in the EDT.
SG

 

Yes, my clock setting on this website is correct.

 

I use a Canadian internet provider who uses an United States email company. It takes about 40 minutes for an email to reach me.

A different problem is the clocks on most of these forums is on a different time zone from mine and I don't know the proper setting.
I posted this at 8:52PM Eastern daylight time.
Checking the clock here, of course it says, "A moment ago", no time is shown.

Yea I can vouch for that. It tells me 7:52. I'm central so you're an hour behind me. It's mostly them not showing up for a long time when they were posted before me. Even responses to my post shortly before another. I figure I'm going to have to start from page 1 and look through it all. I know I missed alot!

 

I have found a LA4550 ic from a built in home audio system. I believe this will just about get me what I'm wanting for now. I'll definitely be playing with transistors of course but I'm taking an easier way out. Tried that "fixed" AB schematic and i had to tweek it all over for it to work. Also I don't believe the "Lil tiger will work with TIPs. They just don't have the gain. I believe I'll be investing in a few amp is meant for this.

 

I don't believe the "Lil tiger will work with TIPs. They just don't have the gain

Not sure what you mean by that. The circuit works using the TIPs, I personally breadboarded and verified it myself. If you mean it requires a higher input signal to get full output then that's just a matter of increasing the gain on the input stage.
SG

 

I have found a LA4550 ic from a built in home audio system. I believe this will just about get me what I'm wanting for now.

It has low output power and uses a low supply voltage because it was used in a little clock radio.

I don't believe the "Lil tiger will work with TIPs. They just don't have the gain.

My post #195:
The circuit provides voltage gain.
The minimum DC current gain of a TIP41 and TIP42 at a DC current of 3A is 15 and its maximum is 75.
3A peak is 18W RMS into 4 ohms. If the transistors have the minimum gain of 15 then the driver transistors must produce peaks of 3A/15= 200mA. Since the absolute max current of a 2N3904 and 2N3906 is 200mA then I would use 2N4401 and 2N4403 that have a max allowed current of 600mA. At 200mA their minimum current gain is 88 so the first transistor must produce 200mA/88= 2.3mA which it can do easily.
I would use compound transistors in the Lil Tiger amplifier, change its 470 ohm resistors to 2.2k ohms and add bootstrapping. Then bridge two of the amplifiers driving a 4 ohm load. a 12V battery will be fine.

 

Not sure what you mean by that. The circuit works using the TIPs, I personally breadboarded and verified it myself. If you mean it requires a higher input signal to get full output then that's just a matter of increasing the gain on the input stage.
SG

I apologize if I was wrong but lately my faith in circuit diagrams has diminished somewhat. Will the "lil tiger" work with a direct TIP substitution or do I need to finagle with the cap and resistor values? I don't mind if it'll work but I finally got the altered ab class diagram from what I posted to work but it was just damn awful. I had to change caps, resistor values and extra diodes, dramatically just to hear words. I did eventually get it to sound "pleasant" from a lot of experimentation but only at low volume(guessing around 1watt output). Also the npn output transistor got very hot. The other pnp/npn were lukewarm. I think a basic AB class transistor amp is likely out of reach with my TIPs. Any suggestions I would appreciate but I think going with ics meant for it is probably best. Not giving up on the war, just this battle.

 

Which post in this 230 posts thread shows the schematic of the "altered ab class" amplifier that you had trouble with?

 

It has low output power and uses a low supply voltage because it was used in a little clock radio.


My post #195:
The circuit provides voltage gain.
The minimum DC current gain of a TIP41 and TIP42 at a DC current of 3A is 15 and its maximum is 75.
3A peak is 18W RMS into 4 ohms. If the transistors have the minimum gain of 15 then the driver transistors must produce peaks of 3A/15= 200mA. Since the absolute max current of a 2N3904 and 2N3906 is 200mA then I would use 2N4401 and 2N4403 that have a max allowed current of 600mA. At 200mA their minimum current gain is 88 so the first transistor must produce 200mA/88= 2.3mA which it can do easily.
I would use compound transistors in the Lil Tiger amplifier, change its 470 ohm resistors to 2.2k ohms and add bootstrapping. Then bridge two of the amplifiers driving a 4 ohm load. a 12V battery will be fine.

There's what I needed. Some numbers. However suppose I didn't have the 2N's? I could buy everything I needed but this thread is about making something from essentially nothing. Building a respectably decent, yet mild power, audio amp from components salvaged from old circuit boards. It seems nearly all transistor circuit's call for newer bjts, that I don't mind buying but I don't see why I should need to. I mean to say I want to use things most of you never would or heard of as opposed to what all of you are use to. C1815 for example. Haven't seen much on it yet it works. But not much mention. Is it so old to forget or to weak to matter. I do salvage my parts from fairly old circuits. A working circuit I'd love so I can tinker with it myself with what I have. Perhaps Lil tiger can be big if I toy with it enough hahaha

 

You have some obsolete 2SC1815 Oriental transistors. Why not look at its datasheet to see that its maximum current is only 150mA, it works poorly above 50mA and it is not allowed to heat as much as the transistors I mentioned so it is not powerful enough to be a driver in this amplifier.
Besides, you need a PNP transistor that matches it if needed on which schematic you use.

Why not order online what you need from Digikey or Newark? If you place an order before 8:00PM then it will be delivered to you the next morning if you are on the same continent.

We design circuits that work, we do not tinker or use "trial and error" with parts. If a transistor conducts 200mA then we do not order and use a transistor that works poorly or is damaged at 200mA.
Somebody could design a nightmare of a circuit using low current gain TIP41 instead of a high current gain little driver transistor and use a 2SC1815 in front of it making a Darlington or compound transistor for a higher current gain. Of course its resistors will need to be calculated.

 

Which post in this 230 posts thread shows the schematic of the "altered ab class" amplifier that you had trouble with?

The eee3 is the altered version. Large photo with the diagram to one side and the rest blank. The first is the original. Granted the altered did work at first but the distortion was unholy. I did tune it with different resistors and adding diodes. Changed around the caps to. Got it to around 1-1 5watt output(guessing ) with decent sound. Did give me an understanding of Class AB amp, however, so I call that a win. I apologize if I didn't give the post number. I think around page 4 to 6. I have a lot to sift through.

 

You have some obsolete 2SC1815 Oriental transistors. Why not look at its datasheet to see that its maximum current is only 150mA, it works poorly above 50mA and it is not allowed to heat as much as the transistors I mentioned so it is not powerful enough to be a driver in this amplifier.
Besides, you need a PNP transistor that matches it if needed on which schematic you use.

Why not order online what you need from Digikey or Newark? If you place an order before 8:00PM then it will be delivered to you the next morning if you are on the same continent.

We design circuits that work, we do not tinker or use "trial and error" with parts. If a transistor conducts 200mA then we do not order and use a transistor that works poorly or is damaged at 200mA.
Somebody could design a nightmare of a circuit using low current gain TIP41 instead of a high current gain little driver transistor and use a 2SC1815 in front of it making a Darlington or compound transistor for a higher current gain. Of course its resistors will need to be calculated.

See that's what I needed to know. If my transistors are sh1t then tell me. I don't want to waste my time chasing the purple dragon! If I need to change my formula then let me know so I can catch it! I understand yall want me to figure some of this out myself but honestly I learn by seeing things done right and copying it in a way that suites me and my knowledge. I seen how to build a cabinet set once. I copied it on another job and through that I expanded my imagination to suite clients. I learn through perfection to perfect it. If that makes any sense??

 

I simulated the ab amp that you "altered" (actually you copied it). Its resistor values are wrong for the little transistors with the high current gain in it, and there is no way its resistor values will work with your TIP low current gain transistors.
The value of R2 in my sim is too low causing the top of the waveform to be severely clipped and the value of R3 is too high causing a different kind of distortion.

My attachment has no contrast because my sim program screwed up 3 times when I tried fixing the resistor values.

 

The eee3 is the altered version

That is the modified circuit that I posted in #100. The resistor values shown are correct for the 2N3904 and 2N3906. There's is no way you will get anything near a watt using those small signal transistors. Output power was about 30mw into a 6 ohm speaker.
SG

 

I got the sim program working and fixed the resistor values but the waveform shows that the top is squashed because bootstrapping is missing.
I added bootstrapping and changed resistor values for correct biasing.
There is crossover distortion because the peak current is 300mA but these little transistors work poorly above about 80mA.​

 

Audioguru I breadboarded your modified circuit with the bootstrap. Granted it does put out a little more power but the standby current is around 80ma. Just for the record I did a couple of revisions on my mod. Decreasing R2 to a 20K gave a symmetrical output. Replacing D2 with a 390 ohm resistor drop the standby current from 20 ma to 4ma with no crossover distortion. Output power around 80mw into a 10 ohm load
SG

 

It is crazy to use low power low current transistors in a power amplifier.