Hello again, I like OP amp based amplifiers , and I just found this schematic, I tried it in LT Spice and it seems fine. Wanted to obtain more power than the OP amp rails can do, and this suits my needs. Please take a look.
I have NE5532 and TIP142 /TIP147 , I can try it.
I dont know why , and what does the " 4n7 cap " does, and in LT spice it affects the " sinewave , distortion " if value is changed. Also " tweaking " the 3.3k resistors from BC547/BC556 bases to ground changes the voltage across the OP-AMP , they act like a voltage regulator ? .
My last OP amp based amplifier was Mr. Rod elliot's Project 113 ( headphone amp ) changed transistors and obtained more power ( limited to OP amp rails ) I think that one is current amplifier . and this one is Current and Voltage amplifier.
Also i have 2n5551 it's complementary , if they are better than the BC's .
Please take a look. Thanks.
Cheers, Bruno.
I have NE5532 and TIP142 /TIP147 , I can try it.
I dont know why , and what does the " 4n7 cap " does, and in LT spice it affects the " sinewave , distortion " if value is changed. Also " tweaking " the 3.3k resistors from BC547/BC556 bases to ground changes the voltage across the OP-AMP , they act like a voltage regulator ? .
My last OP amp based amplifier was Mr. Rod elliot's Project 113 ( headphone amp ) changed transistors and obtained more power ( limited to OP amp rails ) I think that one is current amplifier . and this one is Current and Voltage amplifier.
Also i have 2n5551 it's complementary , if they are better than the BC's .
Please take a look. Thanks.
Cheers, Bruno.
Attachments
Circuits like this run on a knife edge. The voltage developed across the 680 ohms determines if the output transistors turn on or not, and that voltage depends on the current drawn by the IC.
It is not a good circuit for an audio amplifier imo. You would need to tweak the resistor values to suit your transistors and opamp and even then, it would mean running in essentially class B.
It is not a good circuit for an audio amplifier imo. You would need to tweak the resistor values to suit your transistors and opamp and even then, it would mean running in essentially class B.
That circuit is screwy. Imagine using the power draw of the op amp to turn on darlingtons & feed the speaker!
Look at this thread, towards the end: http://www.diyaudio.com/forums/solid-state/304351-having-slight-issue-my-class-ab-output-stage.html
Rather classic op amp driving a stack of resistors, the resistors drive the upper output transistor. Vbe multiplier in the middle to set the idle current, which I don't think he has made adjustable yet. I would use two diodes plus a resistor instead.
He has a 200 ma op amp, so he can get some amps out with just mj15015/16 output transistors and no drivers. With a 2 k impedence out op amp, use a conventional driver ahead of the output transistors, like the marshall 8008. Which is successful on the commercial market. And uses a TL072.
As far as the mismatched 2n3055/D45H11, don't bother. You have matched output transistors available. Use those. He doesn't. A little 2nd or 3rd harmonic distortion will result from his mismatched choice.
Look at this thread, towards the end: http://www.diyaudio.com/forums/solid-state/304351-having-slight-issue-my-class-ab-output-stage.html
Rather classic op amp driving a stack of resistors, the resistors drive the upper output transistor. Vbe multiplier in the middle to set the idle current, which I don't think he has made adjustable yet. I would use two diodes plus a resistor instead.
He has a 200 ma op amp, so he can get some amps out with just mj15015/16 output transistors and no drivers. With a 2 k impedence out op amp, use a conventional driver ahead of the output transistors, like the marshall 8008. Which is successful on the commercial market. And uses a TL072.
As far as the mismatched 2n3055/D45H11, don't bother. You have matched output transistors available. Use those. He doesn't. A little 2nd or 3rd harmonic distortion will result from his mismatched choice.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.