Most of the power amplifier designs I have been looking at use discrete circuits in the input stage. The can get quite elaborate when designing for hi PSRR. Is their a reason why OP Amps are not more commonly used in these applications?
I can think of a few reasons:
But still, I have seen plenty of excellent power amps with op-amp input stages, and I've made a few that worked pretty well too.
- Voltage rating. Op-amps are generally not commonly available at >+/-25V or so.
- Stability. op-amps already contain 3 or more stages, so adding extra stages after that makes stability less easy to obtain.
- They're too easy! Where's the fun in just using an op-amp?
But still, I have seen plenty of excellent power amps with op-amp input stages, and I've made a few that worked pretty well too.
That's the biggest reason...Mr Evil said:
Good for beginners I suppose, but any real DIY'er ought to get beyond them quickly.
After much consideration about discrete vs IC i have made a choice. I will impliment my BlueTooth transceiver in 90nm CMOS rather then discrete 😉 . ICs have many advantages but most thoses advantages dont apply to audio frequencies.
Production
Yes I can see your point. But their are many Hi quality op amps that are very stable, they reduce part count and if integrated properly in the topology they make an excellent choice for manufacturing. Not to mention the reduction in complexity, the large variation in discrete component specs, and ease of troubleshooting and repair.
I own an old Carvin FET 1000 amp that utilize opamps in the front end of their amplifier. I also wondered how they dealt with the large discrepancy in supply voltages. It seems they incorporate resistive networks to reduce the voltage in the NFL to reduce the voltage swing at the input of the opamp. I have to assume there is a trade off in terms of gain, but all I can say it the amp is rock solid and in all the years I have had it never given me any problems and it performs admirably!
In closing I would have to say I also favor conventional discrete circuits.
Yes I can see your point. But their are many Hi quality op amps that are very stable, they reduce part count and if integrated properly in the topology they make an excellent choice for manufacturing. Not to mention the reduction in complexity, the large variation in discrete component specs, and ease of troubleshooting and repair.
I own an old Carvin FET 1000 amp that utilize opamps in the front end of their amplifier. I also wondered how they dealt with the large discrepancy in supply voltages. It seems they incorporate resistive networks to reduce the voltage in the NFL to reduce the voltage swing at the input of the opamp. I have to assume there is a trade off in terms of gain, but all I can say it the amp is rock solid and in all the years I have had it never given me any problems and it performs admirably!
In closing I would have to say I also favor conventional discrete circuits.
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