op amp importance in a pre-amp

[cbdb]

I would bet most consumer active sub inputs go right ito an opamp ( a buffer or the low pass filter ) . Anyone know for a fact?

 

[Andersonix]

In my B&K AVP1000 preamp, the op amps ARE the preamp. And I was very impressed with the two LM4562 I swapped in for the existing two OP249 (and also with the OPA2227 I put in for the LF353 used as the headphone amp). But this may say more about how cruddy the originals were, although I have heard almost nothing but nice things about the LM4562. And I like that it's cheap ~$4, so I can afford to experiment.

 

[nigelwright7557]

It might be worth building a prototype and go for a common package pinout then try different op amps in the socket.

 

[5th element]

As a tool, an op-amp is a very useful device in many signal conditioning applications, but as a pre-amplifier feeding your $100 000 power amp, I think I would give it a miss.

I simply cannot understand this way of thinking. Before the sound even reaches your hifi it has most likely been passed through a long chain of opamps. Using one in a preamp isn't going to remove you from audio nirvana, otherwise achieving it would otherwise be impossible due to the initial recording stage.

Using a preamp with a high input impedance is a good idea as it presents an easy load for whatever your source may be. Then design the output of it to be robust enough to easily drive whatever cables or inputs your power amplifiers may have.

I'd use two opamps per channel. One to buffer the incoming signal with a high input impedance (500k or so), then to drive a pot of a reasonably low value, ~10k. Then another opamp after the pot to drive the output.

PCB design and the PSU are also very important.