[eric the red]

Why do some modders bypass the opamps in cdps and others switch them out? What are the sonic benefits of bypassing  the opamps of a cdp entirely? What is the purpose of an opamp anyway?

[ScottMayo]

Why do some modders bypass the opamps in cdps and others switch them out? What are the sonic benefits of bypassing  the opamps of a cdp entirely? What is the purpose of an opamp anyway?

Opamps (operational amplifiers) are a kind of differential amplifier, which means they react to the differences between two inputs, and produce an output accordingly. They have all sorts of applications, and messing with audio signals is a common one. They are convenient in that from a design perspective, they often do exactly what you need.

But they rarely do it really well. It's hard to make them utterly linear and they tend to have some inherent noise. (Everything does, but sometimes you can get better noise results with discrete components or better opamps.)

Sometimes they are not used to amplify, and are set up to provide no additional gain, but some kind of filtering or feedback instead, or strictly to isolate a signal from the rest of the circuit. Chopping out a "unity gain" opamp to eliminate feedback, buffering or filtering can be a useful trick, if you know exactly what you're doing. It's not something you do on a lark - you need to know exactly what you are giving up, and you'd do it in conjunction with other changes, most of the time.

[ctviggen]

Yeah, you'd have to analyze the circuit to see what the opamps do.  When I fixed my integrated amp, I changed out two opamp chips (each one having two opamps).  I now think I could've bypassed one of the chips, but it depends on the circuit.  Here's an article:

http://ourworld.compuserve.com/homepages/Bill_Bowden/opamp.htm

The "voltage follower" op amp circuit has unity gain and can be be swapped out.   But, note that the op amp can drastically make the circuit different -- there could be high impedance on one side and low impedance on the other with the op amp. Without the op amp, you'll be left with whatever the impedance of an op amp-less circuit would be, which might not be much.  Also, even though there's "unity" gain, the op amp can be used to drive a circuit, such as an interconnect.  Without the op amp, something else has to do that.

[konut]

In pro audio its called gain staging. Its making sure your inputs and outputs are seeing the load intended for their rated operation. Back in the day source components, tape decks, tuners, phono preamps, etc., were usually built to output between .778 to 1V. A preamp was required to boost that to an input that an amp could use, usually between 1 to 2.5V. These days there are a lot of DAC chips that output up to 3V. My opinion is that preamps today are redundant as most source components have very healthy outputs. Their primary usefullness is as swtches between sources. I havnt used an active preamp in many years prefering a remote passive attenuator, the Creek OBH12. Its been my observation that you have to spend mucho dinero to get a preamp that is effevtively 'transparent'. Then again there are those that like a little bit of 'color' in their preamps. YMMV

[Jon L]

Many people will state as a matter-of-fact that op-amps "suck."  I used to buy that b/c after all, larger, more expensive, "discrete" circuits HAVE to be better, right?  

This is true for much of the equipment out there using op-amps, but most of these are designed poorly and/or use very cheap, old op-amps.  

Today's state-of-the-art op-amps, used in proper circuit designs, are very capable of kicking some discrete circuits' behind for much, much less money IMHO  

[eric the red]

Thanks for the informative replies (not that I expected anything less in here)

[Steve]

Like Jon L says, some ICs are capable of good sound. This wasn't so when first introduced years ago. Often, the open loop gain was tremendous but the Open loop FR was dismal, often only a few hundred Hz.