Disadvantages of OP amps in output stage of CD?

First, an op amp (short for "operational amplifier") is an analog device, and cannot produce digital by-products.

Second, I would not by any means NECESSARILY attribute the objectionable sonic characteristics you are describing to the op amp stage of the player. There is a whole lot of other stuff in the player that can also cause or contribute to that, including the player's DAC (digital to analog converter) circuitry. And the sonics provided by a specific electrical design approach, besides depending on the circuit design and on the specific parts that are used, can even differ considerably depending on the mechanical layout and design.

More often than not, though, it can be expected that the choice of an op amp-based analog stage, as opposed to a stage based on discrete transistors (not "discreet," which means something else) will have been made with cost as a key consideration. High-end designs tend not to use op amps, at least in the signal path.

Purchasing a standalone DAC means that you would no longer be using both the DAC function and the output stage of your player. Can that result in a "fuller and smoother midrange"? Certainly. Will it? Obviously, it depends on the particular DAC, as well as on what part of the existing player is the predominant contributor to the problem.

Changing to a different CD player could also, of course, accomplish the same thing, depending on the particular model.

Also, a two-box approach can have its own set of tradeoffs. If not well implemented, noise pickup and impedance mismatches involving the interconnect cable and the interface circuits in the two components, as well as groundloop effects between the two components, can result in random fluctuations in the timing of the conversion of each digital sample to an analog voltage in the DAC, which is referred to as jitter, and which can have very significant sonic consequences.

Hopefully others having particular knowledge of products in that price range will chime in with specific suggestions, covering both one-box and two-box approaches.

Regards,
-- Al

The guys at Burson Audio consider op amps the devils work. I wouldn't go that far but here is there take on it; http://www.bursonaudio.com/DIY_HD_Opamp.htm.

Hope this doesn't make things messier.

All the best,
Nonoise

Al, Thanks for the thorough explanation of the "op-amp" functionality. Yes, I did spell "discrete" incorrectly in this particular context.....I possibly did not mentally transition quick enough from an on-line dating service to Audiogon.

Nevertheless, I think you covered all the options. However, a $1000-1500 DAC will not or can not be done. Equally, even if I can get a refund for the modded 550C, and sell the Rega Apollo, a $3000-3500 CD player will not happen either which may be the (starting) range to as you noted.... "accomplish the same thing" as using a two box appproach.

The Ayre CX-7mp2 comes to mind, and/or the current top of the line Sim Audio player. The Rega Isis, even used, is not worth the money. However, I remain undaunted in finding a more than acceptable alternative and the right sound quality.

To Nonoise, Thanks for the link....maybe "out of chaos comes order" Not sure who said this: either Pee Wee Herman, or Frederich Nietzche??

To Elizabeth, I am sure how your comments are either helpful or productive. Almarg, Nonoise and others who have given their time and knowledge on this thread and others I have intiated are not fools participating in the sport of one upsmanship. Op-amp is not a buzzword, but an electronic device which both designers and consumers like and dislike. Neverhteless, it is better to know what it does and its potential downside in the playback chain. This hobby is driven by the science of electronics not magic.

Maybe, Elizabeth , you could tell us about your audio system, and what aspects could be improved. Regretably, I fell victim to BS and hype surrounding the modded player I purchased. In our excitement to find the best sound with in reason, audiophiles can and do make mistakes.

Happily, the player in question is going back to its owner, whether I send it or deliver it in person. I don't want it because it does not do what the hype claims it can do. I will reinstall the Rega Apollo, and continued to look for a better player, or just find a Rega Saturn which supposedly bests its little brother across the board. That was my original plan which I should have stuck by, and avoid losing the shipping costs that I have. Will keep you all posted. Thanks. Jimbo

I was informed that "op amps" in the output stage of a CD player can produce thin, less full, and bright sound quality in the upper midrange,(which I have heard on my CD player) In addition, I was advised that these digital by-products can be reduced by taking the digital output signal from the player and feeding it into a good DAC with a discreet class "A" output stage

The CD player I have is a modded Cambridge 550C. I don't understand "HOW" this addition will or can improve the sound quality......

just to add to Almarg's very informative post: as you already know, opamps are semiconductor devices which are somewhere in the 2mm X 2mm size region packaged in a variety of different plastic containers for thru-hole or SMD (surface mount) mounting onto printed circuit boards. By the very nature of miniaturization several compromises have to be made since small semicondutor devices cannot carry extra large currents. The biggest thing in circuit design in the bias of the active devices - designers spend 70+% of the time biasing the devices to the correct location for the particular application. In generic opamp or even a application specific opamp, the biasing is done by the manuf as best as they see it for wide-spread use in the market. So, obviously, this bias is a compromise that allows wide-spread use. If any particular audio manuf wants to optimize the performance using opamps there are very limited handles (& sometimes no handles) that allow this. So, the audio manuf hands are tied. This can be a good thing (ease of design & manuf) & a bad thing (compromised overall performance). As Almarg already wrote, it all depends on the final price of the product. Better/higher-end performance products choose not to limit themselves to this compromise & choose to use a discrete version of the opamp. Lower price point products prefer the ease of design & manuf.
Both sides (use of opamps & discrete opamps) have their pros & cons. Some of the cons of monolithic opamps have already been stated by Sunnyjim. Discrete opamps are not easy to make - when you make a discrete opamp you have to worry about the PCB coming into the picture as a parasitic (which is largely out of the pix in monolithic opamps). Plus, you have to worry about very close matching of the discrete parts, which, again, is a much smaller issue in monolithic opamps: If the two sides of a differential opamp are not matched, you have systematic offset & possible output distortion, increases harmonics, lack of suppresion of 2nd-order harmonics, etc.

So, discete opamps is not a panacea. Thus, use with care. Blindly following one thought process often leads to more trouble/disappointment than less! ;-)

With monolithic opamps, one can switch out opamps & get better preformance. This was the case for me in particular with one of my FM tuners. One modifier thought that the venerable OP627 was best but another modifier thought than an Analog Devices opamp was better & swapped out the OP627 for that ADxxxx opamp. Since the opamps were mounted on chip carriers it was easy to pop out one & plug in another.
You might be able to do with your Cambridge 550C?
hope that this helps....

BW, Unfortunately, you are speaking to a somewhat non-technical person. Though, I greatly appreciate your advice and explantion. This player as noted was modded by Mapleshade Audio, the music and tweek internet company. In all fairness to its sound it does have lighting fast transient response and a low noise floor. BTW, I did make a speaker cable change (downward) before acquiring the Cambridge 550C. When I had the Rega Apollo in system, the differences with the less expensive cable (Audio Art SC-5 standard) were apparent but could be lived with. When I plugged in the 550C,. those differences became much more pronounced. The sound was bleached on the top end and through most of the midrange; this is the exact opposite of what I anticpated. and lacked any musicality.

As it stands now, I have ran 550C to about 100 hours burn-in, and 25 hrs actually play time. It sounds the same The third party seller could offer "only" his regrets that the player did not "work well" in my system, which is not a general audio premise I subscribed to I am not going to put anymore money into trying to get 550C to sound better by adding an even inexpensive DAC like the Peachtree I-DAC or eqivalent If anyone has any additional suggestions, please let me know. Otherwise, I intend to sell the unit cheaply, take a finanicial bath, and move on. Jim

As it stands now, I have ran 550C to about 100 hours burn-in, and 25 hrs actually play time.

you know, this just might not be enough time to break-in the mods. all Accuphase components need 500 hrs minimum. I've heard this for many other components. Personally I had to break-in my Virtual Dynamics cables for 300+ hrs per the factory guideline.
So, it's entirely possible that you are making a premature decision/judgement that the Cambridge does not sound good.....

Disadvantage- loss of transparency (as compared to a well executed discrete output) and coloration of sound either north or south of neutral.. IME

Advantage- ability to color the sound by rolling op-amp to suit your taste.

I feel a bit obliged to comment here as it appears SOME of your intial comments may have come from my responses to your previous posts (although seriously misquoted).

The CA audio products (like many others) use IC opamps (monolythic integrated circuits) in their analog output stages. From my direct listening experience, some of the criticism leveled at the CA CD players (like the 840C I own) of "bright" sounding sonic signatures may be directly related to these opamps. If you feed the digital output (upsampled or native) to an outboard D/A with a well designed class A discrete component analog output stage, many of these sonic abberations are abated. In the 840, CA uses the OPA 2134 series opamp which is considered by many to be a mid level amplifier. My comments are limited to the CA 840 with which I have direct experience. By the way, I have noted similar characteristics in an Parasound P3 preamp which uses similar OPA2134 opamps. There is considerable info on the sound of opamps in the headphone community if you want to see how many audiofiles view and rank various opamps. The 2134s are considered medeocre at best.

The biasing in opamps is typically never Class A due to power consumption considerations (more important to the vast majority of opamp users not in high end audio). The need for these amps to drive low impedance loads almost always requires them to employ class AB output stages. IMHO these will never sound as good as a WELL DESIGNED pure class A discrete stage. I am not alone in this opinion. Just ask John Curl what he thinks of IC opamps as high end audio devices.

Regarding the swapping of opamps, this may or not be easy or possible. Firstly, the opamps in the CA products are surface mounted. R/R these amps requires special desoldering equipment to keep from destroying the pc board. They are not mounted in the familiar 8 pin DIP sockets or packages. Secondly, replacing a lower bandwidth IC like the 2132/4 with a very high speed version like the 627 may create severe oscillation problems due to the very high bandwidth of the 627. The bypassing and power supply layout suitable for a 2132 may not prevent oscillation if a 627 is used in its place. So be careful of mods that might look good on paper but be a dissaster in practice.

And, just because a circuit is discrete does not make it necessarily superior to an opamp. I am refering to the Burson "discrete" opamps which have been measured and found to have significant distortion. Much worse than even the 2134 and particularly inferior to the 627/637 series.