Pointers on upgrading CDP output stage.

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As usual I have been sifting through threads for a few days and seem no closer to an answer than when I started. I have a Proton AC 420 CD player that has just joined the family, though very basic (and old) its performance is suprisingly good. The down side is that the trebble is a little unrefined and bass a little lean. Popping the cover has revealed 5 op amps clustered around an oddball Yamaha SLC-A iG-15630 DAC. The OP amps are all JRC's 1x 2068D, 2X 4558D, and 2x 4560D. I have found threads that recomend replacing the 4560D for instance with a Philips NE5532 but have found other threads that consider the 5532 rubbish and instead recomend implementing the OPA 2604. Also as time goes by "great" op amps become "ok", then finally "crap" so I am also looking for some more current recomendations.

Thanks in advance!
 
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Hi, There seem to be a lot of threads about output stages and Opamps at the moment. I am not familiar at all with your player but as for the Op-Amps you might improve the performance, all depends on the rest of the player really. That 2068D that does sound an oldie ? Is it a single or dual inline package ? It's probably used in the servo parts of the circuit rather than audio stages. The 4558 is a dual 741 and the 4560 is, if memory serves correctly similar but with a bit more "umpty" It would drive low impedance loads better. Does it have a headphone socket ? If you want a play, remove the 4558 and 4560 and fit sockets. Try replacing both with TLO72 as these are cheap and suprisingly capable for high quality audio. You wont do any harm, I just wonder about the 4560, it,s extra output capability is there for a reason. Can you tell what it feeds, is it headphones or is it in the servo section. If servo leave it be. If you like what you hear the OPA2604 remains a favorite.
Regards Karl
 
Hi Karl, yep this baby has an output for headphones, I haven't traced the board to figure which set of OPamps drives that output. There certainly are a lot of op amps in there especialy sice the data sheets show at least 4 of them as dual op amps, they are all dual inline packages. I wish I could dig up some info on the DAC, I found like 2 sites that mention it but they are not in english and I couldn't translate. The author of the thread posted a pic of his player a Memorex cd-4000 and it has the identical internals as the Proton AC 420! Well, web hooplah aside my ears enjoy this player very much, stereo separation, imaging and detail are improved over my AMC cd8b, with the nod going to the AMC for smoother highs and deeper bass.
 
An honest correction, not just applying the defribulator to my dying thread. I have a Yamaha ym3020 DAC in the Proton, got confused by my own handwriting:drunk:. I just wish I could find a proper datasheet for the DAC so I could determine analog out puts for left and right channels, not a very popular DAC unfortunately.
 
Hi S.Spielbergo,
i make some research on the net i found only this datasheet for your DAC. A TL072 is a good choice, i replaced a 4558 for TL072 and there was a big change, the high are soft and the bass has good attack. good luck! Maxpou
 

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Try the LM4562, it will happily replace the 4558 and probably the 4560 as well. And it is much more sonically capable imho than the 2604 one of my previous favorites. Look for other possible improvements to the audio path, power supplies, etc.

The LM4562 is available from digikey in both dip and soic packages, currently it is about as close to sota as an audio op-amp gets.
 
I'm going to put in an order with Digikey today, LM4562 and TL072 have made the list along with the venerable NE5532a and two others. Thanks for the suggestions. I'm still trying to map out the board a little so I can see what we have between the DAC output and rca jacks. Anybody know what values are common for the bypass caps just prior to the rca connections, i'd like to give them the heave-ho but all I can find near the rca's are a pair of 4.7uf electrolytics and a few tiny tantulums that I can't read very well.
 
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Good to hear you're having a go. I have not tried the LM4562 myself so can't comment on that, the OPA2604 has a distortion spectrum that is of the "right" type for audio, that is the even harmonics predominate over odd and this can make for a more "musical" sound. The amounts produced are vanishingly small anyway, but the ear does seem to pick up on this. Just as an aside, I used the NE5532 and 5534 some years ago in a rather specialised piece of audio equipment and preamp combined, and the results were dissappointing, very "unmusical" and it was the NE5532/4s . As an engineer I hate it when you can't measure or pin down an effect like this. The prototype used TL072s and sounded wonderful, I broke the golden rule of changing a part without a full evaluation first. Anyway have fun and please let us know how you get on. Oh and change just the Opamps first and do a full listening test before you change any caps etc. Listen over a few days as "experimenter expectation" comes into play here. It's easy to decide that some part or mod WILL be better. Trust your ears and listen to a variety of music.
Karl
 
I got the recomendation for the LME49860 just before ordering so it is also on its way (and its just as well, I was below the minimum). I will be soldering in the sockets I grabbed from Radio Shack over the next day or so.I figure whatever IC is my #2 pick will go into the phono stage of my Proton AM 656 integrated amp. Your right though Mooly, its like working on a car you gotta pace yourself with the mods:D
 
Hi S.Spielbergo,

There are still Rotels on ebay! LOL

Unfortunately, op amp rolling, even though many suggest it, has to be done with some intelligence.

Sometimes you will be lucky and nothing else in your output stage needs to be changed for the best results from that op amp. Pinout is the same, rail voltage is the same, etc. But many times this may not be the case (the etc. is the part that needs to be watched)!

Overall, you need to look at the entire output stage when making modifications. Decoupling cap values have a sonic effect for best results with an op amp as well as the other components around the op amp! You might also need to change some other components values too, like the Output Caps and the resistors aligned with them. Compare data sheets and ask questions when you see differences. This is the only way to give op amp rolling a fair shake. When the stage is optimized for one op amp and not the other (even if ever so slightly), how can you really make a judgement or decision?

This may be why so many have different experiences with the same op amps when doing mods!

Post the output stage schematic or maybe the whole schematic and the Data Sheets of all the op amps you wish to try and ask if you need to make any other changes for a particular op amp to give it a fair chance! This is harder but a better "Methodology" than op amp "Rolling" blind!

Good luck!


Regards//Keith
 
I was looking at some of the Rotels offered on Ebay this past week, a few even had the TDA1541 DAC but I was a little gun shy and failed to pull the trigger when the time was right. I'm not sure why but I just don't get that excited about their CD players, they have a good pedigree and many people on these forums swear by them. I will likely end up with a more conventional (viable) CDP like the Rotel in the future but I wanted to cut my teeth on something cheap and simple like the AC 420. My perspective on IC "rolling" has de-evolved if anything when I first started reading about it I thought "what? How can you just swap out these chips without changing all the support circuitry too?!". Well, rather than beat my head against a wall trying to figure it out, for once I just joined the masses. I unfortunately have no shematic for the Proton, and there do not appear to be any available on line so I'm on my own here, I will post a pic or two of the output stage and see if anybody can provide some guidance. I got into the habit of backing obscure (loathed) equipment when I was a gearhead like my hotrod Renault Le car, Rover SD-1, Merkur(Sierra) XR4Ti'sx3 and so on , its a disease,lol!!:whacko:
 
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Look here, sound.westhost.com/dwopa.htm
The Op-Amp is a building block, and for audio, which is really all very low frequency stuff most opamps will work and behave as per the theory. It is the surrounding parts that determine how it will behave. This does not apply at higher frequencies, where specialised parts are used or more critical applications where other parameters have to be taken into account. So if we want an inverting amp with a gain of 10 it really is just two resistors that determine this, our choice of opamp is "irrelevant" (note, we not talking here about which may sound the best), so our 40 year old 741 or a new LM4562 will both perform the same. Very much simplified but hope you get the idea.
Karl
 
Karl,

Nice link, that went right to favorites!

S.S,
Yes there were lots of RCD-855s and RCD-955AXs in the past few weeks going for < $100 (with the TDA1541). Also there were 965s as well. In fact there is a RCD-965BX LE right now.

Too bad about that disease! Can't you take something for it?

I caught it too but I took medication. It was my first car.... It was a 72 Fiat 850 Spyder. After banging my head against the wall trying to get it to run well, I find that the uni-body sheetmetal where the parts of the front end bolted to the car was all rotted out! That was my medication and never went down that road again!

I may do it only once more if I ever get my hands on a Sunbeam Tiger.

OK so I can see why maybe you were allured by the Merkur, but the Renault? I guess those Remy Julienne commercials really had an impact on you! LOL

It's funny, as you know with the cars, it's all about the details and your first instinct about the "Rolling" was correct.

Anyway, when you finish your CDP and I finish mine, we will have to meet (I have the RCD-965BX) and compare them. LI is not too far from CT. You just might find out why so many people suggest the Rotels for low cost modding projects with a big bang! Because they already sound great without even touching them except to press the play button!

Post some close and detailed puictures, they can only help!

Regards//Keith
 
Yep, great link!! I got a few paragraphs into it when my woman decided on cleaning some of the Saab, Volvo Renault guts out of the garage. Too bad about the Fiat Keith, the 850 is a bad a$$ car, I just saw one in the junk yard in RI this past November, neat little 3 banger, body wasn't bad though. My Alfa's always had issues with rot, Italian thing. Good luck on finding a Sunbeam Tiger, they are cool as hell but have become scarce and EXPENSIVE, I've been fantasizing about A Bitter SC or Fiat Strada (!!!) lately myself.

I'm sure your Rotel would slaughter the AC-420, now a AC-620 is a different story but I'm still looking for one. I'll post some pics of the Proton today. Any pics of the Rotel?
 
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Mooly said:
Look here, sound.westhost.com/dwopa.htm
The Op-Amp is a building block, and for audio, which is really all very low frequency stuff most opamps will work and behave as per the theory. It is the surrounding parts that determine how it will behave. This does not apply at higher frequencies, where specialised parts are used or more critical applications where other parameters have to be taken into account. So if we want an inverting amp with a gain of 10 it really is just two resistors that determine this, our choice of opamp is "irrelevant" (note, we not talking here about which may sound the best), so our 40 year old 741 or a new LM4562 will both perform the same. Very much simplified but hope you get the idea.
Karl


Hi Karl, I used to believe that as well, and in theory it is exactly as you state, but using the highest quality passive components and proper layout, bypassing, and regulated supplies over some 25yrs or so when actually listening I have not found this to be the case. Starting with the not so subtle differences between 741 and 5534 back when I was very young, to the not so subtle differences between good current op-amps like the 2604 and 4562..... You are right though that often the passive components also play a large role in overall sound quality as well.
 
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Hi Kevin, I have just re-read my reply and I could have worded it a bit better, sorry if I misled anyone. I did'nt mean to say it was the passive components that wholly influence sound quality or performance. What I was trying to get across was (now let me try and get this right) , was that the circuit behavior is unaffected by our choice of Op-Amp (in applications like this). If a C.D. output stage calls for a 2nd order low pass filter of a given type and with a voltage gain of 3, we design according to the theory, we assume a perfect model for the Op-Amp. In practice even a 741 will perform correctly. It is the passive components (their value) that solely determine the characteristics of the circuit, gain filterpassband etc. All these parameters are unchanged by swapping the Op-Amp. I think this is what S Spielbergo was having a problem with, wondering why if we change a complex part made up of dozens of transistors, why don't we have to change surrounding parts as well. When we move on to sound quality we can measure some differences, our 741 will have for e.g. higher distortion, maybe a little crossover distortion etc. This is where it gets interesting for there are differences we hear that are not currently measurable. As for passive components, again there are audible differences. If we make our output filter above using brand x resistors and brand y capacitors, and then make another using different brands, provided the component values are identical both will measure the same. They may sound different but we can't measure that yet. All good fun :) Now why won't that 741 aeriel amp work :smash: Only joking. S Spielbergo, have'nt you fitted those bits yet :mischiev: We want to know what you think. Above all ENJOY.
Karl
 
OK the op amps arived the other night and as luck would have it I have had some loooong work days (nights) ever since. Prior to swapping out the op amps I did remove the mute transistors, bypass and output caps just downstream of the RCA jacks. Replacing the old polarized electrolytics had the greatest effect on the sound quality, I installed some low/mid grade Dayton poly caps instead. I have tried all the op amps a couple of times so far, (LME4986, OPA2134, LM4562, OP275, NE5532 and TL072) but I'm having some trouble finding any huge differences between these IC's. I wasn't epecting much and thats about what I got, all sound better than the 4558 I pulled out so I'm certainly not complaining I just need some more time for comparrisons. So far the LM4562 has been on top of the pack, smooth and spacious.
 
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Great to know you've fitted the parts. As you say, differences can be small, but you do need to listen long and carefully. When you settle on a particular I/C it may be worth removing the socket and permanently soldering it in. I would also add a small 1 to 10 mfd cap directly across pins 1 and 8 (observe polarity and voltage rating). Ultimately perhaps the player itself is also a limiting factor, from your description it does appear to be an early model, possibly with a "time shared DAC". Now you've had a go why not get something cheap off EBAY or similar, and explore the possibilities.
Regards Karl
 
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