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Which opamps are best?

M

mikesnowdon

resU deretsigeR
Hi.

I recently got into this modding stuff and replaced the NE5532P with LM4562NA in my CA 640C V2. The LM4562NA are fantasticly detailed and the dynamics are awsome, also the bass is more articulate. However there are some negatives also: The treble seems a bit hard and shut in, bass level is a bit low and the overall smoothness isnt as I'd like it to be. There may be other issues with the player which the LM4562NA have brought out.

Im really looking for a nice smooth sound with good detail, dynamics. Something natural. Before doing any further mods I'd like to try some different opamps but Im not sure what to try. There have been lots of different suggestions on the 'CA 640C V2' thread and another on 'DIYaudio'. Thing is im not sure what to try.

Can anyone advise which opamp wil give the sound Im looking for? Are there any reviews/write-ups anyone knows of, on how different opamps sound?

The CA has 6 opamps, therey perform some kind of filtering network after the DAC's and the last 2 are the for the output. I changed all 6 to LM4562NA so maybe I can mix and match some warmer sounding opamps with the LM4562NA?

Thanks in advance.

Mike
 
Hi Mike

I tried some LME49710 in place of the NE5534's in the output of my AAA5, they were kindly sent to me by a fellow PFM'er, immediately they seemed to be the answer to all my questions, sadly after some prolonged auditioning they did grow a little tiring, to be honest exactly as you describe with your experience. I have tried AD825, AD797 and OP27G, of all the above the OP27G's give me the most rounded and acceptable sound, not boring, just not as immediately impressive as the others. However if you take a peek at my thread here:

http://www.pinkfishmedia.net/forum/showthread.php?t=46579&page=2

read the last few posts you will find a better solution to your question, I would plump for the OP27G's and change the AC coupling caps as I have done with my AAA5, the difference is totally worth the time and effort to undertake, also if you have ceramic capacitors in the signal path, be suspicious of them, they were across both outputs of my AAA5 and these were removed with no adverse effect on the players operation, but these could have contributed to the harshness I was experiencing prior to the AC cap change and the removal of the ceramics.
Good luck, let is know how it goes and post your experience please.
Paul

Sorry Mike just realised that your CDP uses 5532 the dual op-amp, my mistake but there are dual versions of the devices I have suggested above, sorry for the misinformation :(
 
Some stuff here if you haven't already read it:

http://tangentsoft.net/audio/opamps.html

My faves from playing around are:

LM4562
AD8620
AD826
LM6172

I think if I started playing around with my cdp again I'd be inclined to leave the original opamps in there though and look at psu regulation, clock/supply etc and once that's all done try some opamps out. Although it has to be said opamp rolling is by far the easiest and most tempting tweak.
 
Mike,
I'd put money on it that when you replace the regulators (opamps and dac supply) for Teddy regs or ALW super regs the harsh sound will go.
You've opened up the signal path by removing the electrolytic coupling caps.
 
Very true.

I suppose the circuit is optimised for the original opamps. I dont know enough to confirm this though. Others have suggested reading the opamp datasheets but that way over my head. I do have schematics of the 640.

You say you like the LM4562? Did you experience the same probs as me, if so how did you improve it?
 
do look at the coupling caps between dac and output stage if there are any. They were panasonic fcs in my rotel which I've replaced with polyprop caps. That reduced graininess and I find the 4562s more acceptable now. I did previously find them overly detailed and harsh and unmusical (ie the music didnt seem to hold together as a performance). I've supplied them with separate regulation now as well, which may have helped. I'll test teddyregs in there once the pcbs arrive.
 
Good idea.

Can you tell me exactly which caps thise are? I think I know but I'd like to be sure. I have schematics.
 
I dont believe there is an overall best op amp. It depends both on the application and on the personal preference of the listener. I have tried OP27,AD797,AD746, AD827,OP275,OPA627,LT1028,OPA2604,OPA2134,LM833,NE5532,SSM2139(rare but good)in various CDs, pre amps and phono stages.
Of these, my favorites are OPA627,AD797 and OPA2134. The 2134 might be a good choice for your CD player. It is unfussy and always sounds big and bouncy and with lots of tonal colour, to me. Many people dont like their "darker" sound however. The 627 and 797 are more specialised and not available as duals anyway.
One thing i have noticed is that the precision types, 627 and 797, are more detailed than the so called "audio" op amps. Assuming that the rest of the circuit will allow it. They are more fussy about power supplies and circuit impedances though.
 
IIRC there is only one set of caps in the signal path. I havn't got the circuit diagram with me, to double check though. . .
 
Thanks and thanks for the data sheet. Will read them later, I think I'll be using Wikipedia alot to get things defined though!;)
 
There is no 'best' because what works well in one circuit may work less well in another.

Assuming the NE5534/32 can be bettered without proper regard to the implementation is a very common mistake.
You need to know what the requirements of a a particular circuit are and what, if any the failing of a 5534/32 might be in that circuit. Often it is the best choice but sadly it isn't a particularly fashionable chip because 'a' it's cheap and 'b' it's old.
 
I think my knowledge isnt great enough to really start looking at the circuits etc. The watchword (phrase) seems to be 'trial and error'. As I have 6 opamps to play with It could go on forever.

Been listening to some music tonight and the sound is growing on me. Theres not as much bass as befor but its better quality bass, when I upgrade my amp this will get even better. The treble seems a little high and 'shh' sound in vocals sounds a little odd. I can cure this by using smoother sounding resistors in the singnal path. Also planning to upgrade to regulators. If all else fails, and after trying some others, I can always reinstall the NE5534/32.


Lots of experimenting to do and a clock upgrade on the horizon.

Mike
 
I'm only a novice at this but I've recently done some op-amp trials using my Audio Alchemy Dac-in-the-Box as a test board. What I found very quickly is that you can't just pop in a modern, high bandwidth op-amp into a circuit designed for an NE5532 (or in the DITB's case an OP275GP) and expect it to remain stable.

I don't know the circuit layout of the CA 640C v2 but I wonder if it would have sufficient bypassing of the power supplies to get the best out of the LM4562?

I tried AD827, LM4562 and LM6172 in the DITB. The LM6172 in particular is a really difficult op-amp to stop from oscillating. What finally worked was replacing the original 100nF MKT bypass caps for V+ and V- with a 22uF Sanyo Oscon plus a 100nF smd x7r ceramic in parallel (mounted undeneath the pcb). I also soldered 10nF axial x7r ceramics directly from the V+ and V- pins to ground. To top it off was a 220nF axial x7r ceramic between the V+ and V- pins.

For me the LM4562 was preferred just ahead of the AD827. The LM6172 was also good but possibly just a touch clinical for my tastes.

The lessons from this I'll apply to the re-cap/upgrade of my Rotel RCD-855.

Dominic
 
Thanks.

I upgraded the bypass caps to BlackGate Std 10uf, as advised by Brent on DIYaudio.com.

Whats ocsilating anyway? I heard this before but I only know of one definition and I dont think it fits the context here. Someone elighten me, what does it sound like?
 
Yes it is that kind of oscillation, in an electrical sense. It usually means that an amplifer is being driven into producing an uncontrolled output tone(s). This may be way, way above the audio band, so you can't hear it directly, but the side effects are measurable and audible. Typical tell-tales are unusually warm/hot running (check for high current consumption by the opamp, above the quiescent values given in the datasheet) or odd DC offsets at the opamp output that cannot be traced to DC conditions in the circuit. 'Oscillation' means that the circuit is no longer working linearly (the fundamental requirement of audio circuits!) and the unwanted cyclical noise interferes either directly or by intermodulation with the wanted signal. If it's particularly bad it may produce audible effects - the sense that something is 'wrong' tonally; either bass weight missing, or peakiness in the presence range/treble if you have oscillation happening near the upper end of the audio band.

The causes usually come down to inadequate, poorly-chosen or poorly-placed decoupling, or insufficient (electrical) damping; but layout, parts choice, loading, circuit layout and parasitic loads all come into it. The most cogent and thorough single document I'd recommend reading in relation to using opamps is Linear Technologies' Application note AN47 - High Speed Amplifier Techniques

Note oscillation is a risk anywhere there is gain in a system: this includes voltage regulators! Getting this stuff right makes an enormous difference to output quality, and IMO it's 95% of the problem with uninformed* modification.


*as in an uncontrolled / unmeasured /'always-chuck-the-same (boutique) parts at it' approach. Not that things can't work out, but it's often the case one simply gets lucky, or is alwready working on a good pre-existing layout...
 
Martin, I'm considering getting an oscilloscope to have a poke around with - any recommendations/pointers for what to look for?

Cheers

James

PS (w/e in Bath was most enjoyable, but trying to get fed in the evening without pre-booking was a nightmare)
 
General audio work - anything 'slow' by o'scope standards (ie 20-50MHz bandwidth) is good, because with high bandwidth scopes you often end up measuring your probing technique ;) And old 'slow' scopes are very cheap... have a look at, say the Stewart website for a wide choice, or ePay of course.

Once you've got a scope, the single most useful thing you can do is build a battery-powered little instrumentation amp that goes between probe and o'scope and has a restricted bandwidth (maybe 20-30Khz) and switchable gain, say 10x / 100x. This will give the ability to measure down to the 100uV level in the audio band, very useful for noise and power supply investigation. This is because most scopes resolve only down to 5mV/ vertical division - or 2mV/div for some - and the filtering really helps 'cleanup' the trace / keep it relevant to what you hear directly
 
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