Op amps

Join date: 2009-09-11 Posts: 144

How much difference does changing op amps make to the sound, are the worth doing? which are the best makes?

Subject: Re: Op amps Thu Nov 12, 2009 9:18 am

hifi nutter wrote:

How much difference does changing op amps make to the sound, are the worth doing? which are the best makes?

Yes, changing them DOES make a difference, anything from ruining the sound to elevating it to new heights. It all depends what you put where.

Whether it's worth doing is impossible to say in advance. In principle, changing something like the ubiquious NJR op amps, or the impossible-to-kill NE 553x for something better does yield better sound, but how much better is a moot point, it's a heueristic thing, try it and see.

A number of companies make high quality op amps, however, they will all sound different. Often you'll find that despite all logic and reason, one op amp may shine where others have failed, despite the fact that on paper, it is outclassed all around. Case in point - if we're dealing with a say Marantz CD player, over the years I found that the OP 275 will be the ideal choice in the end. It appears its input stage is best suited to its position in the circuit and the role it is expected to play (it is one of very few op amps to use a Butler input stage, which is a great combination of FETs and bipolars).

There is no clear cut answer to the question who makes the best. Many people will swear on Burr-Brown's OPA 234x series, while I find them extremely distasteful to me. It's come to that I can generally recognize their particular sound in a product. To me, they are cold and lifeless, others find them detailed and analytical (whatever the hell THAT means! Hey, I'm no music proctologist, I just listen to it!).

Over the years, I have developed a taste for Analog Devices (AD) op amps, and consequently keep a considerable stock of them at hand. Having just said what I did about BB, I must add that I find their venerable old OPA 2604 to be a great sounding op amp with the added benefit of somewhat higher operating voltages, at a very reasonable price.

If you told me what you want to do with them, and/or what is already installed in what, I could be more specific. A few years ago, I advised an Internet friend from USA to tune his Marantz 7000 integrated amp by exchanging op amps, he had a qualified technician do it for him, and ended up a very happy man.

The usual technique is to carefully extract whichever op amps are installed, then in their place insert high quality, gold plated sockets. This makes change of op amps easy and safe, so you can experiment to suit your taste.

Join date: 2009-09-11 Posts: 144

I'm noticing that more and more dacs are appearing now where it is quite possible for the end user to tailor the sound to his taste by changing the op amps, the latest Beresford dac now I believe has this option where the op amps are simply pop in/pop out leaving you to be able to change the op amps yourself to suit however you want it to sound, so it was thinking just how much of a difference do they make to the final sound, can they really make or break the sound? Is their effect that influential?

I was under the impression that the Burr Browns were a very good choice, so you don't really rate them?

Subject: Re: Op amps Thu Nov 12, 2009 5:14 pm

hifi nutter wrote:

I'm noticing that more and more dacs are appearing now where it is quite possible for the end user to tailor the sound to his taste by changing the op amps, the latest Beresford dac now I believe has this option where the op amps are simply pop in/pop out leaving you to be able to change the op amps yourself to suit however you want it to sound, so it was thinking just how much of a difference do they make to the final sound, can they really make or break the sound? Is their effect that influential?

Yes, they very definitely are that influential, and then some.

Quote:

I was under the impression that the Burr Browns were a very good choice, so you don't really rate them?

A good part of the industry, and all of the Scandinavian industry, swears by Burr-Brown op amps. To me, they sound too cold and way too disinterested, with the exception of the aforementioned OPA 2604.

There are a number of reasons for this. First and foremost, in their day, Burr-Brown was God for DACs, no two ways about it, everybody else was just trying to catch up. That lasted some 15 years or so, say 1985-2000, and they were deservedly held in high regard in the pro sector.

Then, somebody there got ambitious and decided that God should make analog op amps as well. And they did, only to hit their heads against reinforced concrete wall called Precision Monolithics International, Inc. (PMI) and their manufacturing partner Analog Devices (AD). They discovered there and then what it feels like to be just a wanna-be. In their imagined omnipotence, they persevered, and as a result, went almost bankrupt and were bought out by Texas Instruments. Today, Burr-Brown is more or less just a name, while inside the TI they are called simply "The Tucson Operation". Whereas AD makes outstanding DACs today.

The second reason is customer inertia. When you use somebody's products for 20 years or more, and have never had any problems with them, you naturally tend to stick with these people and leave experimenting to others.

My issue with BB is not reliability, price or something like that, in that respect, they are beyond reproach, my issue with them is the cold and disinterested sound they produce - or so I think. They struggled to get maximum clarity, but appearently at the expense of other aspects. I could name a few op amps which are as clear, if not clearer, but with no sacrifices elsewhere, and in fact, bettering BB elsewhere at the same time.

Not to bore you, I'll name just one example, which will also give you an idea why op amps do sound different. We all know that theoretically, we need as fast a response as we can get, since the ideal response time is zero. On that, everyone agrees. What almost nobody ever mentions is the fact that we also want our settling time (reverse of rise time, i.e. the time it takes an op amp to get down from 90% to 10% signal strength) to be as short as possible, we don't need any overhang. This is particularly important with spatial information, the feeling of air and space; if the signal stops, and our op amps takes its sweet time to return to normal, then we will obviously get little, if any, spatial information, since it is by its nature on a much lower level than the basic signal.

Well, BB's 213x op amps, most popular, take 2,000 nS, or 2 uS, to fall back from 90% to 10% of the signal. AD's audio specific OP 275 op amps takes just 200 nS, or 0,02 uS, for the same job, and to add insult to injury, it is in fact faster than the BB op amps. And once you discover AD's star performers, you'll find that the same settling time is just 45 nS, 5 times faster than their own 275 and 44.4 TIMES (sic!) faster than the BB op amps. On models such as AD 817, 818, 825, 826, 829, etc.

As for signal response speed, BB's offerings can do 15 V/uS, AD's do 230 V/uS and up until 450 V/uS. In most audio applications, this is not of great importance, but in some, where high gain is required as in phono RIAA amps, that becomes a critical aspect.

The odd man out in this story is almost 30 years old. I refer to PMI's OP 37. In my view, it is one of the most neutral, if not THE most neutral sounding op amp of all time, despite its rather mundane Data Sheet characteristics. It's widely available, very much low noise, extremely wide bandwidth, and its only downside is that it is decompensated. This means it will be stable with gains of 5:1 or over, and if you need unity gain stable, buy its brother, OP 27, which is the same, but unity gain stable at the usual trade-off, it's Slew Rate is 4 V/uS, whereas the 37's Slew Rate is 15 V/uS.

The trouble with op amps is that they have been taken too much at face value and are generally used for a quick, short development projects. This is a nice way of saying that far too many designers don't take the time or trouble to sit down and make those op amps come on song. This inevitably calls for hybrid circuits, mixing op amps with some discrete transistors; yes, it is extra trouble, but the end result can far surpass in benefit the extra time and trouble.

Some did get wise, for example Classe, but most never caught on and kept on designing by technical rather than musical standards.

Subject: Re: Op amps Mon Nov 23, 2009 1:08 pm

hifi nutter wrote:

How much difference does changing op amps make to the sound, are the worth doing? which are the best makes?

I have changed the op-amps in my computers soundcard, originally fitted with five NJC NJM4508D which were swopped for National Semiconductor LM4562NA which did improve the sound quality.

Also have changed some of the op-amps in various headphone amplifiers, in the case of my Travagan Red amp someone over on Head-Fi did a lot of testing with op-amps and just read his reviews and selected one that appealed to me and it worked very well so have left that in the headphone amplifier.

No soldering was required as all the op-amps just plugged directly into a socket, easy.

So am now happy with the sound of the amp so will not be trying any other op-amps will just enjoy the music!

Harryo

Subject: Re: Op amps Mon Nov 23, 2009 3:02 pm

I still maintain that for the ultimate quality, nothing beats discrete.

I'm not putting op amps down, after all, I have quite a collection of them and use them regularly in some applications in which they are a Godsend (for example, DC Servo cicruits, protection circuits, displays, etc).

For quick and cheap projects, they can be a good solution.

However, for the best in sound quality, their greatest virtue becomes their greatest problem. They are closed, they are what they are and that's it, you can augment them a bit, but that's where it stops. In a discrete circuit, which is always much larger, much more complicated, you as the designer nevertheless always control each and every part, so you can, for example, use the best transistor for a given job, or use a 1W resitor instead of an 0,6W one, use Dale instead of no-name, etc. Also, because of much greater power supply rails, a discrete circuit has far more dynamics available than an op amp.

Last but not least, op amps work on basis of very high Negative Feedback (NFB) factors; just take a look at their open loop (with no NFB) gains, they often exceed 100,000:1, so for a gain of say 100:1, you have to apply 60 dB (1,000:1) NFB. With discrete, you can design for low gain but ultimate quality, and can usually do it with no more than 20 dB (10:1) of NFB, which is 1,000 times less than with an op amp.

Subject: Re: Op amps Mon Nov 23, 2009 3:46 pm

I must admit that at the time I purchased my headphone amplifiers I had no idea about the circuitry they employed.

When researching on Head-Fi a lot of the talk was about swopping op-amps for improved sound quality and I must admit that I was drawn in by this!

Now I'm looking for a quality headphone amplifier that I will not have to start swopping-out op-amps in order to improve the sound.

Some of the Chinese valve amps look appealing but am not sure whether this is partly because I have fond memories of as a boy sitting around the family radio in the dark with valves glowing brightly listening to 'd Barton Special Agent'.

I have tried Googling 'DDM Headphone Amplifiers' but it comes-up with Behringer products and one PDF page for DeZorel products, dvv do you have a website for DDM products?

Harryo

Subject: Re: Op amps Mon Nov 23, 2009 7:28 pm

Harryo wrote:

... I have tried Googling 'DDM Headphone Amplifiers' but it comes-up with Behringer products and one PDF page for DeZorel products, dvv do you have a website for DDM products?

Harryo

Not yet, Harryo. It's under construction, in fact, the whole site is under total reworking, from scratch.

Not to misuse Adam's hospitality, drop me an empty message into my private e-mail box, dvv@bitsyu.net , and I'll supply as many photos as you like.

In general, I'll outline my overall concept, which applies to everything I do, business and fun-wise.

I believe in traditional work. This means using selected discrete components, buying a batch of them, then sitting down and pairing them up. Also in soldering by hand. Machines do it well, no doubt, but I still believe in Ersa soldering stations and Flutin (German made solder with a high percentage of silver). Experience has show that this always somehow manages to sound better than the competition in form of mass produced items.

In terms of topology, I believe in the fully complementary designs. That has been with us since James Bongiorno invented it in 1971, and over time, it has proved itself to be a superior platform by design. Its initial, or natural, distortion is lower to an order of magnitude lower in comparison with traditional designs, and it's thus an excellent starting point for further refinement. If I disregard the real estate it requires as a fault, this concept has just one condition to work like a charm - it MUST be well paired all around, very tight selection. I freely admit to being a freak, so, mass industry is happy with a 5% match, High End uses 3...2%, and I won't go above 1%. My personal freak-out.

Obviously, pure class A operation is assumed, but even so, I like to take it a bit further, to what I call Enriched Pure Class A. Behind the sexy moniker, it's really quite simple - if for true class A operation I need say 10 mA (for preamps, phono stages, etc), the wise thing would be to use 12 mA just in case, so I use 15 mA. Razz

I know the extra 50% of bias isn't strictly speaking neccessary, but I just love to have it.

Next, the output stage. This is the place where the mass industry fails miserabely. If you want high load tolerance, and I want almost COMPLETE load tolerance and won't have it any other way, you need powerful output devices and a beefy power supply. There are no two ways about that. Not because I think somebody is going to sit down and listen to full power sine waves over his 4 Ohm speakers which dip to 2 Ohms, but because of the moments when you have that big transient whose FAITHFUL reproduction will make or break any amp - it has to be flawless. Thus, it stands to reason that if your amp can operate into 2 Ohm loads on a continuous basis, with low distortion, under normal listening conditions, it is most unlikely you will ever catch the amp with its trousers down. Ever!

Remember the Holy Grail of all amplifiers - straight wire with a gain into whatever you call a load.

Lastly, or should I say primarily, the power supply. Time and time again, I have heard the shunt type provide results no other supply could ever even get near to, so that's what I use. Shunt is really no more than a class A power supply. So, if it has to provide xx Volts at yy mA, I first measure the actual consumption, say 25 mA. To play safe, I'd need say 35 mA, so I use 50 mA. Twice what is required. Obviously, this costs money, I have to use a lot of not so small heat sinks, the usual U profile is way below my requirements.

Consequently, I am not a purveyor of sexy packages with fairly regular insides, rather I am a purveyor of asexy insides within a fairly standard case. Everything I do is like, including my batchelor car (as opposed to my family car, which is a very standard serial job). That car never ever even saw the factory, it was quite literally made from the ground up by me and my friends. We created a product which did not exist. Why? Because I simply cannot abide with run-off-the-mill stuff in the long run. If no ready made suit can ever fit you as well as a tailor made suit, why are cars, or audio, any different?

I'm like that with my cooking, too, as a matter of fact, I have a qualification as a cook - but there's a story which is quite pointless over the Internet. Just show me where your kitchen is, and I'll make my point. Razz

All this has a further point. If talking to only Harryo, I could have said as much, and more, in private communication, but I think all this may be of some interest for the whole forum. Exactly how, I'll elaborate in another post, right now I have to do some work for my good wife, so a pause is in order. She's great in her profession (pharmacologist, senior professor, head of her institute, .....), but she hates computers, and believe it or not, they hate her back. So I get to be The Buffer. clown

Subject: Re: Op amps Mon Nov 23, 2009 9:25 pm

Let's not pollute this subject, let's move here: http://mundoaudiofilo.forumotion.net/diy-f10/diy-amplification-t342.htm#3144

Subject: Re: Op amps Thu Dec 31, 2009 10:31 am

I've decided to pick up some KingRex UD-01 USB DACs. Inside are:

Low pass filter op amp: Burr-Brown OPA2604
DC Servo: Texas Instruments TL072

I'm thinking also of the Burr Brown twin Burr-Brown OPA627, so I'll need four of them? Do you think Analogue Devices would be better dvv?

Another solution is some from Burson Audio.

This is my new project to see how good I can make the KingRex UD-01 sound.

Subject: Re: Op amps Thu Dec 31, 2009 12:06 pm

adam wrote:

I've decided to pick up some KingRex UD-01 USB DACs. Inside are:

Low pass filter op amp: Burr-Brown OPA2604
DC Servo: Texas Instruments TL072

I'm thinking also of the Burr Brown twin Burr-Brown OPA627, so I'll need four of them? Do you think Analogue Devices would be better dvv?

Another solution is some from Burson Audio.

This is my new project to see how good I can make the KingRex UD-01 sound.

BB 2604 is the only BB op amp I consider to be really very, very good. Unlike others from BB, it has a nice, flowing sound and is not in the least bit harsh.

The only potential problem with exchanging it is the fact that it is capable of using higher power supply rails than most others, so before any change is made, Adam, you must see what the power supply is like. If it's +/- 15V, then experiment at will.

I have no way of knowing whether an AD op amp would be btter sounding, but if you do want to try, do try AD 826 AN, that is a pin-to-pin replacement. Very fast, great sounding.

The TLO72 is a garden variety op amp, and as such, is a typical commrcial product compromise. Do replace it with a National Semiconductor LF 412, which is an ultra low drift, high speed op amp ideal for that function. Not expensive at all, widely available.

Subject: Re: Op amps Thu Dec 31, 2009 12:19 pm

Thanks dvv, is the AD 826 single unit direct replacement then? just pop it in place? Is it worth doing the BB2604 with the same ? some guys changed to all OPA627 and found it better, do you rate this OP amp? or the AD826?

Subject: Re: Op amps Thu Dec 31, 2009 1:31 pm

adam wrote:

Thanks dvv, is the AD 826 single unit direct replacement then? just pop it in place? Is it worth doing the BB2604 with the same ? some guys changed to all OPA627 and found it better, do you rate this OP amp? or the AD826?

Adam, a long time ago, I learnt my lesson - NEVER rate any op amp as is, or per its Data Sheet, because life can play very strange tricks on you.

Logic dictates that a faster op amp will fare better in a Marantz CD player, yet after trying out a slew of them, I discovered that OPA 275, a middle-of-the-road op amp, somewhere between garden variety and ultra fast, simply SOUNDS the best in a Marantz. Also in a Philips 721 player. Whereas in my Yamaha CDX 993, AD 826 did best. Go figure.

Thus, there are no carved in stone rules. You simply try it and see, there is no other way. Applies to everybody and everything. Sometimes, one op amp will for no appearent reason, or even against all logic, sounds better than others which should run circles around it.

As for BB 627, I am aware that it is highly regarded, and it seems to be a very good op amp, but my hands-on experience with it is exactly zero, so I cannot comment.

Subject: Re: Op amps Sun Jan 03, 2010 8:18 pm

Your dead right dvv, so I'm going to order a few different ones from Burr Brown, AD and burson and see how the little KingRex responds, it should be fun to hear which works best.

Subject: Re: Op amps Mon Jan 04, 2010 12:35 am

Adam, in case the op amps are soldered directly to the PCB, ask your DIY friend to obtain and install some high quality, nylon with gold plated pins sockets. Then let him solder in the sockets, making firther experimenting very easy.

Remember to first use a smaller screwdriver to first loosen the op amp on one side, and then on the other. Remember that op amp pins can be deformed very easily, and once deformed, are next to impossible to bring back into original shape.

Or buy or borrow a DIP-8 extraction tool from the said friend.

Point is, do be careful. No damages.

Exercise caution and care, with much patience thrown in, that's how you will enjoy experiementing the best.

Lastly, remember that to evaluate anything, you have to listen to it for several days, using different, most varied music material, in at least most moods you are likely to be in. Say, at least a week with each op amp in the first run, then narrow it down to two, and say 5 or 6 days for the big showdown.

I'd try Analog Devices AD 826 AN (fast, oustanding dynamics), AD 847 AN (similar, but lower cost) and AD OPA 275 (trustworthy, warm yet detailed sounding op amp, has a way of surprising you, I think it's a bit more detailed than the BB OPA 2604).

Then let us know what you discovered. I for one am rather curious.

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