Does a DAC need a pre-amp

[gmgraves]

11 minutes ago, gradier said:

I am playing my music collection (ALAC files) through JRiver and listening via an IFI IDAC2 and M-Audio M-38 powered monitors. Right now, I have to use the mouse on the computer to control volume (the IDA2 does not have  volume control for the RCA OUTS). Is this a scenario where I would benefit from having a pre-amp? If it had volume control, that would be a possible benefit, but my real question is this: Is there any advantage from the point of view of sound to adding a preamp to the chain between the DAC and the powered speakers?

The main answer is that generally speaking, the shorter the path, the cleaner the sound. Any additional active circuitry that you place between your source and your speakers will definitely compromise SQ. The question then becomes (1) can or can you not actually hear the insertion loss in real listening situations, and (2) is any loss of SQ worth the added advantage of being able to control the volume conveniently?

Some will tell you that a passive volume control is all you need (such as the one sold by Schiit), but I hesitate to make such a suggestion because most passive volume controls are merely potentiometers in a box. These not only vary the volume, they also vary the source impedance that the power amp sees. Most source components have a very low output impedance of less than 600 Ohms (usually), and most amps have input impedances of 10K Ohms or greater. The output of a simple pot, may (or may not) mess with the amp's frequency response. The exception is if, instead of a pot, the control is a true "T-Pad". Then there would be no impedance mismatch, but these are few and far between. If you decide to try a passive volume control, my advice is to use the shortest connection between the control and the amplifier possible. Between the source and the pot, the distance is not critical, but it can very well be between the pot and the amp. I hope this helps.

[gmgraves]

15 hours ago, Speed Racer said:

My experience is that a quality active preamp sounds better than no preamp or a passive preamp.  

 

You are misinterpreting what you have experienced*. Every active stage adds distortion. It's a fact of life. it has to be, there are no if ands and buts about it. Now, it is possible that the distortion in a modern preamp is so low that you don't notice it, but if you measured the chain from the source to your speakers, an active preamp will measure poorer than a passive one (or no preamp at all). Like I said, passive volume controls like the Schiit SYS, can cause frequency response problems with some amps. After all, as the specs for the SYS say the maximum output impedance for the control is 5KΩ. With an amp that has an input impedance of 10KΩ (which is typical) a variable source impedance can alter the frequency response curve. This would make the system sound worse than an active preamp where the controls are buffered and present the power amp with a constant low impedance load.  

 

* Interesting how misinterpretation of observed data can result in mythology so entrenched in society's consciousness that it is taken almost as gosple. Take, for instance, the old wives tale that one's hair and nails continue to grow after death. It's nonsense, but people will tell you that they've observed the phenomenon. What they have really observed is the shrinking of skin after the blood (no longer circulating) pools at the body's lowest point. as the skin shrinks it pulls away from the nails and the hair. making it look like a man's beard has grown since he died, thus giving him a 5 O'clock shadow that he didn't have at the moment of death, and fingernail that seem longer than they were at the moment of death. To the casual observer, it looks as if these have continued to grow. They haven't. 

[gmgraves]

3 hours ago, Fitzcaraldo215 said:

For decades, I have found that the introduction of additional analog stages to the signal path inevitably introduced some loss of transparency.  Expensive preamps were better in this regard and their degradation less noticeable, but the issue was still there. No getting around the fact that good analog volume controls are expensive.  Excellent, totally transparent, digital volume controls are much cheaper to produce.

 It's not just your experience, it is a product of the physics of active analog electronics. All else being equal, a preamp or buffer stage with 2 transistor (or op-amp) gain stages is going to sound (and surely measure) better than one with more than two gain stages as each adds it's own set of non-linearities to those inherent in the preceding stages and the effect is cumulative. Just as in a mechanical system, everything adds it's own friction to the overall.

[gmgraves]

4 minutes ago, Speed Racer said:

 

Hold on there. You don't get to tell me that I am misinterpreting my experience. Passive preamps have always sounded a bit flat to me...lifeless and boring.

 

Sorry, I didn't mean to cause offense, I was merely stating a fact. If someone's experience runs counter to known fact, then there is one of only two plausible reasons (well, maybe three if we consider that the observer might be lying about his experiences. But let us set that aside here): his experience is either based on a false premise, or he is misinterpreting what his senses are telling him. I never took any issue with the fact that you might find an active preamp to sound better than a passive one or no preamp (as a matter of fact, in most circumstances, so do I) but that doesn't mean that the addition of such a component doesn't make the overall sound more colored. It's that the trade-off of other factors makes the addition of a pre-amp a more predictable matter in terms of overall sonic performance. I often found that when I bypassed my Audio Research SP11 and ran my Otari MX5050 reel-to-reel recorder directly into my VTL mono blocks, that the sound was cleaner and it was instantly apparent that several "veils" had been removed from the recording. Still, I didn't replace my SP11 with a passive device because some of my components (such as my phono-preamp) couldn't drive my power amp to a sufficient loudness to satisfy me and certain other components sounded kind of thin (for some reason, which might be to what you are alluding). 

[gmgraves]

13 minutes ago, Speed Racer said:

A passive preamp may very well measure better. But that does not mean it will sound better. That's like saying an amp that measures better is going to sound better which is so completely untrue.

 

We still seem to be talking at cross purposes. We are certainly talking about two different things. You are talking about overall sound quality (which is, subjectively speaking, an opinion, that, as I have indicated, I share), and I was talking about adding distortion to the chain by introducing more active components to that chain, which is indisputable. 

[gmgraves]

1 minute ago, Speed Racer said:

 

No, you are merely stating your opinion.

 

I don't see how you can say that. Do you mean that you dispute that adding more active electronics to an audio chain will add more distortion? I can point you to any number of textbooks which state that outright. It is, my friend, not an opinion, it is a fact! And it is indisputable and easily demonstrated. As to whether it makes a system sound better or worse, that's another issue altogether and is a product of more factors than just added non-linearities.

[gmgraves]

Just now, Speed Racer said:

Come on, George. This whole hobby is about sound quality, what sounds better, not what measures better.

 

That's not the issue. And I certainly know that. But that knowledge doesn't make my argument any less correct. 

[gmgraves]

17 minutes ago, davide256 said:

 Pre amps are important. I think of them as  the diplomatic buffer and negotiator  between two parties that don't get along well face to face, your sources and your amp.  More of the music gets heard with a good pre-amp in the picture

 

Well stated. The fact that an active preamp, even the best of them, adds noise and distortion to the system notwithstanding, most systems are better with a preamp than without one and largely for the reasons you state. 

[gmgraves]

Just now, Speed Racer said:

I could put a system together with very low distortion numbers that sounds like crap. I can put a system together with much higher distortion numbers that sounds sublime. 

 

Again, I agree completely, but you keep missing (or seemingly missing) my point which was introduced purely as an academic aside.

[gmgraves]

33 minutes ago, Speed Racer said:

 

No. You said that I am misinterpreting my experience. My "experience" said that passive preamps did not sound as good as active preamps. I never said anything about how they measure. How they measure is meaningless in regards to what I said.

 

Like I said, we were talking at cross purposes. 

[gmgraves]

9 hours ago, esldude said:

I thought it was posted unless it was wiped out in the forum upgrade.  There are a couple items I probably haven't updated in that list. I don't have it in my signature anymore.  Evaluating the worth of someone's ideas by looking at their gear is not exactly great anyway.  

 

I use Soundlabs speakers, and Wyred4Sound CLASS D amps.  So I know you just quit listening. 

Recently I use a couple different ADC/DAC recording interfaces for the preamp.  Most recently some Antelope audio gear. 

 

 

SoundLab Speakers are not just good speakers, they're GREAT speakers. I'd put a pair of Majestic 945PX against the highest price Magicos or the Wilson Audio Alexandria XLF any day of the week. For natural sound, they cannot be beat. Not even the Lovely Martin-Logan Neoliths (at twice the price of the 945PX's can match them for shear top-to-bottom cohesiveness and absolute realism). I envy you. I have to be content with a pair of Martin-Logan Vistas (not that they aren't excellent speakers, mind you, it's just....)  

[gmgraves]

5 minutes ago, GUTB said:

Okay so, there’s this thing called a “digital potentiometer” — a little IC package that costs a few dollars that does a stepped resistor ladder. Is this what the Mytek uses?

 

I dunno, but keep in mind that a digital potentiometer, while eliminating problems with impedance mismatch, must convert analog to digital and then back again. And we argue for hundreds of posts about the merits of various commercial DACs and now some are advocating digital volume control chips which do a do a double conversion? 

[gmgraves]

10 hours ago, Speed Racer said:

 

No. You said that I am misinterpreting my experience. My "experience" said that passive preamps did not sound as good as active preamps. I never said anything about how they measure. How they measure is meaningless in regards to what I said.

 

I don't think that I can fit any more angels on the head of this particular pin. I'm through with this "debate". See you at our next encounter. 

[gmgraves]

7 hours ago, mansr said:

That's not what a digital potentiometer is. A digital potentiometer is simply a digitally controlled variable resistor. Here's an example of one: http://www.analog.com/en/products/digital-to-analog-converters/digital-potentiometers/ad5142a.html

 

Indeed? Never thought of that! Never mind my criticism. The only digital volume control of which I've ever heard uses an ADC and then a multi step volume control which works in the digital domain, and then requires the digital signal to be returned to the analog mode via a DAC. Not a great high-end audio solution in my estimation. However the one you describe should be fine.

[gmgraves]

11 hours ago, Speed Racer said:

 

You start out with one argument and then pivot to one we weren't even having. You must be trying to fit angels on the head of a pin..... 

 

My good friend. I didn't start out with any argument at all! I merely stated that adding more active stages (as in a pre-amp) to an audio system adds distortion because no active electronics are distortion free. There is no such thing as Stewart Hegeman's mythical "straight wire with gain"*. I never stated nor intimated. that a system couldn't still sound better with a preamp than without one. Several times, I recall agreeing with you that I'd rather have a system with a preamp than without one. But you kept arguing with me anyway.

 

*That's not actually 100% accurate. There is a British "pre-amp" that uses a pair of  auto-transformers to provide gain, and the transformers are tapped to provide a stepped volume control. I don't remember the brand, but this device offers gain without adding noise or distortion because that's the nature of transformers. So technically, such a device could be considered a "wire with gain" if not actually a "straight" wire! Because the inputs are isolated from the output, the load to the power amp is constant. I don't really know if this theoretical advantage translates into a practical sonic advantage or not, but harmonic and IM distortion added by such a device should be , essentially, nonexistent. 

[gmgraves]

Just now, mansr said:

There are also devices like this one: http://www.ti.com/product/pga2311

That's basically a variable resistor combined with an opamp to produce a variable-gain device with fixed input and output impedance.

 

Of those, I am aware. I am also aware of Voltage Controlled Amplifiers or VCAs where a DC variable control voltage is applied to an op-amp-like component which varies the "gain" of the device from passing no signal all the way to unity gain output depending on the amplitude of the voltage applied. These are used in lots of consumer grade appliances such as televisions that offer remote volume control. Performance, again, is not what I would consider worthy of a high-end audio system.

[gmgraves]

42 minutes ago, GUTB said:

 

No it doesn't depend. There's certain things that should be matched correctly. But generally speaking, better speakers are better speakers, better amps are just better amps, and so on.

 

For example, Magicos are better than Magnepans. 

 

Pass is better then Adcom.

 

Ayre is better than Logitech.

 

Nordost is better than Blue Jeans.

 

Etc and so on.

 

If a VAC Reference stack was dropped in beside your NuPrimes, Adcoms, Onkyos, Yamahas, etc, 10 out 10 of you guys world prefer the VACs.

 

I would say that whether Magico's are better than Magnepan's would depend on which Magicos and which Magnepans. For instance, a pair of Magnepan MG-20.7s will easily outperform a pair of Magico Q1s even though the latter cost ten grand a pair more than the Magnepans. 

 

Also I would argue that Nordost and Blue Jeans are sonically and measurably equivalent. The Nordosts, being audio bling, just cost more, that's all. 

 

The notion that the level of cost = the level of quality, either aesthetically or sonically is simply not applicable when it comes to high-end audio. 

 

I wouldn't bet money on your last assertion, either!

[gmgraves]

3 hours ago, Speed Racer said:

 

That is not accurate. I said (complete quote):

 

"My experience is that a quality active preamp sounds better than no preamp or a passive preamp."

 

You came back with:

 

"You are misinterpreting what you have experienced*." 

 

An then you went on with this:

 

"Every active stage adds distortion."

 

So you did not "merely state" that active preamps add distortion. You said I was misinterpreting what I have experienced. Since my interpretation said that "a quality active preamp sounds better than no preamp or a passive preamp", you must be saying that is not the case. That a quality active preamp does NOT sound better than no preamp or a passive preamp.

 

Own up to what you write......

 

Since my statement: "You are misinterpreting what you have experienced." seems to be what's stuck in your craw, let me apologize for a poor choice of words. What I meant by that is just because you find that an active preamp sounds better than a passive one (or no preamp) doesn't mean that an active preamp doesn't add noise and distortion that a passive unit does not add and I read your remarks as denying that statement and confusing SQ with a basic fact of electronics circuitry. Obviously I was wrong, and we were just posting at cross-purposes.  

Now can we get by this? Don't we have better things to discuss than to make verbal mountains out of molehills? I have apologized for the poor choice of words and my misunderstanding. Now, what else do I have to do to get off this particular merry-go-round without causing you ill feelings; which is the last thing I want? 

[gmgraves]

23 hours ago, bobbmd said:

i have an AQ DFR connected to my iPad air 2 out to a vintage Pioneer Elite c-90 preamp and m-90 poweramp both circa 1987/88 and stream TIDAL Deezer Qobuz Spotify Pandora alone or through A+3/ROON w/iPENG from Apple airport extreme wifi and everything wonderful even <=325 kbps stuff and ROON's internet RADIO sound like HiFi

All MP3 "sounds like Hi-Fi" in that it all has full frequency response and low distortion (I assume you are talking about MP3 since you mention 325 kbps). Where this falls down is the so-called compression artifacts. At low bit-rates, 128 kbps or less, the artifacts are easy to hear even on a car radio when the car is traveling at 70 mph, and at less than 64 kbps, MP3, is, to me, unlistenable. These artifacts manifest themselves as a nasty modulation noise which appears to "ride" upon the waveform. At 128 kbps, the artifacts are less audible on speakers but are still, quite audible (and annoying) on headphones. At 192 kbps, the artifacts are essentially inaudible on speakers (at least they are to me) but occasionally I can still hear them on headphones (where they sound like a rush of noise when dynamics go from soft to loud very quickly, or when listening to a solo acoustic classical guitar or a harpsichord). At 192 kbps (the rate at which WCRB in Boston feeds it's Internet radio channel and thus their live Boston Symphony Concerts) and higher, MP3 becomes, essentially transparent.  

[gmgraves]

7 hours ago, 4est said:

Actually, this sorta is disputable unless we are talking about theoretically perfect circuits. If the active pre sounds better than the passive, it could simply be a mis balance or excessive loading which may actually measure worse in circuit than using an active stage. Not you perhaps, but some seem to think there is very little difference between amps and pre amps. That indicates to me that whatever distortion is present in active circuits is fairly benign and it wouldn't take much mis match to be worse.

What you say is certainly correct, the truth is, that traditional forms of amplifier distortion (and that includes pre-amps) simply are not that audible - as distortion that is. But the amounts and kinds of distortion does alter the sound of the amp circuit, and I've never heard a system that didn't benefit sonically from the simplification of said circuit. Remove a preamp from between a tape deck (for instance) and the power amp, and the tape will invariably sound better than it did through the preamp. It is impossible to amplify an audio signal with either tubes or transistors without adding noise and some distortion. It's possible to minimize the amount of noise and distortion, of course, with the proper components and good design practices, but there is still no such thing as a straight wire with gain, after all.

[gmgraves]

8 hours ago, 4est said:

Well of course there is no such thing as straight wire with gain. There is also no such thing as transmission without losses. In your example using a SP 11, there is nearly a whopping 40db of gain. Of course one can hear that. For this exercise, even a simple unity buffer might have a positive aural effect. All I mean by this is I feel that you are over simplifying. If everything is just right, then yes, likely a pre only adds distortion. IME, things are seldom just right.

I'm not oversimplifying in the least. All active stages do change the sound of the audio chain of which they're a part (heck, to hear some people tell it, a half-meter or so of coaxial interconnect between a CD player and a pre-amp, for instance, changes the sound, but that's another discussion). Whether or not the net result of the insertion change of a preamp is sonically positive or negative is not the issue here. That's a subjective issue, and on that front, i am in complete agreement that in many (perhaps even most) cases, an active preamp sounds better than just a passive preamp or simply a passive volume control between source and amplifier. The only time that one can actually hear "damage" done by an active preamp circuit is when the source component has it's own buffered variable output (few components have this, but most tape and digital recorders do, which is why I used one as an example) and the preamp is bypassed. One doesn't need a DBT to hear this either, the difference in clarity and overall musicality is astonishing if one hasn't experienced it before! 

[gmgraves]

1 hour ago, Ralf11 said:

and Benchmark cautions that putting a pre-amp after their DAC3 will raise the noise floor; tho one may not be able to hear the distortion...

 

OTOH, some distortion may be euphonic (e.g. tubey goodness)

 

Both of your comments are absolutely correct!

[gmgraves]

28 minutes ago, sandyk said:

George

 I agree with 4est.

A good Preamp can  have distortion that is not accurately measurable without using special techniques.

Once you get close to 4 Zeroes in the distortion figures you need to use measuring techniques similar to those suggested by Douglas Self. A good Preamp will also be able to drive today's more recent SS amplifiers with input impedances around 10K ohms far better than any Passive Preamp, even when they use VERY short connecting leads to reduce HF rolloff.

Many people will also tell you that a very wideband Preamp sounds better .

My own DC  coupled Class A Preamp has distortion figures of very close to 4 Zeroes, and can even drive a terminated 75 ohm line without problems. It has a gain of only 3.2 times, so that excessive attenuation is not normally needed.

 

 According to a U.S. friend who also built one, it is :  

 

 

He didn't measure S/N as "there is none to be heard with my CD player connected & the gain wide open."

 

P.S.

 Have you read any of the Amplifier design books by Douglas Self ?

 

I think that I said, essentially, the same thing:

 

"...i am in complete agreement that in many (perhaps even most) cases, an active preamp sounds better than just a passive preamp or simply a passive volume control between source and amplifier. "

 

I have several amplifier design books including one by Doug Self. I also have several design cookbooks by Walt Jung including his famous Op-Amp cook-book. 

[gmgraves]

3 hours ago, sandyk said:

 George

 Is it "Audio Power Amplifier Design Handbook 5th ed - D. Self" ?

 

Alex

 

3 hours ago, sandyk said:

 George

 Is it "Audio Power Amplifier Design Handbook 5th ed - D. Self" ?

 

Alex

I think so. My technical books are in storage so I don't have access to them immediately. That title seems familiar, though.

[gmgraves]

23 hours ago, mansr said:

So get an expert in each and let them build a DAC together.

 

At Schiit it's Mike Moffat for the digital stuff and Jason Stoddard for the analog designs. Both are legendary in their fields. Maybe that's the reason their stuff consistently seems to outperform it's price points.