Adding a pre amp

[diecaster]

Fitzcaraldo215,

 

That is all well and good in theory. But, in practice, that's not how it works out. At least not for everyone. You go ahead and be concerned with what the signal looks like. I will care about how that signal sounds. With my 40 years of experience, I'll take a high quality active tube-based preamp over a passive preamp or a DAC with digital volume control.  

[Fitzcaraldo215]

3 minutes ago, diecaster said:

Fitzcaraldo215,

 

That is all well and good in theory. But, in practice, that's not how it works out. At least not for everyone. You go ahead and be concerned with what the signal looks like. I will care about how that signal sounds. With my 40 years of experience, I'll take a high quality active tube-based preamp over a passive preamp or a DAC with digital volume control.  

There we have it, as it were, in a nutshell.  If some prefer the added "sounds" of the preamp added in a constant and fixed way to the original signal, I staunchly defend your right to do so. I am not concerned with what the signal looks like either.  I just prefer that it not be distorted or have noise added to it as much as possible.

 

I have also been at this for a very long time in decades myself. Count me out on tubes or analog volume controls. Been there, done that.  They  definitely add something, but not positively, in my experience.  YMMV.

[mansr]

59 minutes ago, Fitzcaraldo215 said:

But, Pass also makes and sells analog preamps.  So, would his opinion not also be highly biased, as is, of course, your own?

Yes, but it's class A bias.

[sandyk]

3 minutes ago, mansr said:

Yes, but it's class A bias.

 

 So what is yours? Class AB or Class C perhaps ?

[Fitzcaraldo215]

7 minutes ago, mansr said:

Yes, but it's class A bias.

Yes, classy, and expensive, by the way.

[diecaster]

36 minutes ago, Fitzcaraldo215 said:

There we have it, as it were, in a nutshell.  If some prefer the added "sounds" of the preamp added in a constant and fixed way to the original signal, I staunchly defend your right to do so. I am not concerned with what the signal looks like either.  I just prefer that it not be distorted or have noise added to it as much as possible.

 

I have also been at this for a very long time in decades myself. Count me out on tubes or analog volume controls. Been there, done that.  They  definitely add something, but not positively, in my experience.  YMMV.

 

You can certainly have the cold "accuracy" of solid state preamps and amps along with their harsh odd order harmonics and hard clipping. I'll take the gradual clipping and musical even order harmonics of tubes. Even if there is more of it.

[sandyk]

3 minutes ago, diecaster said:

 

You can certainly have the cold "accuracy" of solid state preamps and amps along with their harsh odd order harmonics and hard clipping. I'll take the gradual clipping and musical even order harmonics of tubes. Even if there is more of it.

 Cold accuracy of solid state preamps and amps ?
 A well designed Solid State Preamplifier and amplifier has a natural warmth to it, just the same as the recordings/sound  it reproduces.

Well designed Vacuum Tube amplifiers can also have this attribute, although it seems that many prefer the colouration due to more even order harmonics.  Hugh Dean ( AKSA in DIY Audio) from Aspen Audio in Melbourn Au. even has some solid state amplifier designs where he deliberately tailors the remaining harmonic distortion products to add some warmth for those who prefer this kind of thing !

[Ralf11]

Let's have examples, either way (cold, clinical) vs. (warm, musical).

[davide256]

3 minutes ago, diecaster said:

 

You can certainly have the cold "accuracy" of solid state preamps and amps along with their harsh odd order harmonics and hard clipping. I'll take the gradual clipping and musical even order harmonics of tubes. Even if there is more of it.

hmm. Tube transformers suck. Go Berning

[sandyk]

2 minutes ago, davide256 said:

hmm. Tube transformers suck. Go Berning

 I also wonder why some worry so much about soft clipping vs. hard clipping.

 NO amplifier should ever be driven into this area if chosen to match the size of the room, loud speaker efficiency etc. AND you value the HF drivers in your speakers, although you may sometimes hear this kind of thing at certain times of the year from some neighbours parties !

[Blake]

[Back drop:  We are all just friends having a friendly conversation at a bar, nobody insulted your mother]

 

Digital vs Analog volume control:

 

http://www.resonessencelabs.com/wp-content/uploads/2012/05/invicta_analog_vs_digital_volume.pdf

 

https://darko.audio/2013/12/kih-3-can-digital-volume-controls-keep-it-honest/  (note at the end of this article, he links to two separate listening comparisons of preamp vs direct)

 

but also see:

 

https://www.soundstageultra.com/index.php/features-menu/general-interest-interviews-menu/311-what-s-wrong-with-digital-volume-controls

 

http://bitperfectsound.blogspot.com/2013/03/digivol.html

 

http://www.audiodesignguide.com/DAC32/digital-vs-analog-volume-control.pdf

 

[barrows]

18 hours ago, diecaster said:

Oh, and no, the output circuit of a PS Audio DirectStream is NOT the same as an active preamp.....

 

OK, for clarity, and to try and educate some people who clearly have no technical understanding of what is at the output of a DAC, and what is at the output of a preamp, I was generalizing, of course.  There are always exceptions to general rules, and the DirectStream is certainly one of those.  Anyone can cherrypick an example which is an exception to a generality.

 

Generally speaking a preamp is this:

 

An input selection device-a volume control-and an active output buffer-sometimes there may be two active stages, with one both before and after the volume control.  But Generally, the three stages listed are what a preamp is.

 

Generally speaking a DAC is this:

 

An input selection device-a digital to analog conversion stage-an I/V stage-and an active output buffer (some DACs can skip the I/V stage as they use conversion stages which also do the I/V part, such as AKM and Wolfson DAC chips which have voltage, rather than current outputs).

 

What matters to this discussion is the output stage.  It is very, vert easy (and not expensive) for a DAC maker to include an output buffer which is the SAME or even better than what is included in most preamps.  An output buffer consisting of two OPA 1632 integrated circuits can drive a cable and an amplifiers input stage as well as any preamps (and many preamps use these same, or very similar parts to drive their outputs).  There are many other ways to make an output buffer, but the point is that it is easy to do and not expensive.

 

It is just not a big deal at all for the output buffer of a DAC to be the equal (or even better than) the output buffer of a preamp, it is very simple electronics, and not tricky or expensive to do.

[fas42]

8 hours ago, KingRex said:

How does a DAC perform volume attenuation?   It has to have some sort of material inside it that varies something in order for the amp to know it needs to send more or less power to the speaker.  I'm asking out of pure ignorance.  My question on a passive vs internal in the dac volume control was to understand just this.  I get what an Alps pot, Autoformer, resistive ladder do.  I was once told how Pass Labs does it but don't fully get it.  I thought it had something to do with a semiconductor that had a ladder inside it. I really don't know.  If your going to say its all software, what is the software driving.

Thanks. 

 

My original CDP had all the goodies, and did it well enough, back in 1987, to give me my first exposure to "competent" sound - the output stage went to 2V, with 47 ohms output impedance, so had an easy time driving power amps. The interesting part was that it manifested 18 bit performance, with a 20 bit digital volume control - at no time could I hear a weakness in this area of the topology.

 

This, http://www.hifi-classic.net/review/yamaha-cdx-1100-149.html, gives a rundown on the internal niceties ...

[barrows]

I kept an analog preamp in my system until the performance of going DAC direct beat it:  I had an very good Ayre K5xe-MP.  But even upon first try, it was obvious that DAC direct had more transparency, but, I did not have quite the Live sound or the dynamics I wanted, so i kept the preamp in the system.  Then the designer of my DAC at the time made a simple change to its output buffer stage: it went from having 1 small signal MOSFET per signal leg to having 3 small signal MOSFETs per signal leg.  the additional output current made all the difference.  When I tested with the new design output stage, now going DAC direct outperformed having the preamp in the chain in every way: better resolution, and more dynamics.  I kept the preamp around for a bit, for further testing, but after about a year it became obvious that I would never want to put all that junk in the signal path again.  

Going from 4 (balanced) small signal MOSFETs total to 12 small signal MOSFETs total added almost nothing to the cost.

 

I have no doubt that there are some poorly designed DACs out there which just sound bad, and there are also some poorly designed DACs out there which may not be quite capable of driving some amplifiers ideally.  But fixing a poorly designed DAC by adding a preamp is the path of an idiot.  If the DAC has a problem, get rid of it and buy a better DAC.

 

Since we have heard mention of Bascom King here, for those who understand what output impedance means, the output impedance of a PS Audio BHK preamp is:

 

"The line output impedance, specified as <100 ohms, was 215 ohms balanced
Read more at https://www.stereophile.com/content/ps-audio-bhk-signature-preamplifier-measurements#le8ReQpqHz55CBRs.99"

 

The output impedance of my current DAC is 4.7 ohms balanced (per phase).  Most current DACs feature output impedances <100 ohms, many much less.  There are plenty of DACs (most of them actually) which are fully capable of driving a cable and the input stage of any reasonable amplifier.

 

Sure, if you look really hard can you find exceptions to this, of course, but those are the outliers, and I would suggest that those DACs should not be used direct, and nor should they include volume controls.

 

[sandyk]

3 minutes ago, barrows said:

It is just not a big deal at all for the output buffer of a DAC to be the equal (or even better than) the output buffer of a preamp, it is very simple electronics, and not tricky or expensive to do.

 

Once again you are assuming that the Preamp uses simple electronics as in your example, and it's only real advantage is the ability to connect different source devices. That may be true of some cheaper Preamplifiers, but certainly not Preamplifiers that have a well established reputation.

 If they didn't add additional value and  higher performance over DACs with generic output devices such as you just quoted, they wouldn't still sell in the era of DACs with good digital attenuation. However, a Vacuum Tube based Preamp is sometimes a different matter, as some like a degree of colouration.

 I do agree however, that not all available Preamps meet this criteria.

 

A quote from  an  E.E. friend who recently revisited Valve Preamp designs.

I don't doubt though that he will be able to further refine it into a very good preamp though.

 

Quote

I got the SC valve preamp going. It sounds quite bright, not at all soft. The tonality of instruments is really nice and organic/natural, but I find it squashes dynamics and sounds a bit compressed. It also tends to emphasise the midrange somewhat - I expect this is due to the AC coupled feedback and generally small coupling caps used everywhere (even though I increased the output coupling cap values by 20x ......

 

[fas42]

55 minutes ago, Ralf11 said:

Let's have examples, either way (cold, clinical) vs. (warm, musical).

 

The sound of the components should be the sound of the recording - decent 'transparency' will mean that every album will sound like the equipment, and the methods used for capturing the event.

 

If you want, say, warm, musical just play a schmalzy pop crooner from the late '50s, with string backing - the sound is like Golden Syrup, from the combo of valves and tape media used.

[barrows]

@sandyk,  i am trying to keep things simple in order to educate.  Your level of technical understanding is higher than a lot of folks here, so my responses may seem overly simplistic to you.

 

But this does not change the facts: It is very easy to put a very good output buffer, the equal of any preamp, in the output stage of a DAC, it is the same type of circuit.

 

Of course there are  infinite ways to implement an output buffer, but all of these circuits can be as easily applied (and are) to the output stage of a DAC, just like they can to a preamp.  Additionally, the contemporary amplifier, in the vast majority of cases, is not difficult to drive properly.  Most common high end amplifiers these days feature input impedances of 30 Kohms or more.

 

I am not advocating that people get a bad DAC and then connect it directly to an amp and expect good sound.  I am advocating getting a good DAC...  

 

Additionally, there are many, very good preamplifiers which use so called "generic" output devices, including some very expensive models form the likes of Jeff Rowland Design, etc.  Of course my example also included discrete circuits using MOSFETs, apparently you missed that.  But in any case, I no longer ascribe to the audiophile myth (I used to, but exposure to some very, very good gear using ICs has shown me the error of my ways) that discrete is ALWAYS better, sometimes it can be, sometimes ICs in a good design can be better, despite being "generic".

[sandyk]

2 minutes ago, barrows said:

 Most common high end amplifiers these days feature input impedances of 30 Kohms or more.

 These days, many designers use the findings of people like Douglas Self who is the author of several Audio design handbooks, (e.g. Audio Power Amplifier Design Handbook 5th ed - D. Self (Focal, 2009) WW) and use an input impedance of 10K, with an even lower input impedance being desirable from the point of reducing the amplifier's D.C. offset.

I didn't miss the point of Mosfets, as I have previously used them in amplifiers, but prefer more recent silicon transistors, especially well matched dual devices and Bipolar output devices with an Ft of 30MHZ or higher. ( My DIY Class A Preamp uses 200MHZ Output devices and a bias of >100mA ,  Toshiba 2SA 1930 and 2SC 5171)

As far as FETs go, they aren't so easy to obtain these days, and often  have very wide tolerances. This may be fine for large companies though where they can request closer tolerance devices.

[cjf]

I've got three outboard DAC's at home. One has no volume control at all (Meitner MA1), one has your standard Digital Attenuator controlled via the front panel knob (Benchmark DAC1 USB) and the last device has both Digital and Analog Attenuators controlled via front panel knob (Lynx Hilo USB).

 

Speaking specifically about the DAC's with their own means to control volume level and driving an AMP directly, both of them SOUND better when their Analog outputs are fed thru my PreAmp verses driving the Amp directly. The extra flavor added to the sound after the signal passes thru the PreAmp is simply better to these ears in every way. Its not even close.

 

IME/IMO using my own equipment DAC Direct does sound Clean/Clear/Clinical & Very Digital. There is zero question you are listening to two speakers sitting in a room attempting to reproduce the original event in a very mechanical way. In contrast, with a PreAmp in the chain, one can on occasion forget about those speakers sitting in the room and possibly even be fooled now and again that a real person or instrument is playing within the listening space instead. Again, IMO/IME I dont get that feeling while listening to music in a DAC Direct configuration.

 

With that said, I have done a bit of experimenting lately with trying a software only volume control (JRiver 64bit) with these DAC's driving an Amp directly with the internal volumes set to full scale and this approach definitely beats  the sound of using the internal attenuation knobs of these DAC's in both Digital and Analog modes. I'm experimenting with this hooked up to my Office system and not my main rig but this software only volume does show more promise of offering better sound then the internal knobs do.

 

Some day I may get up the courage to try software only volume while hooked up to my main Rig but I must say I am VERY afraid of removing that CYA layer offered by my Analog Pre that is sitting nicely between a full scale output from the DAC on its way towards my Amps and Speakers. All it takes is a single Windows/JRiver Volume "Glitch" to bring about financial ruin. And we all know Windows/Jriver glitches are impossible and never happen...right?

[GUTB]

Here's a comment by Michael Fremer, writing for Stereophile:

 

"I've consistently found that running the signal into a separate preamplifier results in a musical picture that's more cohesive, more rhythmically gripping, and more musically holistic, even if all that is perhaps at the expense of ultimate transparency, and perhaps the loss of some detail. These are all personal value judgments that no audio reviewer can make for you."

 

Transparency is important, but quality audio is much more difficult to achieve than a low noise floor and lack of coloration.

[fas42]

29 minutes ago, cjf said:

Speaking specifically about the DAC's with their own means to control volume level and driving an AMP directly, both of them SOUND better when their Analog outputs are fed thru my PreAmp verses driving the Amp directly. The extra flavor added to the sound after the signal passes thru the PreAmp is simply better to these ears in every way. Its not even close.

 

IME/IMO using my own equipment DAC Direct does sound Clean/Clear/Clinical & Very Digital. There is zero question you are listening to two speakers sitting in a room attempting to reproduce the original event in a very mechanical way. In contrast, with a PreAmp in the chain, one can on occasion forget about those speakers sitting in the room and possibly even be fooled now and again that a real person or instrument is playing within the listening space instead. Again, IMO/IME I dont get that feeling while listening to music in a DAC Direct configuration.

 

With that said, I have done a bit of experimenting lately with trying a software only volume control (JRiver 64bit) with these DAC's driving an Amp directly with the internal volumes set to full scale and this approach definitely beats  the sound of using the internal attenuation knobs of these DAC's in both Digital and Analog modes. I'm experimenting with this hooked up to my Office system and not my main rig but this software only volume does show more promise of offering better sound then the internal knobs do.

 

 

This addresses the 'dilemma' of getting competent digital sound quite nicely - the nature of the beast is that digital sound a tiny bit askew can sound awful; and only when after every last issue is addressed will the sound snap into shape, fully. Analogue smoothes the sharp edges nicely, hence is more acceptable as an alternative to many - and a few extra analogue processing stages - the preamp - can do the same thing ... the tradeoff is that the "cotton wooled" version can never deliver the "big hit" of realism that pristine digital is capable of ... horses for courses ...

[Blake]

51 minutes ago, cjf said:

Some day I may get up the courage to try software only volume while hooked up to my main Rig but I must say I am VERY afraid of removing that CYA layer offered by my Analog Pre that is sitting nicely between a full scale output from the DAC on its way towards my Amps and Speakers. All it takes is a single Windows/JRiver Volume "Glitch" to bring about financial ruin. And we all know Windows/Jriver glitches are impossible and never happen...right?

 

Barrows is a good guy, very knowledgeable and experienced and I've always appreciated and followed his insight and input on this forum over the years.  So, I plan to do some experimenting as it has been at least 3 years since I compared direct vs. preamp.  I am open minded and I have a different DAC now so I'll give it a go. 

 

My only fear is exactly as you described above.  I have no doubt that if I end up preferring the direct method, one of these days I will forget to attenuate the volume via software, hit play and blow my speakers.  

[barrows]

2 hours ago, sandyk said:

many designers

I am curious who these designers are.  most amplifiers I see have higher input impedances.  Although it does not take that robust an output stage to properly drive a 10K input impedance either.  Anything <~100ohms should be fine.  As mentioned there are many DACs which fit that bill (Chord, Weiss, etc)

[barrows]

1 hour ago, cjf said:

Speaking specifically about the DAC's with their own means to control volume level and driving an AMP directly, both of them SOUND better when their Analog outputs are fed thru my PreAmp verses driving the Amp directly. The extra flavor added to the sound after the signal passes thru the PreAmp is simply better to these ears in every way. Its not even close.

What you are telling me is that either your amp sounds bad, or your DACs sound bad.  And you are covering up the bad sound by adding more (euphonic in this case) distortions from your preamp.  Do you really think this is the best way to getting the best possible sound?  Would not a better approach be driving an amplifier direct with good sounding DAC, or replacing your bad sounding amp (whichever the culprit may be).

[diecaster]

21 minutes ago, fas42 said:

 

....the tradeoff is that the "cotton wooled" version can never deliver the "big hit" of realism that pristine digital is capable of ... horses for courses ...

 

I would argue that "analog flavor" can deliver a bigger hit of realism since it often sounds more like what you would hear at real life venues. Every concert and event I have been to that uses amps/transducers (99% of them) presents more color/distortion than I will ever have in my home setup. Heck, our speakers at home have more distortion than a high quality tube preamp/amp combination will produce. Also, high quality tube preamps and amps don't necessarily give up much in detail and even harmonics sound much better than odd.