Differences in sound: DAC vs. DAC + Pre-amplifier

[sandyk]

9 hours ago, fas42 said:

From my POV, pretty obvious why ...they are a basket of weaknesses, full of switches, pots, and inputs and outputs that are not terminated, plenty of loose wiring; all of these need to be handled in the best possible way to not impact SQ.

???

 A decent preamp these days rarely needs more than perhaps a quality multi position ceramic switch with several wafers,(or relay input control) and a decent attenuator such as a Goldmund, DACT or Khozmo 48 position. It shouldn't matter if non selected inputs are terminated or not ,when both sides of the selected input are switched through. It should also have a relatively low gain of perhaps 3 times .

 Most high quality preamps these days don't use tone or balance controls , and shouldn't need to.

 Neither should they need Tape Outputs either, which also simplifies switching, or need an RIAA  Phono stage.

[sandyk]

6 minutes ago, barrows said:

@motberg,  Are you aware that LDR volume controls add lots of distortion?  

 

 

IIRC, some years  back, Nelson Pass posted some measurements in DIY Audio highlighting this problem .

[sandyk]

1 hour ago, motberg said:

The maker has posted also his distortion calculations and seems really low to me....

Not sure if the PS has any effect, but mine is powered by mains regenerator into LPS into 4 x LT3045 regulator

The Lightspeed has been on Stereophile Recommended Components list and gets great comparative reviews.

It certainly subjectively was much clearer to me than my Schiit Saga + in passive mode. (already sold the Saga +)

 

 I would suggest that you do a Search in DIY Audio for Lightspeed and Nelson Pass to see if you can find the posted measurements  of actual LDRs

[sandyk]

29 minutes ago, motberg said:

I already saw them... I am sure was well below audibility... remember some decimal points and zeros, etc...

 

 Your idea of audibility may not be the same as others who may have more revealing equipment.

 A Preamp/PA often has distortion levels well below that of most volume controls and many attenuators.

For example, both my DIY Class A Preamp and 15W/Ch. Class A Power Amplifier have distortion figures of well below .0006%

 

https://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-passive-preamp-373.html#post2386530  # 3726 

The quoted figures are far from inaudible when combined with a low distortion Preamp/P.A. 

" 0.25 % THD for -20 dB of attenuation."  

 I saw also that George HiFi also went on the defensive : 

" Get your head out of these finite distortion measurements, and listen to what your ears are telling your brain" 

[sandyk]

3 minutes ago, motberg said:

what is the threshold of audibility ?

That depends on your training, experience,  and the Signal to Noise Ratio of your equipment. Naval Sonar operators can even hear things below the noise floor , as both  Miska and Paul R. can verify

[sandyk]

33 minutes ago, motberg said:

Any scientific back up to the claim 0.25% THD as tested in your example is detectable by average humans?

 I suggest that you do some research for yourself for a change. There is plenty of information available on the subject .

[sandyk]

1 hour ago, motberg said:

I have not seen any valid study done where the THD was reported detected at less than .5%. That is why I was asking, since you seem to be sure 0.25% is audible.

 To quote well respected Audio Amplifier designer Douglas Self :

Quote

Digital audio now routinely delivers the signal with less than 0.002% THD, and I can earnestly

vouch for the fact that analog console designers work furiously to keep the distortion in long

complex signal paths down to similar levels. I think it an insult to allow the very last piece of

electronics in the chain to make nonsense of these efforts.

I would like to make it clear that I do not believe that an amplifier yielding 0.001% THD is going

to sound much better than its fellow giving 0.002%. However, if there is ever a scintilla of doubt

as to what level of distortion is perceptible, then using the techniques I have presented it should be

possible to routinely reduce the THD below the level at which there can be any rational argument.

 

Audio Power Amplifier Design Handbook 5th ed. - Douglas Self p.21  Extract

 

Note that he is talking about distortion figures, not 10 , but  >100 times less than you have stated .

[sandyk]

9 hours ago, DuckToller said:

Bonjour Alex,
please allow me to ask, if you believe these figures (0,002%THD) are audible for common audiophiles (60+ years), the majority of whom may not have been able to meet the requirements for the job as Naval Sonar operators even at young age and therefore had to forego the special training associated with it?
Stay safe and sound, DT

You don't need special training to hear distortion, unlike the Sonar requirements.

Quite a few DIY Audio members were able to hear clear differences between the different states of the attached amplifier with front end modifications. The measurements were posted in a DIY Audio thread by a member from Melbourne. See also :

https://www.diyaudio.com/forums/solid-state/134221-silicon-chip-200watt-ld-amplifier-2.html # 13 and 15

They were also able to hear clear differences with Front End balancing as in the attached link to a DIY Audio thread where Nelson Pass was also a participant.

https://www.diyaudio.com/forums/solid-state/133018-current-mirror-discussion-15.html

[sandyk]

39 minutes ago, DuckToller said:

Alex,
I may qualify your answer sadly as smoke and mirrors rather than a substantial response.
Reading the old DIY threads in consideration of my question was simply a waste of time.
My full answer to your post  will arrive tomorrow in the objective-Fi section, as I do not want to derail this thread further.
Stay safe & sound, DT

Don't bother.

I posted more than enough information already in an area where this was not deemed necessary.

I want nothing further to do with a member like yourself who has already made it crystal clear that he wishes to see me banned from the Objective area, and by the look of it the forum itself .

Any replies from you to me, or quotes from me in that area will be ignored and remain unread.

 

Stay safe & sound

[sandyk]

Re my post #112.

 The Amplifier measurements that I showed were of a published amplifier design from Silicon Chip magazine  with typical Distortion measurements as shown on the front page of the magazine.

 All of the DIY Audio members participating in the threads were hearing an improvement in measured distortion below the typical .002% quoted by the magazine as they were experienced DIY constructors , some of who even used closely matched semiconductors for a further improvement .

It should have been obvious from the posted measurements that the distortion figures were already very low.

[sandyk]

46 minutes ago, barrows said:

 On most DACs and preamps I look at these days, the output buffer is often the same (an IC OPA of some variety, with a lowish value series resistor).  

 

 That has been my experience as well, as many opamps (LME49720/LM4562 etc.) do not like to directly drive capacitive loads of >100pF.

A typical series resistor value appears to be 100 ohms.

[sandyk]

4 hours ago, barrows said:

There are of course some very unusual exceptions, but for the most part, DACs have output z at 100 ohms and often less, and amplifiers these days are usually over 50 kOhms input impedance, so no problem.

 

 Actually, many Power Amplifiers these days have an Input Impedance of 10K to 20K which usually results in improved S/N as well as contributing to a lower DC offset.  e.g. Audio Power Amplifier Design Handbook 5th ed - D. Self.

[sandyk]

9 hours ago, Kimo said:

 

My DAC has a fully balanced output of 300 ohm per phase and my amp has a fully balanced input of 94K.  

 

Do you see any problem with these numbers?

 

 I don't see any problems provided that the interconnects aren't too long.

[sandyk]

4 hours ago, barrows said:

I am not aware of "many" high end power amps with input impedances of 10-20 K?

 

Hi Barrows

These are more recent higher performance designs as per the research by Douglas Self, and variations used in the published designs from Silicon Chip (Au.) magazine etc. , which has published designs with a typical distortion of .0006% ,and a further improvement when using matched devices in the front end. The lower input impedances also markedly reduce the DC offset at the output due to the bias currents of the LTP ,  meaning that no adjustment is normally needed to reduce this provided that the LTP ( Differential Pair) devices are reasonably close in HFE. 

Please check your PMs.

Regards

Alex

[sandyk]

10 minutes ago, barrows said:

Sure, but is not this discussion about real world amplifiers people generally own and can purchase, not theoretical designs, or obscure DIY efforts only available to a few hobbyists?

 

Douglas Self's designs are commercially available from The Signal Transfer Company.

 You will also undoubtedly see the use of his published findings has trickled down into other less well known commercial amplifiers.

[sandyk]

45 minutes ago, barrows said:

@sandyk,

 

Yes, but that does not make this statement any closer to being accurate:

 

"many Power Amplifiers these days have an Input Impedance of 10K to 20K"

 

I would also suggest that for the purpose of this discussion, even an amp with 10K input impedance can be driven properly by many, many DACs available these days.

 

Yes, a DAC with a 100 ohm output impedance can successfully drive an amplifier  with a 10K input impedance, but a Power Amplifier with a 100K Input Impedance will have more HF rolloff with longer interconnects . These days, most power amplifiers with such a high input impedance use Vacuum tubes .Neither is it good practice these days to use such high impedances with solid state amplifiers due to Johnson noise. It is non intuitive to use a high resolution 24 bit DAC  with a Power Amplifier which isn't way quieter than the requirements needed for Red Book CD. 

[sandyk]

7 hours ago, barrows said:

All are for balanced connection, which I consider the norm these days, as most DACs we are talking about here have balanced outputs.

 

 I would put it to you that the amplifiers that are in common use by the vast majority of consumers do not use balanced topology, as do the vast majority of affordable commercial DACs, some of which MAY provide this facility , but is often not used by typical consumers.

You appear to be taking an elitist position here, as there is very little, if any, advantage to Balanced Topology in most domestic situations,where relatively short interconnects and speaker leads are used.

 

[sandyk]

31 minutes ago, barrows said:

Alex, I just did not understand what you keep posting these things?

 You appear to be under the impression that the majority of members are using balanced topology.

 I would suggest that they are only owned by a relatively small percentage , probably no more than 20% of our members and readers, as they are simply not necessary in a typical domestic situation.

 My posts have everything to do with improving the performance of the analogue area using a Preamplifier etc. vs. using Digital Attenuation, the quality of which will vary depending on the way it is implemented.

Until there is standardisation on the output levels of DACs ,and the Input levels and gain of various Power Amplifiers, and no longer the need to listen to other legacy formats such as Vinyl. FM Stereo etc. , a direct connection between the DAC and the Power amplifier is not always the best way to go for many members, and may even lead to degradation in a few cases .

 

Perhaps we should simply agree to disagree on this issue ?

[sandyk]

5 minutes ago, barrows said:

In my opinion, you are living in the long past:

 

You could have simply agreed to disagree as I suggested , but possibly due to commercial High End product affiliations ,  you chose not to.

My experience ,like quite a few other members is very different to yours in this area, where I have been able to directly compare components in systems worth >$100K in well set up rooms using both Digital attenuation and Preamplifiers (Au$50K) so I will leave it at that.

 I will not be responding further in this thread, and I would hope that you choose to do the same.

[sandyk]

5 hours ago, barrows said:

The addition of a preamp is adding new distortion harmonics to your playback which are the cause of the additional "body" which you perceive.  So, the preamp is adding a coloration which is not part of the source recording.  

 

I apologise for feeling the need to again rejoin the discussion that I had hoped would result in us choosing to disagree.

 

Rubbish. You have painted yourself into a corner. Many high quality Preamplifiers these days have distortion figures with 3 Zeroes, with some approaching 4 Zeroes. My own DIY Class A Preamplifier for example has <.0006% distortion, a -3dB bandwidth of 1.5MHZ, is considerably lower noise than most and is also fully DC coupled .
I doubt that any of the Objective crowd here would even agree that distortion much below .001% can even be noticed by the average Audiophile. In fact one of them started a thread about it in the forum's Objective area.

What many EEs and designers refuse to accept, is that the PSU area of a Digital device is every bit as important as an Analogue device, and perhaps even more so. Many use PSUs with the output impedance considerably lower in the >100KHZ to 1MHZ area than at the low end. This often results in a sound with a great soundstage, but a little cold and clinical sounding with very little NATURAL warmth, even though the PSU itself may be a very low noise design such as achieved with voltage regulators such as the LT3045 . 
  I feel sure that Alex C also agrees with the need for a very low noise PSU with a low and flat output impedance from almost DC to 1MHZ.

This cold and sterile sound in many DACs and Media players is an ongoing criticism of Digital by many members, and is also part of the reason for the resurgence of Vinyl.
Incidentally, I have heard a friend's Bricasti M1 in my own System, and my DIY DAC and Class A Preamp easily outperformed it. So much so, that my friend who was a Telstra Engineer investigated forcing it's output stage into Class A operation.
 This Bricasti M1 DAC was actually sold to my friend by David when he upgraded to a Gryphon Kalliope.

[sandyk]

35 minutes ago, sandyk said:

Many use PSUs with the output impedance considerably lower in the >100KHZ to 1MHZ area than at the low end. This often results in a sound with a great soundstage, but a little cold and clinical sounding with very little NATURAL warmth, even though the PSU itself may be a very low noise design such as achieved with voltage regulators such as the LT3045 . 

 To further expand on this statement. Quite a few members in other areas of the forum, such as Cornan, have even used generic implementations of " daisy chained"  ultra low noise LT3045 etc. voltage regulators to try and increase HF detail (artificial HF detail ?) in lacklustre sounding streamed digital files.

[sandyk]

7 hours ago, barrows said:

 If one prefers a colored sound, rather than an accurate one, that is fine with me.   

 Here we go again !

 

Keeping repeating it, is not going to convince a single member that it is always true.

 The same as non Balanced is always inferior to Balanced in a proper design using short well constructed interconnects.

[sandyk]

5 minutes ago, One and a half said:

unbalanced works in phono cartridges since there’s no loop to create,

 In my case there should be no loop because the reference ground is extended all the way back from the 10 ohm earth lift resistor in the P.A, then switched through the Preamp to the DAC

[sandyk]

1 hour ago, CG said:

If you go to your favorite search engine and type in "distortion cancellation mechanism series amplifiers" you'll get "About 3,140,000 results".  

 I feel cheated. I only got "About 2,730,000 results  (0.45 seconds) "

 

 For anyone interested in learning more about many of the amplifier distortion mechanisms, a good reference is

Audio Power Amplifier Design Handbook 5th ed - D. Self (Focal, 2009) where he details 11 Different types of Distortion

 

The distortion mechanisms
Distortion 1: Input stage distortion
Distortion 2: VAS
Distortion 3: Output stage distortion
Distortion 4: VAS-loading distortion
Distortion 5: Rail-decoupling distortion
Distortion 6: Induction distortion
Distortion 7: NFB take-off distortion
Distortion 8: Capacitor distortion
Distortion 9: Magnetic distortion
Distortion 10: Input current distortion
Distortion 11: Premature overload protection

 

(VAS  = Voltage Amplification Stage)

[sandyk]

6 hours ago, Miska said:

 

He also had nice series of articles on these topics on the Electronics & Wireless World magazine back in the days.

 

My current amplifiers are actually designed by him (pre- and power)…

 

 Hi Miska

Yes, I have seen some of his earlier articles.

 Both my >15W/Ch Class A and Class A Preamp embody his principles, as well as very low noise (4uV) separate regulation for the P.A. front ends and being completely DC coupled with a monoblock type construction, although in the same metal rack case, and separate regulated power for each channel of the P.A. (2 x 21-0-21V windings on the same screened toroidal transformer) and individual external toroidal transformers for both channels of the Preamp. All of the main power is in a separate 2U rack case with the Preamp fed 2 x 18-0-18VAC, and the P.A. fed 2 x regulated + and - 20V

 

Regards

Alex