Digital Audio and Amplifier Noise Floor Comparison - Is 16bit/44.1kHz All We Need ???

[sandyk]

7 hours ago, Shadders said:

Hi,

The specification is A-weighted, so please correct if wrong, removes noise due to the filter. The ASR review probably does not use A-weighting.

Regards,

Shadders.

Hi Richard

The Benchmark is not alone in giving decent Unweighted and Weighted noise figures these days , with even many kit amplifiers performing very well at a cost, typically including metalwork , transformers etc. of <Au $1,000 

 Even the recent less ambitious Silicon Chip magazine designed 200W SC200 Amplifier specifies Signal-to-Noise Ratio: -116dB unweighted with respect to 135W into 8Ω(20Hz-20kHz)

I have attached the specs for the previous more ambitious SC ULD3 amplifier (123dB Unweighted)

from March 2012, as well as their DAC from way back in Sept.2009 which is capable of further improvement using more recent voltage regulators etc.

 Undoubtedly there are numerous commercially available amplifiers and DACs that easily surpass the performance of these older designs these days.

 

Regards

Alex

[sandyk]

6 hours ago, Shadders said:

Hi,

Sandyk can confirm this, but the specification for the SC200 was measured for the completed amplifier - not simulation. The ULD was also the measured performance. If you purchase the kits/PCB, and follow the article instructions, then you will achieve the measured performance.

Regards,

Shadders.

Richard is correct.

Note also that in the specifications for the  S.C. ULD 3 they also quote typical and maximum distortion figures.

Silicon Chip magazine does not go out of their way to select matched pairs either, so their figures can possibly be improved on a little.

 The kits are supplied with generic electrolytic and normal type capacitors, so it is also possible to use higher quality types in their place, as well as the use of very low noise resistors such as naked bulk metal film resistors in areas such as the gain setting, and use matched .1% resistor pairs in other areas such as the differential pair and current mirror. In fact, you can also purchase a few extra devices as used in the differential pair and current mirrors areas later if you are so inclined, and retrofit closely matched pairs in those areas for a further small improvement. All this can be done at quite a modest additional expenditure.

 All of this is something that I normally do, and the improvements can be heard.

 I don't have access to the original article for the SC200 which is mainly based around the older SC ULD3/4 but uses some surface mount components.  I can however provide full relevant info for the SC ULD3 via PM if requested . 

[sandyk]

37 minutes ago, Shadders said:

This is the discussion on whether Red Book CD (RBCD) is all we need fro audio reproduction given that amplifiers may or may not have a lower noise floor.

 

Any modern amplifier that doesn't have a S/N in EXCESS of 110dB is poorly designed !!!

[sandyk]

15 minutes ago, psjug said:

  Maybe amplifiers can be better than 16 bit equivalent, but doesn't room noise kill the possibility of realizing that much dynamic range in practice?

 

 Why ? Many people listen to music at quite high SPLs, often in excess of the requirements of the source material.

Why limit this to just RBCD when many people even listen to TV via their main system, and that may also include music videos .

 With TV audio the max. level is limited anyway to suit the medium, but dialogue etc,. is often listened to at higher than the original voice levels. 

[sandyk]

24 minutes ago, esldude said:

Thinking a sound level meter shows noise levels in my listening room of say 35 db SPL means that sets a lower limit is deceptive.  Most room noise is heavily weighted toward low frequencies.  If you split the bands up like our ears do, in our most sensitive frequencies 3-5 khz most rooms are anywhere from 0 db SPL to 10 db SPL in that range.  Some treated studios can be -10 db SPL in that range. We also can hear into noise 10 or 15 db as well.  So as a basic starting point I would suggest we assume 0 db SPL as our in room noise floor.  

 

Yes, that is food for thought.

 Let's not get into the area of how loud breathing can sound though.

Quote

If you’re happy with Redbook, I don’t think you’ll find anyone here that will say you’re wrong, because you’re not. - SJK

That is a very valid point, with a large % of members preferring high res and DSD over RBCD. 

[sandyk]

1 minute ago, psjug said:

 

I'm not sure I am following you.  Are you saying it is nice to have extra amplifier dynamic range to account for level mismatches when paired with multiple sources?  I can buy that argument.

In part. Many sources such as Vinyl and Surround Sound, especially in live performances from DTV may  have channel levels well below that of the nominal 2V of RBCD

[sandyk]

4 minutes ago, Hugo9000 said:

Isn't there a meme about hearing people breathe?  Like "if I can hear you breathing, I have fantasized about your death" or something?  Or is it chewing that bothers most people?  I personally don't want to hear chewing or breathing!

 

Sorry for the OT!

 You can often hear the breathing of many recording artists. An example of that is " Queen-Another One Bites the Dust" where with a good system you can even hear the spittle in Freddy Mercury's throat . (so I have been told )

[sandyk]

27 minutes ago, psjug said:

But if you hear your own breathing, what does that mean?

 

 Perhaps due to Asthma/Bronchitis, Influenza, Sex ?

[sandyk]

12 minutes ago, fas42 said:

What is important is to have a electronics chain where the gain can be varied by a large amount with no deleterious effects, such as starting to hear hum or conventional circuit noise

 

 Assuming that your hearing isn't too aged, if you can hear hiss or hum from a Speaker with your ears close to it, then it WILL degrade low level material a little .

[sandyk]

33 minutes ago, psjug said:

Keeping it simple - if playing a silent track from your highest level source (or maybe your preferred source) at full volume is not audible, doesn't that mean your amp has all the SNR that you need?

 

That will depend on  whether you are at the listening position or with your ears close to the speakers.

[sandyk]

23 minutes ago, esldude said:

If from the listening position, I'd say it is fine from the listening position.  

I disagree.

 I have been able to hear a small but worthwhile improvement from the listening position after further reducing the already very low noise level contribution from a DC Offset Corrector, which wasn't audible from the listening position, and really only JUST visible at the Preamp's Output at maximum gain and a 1K resistor across the Input, with  a CRO at maximum gain PRECEDED by a Low Noise 10 x gain battery powered Preamplifier !

[sandyk]

36 minutes ago, PeterSt said:

The latter picture plays a 24 bit file. When 16 bits is played, 20dB of noise adds (I don't have a picture of that for this power amp measurement).

 

 Probably a silly question, but what happens when you add Dither to a 24 bit file ?

[sandyk]

Interesting.

Thanks Peter.

[sandyk]

10 hours ago, psjug said:

Even though you were trying to reduce noise, and did so, how do you know that the improvement that you are hearing can be attributed to noise reduction, and not an improvement in something else like some form of distortion?

psug

I can only go by what I saw on the screen of the C.R.O both before and after the changes. The original DC offset corrector from 1987  that mine was based around  used a TL071 I.C. and you could also see and hear the improvements simply by changing to lower noise opamps.

Initially I changed to a AD744, then finally a low noise OPA134.  Another constructor of my design suggested that I change from a 2n2 capacitor across R8  to a  4n7 as he had noted a further small improvement;. I also noted a further minor improvement, although the C.R.O. was unable to confirm this visually.

Any residual noise from the Offset Corrector goes into the base of a transistor in the differential  input pair.

Incidentally, this amplifier and the Preamp versions have a distortion of <.0006 %, so I doubt that you would readily  hear any further reduction in distortion figures.

 I use DC Offset Correctors because both my Class A 15W/Ch. and Class A Preamp/HA are fully DC coupled.

i.e. there are no input capacitors or a capacitor in the gain setting areas.

Alex

[sandyk]

7 hours ago, psjug said:

Did you only change the op amps in one of the circuits, or did you replace the bottom circuit with the top circuit?  I would think it is possible that what you hear is related to better power supply rejection, or from the top circuit providing more complete removal of the AC in the input.

The bottom circuit was part of the original design from 1987 that I constructed. There weren't that many low noise opamps to choose from back then. My own Class A fully DC coupled preamps and 15W Class A were constructed many years later ,where I realised that the original circuit could be markedly improved in order to reduce noise going back into the differential pair,  as well as provide a much smoother correction with abrupt volume changes by using the 2 stage input filter.  Opamp noise becomes a problem with such high gain used. I also used a very low noise 10 x battery battery preamp ahead of my CRO to confirm the initial improvements with my Preamp.

 Later improvements could only be verified by extended listening, as well as reports from other constructors of my design.

 The Offset Corrector can be seen in the bottom right hand corner of the Preamp/HA PCB

[sandyk]

10 hours ago, psjug said:

So to get back to whether you are hearing the improvement because of lower noise or something else... 

Don't you think that greater attenuation in the audible band in the revised circuit  should result in lower overall distortion from the power amplifier?  And so maybe this is the improvement you are hearing, not the lower noise?

I believe that it is both, because the added 4n7 capacitor across the 1M resistor was mainly aimed at further reducing the HF noise  from the opamp itself at such a high gain, and  resulted in a further small improvement. The original version didn't have this capacitor, but a later version had 2n2 added. Feedback from other members resulted in me increasing this to 4n7.

Not too many are likely to agree that we can hear a further reduction in distortion below the already very low level of < .0006%

 

[sandyk]

35 minutes ago, psjug said:

Is this the 0.0006% figure for the op amp?  The distortion I was talking about would be from the residual of the filtered power amplifier's waveform (audible frequencies), which is part of what is sent back to the amp for the purpose of offset correction.  In the original circuit (bottom image), I think this has a 90 degree phase shift in the audible band, which can't be good.  In the updated (top) circuit, the two pole input filter gives a 180 degree phase shift, so I would guess this and also the much greater attenuation by the input filter would give a very good improvement, much more than the lowering of the noise.  Correct me if my thinking is wrong; I am not very experienced in audio circuit design.

 

No, the <.0006% figure is for both the Class A Preamp/HA and the 15W Class A amplifiers.

The original Silicon Chip 15W Class A  article that it was partly based around, but never as a Preamp/HA, gave those figures as typical, but my version uses way better matched devices and resistors etc . as well as dual mono construction, DC coupling,  separate external transformers and a very low noise PSU PCB (<4uV) for the front ends as well in the 15W Class A P.A. The Preamp/HA uses the same low noise PSU PCBs for the individual channel PCBs .

 A friend of mine confirmed my Preamp as <.0006% distortion , but test equipment used couldn't go lower, so it is likely to be better than .0006%. The photo was of course just the PCB for a single channel.

 

Click on the image several times for a larger than life image.

[sandyk]

2 minutes ago, fas42 said:

A rule of thumb I use is that an amp design has to be capable of intrinsically doing 200KHz

 

A U.S.A. constructor of my Class A Preamp/HA measured it as -3dB at 1.5mHz

[sandyk]

2 hours ago, sandyk said:

 

A U.S.A. constructor of my Class A Preamp/HA measured it as -3dB at 1.5mHz

Correction.

-3dB  @ 1.5MHz

 

[sandyk]

 

For know-it-alls like Ralf11 who obviously thinks that I am making this up:

 My Class A Preamp is biased into Class A at a little over 100mA, although it can go much higher, and  It is capable of directly driving a 75 ohm correctly terminated cable, and will even pass through VHS quality Video.

[sandyk]

25 minutes ago, Ralf11 said:

 

what's with the personal attacks, twinkie?

 

 Work it out for yourself Muffy from your posted reaction to my posted measurement.