John Curl's Blowtorch preamplifier part II

[fas42]

The silliness of the SACD vs. CD argument of course is confusing the messenger with the message. The CD is an information carrier, as is the SACD, and DSD. And that information is totally sufficient in each of those cases to provide as detailed and "correct" a picture of the encoded event as anyone could want. Where the faltering occurs is that the mechanism that does the real time looking up of the information is not too brilliantly implemented much of the time, and "roughens" up the message at the time of delivery.

I've done enough experiments to be thoroughly convinced that I could take the highest resolution, "audiophile" recorded digital files, DSD128 or PCM 352/24, drop them down to boring ol' CD information density level, and in fact go yet another step, turn them into high quality MP3 files. And then reverse the operation, translate from that MP3 right back up to the original high resolution format. Now have the original, and a "severely corrupted", multiple generational degraded version thereof - have people play the two on the "best", most discriminating setup, AB style, and would happily put money on "golden ears" not being able to differentiate them ...

A couple of days ago I downloaded a demo track from a new, "audiophile" website doing double speed DSD downloads -- ultimate resolution versions from master tapes. And what were the highest frequencies that had any meaning in that track? About 23KHz - the striking of a metallic percussion instrument. I separated out all content above 20kHz, and replayed only that material at maximum volume, with my ear pressed hard against the driver. And what did I hear? The hissing and slight gurgling of the electronics, precisely the same as when I pressed the stop button ...

Frank

[kgrlee]

Originally Posted by john curl

OK, I computed the distortion coming from the Blowtorch, based on its rated distortion at output, at the listening levels that I use.
I came out with: 1/1million % 3rd to 1/1000 % third, second slightly higher at lower levels.

JC, got some measurements to 'prove' this MYTH?

You seem fixated on 'revealed knowledge' as expounded by Yourself and scorn measurements of any sort .. both those you have promoted in the past ... as well as other peoples.

If you can't measure distortion, Sam will be happy to oblige to test Blowtorch for you.

There are many factors that are vital to low distortion and good sound ... such as good decoupling and earthing practice that are MORE important than using Golden Pinnae parts hand carved from solid Unobtainium by virgins.

Theoretical calculations mean nothng if basic principles are ignored.
_________________

Most speakers produce anything but a nice resistive loading on the circuits and many are much worse than that at least in the reactive and resistive loading.
Can someone compare a circuits distortion product using a typical speaker vs one where the impedance and inductance curve has been corrected to produce a resistive loading with a conjugate network that corrects for these problems. How much does this affect the distortion levels as measured at the output of the amplifier?

Hornman, I can confirm that many (all?) Golden Pinnae amps, (including some designed by JC which he now disowns) have worse distortion into real speakers.

Often they will show signs of oscillation on parts of the waveform and this is dependent on the thermal and signal history too.

[kgrlee]

Originally Posted by john curl

KINKS:

Can you explain what we are seeing? Test conditions? Load? What are you measuring? What are the 2 curves?

[simon7000]

Originally Posted by Waly

Huh? Unless you are redefining the "ripple" concept, the 50p 7815 (hope this qualifies as "a lowly 15 volt IC supply") has 70-80dB ripple rejection @120Hz.

Regulation was not under discussion, but:

TI's is around 55 db at 3 kHz, ST's is under 45, A good opamp such as the AD797 adds another 95 dB. Now ST lists 90 uV/V broadband noise.

But when you use a regulator IC you often have ripple much higher than 5%. (3 volts is typical before a regulator.) Add Fletcher Munson weighting to the energy from a real rectifier and what do you think the final S/N ratio is? (try it around 3K)

Scott, 3V -55 dB -95 dB -40 dB (harmonic level at 3K re 120 Hz as measured on a DC supply) + ? dB (preamplifier gain) + ?dB (amplifier gain) / 2.83 V (1W 8ohms) = -? dBw. That's my math before you ask. So what is the loudspeakers sensitivity. Headphones would show it, if used as a microphone or phono preamp under I think most all conditions! (90 dB/W loudspeakers at 10 cm. also.)

Oh don't forget the noise goes into all the preamp stages but adds mostly to the input stage S/N.

[elektroj]

Originally Posted by Esperado

Mainly silicon, i believe
<snip>

Topology, if I'm not mistaken, is similar to Vendetta's first stage.

Best,

[Waly]

Originally Posted by simon7000

Regulation was not under discussion, but:

TI's is around 55 db at 3 kHz, ST's is under 45, A good opamp such as the AD797 adds another 95 dB. Now ST lists 90 uV/V broadband noise.

But when you use a regulator IC you often have ripple much higher than 5%. (3 volts is typical before a regulator.) Add Fletcher Munson weighting to the energy from a real rectifier and what do you think the final S/N ratio is? (try it around 3K)

Scott, 3V -55 dB -95 dB -40 dB (harmonic level at 3K re 120 Hz as measured on a DC supply) + ? dB (preamplifier gain) + ?dB (amplifier gain) / 2.83 V (1W 8ohms) = -? dBw. That's my math before you ask. So what is the loudspeakers sensitivity. Headphones would show it, if used as a microphone or phono preamp under I think most all conditions! (90 dB/W loudspeakers at 10 cm. also.)

Oh don't forget the noise goes into all the preamp stages but adds mostly to the input stage S/N.

Are you talking noise or ripple here? Or none of the above?

But when you use a regulator IC you often have ripple much higher than 5%. (3 volts is typical before a regulator.)

Where are you pulling this 5% number from? I'm looking in the 7815 datasheet and it says ripple rejection better than -60dB.

[SY]

Originally Posted by Waly

Where are you pulling this 5% number from? I'm looking in the 7815 datasheet and it says ripple rejection better than -60dB.

I think he's talking about raw supply (before the regulator) noise. By bringing 3kHz in, he sorta forgets the weighting of the terms of that order in the Fourier series representing 120Hz ripple...

[Bonsai]

Originally Posted by Esperado

I used the same concept for my protection circuit and as a dynamic distortion magnifier to look and listen to them.

I think this idea could help to design an OPA, with a reduced open loop gain and a high open loop bandwidth, in order to reduce further the distortion.
But i don't know if it is possible to fine tune enough resistances values on the wafer.
There is several known tracks for error corrections, i wonder why they are underused.
http://www.tubecad.com/2010/04/04/Tringlotron.png
The Tringlinator: a MOS-based Tringlotron amplifier

John asked how it sound.
My thoughts:
First, you can only remove around 20db of distortion this way (but it is not so bad). you are limited by stability.
Second, the good one, the OPA i used (if you use some) does not add its signature.
Third, as i tested it on a yet very good amp (while mid-fi :-), i am not sure of an obvious listening change, while measurements where better. It would be interesting to test this on a amp with more previous THD than mine.

Just AFEC it!

[Esperado]

Originally Posted by fas42

The silliness of the SACD vs. CD argument of course is confusing the messenger with the message.

Yo ! I was happy to know that we can make recordings (and save them for the future) in a overkilling format.
From there to claim that CDs are just garbage seems (a little ?) excessive.
I have wonderful CDs witch sound absolutely wonderful. And i can even enjoy MP3s in my phone, listened across my Koss Porta pro (i love deep basses :-)
May-be i'm more involved by the music than the ultimate perfection of my (midle-fi) system ?
This said, if i understand well, and in order to be hype, i have to pretend that there is no life below 24/96, with the exception of vinyls which are the audio nirvana despite the surface noise, the clics, the distortion and this incredible distance with the master copy i own on tape ?

[Kindhornman]

Fas42,
I follow you on the down sampling of a high res file down to the red book cd level, that would seem plausible, but to then turn that into an MP3 and say that you can get back to where you where I don't see how that is possible. The MP3 format is a lossy format, how do you not lose information if you have losses in the basic format? Something has to give to in effect zip the music down to MP3 or am I missing something here? Now if you said you used a flak file or Wave file with no loss I can accept what you are saying, but MP3?