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Old 6th July 2013, 01:32 AM   #871
fas42 is offline fas42  Australia
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Originally Posted by sandyK View Post
Hi Frank
The problem here, as Owdeo has already pointed out, is that PCBs like this are not DIY friendly as regards modifications
...
Kind Regards
Alex
Ciao, ...

Yes, I know the dilemma with modifying in tight areas - I've done my fair share of ending up with bits of copper track lifting and fracturing, and parts of the circuit end up looking like the dog's breakfast. However, to truly assess whether a particular configuration is 'superior' to another I've found that the only way to make a final judgement is to restore full integrity every time and let it, and me, fully stabilise before making up my mind.

It's a right pain, and I give up in disgust at times, for a period -- but I've learnt this is the only way I can make decisions that are 'correct' in the long term ...

Cheers,
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Old 6th July 2013, 01:33 AM   #872
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Originally Posted by abraxalito View Post
But that's a deflection away from the question, which I'll state again. When you mentioned 1% as your figure of distortion, were you talking about THD or some other measure?
I was talking about distortion as a whole, not THD neither IMD alone, as they both occur at the same time when listening to a real sound (like music). But the resulting total distortion value is, at least, as high as the highest value.
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Old 6th July 2013, 01:43 AM   #873
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Originally Posted by ezavalla View Post
I was talking about distortion as a whole, not THD neither IMD alone,
I can't see how you can give a 1% figure for 'distortion as a whole' as no such measurement exists that I'm aware of.

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as they both occur at the same time when listening to a real sound (like music).
This is of course the case yet if you read the Belcher article I mentioned you'll see that he mentions when the spectrum is rich in tonal content (as real music is) the IMD dominates over the THD by at least an order of magnitude.
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Old 6th July 2013, 02:11 AM   #874
jcx is offline jcx  United States
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I have read the Belcher article, linked to it several times myself - and I don't recoginze at all the interpertation and weight you seem to give it

it was significant for loudspeakers with % distoriton - the text claims correlation with listening test went away at better than ~ -30 dB "noise fill" numbers

I believe Scott Wurcer posted an example soundcard loopback with 30? multitones that showed little more than the window noise floor anywhere but signal bins - no exotic op amps, not even Class A bias required - very vanilla electronics doesn't show any new behavoir with the Belcher test for audio multitones

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Old 6th July 2013, 02:34 AM   #875
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Originally Posted by abraxalito View Post
I can't see how you can give a 1% figure for 'distortion as a whole' as no such measurement exists that I'm aware of.
I just did a "dirty addition" of both output results, as it is the only point where I can do an addition (choose among linear, RMS, whatever). As you know, both THD and IMD generation are non-linear processes and I won't try to combine them to get a more correct result , even when they probably are a bit interdependent (hummm....nice task )
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Old 6th July 2013, 07:05 AM   #876
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Originally Posted by jcx View Post
I have read the Belcher article, linked to it several times myself - and I don't recoginze at all the interpertation and weight you seem to give it
The operative word here is 'seem'. The interpretation and weight I am giving it diverges significantly from your perception of that interpretation and weight I conjecture, based on previous interactions we've had over the years.

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I believe Scott Wurcer posted an example soundcard loopback with 30? multitones that showed little more than the window noise floor anywhere but signal bins - no exotic op amps, not even Class A bias required - very vanilla electronics doesn't show any new behavoir with the Belcher test for audio multitones
I'm not proposing the Belcher test myself, just drawing on his understanding of the nature of distortion in real world music signals fed through electronics. What led to the choice of 30 tones? To me this doesn't look representative of a musical stimulus, at least not the kind of music I listen to (orchestral, choral).
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Old 6th July 2013, 08:19 AM   #877
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Originally Posted by fas42 View Post
The 'why' is that such issues can inject low level distortion into the final output sound, which determines whether one setup sounds "better", subjectively, than another - the very thing that one uses to say that one opamp is better than another ...

Having myself spent years playing with audio gear, attempting to resolve the issues being discussed here, it's a no-brainer to have absolute integrity with every connection ...
Ok, it's not really a technical argument then, just a vague speculation that "low level distortion" is being injected due to supposedly faulty contacts. I can see how with say a power amp's speaker terminal connections a soldered contact might be better than crimp lugs due to the impedances and currents there and a small non-linear contact resistance being a significant proportion of the total.

But with a preamp we are talking ~kR impedances where any slight non-linear joint resistance is a tiny fraction of that of the linear parts. And you haven't even explained why a turned-pin gold plated IC socket will not make good connections to the IC pins.

Are you saying that you're 100% sure that the character of sound of this design and of opamps themselves is purely a result of poor connections? Would the major hassle of unsoldering all those sockets and soldering in the opamps 100% make the SQ of this design equal to that of the others? Surely you can see there's a logical flaw in that argument - swapping opamps produces a different sound but they are in the same sockets! Furthermore, the other opamp preamps I'm comparing it to contain the same dreaded socketed ICs and yet they are ok
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Old 6th July 2013, 08:23 AM   #878
owdeo is offline owdeo  Australia
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Originally Posted by abraxalito View Post
From what I can fathom from a quick Googling, looks like its using sucky S-D DAC chips. So a complete re-work would be in order - probably better to start from scratch with a design conceived from the ground up for subjective SQ rather than measurements
Yep, AD1955 from memory. And OPA2134 I-V opamps running from a switching +/-15V supply. And all SMD of course. Good decision
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Old 6th July 2013, 08:59 AM   #879
Bonsai is offline Bonsai  Taiwan
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I am struggling to understand why an AD DAC would be yucky . . . .
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Old 6th July 2013, 09:44 AM   #880
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Not 'yucky' that would indeed be going too far, rather 'sucky'. Meaning the noise modulation bothers me subjectively.

Was your reference to 'AD DAC' (rather than the specific part number owdeo cited) to imply that the AD brand was some guarantee of subjective SQ incidentally? They not so long ago discontinued one of the last of their stellar sounding DACs, the AD1865.
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Last edited by abraxalito; 6th July 2013 at 10:04 AM.
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