[nick_charles]

Quote:

 
Regarding what one professor considers at a Big Ten (i.e. not Ivy League, for the record - not that it matters but we might as well get ALL of our facts right while we're at it) university thinks sounds better is more than a bit presumptuous considering that he happens to sell what he's hawking to you.  Not to mention on top of that that he is an electrical engineer, not a psycho-acoustics expert.  Not that we are, either, but guess what?  We're not trying to hawk an amplifier design from which we profit.  You know another thing about designing, creating, and selling products?  Marketing decisions trump engineering decisions as often as not.  There's a big market of gullible audiophools out there who eat up zero feedback amplifiers - if you know you can cater to them and profit, why not?
 

 
Kevin Gilmore is not a Professor, he is a staff EE at the Chemistry dept where he works in a support capacity - and is highly regarded in that capacity. I am not sure (I am happy to be proven wrong)  he actually has a PhD as I can find no record of a dissertation nor any published academic papers attributed to that particular Kevin Gilmore, nor does his public profile list doctoral studies, when mentioined in NU web pages he is consistently referred to as Mr i.e http://aslloginsrv.chem.northwestern.edu/Documents/2011%20IMSERC%20Annual%20Review%20Public.pdf - of course none of this has any impact on his design skills but when you are using calls to authority it is important to be factually accurate !. I was mistakenly referred to as "Dr" for many years merely because I was a TA/RA - long before I was awarded my doctorate.
 
 

 

[Chris J]

Yes folks, this is how it really is in the real world:
Quote:

You know another thing about designing, creating, and selling products?  Marketing decisions trump engineering decisions as often as not.

In addition, you get the occassional customer telling you want to do even though it is against their best interests.
You have to design something customers will like.
It has to look nice, the knobs, controls, switches, input and output jacks have to feel "right".
Cost constraints.
Time constraints.
Meet UL approval.
You have to write an operating manual.
Then you have to assume the owner will not read it.
So you have to build it so the customer will not inadvertantly destory the piece of equipment due to mis-operation, i.e. plugging and unplugging cables at full volume. Putting hot equipment in confined spaces. Using homemade or audiophile cables that may be way too capacitive. 
The design process is never about just measuring stuff.  But you really do need to measure, test, specify, run computer simulations. Designing is always part art, part experience, part science.
 
 

 

[leeperry]

 

The worse crime however is for those deploying such uber-chips to 1) Use the chip manufacturers specs not actual measurements and  2) not measure the complete circuit which is often rather worse measuring - there is a manufacturer (popular round here) that does this - and achieves the feat of taking a 32 bit chip and creating an (approximately) 16 bit circuit - inspired engineering at it's best ! - granted analog stages incur more noise but even so losing 1/2 the bits is a tad careless

Oh, this is worse...this is commercial fraud, many companies did it when the AK4396 hit the market. All of a sudden, tons of 120dB SNR soundcards popped up, like the Audiotrak Prodigy HD2 that barely reached 100 dB in real world measurements. This said, it sounded better and far less shrill than the Essence STX...and that's what both many friends of mine and I personally witnessed on very different gear. Again, THD measurements will never be the warrant of anything as far as subjective human perceptions are concerned. And the HD2 has 2 discrete clocks for 44.1/48kHz multiples when the STX only has one 24.576Mhz(48kHz*512) crystal.
 
This said, it was merely happening in the $100 internal PC soundcards market...I wasn't aware that some self-proclaimed audiophile companies were still doing it these days?
 
I was talking about this Sabre powered unit: http://www.calyxaudio.com.au/index.php/calyx-dac
 
Not a single word on its output stage, simply innocent killer specs:

THD+N: 0.0005% @ 1KHz, 0dBFS
SNR: 125 dB, A-weighted, 2.2 Vrms
Channel Separation: 140 dB @ 1KHz, 130 dB @ 20KHz

 
Or maybe they're being vague on purpose considering that they gave the "DAC Specifications"? "DAC device" or "DAC chip"? haha.
 
If a company is not clear about something, it usually means that they have something to hide. All I can see is a shiny box w/ a Sabre ASIC that does it all at once: S/PDIF input, DAC, I/V opamp based output stage. This is merely a deluxe edition of the Realtek ASIC's. The markup on those chips must be stellar, I can understand why ESS ask to sign NDA's in order to access their datasheets material. Golden goose at work.
 
The Calyx DAC is USB powered...but sure, it's "cutting edge" blablabla, thanks to its very noisy 5V PSU probably =)
 
Quote:

Cheap-ish audio opamps are pretty much perfect for many applications, such as in DACs and headphone amps.

"Perfect"? Please define, I didn't realize that perfection existed. Do you realize that some ppl spent their lives looking for it? You might actually be onto something, so don't give up just yet

 

I'll bet you'll come back with a snip about how he wouldn't risk his reputation on such an assertion - I'll retort in advance with another reminder that he is an electrical engineer (and a very, very good one, yes), not a pscho-acoustics expert.  His claims as to subjective sound aren't directly related to his field of expertise and thus do not threaten his reputation as such - for example, I'm sure he could design a massive negative feedback design amplifier more than competently if he so desired.

 
My main reply will be that I didn't spend hours looking for "no feedback" audio designers...I'm sure there are many more, and the most notorious on head-fi has to be Kingwa. He has taken the DAC market by storm with his DAC-19, and he's been so successful that he decided to call his all newest units "NFB" just to make things very clear in ppl's minds. I read ppl raving about his NFB-2 all the time, and not just fanboys. There are many discrete believers that also got into NFB, and once you've heard the NFB gear the usual "by the books" PCM179x datasheet topology blabla goes up in smoke SQ-wise.
 

Personally, I have no problem with either design, as long as it is properly implemented.  And that's the key.  But obviously that doesn't matter because if something anecdotally sounds bad then it is "evil", right? 

 
Well, the K.I.S.S. PCM179x implementation cannot possibly sound good IMO..even worse when it's a voltage output DAC chip with a built-in I/V stage: you can slap any top of the range opamp behind a PCM1793, it will never allow you to extract all the details of the source. And using 4x single opamps for I/V and two more to buffer a PCM1794 won't do miracles either. OTOH, I have to admit that Asus decided to use a "discreter than discrete'" topology in their new "Asus One" USB DAC, and I have to say that I've been impressed:
 
They used a toroidal transformer(that provides galvanic isolation if I got it right), a very smart S/PDIF receiver that resyncs silently when switching sample rates, a Sharc DSP that reclocks all inputs and a whole bunch of 22 single opamps in the signal path using a fully dual-mono design..yay! And Asus aren't exactly newbies when it comes to PCB design either. This DAC sounds very promising, too bad they had to reach for as low of a street price as possible so they skimped on the opamps..they're 5532's and 4562's =/
 
But I'll soon be hearing it w/ an army of AD797 opamps, and I think it will deliver. Yes, OK, when using good chips within a never seen before dual mono topology, opamps might be a good option...but it doesn't come cheap either, because good opamps cost around 10 bucks a pop.
 

So which opamps would you suggest I get that will make a very noticeable difference?

Personally, I would use either 6*OPA1641 or 4*OPA1641 + 2*OPA602BP. OPA1641 is very cheap and is one of the latest designs from TI(circa 2010), they advise to use it for high-end bluray players and I can see how it would be greatly successful in this role. This is not a "rock your world" discrete design, but its price/SQ ratio is stellar. The NJM1114D's that can be found on the STX are merely NE5532 clones with slightly better specs, the 5532 is like +30 yo AFAIK. And dual opamps don't hold a candle to single opamps either, even TI acknowledged the problem: http://www.ti.com/product/opa1612
 
"The dual version features completely independent circuitry for lowest crosstalk and freedom from interactions between channels"
 
Cheap can sound good, OPA1641 is a perfect example of this...but again, don't expect a $1.15 IC to sound as good as a top of the range discrete design...not gonna happen.

 

[Head Injury]

Quote:

Cheap can sound good, OPA1641 is a perfect example of this...but again, don't expect a $1.15 IC to sound as good as a top of the range discrete design...not gonna happen.

Why not?

 

[Rebel975]

Quote:

Personally, I would use either 6*OPA1641 or 4*OPA1641 + 2*OPA602BP. OPA1641 is very cheap and is one of the latest designs from TI(circa 2010), they advise to use it for high-end bluray players and I can see how it would be greatly successful in this role. This is not a "rock your world" discrete design, but its price/SQ ratio is stellar. The NJM1114D's that can be found on the STX are merely NE5532 clones with slightly better specs, the 5532 is like +30 yo AFAIK. And dual opamps don't hold a candle to single opamps either, even TI acknowledged the problem: http://www.ti.com/product/opa1612
 
"The dual version features completely independent circuitry for lowest crosstalk and freedom from interactions between channels"
 
Cheap can sound good, OPA1641 is a perfect example of this...but again, don't expect a $1.15 IC to sound as good as a top of the range discrete design...not gonna happen.
 

 
 
 
I'm trying to find some 2x single SOIC to DIP8 adapters but I'm not having any luck. Seems like everything would be way simpler if I used OPA1642's instead. Unfortunately they are dual channel, and would surely invalidate any results I get. Although, there is no way I can effectively DBT these (unless 3-5 minutes between tests is acceptable), so I don't know if I should bother. 

 

[kevin gilmore]

I've said this a few times before, most people either don't understand or ignore the fact that
for current analog semiconductor integrated circuit manufacturing you have the choice between real good
vertical npn transistors and not so good lateral pnp transistors, or the other way around.
Which also means that when you need a good pnp, you use a lousy pnp paired with
an npn to simulate a good pnp. This results in designs that are not fully complementary or
even close. All current sources are npn's only. For noise reasons, the inputs are almost
always npn's or n-channel jfets or mosfets.
 
There are new chips with newer technologies that alleviate much of this. But still this
comes down to the number of ion implants you want do do, which directly goes to
the bottom line.  And lets face it, most of this strictly price based.
 
IBM started this, and both INTEL and AMD have current technologies including
3D gate and the high K stuff which would make fully complementary mosfet
analog processes possible. The chances that any of these companies would start
doing analog is as close to zero as possible. Anyone else wanting to get into
business doing this would face an equipment cost that no vulture capitol person
would fund.
 
With TI owning Burr-brown and now national semiconductor, and Analog devices
owning virtually everything else, the chances of new and better products seems
unlikely unless there is a MASSIVE need. Say a few million parts. A WEEK.
On-semi buying out sanyo semiconductor does not help either.
 
So you can currently while parts are still available do much better designs
all discrete. ALFET lateral fets specifically designed for audio are great
devices although pricey. linear systems is 3 years late in delivering
p-channel jfets. I was supposed to have working samples 3 months
ago. Instead of releasing the parts they have now, they are on a
witch hunt to get both lower noise and lower IDSS at the same time.
Much easier to design with the higher IDSS, all of my designs tolerate
this no sweat.
 
It sucks.
 
The situation with high voltage parts suitable for electrostatics is even worse.
 
While the following is a gross overgeneralization, anyone that thinks an
original lm741 (from about 1975, not the stuff labeled as lm741's which could be anything these days)
and an ad797 sound the same needs to go back and listen harder.

 

[Paul Clark]

As Fats Waller once proclaimed loudly to the audience when Art Tatum entered the room,
 
"I just play the piano, but today, God is in the house"

 

[maverickronin]

Quote:

While the following is a gross overgeneralization, anyone that thinks an
original lm741 (from about 1975, not the stuff labeled as lm741's which could be anything these days)
and an ad797 sound the same needs to go back and listen harder.

Agreed.  I'm pretty sure those differences would show up in all those measurements that according to the OP, "don't mean jack IRL" though.

 

[nick_charles]

Quote:

Agreed.  I'm pretty sure those differences would show up in all those measurements that according to the OP, "don't mean jack IRL" though.

 
some measurements of these two chips and others courtesy of Douglas Self

http://www.eetimes.com/design/audio-design/4218273/Op-amps-in-small-signal-audio-design---Part-3--Selecting-the-right-op-amp
 
 

 

[leeperry]

 

 
Agreed.  I'm pretty sure those differences would show up in all those measurements that according to the OP, "don't mean jack IRL" though.

 
You're still missing my point, hopefully on purpose. I'm just saying that opamps measurements don't meant jack as far as human perceptions are concerned...I never said that they would all measure the same, heck they all sound way different.
 
Everyone's raving about 5532/4562 based DAC's as if their measurements were the warrants of uncolored pristine SQ. This is a fallacy. I don't care that THD is 0.000000000000001%, and it doesn't mean anything considering that the very essence of opamps is to internally compensate in order to provide the best measurements. You cannot measure subjective SQ, and if 5532 and 4562 sounded "uncolored" as their über-low THD rates seem to imply, the fairy tale would be real. It is not, these two chips sounds utterly colored...meaning that throwing very low THD figures trying to prove that you sell uncolored equipment is a plain lie to your customers.
 

I'm trying to find some 2x single SOIC to DIP8 adapters but I'm not having any luck.

 
http://www.head-fi.org/t/432749/the-opamp-thread/3585#post_7940995

 

[Head Injury]

Quote:

heck they all sound way different.

How?

 

[BlackbeardBen]

leeperry, why do you continue to reference anecdotal sighted opinions as fact?  You know that those are not acceptable evidence here, so why do you continue to use them?  Do you think that repeating them over and over will make them more valid?

 

[leeperry]

 

leeperry, why do you continue to reference anecdotal sighted opinions as fact?  You know that those are not acceptable evidence here, so why do you continue to use them?  Do you think that repeating them over and over will make them more valid?

So to make this perfectly clear, any DAC device giving 0.00000x% THD is beyond audibility and they would all sound the same in a DBT..am I getting this right? The crappy SS that 4562 projects is an "anecdotal sighted opinion" to your ears? May I ask what opamps you've heard so far exactly? So AD797 and LM4562 both provide very low THD(beyond audibility of course), will they sound the same to you? Have you even heard them, or are you like 95% of the ppl in this thread talking about gear you haven't heard and mostly speculating at this point?

 

[Head Injury]

Quote:

So to make this perfectly clear, any DAC device giving 0.00000x% THD is beyond audibility and they would all sound the same in a DBT..am I getting this right? The crappy SS that 4562 projects is an "anecdotal sighted opinion" to your ears? May I ask what opamps you've heard so far exactly? So AD797 and LM4562 both provide very low THD(beyond audibility of course), will they sound the same to you? Have you even heard them, or are you like 95% of the ppl in this thread talking about gear you haven't heard and mostly speculating at this point?

You're welcome to provide objective evidence if you're so concerned about what we think 

 

[Currawong]

Quote:

Quote:

Agreed.  I'm pretty sure those differences would show up in all those measurements that according to the OP, "don't mean jack IRL" though.

 
some measurements of these two chips and others courtesy of Douglas Self

http://www.eetimes.com/design/audio-design/4218273/Op-amps-in-small-signal-audio-design---Part-3--Selecting-the-right-op-amp
 
 

From that article:
 
 
 
Quote:

As can be seen from Figure 4.20, the 5532 is almost distortion free, even when driving the maximum 500 Ω load. The internal circuitry of the 5532 has never been publicly explained, but appears to consist of nested Miller loops that permit high levels of internal negative feedback. The 5532 is the dual of the 5534, and is more commonly used than the single as it is cheaper per op-amp and does not require an external compensation capacitor when used at unity gain.

The 5532 and 5534 type op-amps require adequate supply decoupling if they are to remain stable, otherwise they appear to be subject to some sort of internal oscillation that degrades linearity without being visible on a normal oscilloscope. The essential requirement is that the positive and negative rails should be decoupled with a 100 nF capacitor between them, at a distance of not more than a few millimeters from the op-amp; normally one such capacitor is fitted per package as close to it as possible.

 
My current thinking is that if there is any relevant point to the discussion of measurements versus perception, it is exemplified by the point above, that (ignoring biases), finding measurements that explain why we perceive what we do is difficult and regular RMAA tests, and even scope measurements, don't tell the full story. The graph on that page, however, suggests to me that the 5532 under load has higher distortion in the treble, which might explain why some people perceive it, in some devices, to produce an unpleasant sound.
 
Sound cards are a good example too. I'm sure that the manufacturer's measurements are under the most ideal of conditions. Even tests I've seen on computer review sites usually involve a dedicated computer with top-of-the-line components. How they'll perform in different computers with different power supplies isn't so clear. Considering the great variety of circuits an OPAMP might be used in, I don't see why the degree of variability is any less.
 
Just my $0.02