Probably because it's incorrect. Conventional pots and stepped attenuators have orders of magnitude better linearity than any LDR, assuming that you don't do something stupid with the design.
At best, with a great deal of effort and expense, you might be able to get an LDR-based control to work OK with respect to linearity, but given that the manufacturers of these devices are loathe to publish test data, it's unclear how close they can get to the performance of simpler and less expensive technologies. The response of the guy pushing his product here was indicative- no measurements, no valid listening data, but a good story, fanboys, and testimonials. Pretty much the same as any quack nostrum.
You seem to assume I was seeking to compare LDRs on the one hand with SAs, pots on the other. In fact, I was pining for data on all three. Meanwhile, where does this "orders of magnitude" meme come from? No doubt you have data to hand . . .
You reply to my comment that "comparative data are hard to come by" with "probably because it's incorrect". How can something that isn't there be incorrect? You're at risk of falling over your own words in a haste to belittle.
See above. I pointed you to a pertinent paper c/w graphs and figures and all the biz so recently that you can't possibly have taken time to skim it, let alone read it critically. If you had, your point about "orders of magnitude" might have been less obviously a guess.
Though some finished, c/w input selectors, cased, marketed, dealer-marked-up LDR-based passive pre-amps are as pricey as their SA cousins, that's because the LDRs are only a tiny fraction of the total cost.
In DIY terms (relevant, I'd have thought, in a forum called DIY-Audio), they are IME cheaper. LED PSUs aside, they are unarguably simpler, a point repeatedly made by the designers you decry for their reticence and others belittle as "vendors". (I accept that there are recent, more complex DIY solutions but even they, AFAIK, use the same attenuation circuit.)
I presume you're referring to WAPO54001. He never even mentioned his product, let alone pushed it. Again, you seem to be getting over-excited.
The problem as I see it is that you and others invariably dismiss favourable subjective reports (how else can you report on how something sounds?) as the mutterings of the self-deluded. From where I sit, esp in the context of critics seemingly proud not to have heard the devices they so despise, that's a circular argument verging on solipsism. No reply is possible. (Had Mencken been into audio, he'd have had a field day with it. The 'Scopesoisie?)
At the risk of repeating myself, ad hominem arguments do not impress me.
The LDR datasheets linked on this thread. Nelson Pass's measurements linked on this thread. So you have the "data to hand" and are certainly free to peruse it.
Thank you for the links. I found them eventually. I'm happy now to accept that Wapo discussed his project at length in earlier posts but can't readily see how you get from the Silonex datasheets to "orders of magnitude" higher distortion in LDR VC circuits compared to comparable devices, let alone from the app note I cited.
Ditto for the Nelson Pass posts though they're interesting. My recollection is that NP rather liked LDR attenuators but, as I noted earler, I no longer use them so my recollection may well be at fault.
Oh really. How can my opinion be mistaken? It was based solely on what I heard and I am the only one privy to what I heard.
BTW, you are a single poster writing as such and are not a "we".
Probably? what about distortion measurements of conventional pots , and
linearity of dual gangs ?.
I experience no issues with linearity using a single audio taper gang 500k pot,
volume range mimics a conventional pot perfectly with no LR channel mismatch.
If care is taken with matching LDR's, and circuits providing current, they are in my
experience the equal with linearity of the best a conventional pot can achieve.
If care is not taken... that is another story altogether and probably the cause of your concern.
The best published data remains that provided by Silonex. New owners
Advanced Photonix appear to be gearing up for a new technical section.
Cheers / Chris
Below -120dB, at least for any of the pots I use (nothing fancy, mostly Alps).
It's trivial to make a line amp with distortion products in the 0.001% range using conventional pots. The nonlinearity of any LDR is quite a bit greater, so to match the distortion from a conventional pot, heroic measures need to be taken. One can get the same or better performance with about $5 worth of conventional parts. Hey, I design and build tube stuff but I don't pretend that I can't get better performance for a fraction of the price using opamps and transistors.
A better question to ask is, why are the folks selling LDR-based preamps not showing their distortion data?
Are you sure you guys are talking about the same thing? Dual pot tracking and the THD of either channel are very different things but both are referred to as linearity in some contexts.
I suggest you buy one of the cheaper DIY version and listen. There is a very good chance you will like what it does.
After you have convinced yourself that is what you want you could buy one of the more expensive versions. Wapo has released pricing data, George's Lightspeed is already on the market. The Tortuga got a glowing report in post1.
The DCB1 can have the vol pot replaced by a DIY LED/LDR control.
The only one I can't recommend is Blues' version, he refuses to give technical data when asked.
This is true but whether that 0.001% figure tells you very much about how it sounds is, many argue, a different matter. As we're all citing Nelson Pass, it's perhaps worth revisiting:
https://passlabs.com/articles/audio-distortion-and-feedback
and Cyril Bateman's paper on the same topic (both slightly OT but IMHO pertinent for all that). The NP paper prompted me to try a tube-based, non-NFB I/V stage in my DAC. Despite figures nominally way poorer than the op amp circuit it quickly replaced, the sound was much better. I put that down to the reasons - measurements, even - NP offers.
Another good question to ask is why do you and other critics of the technology invariably seek to imply that its designers somehow lack integrity or that its users are self-deluded? Though the habit doesn't dent their credibility, it tends to lower yours, at least in my eyes.
So what's your motive for building inferior kit?
From experience (the very idea - we've got books you know . . .), I second that.
Very good question that deserves an answer.
A few years back I sent one of my earlier LDR preamp boards to an independent test technician that had all the gear necessary to assess distortion and a bunch of other technical specs. Mostly because I was curious but also because a few folks had asked for detailed performance data.
The tech did some quick tests and then called me to discuss what he was seeing before proceeding any further. He rattled off some distortion numbers that were neither great nor awful but were in line with what Silonex (now Advanced Photonix) had already disclosed in their published spec sheets regarding their audio LDRs and their distortion characteristics. Basically no surprises. He did mention that the distortion was predominately 3rd order which I wasn't previously aware of.
He then offered a perspective I certainly wasn't expecting. He said that after he ran the tests, he'd hooked up the LDR attenuator to his system and spent some time listening to it. I asked him what he thought. He said that the test results were essentially irrelevant from a subjective listening perspective because the sonic improvement he clearly heard compared to his regular preamp was undeniable; something the test data by itself was not able to predict either positively or negatively...in his view.
After mulling that over I made the business decision that it would be a waste of time publishing detailed performance test data on our LDR attenuators. Because it was an audio catch-22. Hard core objectivists would conclude the data proved the performance couldn't be all that great and so wouldn't even bother to actually listen let alone purchase our gear. Meanwhile, this same info would be largely irrelevant to audiophiles who take a subjective approach and who would only decide after actually listening and deciding if they liked it.
The tone and content of much of this thread has reinforced the wisdom of that business decision.
Meanwhile I continue to get notes from customers who, after trying numerous alternative preamps, and then trying our LDR preamp, are blown away by the sound quality. You can denigrate and negate that any and every way you like including dismissing it as "promotion" or shared delusions but there are too many real live people offering up their honest first hand opinions just as the OP did who started this thread that confirm the positive attributes of LDR attenuation.
And then there's this from those delusional folks over at The Absolute Sound regarding our LDR3.V2 Passive Preamp...
Beats the 'wife in the kitchen' story I guess.
But agree with you, the TAS staff are pretty delusional. 🙂
But agree with you, the TAS staff are pretty delusional. 🙂
Ran across a book title years ago. Never read it but the title stuck with me.. "Claim Everything, Concede Nothing, And If Defeated Allege Fraud". Funny how that title turned out to fit with so many situations in life.
Over and out. 😀
I don't believe that's a catch-22 at all. If you have objective data you should publish it. If nothing else but to differentiate yourself from some other LDR vendors.
Put in an area of your website called "Objective data...FWIW."
Dave.
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It seems quite obvious that some people use the word opinion as a soft or passive aggressive way of saying you are either lying or delusional..... or maybe they haven't a clue what an opinion is?
You actually have an Informed Opinion as you have actually listened to the technology in question, unlike may who are just making assumptions
you have the power to just ignore these people or through the ignore list function located on the members profile page not see their posts
regards
james
I don't think I understand the question. Are all opinions equally valid? If I held the opinion that the Moon is made of green cheese, would that be a mistaken opinion or a valid opinion?stvnharr said:
By "we" I mean those of us who believe that LDR volume controls distort the signal more than normal arrangements and have said so in this thread.