I looked at the thread the other day and couldn't find enough technical information to get an understanding of what he was doing or how he was doing it so really not in a position to comment further.
Current draw on our kits is 3.4ma with resistance ON being typically 70 ohms
across pairs.Using a 500k pot, silence at minimum volume is easily achieved.
Allowing just the cathode to ground for shunt and series, provides ability
to use a single gang pot. Use cap multipliers in earlier stages and paramount !
avoid any resistance or capacitance to ground, that is directly in parallel with the LDR.
Cheers / Chris
across pairs.Using a 500k pot, silence at minimum volume is easily achieved.
Allowing just the cathode to ground for shunt and series, provides ability
to use a single gang pot. Use cap multipliers in earlier stages and paramount !
avoid any resistance or capacitance to ground, that is directly in parallel with the LDR.
Cheers / Chris
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To use your analogy, the OP is telling us about the wonderful new ice cream he has discovered which he believes to be pure dairy but we know that it contains some non-dairy products (not much, but some) and we suspect that he actually likes the taste of these extra ingredients but is wrongly ascribing his preference to the supposed pure dairy contents. So we just tell him so, as a public service to him and others.Bibio said:
Meanwhile, ice cream makers pile into the thread and argue about exactly how they make their product - while seeming to overlook the extra non-dairy ingredients?
Hi All,
Thought I'd share some perspective as well as clarify some technical items regarding the Tortuga Audio design.
I started working with LDRs around 7 years ago and at the time had my doubts that they were worth bothering with sonically or that they were practical to use in a commercial design. Turns out I was quite wrong on the first point and much closer to right on the latter.
While fully accepting the reality that a passive LDR attenuator will not be a universal fit between all combinations of sources and amps, the practical reality is it fits with most. Moreover the sound quality delivered by an LDR attenuator has be heard to be believed. I know of no way to arrive at the conclusion objectively that LDRs provide superior sonic performance relative to pots, resistors or even transformers. Yes, they are horribly nonlinear over a wide range of resistance, and yes they've less that pristine specs regarding distortion. Yet they sound awesome. You can't measure your way to that conclusion, you have to listen. I realize in stating this that some will reject this unequivocally because it lacks sufficient objective technical rigor. I have no solution to that conundrum.
Yet, the positive conclusions of Tortuga Audio's own LDR preamp customers and customers of other LDR brands plus all the accumulated DIY experience with LDRs can't be negated simply by calling BS on the subjective experience.
On to technical matters. After our early experience working with LDRs we decided the only way to overcome the nonlinearity, variability, and longer term performance drift of LDRs was to use a digital (software based) control of the LDR current to control their resistance levels. Initially we did the manual matching of LDRs but eventually moved away from that and now use on board calibration or what we call "autocal".
During normal operation the autocal circuit is disabled and isolated from the audio signal. When autocal is enabled, each of the 4 LDRs (1 series and 1 shunt per stereo channel) are run through 70 attenuation steps where we actually measure the resistance level in a closed loop and store the resulting 12 bit control command values in a memory chip for later lookup during normal operation. Our attenuation range is from -60 to 0 dB. To get down to -60 we run our LDRs between 100 ohms and 100,000 ohms. By limiting the minimum resistance to 100 ohms we run our LDRs in the low single digit milliamps to maximize their longevity. Running LDRs up to as high as 100k ohms means we run them well up into their highly nonlinear range. As long as the settings are reproducible over this range (and they are) you can program them to hit predictable resistance levels (and thus volume levels) using a microcontroller, software and simple DACs. This is done open loop during normal operation. In the event the behavior of an LDR drifts sufficiently, you can rerun autocal and 15 minutes later everything is tuned up and working. Autocal may be warranted every few weeks or only once a year. It really depends on the individual LDR. Should an LDR fail outright (unusual) or drift out of calibrateable range (less unusual but still quite rare), our LDRs are socketed so you can easily remove and replace them.
Since our design is software based we also added the feature of adjustable impedance wherein the impedance of the attenuator can be set between 1k and 99k with 20k being the default. Frankly, I had my doubts as to how effective this feature would be but based on customer feedback some have been able to clearly optimize the performance of their systems by moving the impedance level higher or lower.
Happy to answer any questions if I can.
Happy New Year,
Morten
Thought I'd share some perspective as well as clarify some technical items regarding the Tortuga Audio design.
I started working with LDRs around 7 years ago and at the time had my doubts that they were worth bothering with sonically or that they were practical to use in a commercial design. Turns out I was quite wrong on the first point and much closer to right on the latter.
While fully accepting the reality that a passive LDR attenuator will not be a universal fit between all combinations of sources and amps, the practical reality is it fits with most. Moreover the sound quality delivered by an LDR attenuator has be heard to be believed. I know of no way to arrive at the conclusion objectively that LDRs provide superior sonic performance relative to pots, resistors or even transformers. Yes, they are horribly nonlinear over a wide range of resistance, and yes they've less that pristine specs regarding distortion. Yet they sound awesome. You can't measure your way to that conclusion, you have to listen. I realize in stating this that some will reject this unequivocally because it lacks sufficient objective technical rigor. I have no solution to that conundrum.
Yet, the positive conclusions of Tortuga Audio's own LDR preamp customers and customers of other LDR brands plus all the accumulated DIY experience with LDRs can't be negated simply by calling BS on the subjective experience.
On to technical matters. After our early experience working with LDRs we decided the only way to overcome the nonlinearity, variability, and longer term performance drift of LDRs was to use a digital (software based) control of the LDR current to control their resistance levels. Initially we did the manual matching of LDRs but eventually moved away from that and now use on board calibration or what we call "autocal".
During normal operation the autocal circuit is disabled and isolated from the audio signal. When autocal is enabled, each of the 4 LDRs (1 series and 1 shunt per stereo channel) are run through 70 attenuation steps where we actually measure the resistance level in a closed loop and store the resulting 12 bit control command values in a memory chip for later lookup during normal operation. Our attenuation range is from -60 to 0 dB. To get down to -60 we run our LDRs between 100 ohms and 100,000 ohms. By limiting the minimum resistance to 100 ohms we run our LDRs in the low single digit milliamps to maximize their longevity. Running LDRs up to as high as 100k ohms means we run them well up into their highly nonlinear range. As long as the settings are reproducible over this range (and they are) you can program them to hit predictable resistance levels (and thus volume levels) using a microcontroller, software and simple DACs. This is done open loop during normal operation. In the event the behavior of an LDR drifts sufficiently, you can rerun autocal and 15 minutes later everything is tuned up and working. Autocal may be warranted every few weeks or only once a year. It really depends on the individual LDR. Should an LDR fail outright (unusual) or drift out of calibrateable range (less unusual but still quite rare), our LDRs are socketed so you can easily remove and replace them.
Since our design is software based we also added the feature of adjustable impedance wherein the impedance of the attenuator can be set between 1k and 99k with 20k being the default. Frankly, I had my doubts as to how effective this feature would be but based on customer feedback some have been able to clearly optimize the performance of their systems by moving the impedance level higher or lower.
Happy to answer any questions if I can.
Happy New Year,
Morten
No I don't. Per my note, the sonic superiority of LDRs is not something you can arrive at objectively through measurement or comparative data. LDRs won me over subjectively after listening to numerous other attenuators types both active and passive. I was sufficiently impressed that I started a company to design and produce LDR based preamps.
I'm a skeptical engineer and well aware of that subjective experience can be misleading. Yet at some point, subjective perception takes on a weight of its own notwithstanding the fact that you can't explain it in objective engineering terms. I'm fully aware of the snakeoil logic trap that this presents.
All I can offer by way of explanation is that the nature of the conductive material used in LDRs (cadmium sulfide) is very different from any pot or resistor and is therefore the most likely starting point for explaining the positive difference in sonic performance. As to specifically why is the realm of materials science and the physics of quasi semiconductor materials like cadmium sulfide - all of which is beyond my expertise.
Give LDRs a try. If you like/prefer the results, great. Most who try LDRs really like the results.
yes but all other forms of volume control are not pure dairy either and according to some on this forum a resistor has no effect on sound quality. now since all volume control apart from digital is some form of variable resistor then technically it should not have an influence on the sound quality.
i still dont understand why the OP got shot down for posting their findings. should we not be happy that they are happy with their new product.
personally and i dont know much about anything but i like the idea of what is commonly referred to as an 'LDR' volume device due to it not having any mechanical parts in the signal path even dumbass me can see the benefit in that.
I started out as a total skeptic, I didn't believe that an LDR attenuator could make such a difference. But, I was an audio hobbyist, and also a digital hobbyist and it was plain to me that the technologies could be combined to do away with the difficult hand-matching of LDRs to create a working stereo volume control. So, I did it, just for the challenge as a hobbyist, and wound up with something that is simple yet extremely effective as an LDR control.
But when I inserted my first working prototype into my own mediocre stereo system, it was "Oh-My-God!" good. The sound was transformed, the music drew me in emotionally like it had not done in years, and I was fully hooked.
Let me quote my first paying customer who said: "Not too good with describing exactly what has improved but it's across the board; I am hearing new things in recordings I'm familiar with, so can't ask for more than that. Low level listening is now a lot better."
I don't remember anyone saying, after listening to an LDR system, that they couldn't tell any difference.
Really, folks, if you've never listened to a system with, and without, LDRs involved, you're not entitled to denigrate them. You need to hear the difference first.
But when I inserted my first working prototype into my own mediocre stereo system, it was "Oh-My-God!" good. The sound was transformed, the music drew me in emotionally like it had not done in years, and I was fully hooked.
Let me quote my first paying customer who said: "Not too good with describing exactly what has improved but it's across the board; I am hearing new things in recordings I'm familiar with, so can't ask for more than that. Low level listening is now a lot better."
I don't remember anyone saying, after listening to an LDR system, that they couldn't tell any difference.
Really, folks, if you've never listened to a system with, and without, LDRs involved, you're not entitled to denigrate them. You need to hear the difference first.
The underlying premise of all these LDR projects is the subjective performance/superiority.
As Bibio alluded.....I don't see any point in shooting down people and/or issuing snarky comments to posters who are simply relating their subjective evaluations.
Non-linearities, distortion performance, LDR matching issues, longevity, etc, etc, are all valid discussions......but they weren't the premise of this thread. There are already plenty of other threads here on DIYaudio for that.
Probably time to give it a rest.
Dave.
Constellation
The $60k Altair preamp circuit is by John Curl(?) I think.
Quoted from their description..."Instead of the mechanical potentiometer found in most high-end preamps, the Altair uses optically controlled resistors that can be adjusted to an accuracy of 0.1 dB. To maintain the Altair’s perfect positive/negative signal balance and left/right channel balance in all operating conditions, we use 48 of these resistors—an expensive but undeniably superior design."
It would seem to me that Constellation are not a bunch of idiots.
But I dunno if the above has any relevance.
tim
The $60k Altair preamp circuit is by John Curl(?) I think.
Quoted from their description..."Instead of the mechanical potentiometer found in most high-end preamps, the Altair uses optically controlled resistors that can be adjusted to an accuracy of 0.1 dB. To maintain the Altair’s perfect positive/negative signal balance and left/right channel balance in all operating conditions, we use 48 of these resistors—an expensive but undeniably superior design."
It would seem to me that Constellation are not a bunch of idiots.
But I dunno if the above has any relevance.
tim
Yes, and if there's something "special" audible that cannot be shown through measurement data, ears-only listening data are appropriate. Unless by "subjective," you are meaning "not audible."
So... since CaptainWatt has offered to answer questions about the product he's selling, this is a reasonable question. If the answer is, "No, I have no listening data either," that's useful to know as well.
I think it would be more interesting to see some distortion measurements of low and high level signals running through one of those attenuators at low and high attenuation settings.
I do, there is no conundrum.
The countless positive conclusions of magic bracelet customers, magic plastic puck (placed on speakers to improve sound) customers or magic pebbles (e.g. taped onto interconnects to improve sound) customers or sugar gobules or magic water drops customers ... cannot be negated either, right?
You see, there are two approaches. One is the above, but maybe with some compartmentalization or special pleading thrown in to justify why only your specific product improves sound or "works"... which is neither a rational nor consistent position to take, and the other position - the complete opposite - which recognizes these impressions for what they are plus all the flaws and problems with them that have been identified over the past centuries.
Btw, have you tried the magic bracelets? Most people that try them really do feel something... sigh.
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Thanks! Can you explain how the ears-only tests were conducted? I'm especially interested in the set-up and what controls against non-auditory cues were used.
Sorry if I'm not being clear on this.
By subjective "ears-only" I'm referring solely to subjective feedback from actual customers (or reviewers) who have actually listened to our preamps and compared the results with their experiences with their current/previous owned preamp (passive or active). Not unlike the OP of this thread who was offering his subjective impressions - for whatever you think that's worth or not.
Many of our customers were using hi end $10k+ preamps and informed us that our LDR preamp outperformed their existing gear. We offer a 30 day in-home buy-try-decide audition policy with no restocking charge. If our LDR preamps don't actually sound better than what they've been using they can return them. We rarely get returns. I suppose that's a type of test in its own right.
Other LDR attenuator brands who've contributed to this thread have had similar positive feedback from their customers that further convinced them they weren't delusional in the perception that their LDR attenuators really do sound better than practically all other alternatives.
My recommendation is go give one a listen.
Namaste
Morten
Nobody says that "a resistor" has no effect on sound quality. Many say that a normal resistor usually has no effect on sound quality. An LDR is not a normal resistor; it is somewhat nonlinear with respect to signal. All the calibration systems in the world (designed to get a good volume control law and good channel matching) cannot correct this - I suspect that some LDR sellers can't or won't distinguish between these two quite different aspects of LDR non-ideality as resistors.Bibio said:
He didn't get "shot down". He got corrected. That is what happens on here when someone says things which are untrue, however sincere he is.
His happiness is not the issue. The issue is whether a nonlinear resistor adds distortion. At best, it can behave only slightly worse than a normal ohmic resistor - in which case it should be indistinguishable from a normal pot. At worst, it will add significant distortion - which some listeners may prefer.
There is a simple explanation for "the positive difference in sonic performance": it is caused by a small negative difference in signal integrity performance. A well-designed LDR attenuator will only add a small amount of distortion so few people will notice it as distortion but some may notice it as added richness or 'musicality'.CaptainWatt said:
What is the problem with mechanical parts? A well-design volume control arrangement uses an appropriate resistance value for a potential divider, with very light (i.e. high impedance) loading so the track-wiper contact carries very little current. It merely samples the voltage on the track. So you have two linear resistances forming the divider. Less distortion than an LDR.Bibio said: