LDR Attenuator Impressions

[Blues]

...I have posted many pics and screen shots many findings here, you may have to sign in to view them.
Lightspeed Attenuator - Page 4

Cheers George

Whoa! At least be decent enough to credit your source and include a link to Jackinnj's thread, who also made the tests. You're so good at editing to make it appear it's yours. And guess whose post you included at the bottom? http://www.diyaudio.com/forums/analog-line-level/177332-comparison-light-dependent-resistors.html

 

[SY]

That means that the only question of interest is whether LDR distortion, although higher than a pot, is still low enough to be inaudible. If so, an LDR volume control will be indistinguishable from a pot. If not, a preference for LDR is a preference for audible distortion.

This is a point I made earlier and it was totally ignored by the various peddlers of these devices on this thread.

 

[Blues]

Please reference Pano's thread http://www.diyaudio.com/forums/mult...much-voltage-power-do-your-speakers-need.html and view the Poll Results diyAudio - View Poll Results. Out of the 479 who tested a total of almost 71% answered "2V or Less" (185 members) and "Between 2V to 5V" (155 members).

Two years before the poll I posted this #28 http://www.diyaudio.com/forums/vend...optocoupler-volume-control-3.html#post2386926

Referencing Mr. Pass's LDR distortion vs. attenuator output voltage graphs here http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-134.html#post1520243 and here http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-134.html#post1520244, while keeping in mind that power amp voltage gains are 15x to 30x...

1. What will be the LDR attenuator output voltages at the power amp's input for peaks of 2 volts? Peaks of 5V?

2. Where do these output voltage ranges fall on Mr. Pass's graphs?

3. What will be the approximate distortion percentage? And in dB?

4. Will the values from #3 be audible?

 

[Chris Daly]

while everyone is hooked on proving distortion figures. what the life span of carbon track and resistor stepped attenuator mechanisms before they start to show signs of wear which in turn leads to distortion. then at the same time whats the life span of 'LDR' volume devices before the resistors start to degrade.

The LED inside of the LDR if current is not exceeded, is thought to be the
same lifespan of an LED, but LDR's rarely are either fully off or fully On.

I would anticipate lifespan would be then quite a bit longer than the 20 years
given for a LED. A LED, one of the original Hewlett Packard devices with Vf
of 1.4v continues to do its thing on a 40 year old Quad 405 I use.

LDR's, as you point out have advantage over mechanical wiping parts.
with audio path's. Digital pots offer many advantages too, but cannot in
my experience get close to the purity of audio from LDR's.

Cheers / Chris

 

[georgehifi]

Whoa! At least be decent enough to credit your source and include a link to Jackinnj's thread, who also made the tests. You're so good at editing to make it appear it's yours. And guess whose post you included at the bottom? http://www.diyaudio.com/forums/analog-line-level/177332-comparison-light-dependent-resistors.html

Yes sorry there is one of the eight that is Jack's. You should have been a forum cop Blues, you've missed your vocation in life.

Cheers George

 

[Bibio]

what strikes me the most about this thread is the fact that there seems to be very little 'middle ground' which i'm surprised at TBH. instead all i see are people quoting distortion figures and saying that the 'LDR' based volume device is useless and are reluctant to even try and build their own and make their own comparison to what they have at the moment due to technical details written on a piece of paper. on the other side are the people who actually have the device and say that it sounds good.

i dont care what i use and if i never liked the end result then 'oohh well'. nothing ventured nothing gained and i have always had an open mind to new ideas, sometimes ignorance is bliss

if Rega or Linn were to publish their TT specifications people would not touch them with a bargepole but they happen to be two of the biggest selling TT's in the world. why do people buy them? because they have a reputation of sounding good (i have never been a lover of either).

 

[DPH]

I dunno. I think it's largely a contest of terminology. Speaking only for myself, I don't see much in terms of, "you're not allowed to like that".

 

[AndrewT]

You guys have got this all wrong, there is a slight 2HD when the LDR's are over driven,

it has been shown in recent posts that most distortion introduced by the LDR is third harmonic.

is this 2HD an extra level of distortion when LDRs are over-driven?

and seen as a very slight rounding of the tops of the sine waves, just like triodes do.
This only happens when the input signal are way over the 2v standard at 0dbf for Redbook, the only ones I've seen to do this are bench test cd's that have 0dbf sine waves playing on rare high output >3v cdp's.

CDP DVD and many other digital sources put out 2Vac to 2.2Vac. This is approximately 3Vpk.
Most modern CDs send out a signal that hits this 3Vpk regularly.

I have posted many pics and screen shots many findings here, you may have to sign in to view them.
Lightspeed Attenuator - Page 4.........................

When are you going to separate the power grounds from the audio signal return in your schematics?

There is absolutely no reason to connect the signal return to the power ground in an LED/LDR volume control. The audio side can be isolated from the power side.

 

[SY]

saying that the 'LDR' based volume device is useless

No one said that. What WAS said was that claims of performance improvement over simpler and far less complex methods are unsubstantiated. What was also said was that if the units sound different than a conventional line stage (that's an "if" since none of the people peddling them have any data indicating this), then they are distorting in some manner.

 

[youknowyou]

No one said that. What WAS said was that claims of performance improvement over simpler and far less complex methods are unsubstantiated. What was also said was that if the units sound different than a conventional line stage (that's an "if" since none of the people peddling them have any data indicating this), then they are distorting in some manner.

I must have read over 40 times this past couple of days that compared to a alps, tkd or even a dact or goldpoint, that subjectively, over 9/10 prefer the sound of a Lightspeed attenuator. for me, thats evidence. for you, subjective preference means nothing.

thats remind me of you defending your computer soundcard dac as being as good as any other dac.
Theres more to sound then measurements, isnt there?


Ill be comparing my passb1 with alps blue to the lightspeed attenuator.

 

[SY]

for you, subjective preference means nothing.

Of course, that's a total lie. Why do you feel the need to do that?

Try responding to what I actually wrote.

 

[Pyramid]

What about MOSFETs

Ok, maybe time to take a break from the current battle and ask a question that I've asked one of the mfrs of LDR volume controls awhile back, but never received a sufficient answer:

Since the LDR is a semi-conductor whose resistance changes with the application of an isolated catalyst (light), how is it any different than using a MOSFET transistor, especially as the shunt element in a volume control?

If you do a spreadsheet on the values of the series and shunt components for a volume control, the series values seem to center around the sweet spot for LDRs and the shunt value closely matches what I measured on an IRLM1902 MOSFET. The difference being, the MOSFET can achieve much lower resistance values and provide much higher attenuation. The control was more linear as well, and by linear I don't mean its effect on the signal, I mean the change in control voltage vs shunt resistance, compared to an LDR.

Has anyone tried this approach, and if so, what was the effect on the sound?

 

[Chris Daly]

Ok, maybe time to take a break from the current battle and ask a question that I've asked one of the mfrs of LDR volume controls awhile back, but never received a sufficient answer:

Since the LDR is a semi-conductor whose resistance changes with the application of an isolated catalyst (light), how is it any different than using a MOSFET transistor, especially as the shunt element in a volume control?

If you do a spreadsheet on the values of the series and shunt components for a volume control, the series values seem to center around the sweet spot for LDRs and the shunt value closely matches what I measured on an IRLM1902 MOSFET. The difference being, the MOSFET can achieve much lower resistance values and provide much higher attenuation. The control was more linear as well, and by linear I don't mean its effect on the signal, I mean the change in control voltage vs shunt resistance, compared to an LDR.

Has anyone tried this approach, and if so, what was the effect on the sound?

I have tried a h11f1m in a series signal side connection
which needed 500k of preceding resistance to make them
sound, not much better than a portable radio.

If using a IRLM1902, how do you circumvent DC coupling ?

h11f1m work quite well though, for supplying LDR anodes.
I used them in a project to reduce current across input selection
switches, and they worked well. Resistance using control board
then in series to the h11f1m internal LED, sounded best at
about 18k

Cheers / Chris

 

[LBHajdu]

while everyone is hooked on proving distortion figures. what the life span of carbon track and resistor stepped attenuator mechanisms before they start to show signs of wear which in turn leads to distortion. then at the same time whats the life span of 'LDR' volume devices before the resistors start to degrade.

lets say we took each device and used it from full off to full on 10,000 times, which would still be nearer the original figure of manufacture.

carbon track no matter how good all wipe the carbon from the surface of the wafer rendering it useless. resistor based stepped attenuator is like carbon track but the contacts will wear out instead of the carbon track rendering it useless or in need of repair. 'LDR' have no moving parts so its down to how long the resistor/led life span is, ok so the LDR still rely on a conventional pot or rotary encoder to control the currant to the led so will need replacing as the pot/encoder wear but you can use the cheapest parts you can get your hands on as a replacement.

Just my two cents on life expectancy:

I agree that pots seem to have a mayfly life expectancy. The one on my modern se tube amp (another high THD technology many people seem to like) is starting to crackle (it's a generic, not a Alps Blue Velvet or anything) at a point in the rotation now. And on base guitars it's a very common repair. I don't like pots for this reason, though I don't think this adds THD as whatever speck of carbon remains is stable electrically.

By contrast LED's as long as not over-driven seem to last forever. Anyone with an understanding of ohms law should be able to build such a driver for an LDR weather by microcontroller or potentiometer drive. By extension optical rotary encoders last forever is well. I still have a ball mouse, can you believe, on this computer, which uses two of them and it refuses to die.

The CdS I am a bit wary of (but I have no experience) Wikipedia says:
"If the operating temperature does not exceed the limit (typically 75 °C or less) then for each year of continuous operation, the dark resistance falls by 10%; at higher temperature such changes can occur within minutes."

Link Here:
https://en.wikipedia.org/wiki/Resistive_opto-isolator

The very high dark resistance of meg ohms is not used for attenuation, I am just wondering what the effect is over five or ten years.

I personally would like the thank georgehifi for introducing us to this attenuation circuit technology. And I would encourage more commercial designers to share with our community.

 

[stvnharr]

That means that the only question of interest is whether LDR distortion, although higher than a pot, is still low enough to be inaudible. If so, an LDR volume control will be indistinguishable from a pot. If not, a preference for LDR is a preference for audible distortion.

Why are so many people wriggling and squirming to avoid or deny simple facts? Why are people so surprised to discover yet another example of how a small amount of low order distortion can be pleasing to many people (single ended triode amps are another example of this phenomenon, as are most 'tube buffers')?

The question of audibility basically involves listening to music with an LDR volume control. I have done so and as previously written I do not sense any presence of 3rd harmonic harshness, so it seems to be inaudible to me. Others can listen and chime in as they wish.

At some later point in time I can even do an A/B of my LDR with an Alps potentiometer as the volume control.

With the rather pointed last sentence in the first paragraph above as a benchmark, then I presume that those with a preference for single ended triode amps and tube buffers also have a preference for audible distortion, and likely large amounts of it that are easily heard. I might add that most other tube power amplifiers would likely be much the same.

 

[georgehifi]

For the forensic scientists, what I'm saying is even with the lesser NSL32SR3 (thanks to jackinnj for his 2010 AP measurment) the 3hd is very low and the 2hd can over shadow it if the ldr is over driven, which in normal redbook instance will not happen, and yes the circuit has to be changed one day, keeps builders on their toes.

Cheers George

 

[stvnharr]

For the forensic scientists, what I'm saying is even with the lesser NSL32SR3 (thanks to jackinnj for his 2010 AP measurment) the 3hd is very low and the 2hd can over shadow it if the ldr is over driven, which in normal redbook instance will not happen, and yes the circuit has to be changed one day, keeps builders on their toes.

Cheers George

Thanks George.
Those H2 and H3 numbers are exceedingly low at over 100db down. No wonder I cannot hear any of it.

 

[Blues]

24 hrs, 14 posts later...

No one has stepped up to the plate and answer the 4 easy questions on post #183? Do I sense a dilemma if the answers are made known?

 

[DF96]

With the rather pointed last sentence in the first paragraph above as a benchmark, then I presume that those with a preference for single ended triode amps and tube buffers also have a preference for audible distortion, and likely large amounts of it that are easily heard.

Preference, yes in most cases. Not large amounts, though. Large amounts of distortion are heard as distortion by almost everyone, but smaller amounts of distortion are not recognised as such. They change the sound (so they are audible) but in a way which some people prefer.

I might add that most other tube power amplifiers would likely be much the same.

That would depend on the aims and skills of the designer and builder.

It is interesting that in one thread -100dB distortion can be ignored (when it comes from an LDR) while in another thread -140dB (or was it -160dB?) distortion (from a resistor) causes 'night and day/wife in the kitchen' changes.

 

[xnor]

the 3hd is very low

Under what conditions?


Anyway, either
a) these attenuators do not produce significant distortion, i.e. don't degrade the signal audibly, which does not fit what people report ... (so they hear what they want to hear), or
b) these attenuators do produce significant distortion, which explains that differences are heard, but not the contradictory impressions ... (which again supports that people hear what they want to hear).