Isn't 3rd greater than 2nd harmonic distortion in LDRs?
It looks to me like (from posted FFTs and my limited testing) that 3rd harmonic distortion is up to 20dB greater than 2nd Harmonic distortion.
This might account for better transient response as 3rd harmonic could accentuate edges.
It looks to me like (from posted FFTs and my limited testing) that 3rd harmonic distortion is up to 20dB greater than 2nd Harmonic distortion.
This might account for better transient response as 3rd harmonic could accentuate edges.
Okay, I've just gone through the whole thread.
George posted a distortion graph in post #196 and it shows slightly higher 3rd than 2nd.
Mort Sissener posted in post #134 the results of the distortion tests on his units, which showed distortion to be predominantly 3rd order.
I use Mort's controller unit so I stand corrected.
Assuming that the LDRs are roughly symmetrical in construction and are not subject to a DC bias, then 3rd would be expected to dominate. If coupling caps were missing or leaky then 2nd could dominate.
I had meant to include your post in my mentions. Yours is further corroboration of the distortions present.
Here is a distortion graph comparing 3 ldrs that I don't use as they don't go low enough in impedance (volume) even with max led current.
The other one the NSL32SR2S that I use does go low enough to 40ohms and with 1v to 2v as you can see is around .01% and with normal Redbook as Andrew says 700mV will be even better.
Cheers George
The other one the NSL32SR2S that I use does go low enough to 40ohms and with 1v to 2v as you can see is around .01% and with normal Redbook as Andrew says 700mV will be even better.
Cheers George
Attachments
Georgehifi,
could you tell us what the left plot is showing?
I can see a test signal of 1.0195kHz
What is dv = -12.753dB?
I can see that 3.0203kHz is @ -112 to -112.9
what is this measured relative too?
In the right hand plot and can just about work out what the left scale is: 0.0 to -100.0
What is that reading? I can't make out the top legend.
The bottom scale is: 1.00 to 5.00.
What is that indicating?
The right scale is logarithmic from 10 down to ?
What is that?
again the legend at the top is illegible.
What does the black legend say?
could you tell us what the left plot is showing?
I can see a test signal of 1.0195kHz
What is dv = -12.753dB?
I can see that 3.0203kHz is @ -112 to -112.9
what is this measured relative too?
In the right hand plot and can just about work out what the left scale is: 0.0 to -100.0
What is that reading? I can't make out the top legend.
The bottom scale is: 1.00 to 5.00.
What is that indicating?
The right scale is logarithmic from 10 down to ?
What is that?
again the legend at the top is illegible.
What does the black legend say?
My post was placed to correct the misinformation you gave earlier. I have already reposted to confirm that.
The CD replay volume allows about 2Vac to 2.4Vac, not 700mVac.
Andrew, You'll have to ask the member that did them on the Lightspeed Attenuator thread, I just took a copy of it.
I believe you said "The average music/audio that comes out of most digital sources is quite a bit lower than 1Vac." I think an approx of 700mV is acceptable then, giving even less distortion from the ldr's.
Cheers George
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Using a 2:1 Series-Shunt divider, the following measurements of 3rd harmonic wrt fundamental were made using GL5506 LDRs driven by green LEDs.
Vin 3rd Harmonic relative to the fundamental
2Vrms in -80dB
1Vrms -91db
0.5Vrms -93.5dB
0.25Vrms -95dB
0.125Vrms -99dB
This pretty much supports the contention that at normal line levels the distortion contributed by an LDR is minimal, unless your PA has a very high gain.
With low gain amplifiers and mid 90dB/S-M speakers I suspect the distortion will be undetectable by most people.
Vin 3rd Harmonic relative to the fundamental
2Vrms in -80dB
1Vrms -91db
0.5Vrms -93.5dB
0.25Vrms -95dB
0.125Vrms -99dB
This pretty much supports the contention that at normal line levels the distortion contributed by an LDR is minimal, unless your PA has a very high gain.
With low gain amplifiers and mid 90dB/S-M speakers I suspect the distortion will be undetectable by most people.
+1 TheGimp
What I've tried to say all along, it sounds just like direct in, save for an extra set of interconnects.
My system should be able to resolve, with me or any countless friends that have heard it.
http://www.diyaudio.com/forums/digital-line-level/227677-using-ad844-i-v-102.html#post4981398
Cheers George
What I've tried to say all along, it sounds just like direct in, save for an extra set of interconnects.
My system should be able to resolve, with me or any countless friends that have heard it.
http://www.diyaudio.com/forums/digital-line-level/227677-using-ad844-i-v-102.html#post4981398
Cheers George
The funny thing is, some people get worked up about distortion in ordinary resistors - which is often somewhere in the -170dB region! They carefully choose expensive boutiqe resistors for their amp in order to avoid all this horrible distortion (which they imagine they can hear), yet are happy to use a volume control arrangement with hugely higher distortion (which they feel improves the sound) yet describe this as 'transparent'. Note that -90dB is hugely higher than -170dB, although probably still inaudible.
If as it seems the LDR is generating 3rd Harmonic Distortion, that 3HD could easily be in a form that adds to the overall sound level, or at least, to the sound level of the third harmonic. Which probably should sound a little louder at higher SPLs than at lower levels ... a "mild volume expander" if you will.
As a practical matter it's not or to the extent it is it hardly matters. I think any of us who work with LDRs in actual preamp product applications are generally aware of their distortion characteristics and yet they perform remarkably well as the OP to this endless thread continues to assert through first hand experience. Tubes are naturally distorting as well and yet produce very satisfying audio. If people objected to the way LDRs sounded in their systems, George, myself and others would just say they suck too and we'd all go do something else with our time. I just know I'm going to regret saying anything here.
Tubes can be linearised with NFB. Volume controls cannot, so you have to keep the signal level sufficiently low.CaptainWatt said:
I recently bought a 'george hi fi' lightspeed attenuator on Ebay for use with a pair of Exposure 3012 monoblok amps (input impedance approx 50k, sensitivity 1.7V) being driven with a 2Qute DAC (3v output).
There was absolutley no comparison with the Exposure XXVIII pre I was previously using: the sound was flat, compressed and lifeless. I really wanted the lightspeed to take me to another level, but unfortunately it displayed all the weaknesses associated with passive preamps I have previously experienced.
The XXVIII is now back in service, despite my genuine belief that the lightspeed would leave it for dead.
Sorry George.
There was absolutley no comparison with the Exposure XXVIII pre I was previously using: the sound was flat, compressed and lifeless. I really wanted the lightspeed to take me to another level, but unfortunately it displayed all the weaknesses associated with passive preamps I have previously experienced.
The XXVIII is now back in service, despite my genuine belief that the lightspeed would leave it for dead.
Sorry George.
Odd "recently"???, I have constant eBay searches out for anything "Lightspeed Attenuator" and there hasn't been one on eBay for over a year now.
Can you post a link to it, as they are cached for 6mts so we can still see it.
The only thing that was Lightspeed Attenuator related was a tube buffered clone in the US way back in February
Light Dependent Resistor tube preamp LDR Silonex bottlehead foreplay lightspeed | eBay
Cheers George
Can you post a link to it, as they are cached for 6mts so we can still see it.
The only thing that was Lightspeed Attenuator related was a tube buffered clone in the US way back in February
Light Dependent Resistor tube preamp LDR Silonex bottlehead foreplay lightspeed | eBay
Cheers George