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Warpspeed -An Optocoupler Volume Control

People who believe in their ears in defiance of the measurement are the same that those who prefer the religion to faith!

OndesX

If it's music reproduction, I'd rather believe what I can hear...am I going to force myself not to believe because the numbers say so? First I'll probably say, "It can't be!" but I'll probably conclude, "...but I like it!" -which is what matters in our hobby, not religion or faith.
 
hehe touche, well I think i'm just going to watch from the sidelines for a while, the other thread is getting rather heated up and I must say any critique of this device by zealots does tend to bring on the battle from all corners. it may not be palatable to me for my current usage, but I respect others right to their own taste or motivations in this hobby.

The fact is it measures badly, that is a fact, there are simpler ways of adding pleasing 2nd harmonic distortion in less strange places than at an input where you cannot turn it off, but we all know that is not the whole story. how much of the story it is for any one person is a matter of taste and I cannot argue with that.

I have mostly built up the boards I have had here for some time just recently, but I do not know when I will get a chance to listen to it, my system and everything in it is balanced and this presents some problems, as does the output and inputZ, but that will not stop me trying it out, I have heard it in a friends system, but only with tubes, which are not really my taste so this probably wasnt a fair test.

try and keep it a clean fight chaps :cheers:
 
The fact is it measures badly, that is a fact, there are simpler ways of adding pleasing 2nd harmonic distortion in less strange places than at an input where you cannot turn it off, but we all know that is not the whole story. how much of the story it is for any one person is a matter of taste and I cannot argue with that.

cheers:


"measures badly" I would not consider .01% 2nd harmonic a bad measurment, at full level 0dbu from a cdp which they never reach on normal cd's it's still only .1%.

Then consider the lack of distortion "diode rectifcation effect" a pots wiper contact gives which can't be measured, this is why so many say the Lightspeed is the cleanest full bodied sound they have heard. Trust your ears as well as the analysing equiptment.


Cheers George
 
Going back to these postings by Mr. Pass http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-134.html#post1520950 and the attached %THD vs V curves...if you look at it, most systems would operate in that valley region up to 0.5V.

With an amp with a gain of 10 this would already be 5V at the loudspeakers very loud even for moderate speaker sensitivity. Voltage peaks this high will only be instantaneous hard drum whacks very short in duration so it's not like you are listening to a continuous 0.025% distortion like if it were a sine wave fed into the amp. An F5 at gain of only 5 will also be already loud.

Correct me if I'm wrong Mr. Pass, your test set-up was the 600R source with a shunt LDR? Will there be an improvement with series-shunt LDRs' distortion cancellation especially at series LDR = shunt LDR values?
 

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I'd think common sense should prevail. Or maybe not.

Hey, thanks for lighting up my butt...I went ahead and tested the players I mentioned before -

Test signal is 200mV, 1kHz

Toshiba CD/HDCD/DVD -quoted Z=200R
Vunloaded=200mV
Vloaded=67mV
Rload=100R
Computed Z=199R

Sony CD/SACD -quoted Z=10k
Vunloaded=202mV
Vloaded=28mV
Rload=100R
Computed Z=621R

Sony Blu-ray/DVD/CD -quoted Z=10k
Vunloaded=216mV
Vloaded=21mV
Rload=100R
Computed Z=929R

L & R of all three were pretty close. So yeah Sony is way off with their specs...and yeah common sense prevailed so I went ahead and tested:)
 
So yeah Sony is way off with their specs...and yeah common sense prevailed so I went ahead and tested:)


Well done! I don't really think Sony are trying to down-spec their own creations. What the spec was probably supposed to mean was the minimum recommended load and 10k certainly makes sense. Somehow got lost/distorted in translation.

Otoh, i am long overdue to build a ligh/warp speed device. Maybe this thread will finally prompt me into action.
 
"measures badly" I would not consider .01% 2nd harmonic a bad measurment, at full level 0dbu from a cdp which they never reach on normal cd's it's still only .1%.

Then consider the lack of distortion "diode rectifcation effect" a pots wiper contact gives which can't be measured, this is why so many say the Lightspeed is the cleanest full bodied sound they have heard. Trust your ears as well as the analysing equiptment.


Cheers George

i'm aware of your spiel, but it does not apply to any attenuator I would consider using ie relay or digital (I use digital on my sabre) well my dac IV has 5v p2p output, distortion would be higher, then add gain and that is too much for an attenuator for my taste. not for others no problem, just a personal thing.

all of my gear is balanced so this causes a problem for trying it out, as from what I read this is problematic. I bought some boards from oliver, but decided if I was going to try it it would be as a separate unit not built in where it cannot simply be taken out of the chain if desired.

I will finish building them one of these days, but for now I only have experience with listening in a friends system with a tube amp which is not really to my taste, so thats really not a fair test. There were other issues such as the outputZ caused hesitation at the time too, but mainly it was the fact that all of my gear is integrated with amps built into the same case as the dac, so when I tried out mCU based volume on both my sabres there was no turning back, cheap, perfect channel matching and no effect on the signal (unless turned right down) or surrounding circuits at all. so my search is over until I build another standalone amp, at which point I will revisit the LED based devices.
 
Warpspeed Attenuation Chart

Cells in green have drop-down selection for your system's flavor. Let me know what additional data we should add or if I missed/messed something.

Also, please verify my :warped: math...
 

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Warp speed ahead

Hi Blues,
I use a single ended lighter note ldr preamp that I got as a kit from Uriah. I love it. The sweetest sound for a preamp I have ever heard. Build An Amp
I have a set of 8 matched ldrs from Uriah to build a balanced ldr lightspeed type preamp. I also have a wireless remote kit I got from diyclub. the pot is a 6 gang 100k type. If I'm lucky and the seattle weather continues I will have a rough build this weekend. I had planned on a basic ps for the ldrs but your warpspeed ps looks nice. Whats the chance it would work in a light speed type circuit.

http://www.diyaudio.com/forums/atta...ew-passive-preamp-lightspeed-mkii-circuit.gif
 
...Whats the chance it would work in a light speed type circuit.

A much better schematics for balanced LDR use in audio is presented on the following figure... Then you just need 6 instead ! A working high precision stereo balanced LDR based on this circuit is presented in the LS thread posts #3703 and #3705.

Hope this helps !
 

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