You need to look and measure that the I/O impedances of both channels at differing levels remain the same to each other, if not and they have different values of Z in and out (i/o), this will effect the sound quality of each channel hence may/will effect the stereo imaging. It will simulate the same effect as having large different lengths of interconnects for each L and R channel.
That is why quad matched sets have a consistency between channels, they remain equal for both at all levels of listening, unlike some of the pseudo Lightspeed Attenuators that are comming thick and fast. There is no free lunch.
Cheers George
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My understanding is you recommend a constant fixed value for the LDR then, set by a trimpot? From your experience, can this be set to say, in the range of 20k to 40k ohms?
Again, comments appreciated as to why this approach would be preferred over, say, a fixed high quality tantalum or other boutique resistor of the same value.
Whilst your post makes complete sense on it own, from my point of view it does nothing to address the original problem - the sound being overwhelmingly loud at minimum volume (knob turned completely CCW) as stated here -
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-435.html#post2847577
and very useful numbers given here
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-436.html#post2848018
So for a moment, let's assume the chap has a perfectly matched quad of LDR parts. It may not be true, but let's say it is.
If with his 42dB voltage gain Marantz PM66KI amp he gets speaker output loudness of 82dB @ 1M at *minimum* volume setting using his 88dB/1W sensitive speakers, how do we solve his problem to reduce the volume level to a reasonable minimum level?
As stated before here
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-437.html#post2850064
And here
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-436.html#post2848383
The on resistance is much lower in impedance on the NSL32SR2S usually by a factor of three times. You just need to look back a few pages or use the search this thread only tab.
Cheers George
Cheers George
Thanks for your reply. I have read those posts. And the ones around them.
Not sure exactly what is driving your responses, they seem disconnected from the subject at hand.
The original poster has quoted he is measuring a minimum impedance value of 30 ohms.
I really don't think you are here to tell us this value can be reduced by a factor of 3 times.
Even if it is so, it really does not help him, as he needs a lot more reduction. I can post the full analysis from my hand written notes if anyone is interested.
A gain of 40+db in an amp is really high, normally it's like 26db or so. But it seems if more attenuation is needed, that means less maximum gain is needed. Thus. by adding a resistor or constant resistance LDR setting in series with the signal path, you basically reduced the overall gain. How big a series resistor is necessary depends on how much attenuation is necessary.
If he is doing 30ohms with the NS32SR2 then then are now probally blown/damaged as they are typicaly above 100ohms @ 20mA max and cannot get down that low with <20mA, and anything above that will kill/damage them in the end, this could be the reason why he has no low volume as the shunts are now probally damaged or gone open circuit.
Cheers George
Cheers George
I only have 8 of the NS32SR2 and they were supplied as selected devices. So mine are not typical.
None of mine exceed 50r at 15mA. I have not damaged any of them.
What you have stated for "typical NS32SR2" is simply not true.
You could use a single LDR or two set up as a voltage divider. You can set them at those high values but they dont stay stable at those high values. Even at 10k you can see a single LDR fluctuate by 400R or so when you blow on it. The higher in value the less stable. So a voltage divider will do the trick at lower values. Its not the best ever solution, but it will work and will sound better and likely cost less than boutique resistors or at least cost about the same.
OOOH, you could also throw a switch in there that enables the shunt LDRs in your static resistance circuit to go to 40R so when you want very low volume just throw that switch. Its admittedly a kludge but hey it WILL work and its not even special magic.
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I think its time for me to release boards so guys can do their own matching. This way we can avoid all this crazy conjecture and everyone will see for themselves.
Plus I am pretty tired of matching. It truly gets boring. I prefer working on circuits and finding something new.
Anybody thats interested shoot me an email. Will throw in free Lightspeed boards.
Plus I am pretty tired of matching. It truly gets boring. I prefer working on circuits and finding something new.
Anybody thats interested shoot me an email. Will throw in free Lightspeed boards.
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The specs on the data sheets don't lie
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-437.html#post2850064
and this was backed up to me by Fred P. Rohrbacher V.P. & General Manager of Silonex a Casco Company and I have done thousands of these now and I can verify it's fact, that the NSL32SR2S goes far lower in impedance at the same given led mA current than the NSL32SR2 can without stressing by over driving the led with more than 20mA.
Cheers George
http://www.diyaudio.com/forums/anal...uator-new-passive-preamp-437.html#post2850064
and this was backed up to me by Fred P. Rohrbacher V.P. & General Manager of Silonex a Casco Company and I have done thousands of these now and I can verify it's fact, that the NSL32SR2S goes far lower in impedance at the same given led mA current than the NSL32SR2 can without stressing by over driving the led with more than 20mA.
Cheers George
All you proud Lightspeed Attenuator owners and builders, look out for the upcoming Stereophile issue (I think April issue which comes out in March) with Recommended Components listing, as they just emailed me for any changes (pricing, design etc) to be included in the write up on it.
This will be the 5th time your Lightspeed Attenuator has made it into Recommended Components since 2009 when Sam Telling first bought his from me. I have a feeling it may set some sort of record for Recommended Component longevity.
Cheers George
This will be the 5th time your Lightspeed Attenuator has made it into Recommended Components since 2009 when Sam Telling first bought his from me. I have a feeling it may set some sort of record for Recommended Component longevity.
Cheers George
Hi All, I am building a passive pre and heard the lightspeed and was VERY impressed. I am a good and creative builder, but a little lame on the workings of electronics....please forgive. I have heard that the lightspeed needs a certain range of impedance both coming and going. SO, it will be going into a Pete Millete Low Mu preamp then on to 3 amps. For inputs, I have a CD player that goes into a tube DAC, an octal phono pre, music server that goes into the same DAC as my CD, and FM tuner (at some point in time) The tube DAC is the Maverick D1.
So, will the lightspeed work with these inputs and the tube preamp?
So, will the lightspeed work with these inputs and the tube preamp?
Hi djn, the Lightspeed Attenuator in it's purest form, with no buffers or extra series or shunt components, as I have attached, using quad matched NSL32SR2S led/ldr packages.
1: like to have sources (cdp,tuners,dacs, phono stages etc) of less than 200ohms output impedance (which most are theses days)
2: The input impedance of the poweramp should be higher than 47k (which most are) as 47kohms is the industry standard, tube amps are generally higher which is great. Many customers of mine have still had great results down to 33k poweramp inputs.
3: interconnects from the Lightspeed Attenuator to the poweramp should be 1.5mts or shorter and of low capacitance 100pf per foot or less which most good quality one's are.
And you can use one of these led testers (attached) and your DMM on the ldr to do the quad matching, $5 at your local Rat Shack or similar.
Cheers George
1: like to have sources (cdp,tuners,dacs, phono stages etc) of less than 200ohms output impedance (which most are theses days)
2: The input impedance of the poweramp should be higher than 47k (which most are) as 47kohms is the industry standard, tube amps are generally higher which is great. Many customers of mine have still had great results down to 33k poweramp inputs.
3: interconnects from the Lightspeed Attenuator to the poweramp should be 1.5mts or shorter and of low capacitance 100pf per foot or less which most good quality one's are.
And you can use one of these led testers (attached) and your DMM on the ldr to do the quad matching, $5 at your local Rat Shack or similar.
Cheers George
Attachments
With all due respect, the Linn Sondek was in the recommended products for 20 to 30 years and may still be there today.
Thanks George. I think this will work out well. I'd like to have a semi professional look about it. Does anyone sell boards and bits? Also, since I am getting or have gotten old, I want remote controlls on the V-pot. The only ones I can find have circuits of some sort attached to them. Is there anywhere I can get just a V-pot with a remote motor and controll board attached?
