Lightspeed Attenuator a new passive preamp

[maximus]

Do it by the text book every time, get the same results every time.

Instead, thinking laterally can produce new ideas that move the world forward. The Lightspeed is one of these ideas. Simple and elegant.

You can analyse the theory all you want but it works very well in practice.

Those concerned with channel balance should consider adding a balance control instead of trying to match LDRs to rediculous levels of precision.

Regards
Paul

[soongsc]

The next thing would be compensating balance to one's ear performance

[udailey]

I ran a test of 460 and tested at 5 points. Was following Georges comment from several months back that this was best, so why not try it. I got no more matches at 5 points than I do at 4 points and I figured I will stick with 4. It has served me well for a few years now. That said though, it would be great to be able to match at 20 points but way to time consuming. On that little tiny board I have posted schematics of I added a balance circuit (left/right) and it is because while I go for very very close matching it is not always perfect, well never perfect. In my own system when I fire it up for the first time with a new set of LDRs I dial the image into the center with my balance control at normal listening level. I dont find a need to mess with it further even after several months of listening at different volumes. I know for sure that there is a bit of difference between the Left series LDR and the Right series LDR but the image still stays in the center so its not off so much that it needs me to continue messing with balance pot everytime. Bravo for George matching at 5 points. I dont find it necessary and dont have complaining customers but more is always better.
MarkusA, Maximus and SoongSC have that DIY persistence and 'glass half full' optimism that is so commendable and such a great part of this website. I think we sometimes look at audio circuits in a way to "2 dimensional" way. Get out the check list, measure everything, does it meet the checklist? Yes, well it must sound good then. This makes sense only to a point. Its part of the process but if it measures well and sounds poorly then something is amiss. We can and should, I think, measure with our ears, but there also has to be that 3rd or 4th dimension that we arent measuring and dont know to measure that is effecting what we hear. George measured some of it years ago with that fancy HP instrument he was able to use and it gave him some insight to better sound. Its one of those dimensions we dont normally measure. Maybe its because people are not usually able to use such high precision equipment and yet are able to come up with wonderful sounding equipment without those measurements, but perhaps the percentage of great sounding equipment would rise if everyone was measuring what George measured/saw/heard and if more people looked for something new. Maximus, MarkusA and SoongSC all may not have come right out and said it or even meant it but I think I can take from their recent posts that they would agree there is something we arent measuring but that we are hearing and simply because its not measured doesnt mean its not there.
Its just a resistor right? So we can put signal through it and measure voltage, current, resistance, impedance, inductance, distortion, etc etc but obviously it doesnt SOUND like other resistors. So there is something we are not measuring that we are hearing. Talk about measuring all you want but if you cant point out incredible sound on your spec sheets then the spec sheets are not telling the whole story.
Well my mind is obviously all over the place today. Happens a lot but keeps life interesting. Hope you all are having a great time with your families whether you do or dont celebrate the upcoming holidays. We have been having a great time and hope you all are as well.
Uriah

[ondesx]

Originally Posted by georgehifi

Any form of monitoring the resistance of the LDR's means it's going to be tacked on the signal path "not good" and this would be the only other way one could keep all LDR's tracking together, been there and done it.

There are two different ways to "match" these components. One is to buy a bunch of them and then, with a great deal of patience, to measure 5 points until two LDRs are similar enough to consider they are "matched". But I recommend to retry the same measures of these 2 components a day or two after this first measure... Some interesting surprises will arise...

The other method is to determine, whatever the LDRs, the requested value of current for a given resistance. Taking, of course, the same patience for the measures... When a control is performed one or two days after, one will find a better match between the measures than with the previous method.

The other advantage of this second method is that almost all the LDRs can be used without buying bunches !...

One more is that, obviously, if some LDR must be replaced, any new one will do and we don't have to find a new matched set !...

Again, this "5 points method" unfortunately wouldn't work for balanced use... The differential approach of the signal in balanced mode requires a much better "matching" all over the usable range. Whereas in single-ended mode a mismatch can be compensated by a balance control between channels, the same "mismatch" is much more, difficult or perhaps not possible to correct.

I have no good suggestion for "monitoring" the LDRs. But, their "calibration" from time to time is of course perfectly possible and I did it several times !...

The improvement of this method is the "automatic calibration", i. e. the automatic measure of all the LDRs. This will take from one hour to a day long if a very good matching is required. But who cares, it can be done when one is out for the day or the week-end !...

[DRONE7]

@udailey

....something we are not measuring that we are hearing.

Yes, though we are 'measuring' that something with devices appropriate to its format, namely ears and minds.

Why does 'measure' have such a visual connotation.?

[udailey]

Originally Posted by DRONE7

@udailey

Yes, though we are 'measuring' that something with devices appropriate to its format, namely ears and minds.

Why does 'measure' have such a visual connotation.?

I 'hear' you

[DRONE7]

Maybe I even meant

"ears and hearts"

as it is music we're discussing after all is said and done (and measured).



and here's to George and his generosity in sharing his ideas and efforts with us,

A very Merry Christmas to you George !

[soongsc]

Originally Posted by ondesx

There are two different ways to "match" these components. One is to buy a bunch of them and then, with a great deal of patience, to measure 5 points until two LDRs are similar enough to consider they are "matched". But I recommend to retry the same measures of these 2 components a day or two after this first measure... Some interesting surprises will arise...

The other method is to determine, whatever the LDRs, the requested value of current for a given resistance. Taking, of course, the same patience for the measures... When a control is performed one or two days after, one will find a better match between the measures than with the previous method.

The other advantage of this second method is that almost all the LDRs can be used without buying bunches !...

One more is that, obviously, if some LDR must be replaced, any new one will do and we don't have to find a new matched set !...

Again, this "5 points method" unfortunately wouldn't work for balanced use... The differential approach of the signal in balanced mode requires a much better "matching" all over the usable range. Whereas in single-ended mode a mismatch can be compensated by a balance control between channels, the same "mismatch" is much more, difficult or perhaps not possible to correct.

I have no good suggestion for "monitoring" the LDRs. But, their "calibration" from time to time is of course perfectly possible and I did it several times !...

The improvement of this method is the "automatic calibration", i. e. the automatic measure of all the LDRs. This will take from one hour to a day long if a very good matching is required. But who cares, it can be done when one is out for the day or the week-end !...

If all goes as planned, you might see a thesis on this subject. Product may take a while after that; if it happens, I'd like George to have the first opportunity of evaluating whether it fits into his operations or not. Got my fingers crossed.

[soongsc]

Originally Posted by DRONE7

Maybe I even meant as it is music we're discussing after all is said and done (and measured).



and here's to George and his generosity in sharing his ideas and efforts with us,

A very Merry Christmas to you George !

You got at least two with one stone.

[ondesx]

Originally Posted by soongsc

If all goes as planned, you might see a thesis on this subject. Product may take a while after that; if it happens, I'd like George to have the first opportunity of evaluating whether it fits into his operations or not. Got my fingers crossed.

Either I haven't explained it correctly or you don't understand English, but my comments and my explanations aren't any dark theory, or a "to do" list...

This attenuator is already a real functional device. Not a project...

Anyway, I worked a lot on this subject for two years, and I have enough material to write a book on the subject... But who cares ?