Reply with quote #16
If "fascinating" is code for crazy, or delusional, or ?, your right. Just ask anyone not involved in this hobby.
Reply with quote #17
I actually agree with you. I've been involved in audio for a long time. I don't believe in any type of magic parts, fancy cords, etc. When Erick asked me if I wanted to try his what I call "mad scientist" mod, I agreed because he is one of those rare innovative people who thinks in circuits & schematics. He's a long time friend and I trust him. What can I say, except that it works. I am tempted to build another Grid and leave it stock for comparison.
My reference is a Morrison ELAD, a solid state unit that is ruler flat and as quiet and distortion free as possible. And yes, Bruce's OTL amps can sound great with a SS preamp. I haven't compared them yet. The Grid is a really cool design that blows away a lot of super high priced stuff so why not use it as a base for experimentation?
Reply with quote #18
Originally Posted by
PAUL I find it fascinating that that rarely I have seen a response of someone on any of the forums admitting that after spending money or time on a mod that did not make their wigit sound so much better.
I guess that is because that is a frustrating experience. I have done lots of things that did not work out. Most of them did not any worse either.
The second point is that people hear differences that are just not there after they did some changes. That usually happens to me so whenever possible I do a blindtest.
And last but not least, it is a human thing to be overexcited to have found something "fantastic" and therefore wants to cry it out to the whole world so that everybody can benefit from it (might have something to do with evolution, I can imagine some thousand years ago a very hairy guy crying "Uuhhhg me can make fire"! ). It is very uncommon for people to run around and tell everybody about their failure.
Regarding the LDR I have done some reading, I cannot clearly understand the graphs of THD caused by the LDRs postet by Mr. Pass.
However, I will get 16 VTL5C9. PerkinElmer state in their docs THD should be around 0.05% at 3kOhm and 0,08% at 30kOhm at 1V. At 2V 0,08 and 0,15%. The VTL5C9 is rated at 680 Ohm a 2mA LED current, should be about 120Ohm at 20mA, and 10 times the off value compared to the NSL-32SR2 with a much steeper slope.
I will have to measure them but I guess if I use two of them in parallel will give reasonable low resistance at around 60Ohm and will lower channel differences and even reduce noise.
I do not understand the necessity of a mute function, if want that I switch to an unused input. I just want good control in the range I usually listen to - that is in my setup about 90° turn angle.
However, I honestly do not trust this LDR stuff until I have measured it, I did not switch to stepped attenuators because of 3dB and more channel difference of my Alps pots just to revert to something because it is new. Another concern is aging, 10% resistance increase per year (continuous operation) does not sound too god to me, as that will not affect all LDRs equally.
I intended to have the LDRs all the time on, as there is a 10% resistance difference between the LDR when 24 hours with no light and 24 hours with rated light. That is not a good idea when the LDR changes its resistance by 10% after a year on.
In contrast (I have no other data) high precision thin film chip resistors change by 0.25% in 25 years at 25°C (in one year at 70°C).
I really fear that I will have to adjust the LDR volume control once a week or month.
But it is fun, so I will test it.
Anyone here tested the channel balance of the LDR control over longer time?
Zhank you in advance,
Reply with quote #19
Testing over time? I built my lightspeed in the summerof 2007. I use my ears as the guide, and I could not be happier with the performance. I built a version that uses a balance control. All that takes is a second pot, the lowest cost you can find at $1.50, because the pot is not in the circuit. It is simply a light dimmer. The circuit cac be scratch built in a couple of hours for about $50. (depending on your transformer) I used the schematic here.
http://www.diyaudio.com/forums/analog-line-level/80194-lightspeed-attenuator-new-passive-preamp-58.html You can start by owering with an old wall wart. The quality of power does makw surprising improvements. You could tap into th GG filament power and add a choke and some nice oscon caps and have reference quality. There are thousands of posts where people have compared it to all manners of competition from stepped ladders to TVCs to megga$ linestages and to some people it comes up a winner. It is no surprise that in the GG device it could be amazing. People worry about stability of the LDRs and their effect on balance. I can tell you now from 4 years listening they do not drift or have any issue that can be heard. There is a lot of difference in balance on the recorded source material. I find myself tunning the balance to compensate for the source but never for the LDRs. I have a remote control setup that adjusts balance in .1DB increments, and I find myself making minor corrections between CDs.
Reply with quote #20
Originally Posted by
Walter Testing over time? I built my lightspeed in the summerof 2007.
could you measure the resistance of the pots? No need to hurry, just when you get around?
On the schematic, what is "ETH" left and right?
Reply with quote #21
I see, ETh is earth, seems to make sense for a passive preamp.
Reply with quote #22
To the best of my knowlege, I am using a 50k log for the volume and 1000R linear as spec'd. Did you want to know the spec or the measured range of the pots? Walter
Reply with quote #23
Originally Posted by
Walter Tom, To the best of my knowlege, I am using a 50k log for the volume and 1000R linear as spec'd. Did you want to know the spec or the measured range of the pots? Walter
sorry, it should read "LDR" not pot. I wanted to know if the LDRs changed their values over time. If they did not change much since you are using them for 4 years now that would be promising.
Du you turn them off or keep them at 50% as suggested by some People?
Reply with quote #24
I read all the posts about drifting etc. If they do, I can't detect it. I left them on all the time for a couple of years. Frankly, at this stage I typically fire up the system 30 minutes before I plan to listen, then turn it off when I am done. I don't actually think the LDRs change appreciatively. For what it is worth when I built it, I attempted to compensate for warm up and keeping them dark. I actually glued 2 together with silicone, and then covered the whole thing in shrink wrap thinking it would keep the light out, and heat in. I can't say if this was worth while as I don't have a comparison. Perhaps so, as I do have great stability. Attached is a picture if it helps I can email a better resolution. I set it up so the LDR attenuators would be very close to the amp circuit to keep signal path short. The lightspeed power and controls are at the end of 12" of CATV cable for convenience. Attached Thumbnails
Reply with quote #25
I did read about the blind test you mentioned and sorry I blue it off. I saw problems with your testing methods. After 38 years  as an audio fool I have my own way of testing and it doesn't require a blind test. But my way is accurate as long as there is a reasonable audible difference, and if not, who cares. I would also conclude from your blind test that it didn't work out that well for you either or they were to close to tell any real difference. I would tell you why it didn't work but I suppose you would return the favor and blow my comments off as well. I now have a stepped attenuator, a ladder attenuator, a standard 27 mm ALPS, and a motorized 25 mm ALPS and was ready to test. But it looks like you have moved in a different direction. So I won't waste my time. Have fun and enjoy the music.
Reply with quote #26
thank for the information. I will test the LDR volume control and report.
Originally Posted by
sailor I did read about the blind test you mentioned and sorry I blue it off. I saw problems with your testing methods. After 38 years  as an audio fool I have my own way of testing and it doesn't require a blind test. But my way is accurate as long as there is a reasonable audible difference, and if not, who cares. I would also conclude from your blind test that it didn't work out that well for you either or they were to close to tell any real difference. I would tell you why it didn't work but I suppose you would return the favor and blow my comments off as well.
If I spend time and money into a project it will simply sound better. I have not tested volume controls until now.
I have tested cabling. I built two power supplies, one with expensive caps one with standard caps and at another occasion a standard PS and one with much more caps than needed. I cannot hear differences between standard caps and black gates or the like. At least not in a blind test.
That way I have also tested if I can detect relays in the signal path - I cannot. But then again, maybe the relays needed for the blind test cause too much trouble to make the other relays in the signal path audible.
Before I found the way to make my computer switch the relays I needed another person to do it manually.
This my way to rule out if I really can hear differences.
If you see a problem in that concept (apart from relays that might degrade the signal too much) I would be glad to hear it.
I now have a stepped attenuator, a ladder attenuator, a standard 27 mm ALPS, and a motorized 25 mm ALPS and was ready to test. But it looks like you have moved in a different direction. So I won't waste my time. Have fun and enjoy the music.
I will test the LDR system. I have ordered some VTL5C9. I do not know, if I like them. I will report, thank you for your offer. I would still like to know if the series and ladder do make a difference for now it is not so important to me. If I had stumbled across the LDRs before I would not have asked her.
Reply with quote #27
The lightspeed circuit is designed for the Silonex NSL-32SR2S. Avoid the 3S. Ideally you want the matched part. By matching, what they mean is they match within a pretty broad tolerance. Generally you still need to buy a few and find the matches. I bought 10, and found 2 sets of clear matches and another that looked pretty close. We likely should be posting this on the diyaudio site as I don't want to hijack this site for a lightspeed discussion. I only mentioned it earlier because I suspected it would complement a great preamp like the GG, and plan to build one when I get my Transcendent amp up and running.
Reply with quote #28
Originally Posted by
Walter The lightspeed circuit is designed for the Silonex NSL-32SR2S.
I will try the VTL5C9, they are available in Europe, price is OK, I ordered 16 of them.
We likely should be posting this on the diyaudio site as I don't want to hijack this site for a lightspeed discussion.
Which one? I found dozens of freds covering the lightspeed there!
I will post there as soon as I have data, I will post here as soon as I have it integrated into the pre and compared to the ladder type attenuator that I currently use.
Thank you all,
best regards Tom
Reply with quote #29
I have had my Warpspeed up and running for over a month (not in the GG yet but in the Dodd buffer, enjoying the sound too much to change just yet) and I have detected no drift or imbalance issues. The problem is that everything but the LDRs are potted so you cannot see whats going on, but what ever allan Flores is doing he is doing right