Have you done your LightSpeed passive, Ben?

fredv

I just started the hell process to match up the 50's that I have. It is really hard to measure them because the same LDR can vary at different time of the day. However, the reward seems to be great once it is all set and done. So, have you fired up yours yet?

ben62670

Working on it. Jerry and I have to come to an agreement of what we want. There is a guy who sells matched LDR's on DIYaudio. I would rather have him do it and me double check. It is a bear to get them matched! Let me know any ideas for the circuit board and I will send you one.

fredv

I think you are referring to Uriah, he is nice guy. I bought my unmatch LDR's from his group buy. I am doing the matching myself because I wanted to know more about this devices.

I can tell you this much after one long weekend and a few evenings with these things. I only trust the LDR's are matched unless I do the matching myself!!! I am going to do at least 2 rounds of measurement. The 1st round will allow me to group those that have similar characteristics. The second round is to measure each group together. This way I can be sure they are all measured under very very close environment. So, if the readings are close, I can say they are matched.

Hopefully, I will be able to tell you how many matched pairs out of a bulk of 50's soon :-)

ben62670

Well keep me in the loop. I will need 2 sets of 4. I will pay. you have gone way above and beyond helping here, and the work is work;)
Thanks
Ben

fredv

It sounds like you plan to build a balance version. I will let you know what I end up with. Just a heads up, the choice of the impedance of the pot and the number of LDR's one pot drives has a significant impact to the usable range. When I am done, I will share with you what I learn. Stay tuned!!

ben62670

Actually Fred what I have seen from the latest is that they do a voltage divider type of circuit instead of just a series shunt type of attenuation. I lost your number, but if you want to talk soon I would love to hear from you via email. I can call for free. There is 4 of us serious about this project so far. Too much to type about, but some talking may go further to development to a universal board we may all be able to share:)
Take care
Ben

fredv

I will be lot of town sooner today, but I did went through all the posts!! Yes, use LDR for both series/shunt is the way to go. For a stereo SE input, this will need 2 matching pairs, i.e. 2 sets of 2. If the target is to build one like George's original design which is my plan, then it is probably easier to do point to point on a perforated board. I can etch a few boards for this design as well if needed. Now, if you are talking about making a board that uses uC to control the attenuation of of each LDR, then it will be way way beyond my class :-)

My goal is to build the simple series/shunt to try first because most, if not all, stayed with this design and claimed that was the best sonically. There are a few enhancements that can be built on the top this series/shunt basic topology, mostly on enhancing the power supply to the LED.

I will mail you my phone number before I leave home, and I will be back online some time in the afternoon. LOL, I am bring my testing jig with me so that I can do more matching while I am bored :-)