Lightspeed Attenuator - "LDR" Volume Controls

[bpape]

Mike

Where can I find out about the LDR?  How hard is it to do? 

Bryan

[richidoo]

Original thread that started it all. http://www.diyaudio.com/forums/showthread.php?t=80194
Current kit group buy: http://www.diyaudio.com/forums/showthread.php?t=148518
Buy LDRs from Allied: http://www.alliedelec.com/SILONEX/
Silonex mfg of LDRs, sitemap, see AudiOhm products: http://www1.silonex.com/sitemap.html

Like any LED they should be driven with current which will provide linear control of resistance, but the original Lightspeed design drives them with voltage, so matching the LDRs is the hardest part. But it is very simple to build. A guy on diy is selling kits with pre-matched LDRs. MAXIM also makes LED driver ICs http://www.maxim-ic.com/ With a little reading you can probably find an easy path.
Rich

[mgalusha]

Bryan,

Rich already posted lots of info. Another reference is this: http://www.diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/

The LDR attenuator does sound really good but it can be finicky. I've been fighting with mine for about a month. It all started when I wanted to add a balance control. I've been through perhaps a dozen configurations trying to find the best combination of attenuation and noise.

[richidoo]

The idea of microprocessor controlling the resistors via D/A and driver appeals to me. That would solve some issues with analog control, add lots of cool features, but has its own problems, mainly that I don't know how. 

[mgalusha]

I love the possibilities of something like that. I have a 100 step remote controlled attenuator I bought from Hong Kong a few years back. I have been contemplating the idea of using the relays & resistors to control a variable current source so the LDR's would be driven via a CS vs the variable resistor in the current setup. Perhaps a project for the winter, which seems like it's going to arrive all to soon. Bleh.

The guy I bought my matched LDR's from is Uriah Dailey and he was a pleasure to deal with. If he's still running the GB I have zero reservations about buying from him. I've purchased from him twice and could not be happier with the response.

mike

oh, sorry for hosing your thread Rich.

[richidoo]

Hose away, it's sold.   But I thikn I'll move it to a new thread since we might wanna explore this VC.

Yes, it is Uriah's GB.  I read his page about it today, seems thorough enough for a beginner to build. But there's no balanced control,   I personally don't need more balance, I am well balanced enough as I am. 

[rollo]

Hey you gents heard of the Slagleformrers. Hearing dome good things about this passive volume control. I believe bent Audio was doing a joint venture with Dave Slagle. I believe they are about $150.




charles

[richidoo]

My feastrex buddy has the new bent with custom slagleformers, says it is awesome.

[mgalusha]

I have read lots of good things about his autoformers, have not tried them myself.

[bpape]

Hey Mike

When you figure out what works, please post it.  I'll stick with the stock control for now.  I have no idea how good the stock volume control on the GG is.   Would a TKD be worth the money or not?

Bryan

[mgalusha]

Bryan,

The stock volume pot on the GG doesn't track well, at least the one I had didn't.

I have a TKD in the preamp I use at work. I named it the little guy as it has only 1 tube and a small footprint. I used to have a TKD in my main pre but it gave up the ghost about 6 months ago, one of the reasons I started futzing with the LDR's.

I still have more experimenting to do. I am closer, it's sounding very good and I think I have the impedances close as it's not creating too much noise when I turn it up. At first I was getting too much noise from the input tube, I believe this was because the Zout of the LDR was pretty high.

Part of me wants to try the Slagleformers. I've read about them for years and he now has a 28 tap model and I have a nice pair of 32 position Daven switches...

[Regg]

Does anyone here have experience with Ed Schilling's The Truth Preamp?

http://www.thehornshoppe.com/the_truth_pre_amp.html

[richidoo]

I read about it when he first announced it, details cloaked in secrecy. Not heard much about it since then.  Is it LDR based?
Rich

[Regg]

I read about it when he first announced it, details cloaked in secrecy. Not heard much about it since then.  Is it LDR based?
Rich

Based on Ed's comments early on--that his design came about when he "started investigating LDRs"--I'm assuming that The Truth Preamp basically implements an LDR volume control + active buffer in some way, but I don't really know for sure.

Someone mentioned on another forum that they would be comparing their Lightspeed to The Truth when it arrived but I haven't seen that review yet...should be an interesting comparison though.