Lightspeed Attenuator a new passive preamp

[Panelhead]

Nelson I am sure your discrete buffer will help tthose who use either high output impedance sources or low impedance amplifiers.
I used mine for a long time with the primary source being a Pioneer TX-9100. The fixed output impedance was about 4.5k, 6.8K//15K. Surprisingly it sounded fine. Best active tried was great, but ended up getting rid of the big Pioneers. This way the LS works great without a stage on the output.
I can guess a little of the buffer, maybe a fet input and mosfet output. Devil is in the details. Thanks for sharing your knowledge with us.

George

[ventle]

Been reading the entire thread, each and every of the near 1300 posts now, but I still need to ask... how many LDRs do I need to buy to get enough matched pairs?

Thinking of building the 3-way input selector version posted a few pages ago, seems that I'm gonna need seven matched pairs for decent stereo tracking... right? Is buying 30 LDRs (sorted) from Allied gonna be sufficient?

[georgehifi]

Originally posted by ventle
Been reading the entire thread, each and every of the near 1300 posts now, but I still need to ask... how many LDRs do I need to buy to get enough matched pairs?

Thinking of building the 3-way input selector version posted a few pages ago, seems that I'm gonna need seven matched pairs for decent stereo tracking... right? Is buying 30 LDRs (sorted) from Allied gonna be sufficient?

Hi Ventle, you need 2 matched pairs for my standard 1 input stereo Lightspeed Attenuator.

For the 3 input contactless stereo version, you need 7 matched pairs, the seventh pair being the shunt to ground ones on the output, 30 may just get you home in the matching stakes, make sure you have a carton of Panadol on hand and lots of coffee when doing the matching.
I myself would just use a Qed source 3 input switch box, and when it's time for serious listening from one source, omit the switch box and go direct.

Cheers George

[mikelm]

but he wants to know how many he has to buy to get this many matched pairs

[georgehifi]

30 should get him home, but I would go the Qed route.
The Qed that I looked inside of had silver coated oxygen free wiring and for the switch it used a double leaf gold contact rotary Alps brand switch, if you have to use one this is about as high quality as you could go.
But still it was heard to be in the signal path, as when it was omited and the source was pluged in direct, it was as if someone had cleaned all the rca's sockets and plugs from source to amps.

Cheers George

[ventle]

Hi George, thanks for replying.

one of my goals with this "no compromise" amplifier would be getting everything in one box (input selector, volume control and power amplifier - just like the commercial integrated amps) - do you think that the contactless input selector version of the LS is gonna be inferior to your original series/shunt configuration? The way I see it the only practical difference is that with this design, you have two series LDRs connected in series compared to just one in yours, will this affect performance?

thanks again, and keep up the good work

[georgehifi]

I have never tried it myself, yes there is a question mark on the 2 x series LDR's, but who knows maybe it will sound even better.
I think that you will be the guinea pig for this one, as I don't think anyone has built it yet.

Cheers George

[ventle]

wouldn't that be nice, the worlds first LDR-based contactless input selector

anyone know the status of the uC-based LS-project with those italian guys? Been a while since they posted anything on this thread, and checking on their forum won't work as I unfortunately don't understand italian that well...

[georgehifi]

While we're on a roll with posts, time to do some recruiting for our own Passive Preamp forum.
Please vote here if you have not already done so.

http://www.diyaudio.com/request/

Cheers George

[ssmith]

Originally posted by georgehifi
While we're on a roll with posts, time to do some recruiting for our own Passive Preamp forum.
Please vote here if you have not already done so.

http://www.diyaudio.com/request/

Cheers George

done!, and my 10 LDRs have arrived from Allied... just about to get the matching process going...

going through the thread, there was at one point much talk about using bypass caps between the legs of the LDRs. I can;t seem to find an outcome of that discussion, and was just wondering if there was any verdict or if anyone else tried it?

Thanks George again for sharing the design, am looking forward to getting it going!