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NEW Silonex LDRs for Lightspeed Attenuator

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Well, I have been getting more requests for LDRs and have enlisted the help of a fellow DIYer. Sonidos will be helping me with this next batch.

Again we will be donating $3 per set do DIYaudio. Last time I was able to donate $183.

So, an unbalanced single ended set like you would need if you use RCA inputs is $38.42. That total includes paypal fees, donation, and worldwide shipping.

A balanced set is $100.22 which again includes donation, paypal fees, and worldwide shipping.

Last batch of LDRs were matching absolutely great but needed a 500k audio pot to get them working in the resistance range we need. This is a new batch and I expect to once again be using a 100k pot to control them.

Directions to build are here : http://diyaudioprojects.com/Solid/DIY-Lightspeed-Passive-Attenuator/

DIYaudio thread on the attenuator is here: http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194&highlight=lightspeed

This is the EASIEST build on DIYaudio. I frankly cant think of anything easier or more rewarding. The increase in sound quality is absolutely second to none. I have communicated with a few DIYers who own Prometheus TVC preamps which had previously been thought to be the MOST transparent passive pre. Not anymore. They have confirmed that the Lightspeed is beyond the TVC. DIYers are controlling their B1 buffers with the Lightspeed and in cases where a buffer is not needed they prefer a Lightspeed to the B1 which is also one of the best preamps you can find.

So the question of what amps can this drive comes up. So far we know that amps with 100k input impedance and less can be driven. Really this includes nearly everything. Chipamps to Class A and tube amps as well are all game. Personally I have driven a MyRefC, a LM3886 chip amp, an F5 Class A Pass amp.

I will help you build this passive preamp. You are NOT ALONE. You can feel free to ask questions on the original Lightspeed thread or here or you can email me.

Dont over complicate it. This really is as easy as I make it sound. You can build it on perf board or simply solder it to the RCA connectors inside your amp or right onto the amp. The LDRs are very small and will solder easily where I have mentioned.

Read the instructions. Its easy, its a huge increase in sound quality. It will cost you about $50 to build including the order of the LDRs. Maybe a few dollars less.

Well, I will leave it at that except to say that they will ship in 6 to 8 weeks and as we get started on the matching we will let you know how things are going and if the ship date moves up any.

Thanks
Uriah
 
udailey said:


Last batch of LDRs were matching absolutely great but needed a 500k audio pot to get them working in the resistance range we need. This is a new batch and I expect to once again be using a 100k pot to control them.


Thanks
Uriah


Uriah

I wonder the one that I got from you (matched one) few months ago is it to be use with 100k or 500k pot...??? :confused:
 
This is how easy it is to build the best passive pre out there.
There is a single gang pot version and a dual gang pot version. I will post both. Single gang first.
Uriah
 

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If you use a dual gang pot this is how to do it.
This is an older drawing and I leave it as is but suggest changes.
The 100Ohm resistors can be replaced with one 1k resistor in front of the pot in series with 5VDC just like in the picture in the last post. This is to protect your pot from burning out in the long run. I have not had any problem and I have not had any reported problems, but its just a precaution.
Also, this pic shows how to insert trimmer pots if there is a reason you want to change the balance of the passive pre. You can leave them out or use just one on the channel with the least resistance or replace it with a chassis mount pot so you can adjust from the outside of the chassis.
Uriah
 

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Uriah,

I am doing a single LDR shunt circuit for a 6 channel amplifier attached to my home theater PC but I want to use the R3 LDRs not the R2 as the distortion is lower for the R3. I intend driving each LDR individually from a 6 channel programmable potentiometer, the DS1806, which will be connected to the serial port of a PC for control (toggling the Tx, RTS and DTR lines to send the serial bits to the Ds1806 using a .NET program). To get sufficient current to drive the LED I will be using a high current opamp per LDR in a constant current source configuration (MAX4167 single supply high current opamp to keep it simple). This setup will allow me to measure each LDR individually and create a lookup table in .NET to balance the response curve out across all 6 LDRs, as finding 6 perfectly matching R3 LDRs will be pretty hard. The .NET software will keep the volume control level between reboots and will also address each LDR separately for real time fine tuning when changing volume.

So I'm wondering if you would sell 6 "moderately" matched R3 LDRs as I can do the fine tuning matchup in software. If so, how much?

I can share the circuit and software if anyone is interested.

Regards.
Dean
 
Im not sure, but isnt the careful matching to make sure all LDR reacts the same at any SPL levels ?
Or else the difference between them would change at every SPL change ?

I will be using a lookup table on the computer to real time adjust the current levels of the LEDs according to the volume level (not signal level). However this will only work for fine tuning, the devices will still need to be somewhat matched (eg. +- 3db) and have the same curve characteristics.

Uriah, are you still selling unmatched batches? Given that I have to take measurements to build the lookup table, I might as well do the matching myself. I wanted to use the R3 LDRs however after doing modelling I need more low on resistance than the R3 can give (and less of the off resistance range) - so will go for R2s. Let me know how much for 25? Thanks!
 
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