DIY Audio Projects Forum

FS: Lightspeed Attenuator matched LDRs
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Author:  RiGuy [ 30 Apr 2009, 10:20 ]
Post subject:  FS: Lightspeed Attenuator matched LDRs

I am going to buy another 300 LDRs in a few weeks to build the Lightspeed Attenuator. My matching is very very tight. I have now tested and matched over 400 of these things and you will certainly be happy with the product. All profits go to the 'Help Uriah Afford to DIY' fund.
Pricing is $30 for a matched set to make a stereo attenuator. Thats 4 LDRs, 2 matched for series, 2 matched for shunt.
The sound is WAY better than any ALPS or resistor ladder style attenuator. I can attest to that and its not a subtle increase in sound quality its frankly stunning. Many people have said it sounds better than Penny and Giles or TVC style pots. Have not heard these but it would not surprise me at all. This is my standard now and I cant imagine anything sounding better.
Output impedance is on average from 7-10k. I have got up to 25k one time and several times have got up to 15k.
Please search this forum for the Lightspeed Attenuator thread and you will see how to build it (very easy and I am here to help).
Balanced is frankly expensive. Needing 8 matched LDRs it is not only hard to find but it breaks up the possibility for other single ended pairs. So in light of how rare they are its $90 for the 8 it would take to build a balanced attenuator.
If you want me to do the matching I will and if you would like to do it yourself then you can participate in this buy by ordering a recomended 25 LDRs at the reduced price I will get. I can buy them for 2.21 each at the quantity I will be buying so for about $55.25 rather than the $75 it would cost at the 25qty level.
So Single Ended $30
Balanced $90
25 LDRs unmatched and sent to you $55.25
Than add .30 plus 3% and shipping to cover paypal fees.

UPDATE - 11 May 2009: Instructions to construct a DIY Lightspeed Passive Attenuator.

UPDATE - 12 Jan 2010: I put up a site to sell these.

Author:  billnchristy [ 30 Apr 2009, 11:33 ]
Post subject:  Re: Lightspeed Attenuator matched LDRs

A friend let me borrow one that was built by the original designer.

It is a very different sound, or more like there is no sound can really hear how much other pots color the sound.

That being said, I could not use it with my system, my Monarchy does something funky and it could not go to anywhere near zero and ramped up volume way too be aware of your impedence characteristics.

Other than that...go fer it, you won't be disappointed.

Author:  RiGuy [ 30 Apr 2009, 11:41 ]
Post subject:  Re: Lightspeed Attenuator matched LDRs

Very True. On most amps when you turn it up to half turn on the pot it is definitely at full volume. Not a problem to get used to at all though. When you say nowhere near zero, this has not been my experience. I can turn it down to a whisper, not off, but a whisper.
Thanks for your comments on the sound as well, I really hope many people try this as it can be the next thing to an epiphany in audio.

Author:  Gio [ 30 Apr 2009, 12:41 ]
Post subject:  Re: Lightspeed Attenuator matched LDRs

I agree, it is no sound whatsoever and that is what I like about it!

If I turn mine right down, it is not off, but as a whisper as Ri noted.

For low input impedance, you will need to use a buffer with it. Then you can use the buffer to color the sound to your liking! ;)

Put me down for a single ended set.

Ri, have you tried a balanced one?


Author:  RiGuy [ 30 Apr 2009, 14:49 ]
Post subject:  Re: Lightspeed Attenuator matched LDRs

Have not tried a balanced set. I dont use balanced. I kind of think people use balanced and dont most of the time know why they are doing it. When is the last time you saw someone with a balanced output on their CDP? Then they have balanced from pre to amp. Makes no sense to me. Anyway, I just did a full count. I used like 425 LDRs since I started messing with these. I just sent a buddy 40 of the ones that didnt match at all and then sent another 40 to a guy that wanted to mess around with ones that wouldnt match. I am left with 50. So even when I am at the 425 mark I still end up with about 33% losses. The manufacturers are to blame and it really gets me a bit riled up when they charge so much for each of these and then there is no consistency to the resistors so we must go through so much to match them. Well, anyway :) On a lighter note, the pure sound is worth it.

Author:  RiGuy [ 08 May 2009, 12:07 ]
Post subject:  Re: FS: Lightspeed Attenuator matched LDRs

Okay I just bought a huge amount of them. Here is the pricing:

I charge $4 for shipping anywhere in the world. Flat rate.
30 cents plus 3% of final total covers paypal fees.

I am paying 1.54 each for LDRs after taxes and paypal fees they end up at 1.667 each.

Unbalanced Stereo Matched Set = 38.42
Balanced Stereo Matched Set = 100.22

Examples of quantities and pricing for unmatched LDRs including all fees:
25 = 50.44
50 = 93.97
75 = 136.29
100 = 179.22

Here is how it is calculated

((LDRs*1.54)(taxes of 8.25%)) +Shipping + Minimum PayPal fee of 30 cents
Multiply the whole thing by 3%

There are now plenty of LDRs left so please dont hesitate to put your order in.

I am working on a paper describing how to assemble the Lightspeed Attenuator and why it works the way it does.

Update: Here are the instructions to assemble a DIY Lightspeed Passive Attenuator (11 May 2009).

There is an additional $3 in each price that was originally going toward the site, however, our gracious site master has refused it. If you make a purchase I will donate all of the $3 of each order to a charity that helps kids. Dont know which one yet, but if you have a suggestion toss it out there and lets consider it.


Author:  ondesx [ 16 May 2009, 00:41 ]
Post subject:  Re: FS: Lightspeed Attenuator matched LDRs

To RiGuy :

May be some guys don't know the interest of balanced gear, but let me say that most of the professional stuff still remain in this format anyway... Several HiFi DACs are, like several chips, balanced or better said bipolar ! In terms of noise cancellation, there isn't any other way to transport electric signals in LF. The quality of connection is far better than any CINCH/RCA and audio levels are 6 dB higher then in most HiFi world...

There is more than enough to definitely prefer "balanced" or bipolar gear. There is at least one drawback : the price of this improvement ! Of course you need twice the electronics used in unipolar world... But you get what you pay for, don't you ?... :)

Author:  CrazzyAbtTubes [ 30 May 2009, 12:06 ]
Post subject:  Re: FS: Lightspeed Attenuator matched LDRs

I am glad to see that this attenuator has become a project on the site because I really had no idea what it was, now that I see it, I would really like to construct one of these to try in some of my equipment.

I really have to say, I am fed up with scratchy, noisy, cheap pots, that only work 60-70 percent of the time unless you buy one of those super expensive plastic types. :D

Now if I had been smart I would have read the post more carfully, and I could have gotten some good deals on some LDR's. I suspect that I couldn't just go into my local electronics store and order the right ones could I? And even if I did they most likely wont be matched.

So now the question is how do I order? I do not have a visa card of any sort and have never ordered any thing on line other than from Parts Connection by means of phone. :) I did how ever find two LDR's in my salvaged parts boxes, #'s VTL5C4? probably not useful for this project.

Lastly I am greatfull to find out that there is a solution to the potentiometer horror and would like to support this project in any way I can. :up:

Author:  RiGuy [ 30 May 2009, 12:48 ]
Post subject:  Re: FS: Lightspeed Attenuator matched LDRs

It solves all those problems :)
I will be shipping LDRs on July 15th. Will ship after that as well, but if you get your order in now I will ship then.
PM sent.

Author:  megamahi [ 19 Jul 2009, 20:31 ]
Post subject:  Re: FS: Lightspeed Attenuator matched LDRs

Hey Ri,
Been a while since I've actually logged in here, finally got my amp done (after about 5 months :P ), and still working on casing the Pass B1. Do you still have matched LDRs for sale?

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