Passive attack

Light dependent resistor...

 

Mine still not fully run-in but the answer is short.

A great bargain, and actually very good.

 

From an older TVC owner...

Still love it now.
Actually had mine sat on one shelf with a 552 on another (could have had either)
Prefered the TVC and it was a tad cheaper as well...

 

what TVC do you own?

 

MFA 'silver'.

Was a rather refreshing 'wind of change' in my system.
Now nearly 12 months old I guess - talk about eye opening!

I will be investigating your thoughts on double 'c' cores later this year - but for now I am totally happy with what I have, so I just listen to music.

 

anubisgrau, the best way to describe the Lightspeed Attenuator is that it has just one fixed soldered resistor that is in the signal path between the source (cd) or phono stage, and the power amp.

This resistor is soldered in place and has no contact points that potentiometers "pots" (potentiometers) or switched resistor (dact type) or TVC (Transformer) volume controls have.

Now this resistor "LDR" (light dependant resistor) has the ability to change it's resistance according to how much light "LED"
(light emmiting diode) is shone on it, hence it can control the volume without any mechanical contacts needed in the signal path.

It is a known fact that any light weight contacts (switches and especially pots and their wipers) have a diode rectification effect on the AC music signal, "trying to rectify it " which is very bad.
The LDR system totally addresses is diode rectification effect. This is why it is so transparent and totaly honest to the source, not adding any colourations or distortions to the source, it is just like being able to plug your cd players fixed output directly into your poweramp yet having control over the volume.
Ever wonder why when after you have cleaned your RCA plugs and sockets on your interconects, your system always sounds better. This is a similar type of contact albeit a much better one than the feather weight one inside a pot and the wiper contact of a switched resistor type control, because an RCA has a much larger and stronger pressure contact area, but still benefits by keeping it clean.
I hope this has given you a bit more insight to the Lightspeed Attenuator and it's revolutionary way of controlling volume, you can read a great deal more about it and it's history here. It's 60 pages over 600 posts, but interesting.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194

Cheers George

 

this definitely sounds interesting - are there any reports on how the thing sounds. i am particularly interested in to see if it addresses a common passive problem - drive & energy (not necessarily an extension, that's OK) in lower registers.

geroge, how much does it cost?

 

As far as bass, drive or dynamics, these are a non issue so long as the impedence match is correct.
low output impedace of source: lower than < 100ohms
high input impedance of poweramps: higher than >50k
If these two paramenters are achived, there is no problem with bass, drive or dynamics, if anything users are saying the Lightspeed is the most dynamic pre they have ever heard, but in a big effortless transparent way, rather than a squeezed thin shot out way.
What you also have to remember is the frequency response of the Lightspeed is from DC (0hz) to >gigahertz (Lightspeed) hence the name, there is no limiting of the frequency response or current because there is nothing to limit it, it's as though you've pluged your source directly into your power amps.
As for cost, $500 Australian, which is about 200 pound or 300 euro.
If you are up to it you can build one yourself, half way through the 60 page thread on diyaudio I have relented and give all instructions on how to do it for less than half that price, and about 1 days labour (some very tedious matching of the ldr's).

Cheers George

 

what issues would be with driving a low imp power amp (>10k)?

 

If you have a power amp that is 10k input impedance most tube preamps as well the passives will loose some bass attack, this sort of amp in my opinion is a bad design as it will only be driven correctly with a strong transistor preamp like Krell, Rowland Research and pre's of that ilk.
Thank god most good power amps today are finally getting now up to the 100k and more which is great for all types of preamps, amps like Krell have gone from the standard 47k up to 100k and some tube amps like Rogue are up to 1meg input impedance. All is looking good for the Passive Attack.

Cheers George

 

well, there is a number of excellent 100 ohm or less preamps and i luckily have some of these so no issues whatsoever, including every TVC i tried with a 50ohm output imp source

 

George, do you have a website?

 

No sorry Markus, if I were to start and maintain websites, advertising, staff, higher number of orders and all else that goes with it, the price of the units would treble and it would cease to become a passion for me and start to become work, I like things low key that way the passion remains.
And I have great satisfaction in that I have built and calibrated every unit from start to finish, and chatted personally to every owner, about our passion/hobby.
But everything you need to know is on the 60 pages of diyaudio forum I even have pictures somewhere posted there.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=80194

Cheers George

 

A very simple website is now up, too much pressure to get one going.

Cheers George

 

I have built several of these Lightspeeds as I bought a lot of LDRs to get the best price per unit.

I have just bought a motorised Alps pot to go in a remote controlled passive pre that I made years ago to which I have added a L/Speed board.

I have to say that it is really really impressive. I find it hard to get the right volume by keep jumping up and down to make fine adjustments with a manual pot, and your ears can easily play tricks. However with RC you can make fine adjustments and get continuity between tracks on CDs.

I have only used cheap carbon track pots previously because the quality is irrelevant. They are £2.00 each, The Alps was £20, but for the convenience of RC it was money well spent.

 

There was a comparison of these pre amps here:
https://www.stereo.net.au/forums/to...-lightspeed-diy-ldr-pre-vs-stereo-coffee-diy/