Lightspeed Attenuator a new passive preamp

[powerbecker]

snip
as for the distortion, I challenge you to hear the difference between .001% and .1% on a system, and that .1% distortion is at 2volts rms, show me a cd player or dac that gives 2vrms, while playing music, it would blow an amp to kingdom come.
Heinz you have yet to hear one of these. Do yourself a favour and listen to one, I'm sure you'll change your views towards them.

Ok George, I will not hear a difference (but may be other), also because I go from audio to industry (amp) design 1982 and today I hear very seldom music ... it`s to noisy!
BUT I like till today "perfect" things, that`s also necessary in my business.
And as I said before I will compare a LDR attenuator with other ones.. in ALL perspectives!
So I think how to eliminate the main "disadvantages":
1. Stability (Temp/Time)
2. Equality
3. Distortion
and I believe that together with a little bit more "electronic" one can get a fare more "perfect" thing
Regards
Heinz

[georgehifi]

Too much perefect specs can be a bad thing, trust your ears and the specs. We can always hang plenty of feedback around amp thing to make a perfect spec, but not awalys for a perfect sound, I noticed you listen to some Class D amplifiers, You could'nt pay me to try to enjoy a Class D amp, I also love to listen to good high power (50watt) single ended DHT 805 tube amps, shocking specs great sound. As always trust your ears.


Cheers George

[powerbecker]

snip
I noticed you listen to some Class D amplifiers

?? Never heard such a amp though a build a lot of them,
the last one i see deliver 80kW...but was limited to 15 kHz....to test big generators isolation....i had to look for a speaker!
Regards
Heinz

[gfinlayson]

George,

I don't believe distortion from the LDR to be an issue either. My power amps will start to clip at about 1 V rms input, which for the VTL5C3 is worst case maybe 0.1 % distortion. By that level my ears will be bleeding, so I won't be able to hear the distortion anyway.

Graeme

[georgehifi]

Originally posted by gfinlayson
George,

I don't believe distortion from the LDR to be an issue either. My power amps will start to clip at about 1 V rms input, which for the VTL5C3 is worst case maybe 0.1 % distortion. By that level my ears will be bleeding, so I won't be able to hear the distortion anyway.

Graeme

Agreed, it's not a problem at all, it's the cleanest most transparent active preamp or passive-preamp that I've ever listened to, and it goes from dc to gigahertz in frequency.
Even if it did manage to give 0.1% distortion, it's second harmonic in nature which is pleasing to the ear, not that you would hear .1%. Some good tube amps give more than 1%, a lot of them are hard to beat sound wise, not to mention speakers, up to 10%
All of my customers have said that when they have used the Lightspeed Attenuator, it's been the blackest background they have heard on their systems. So feel confident in making one and report your findings back here, I would love to hear your comments.

Cheers George

[gfinlayson]

George,

Thanks for sharing the design. I'm just trying to find a stockist who has the PE VTL5C3 available in the UK. Once I've got some, I'll whip an attenuator together and try it out.

Graeme

[georgehifi]

For those of you who are interested a couple of photos.

Front

[georgehifi]

And rear.

Cheers George

[chewrock]

Am I reading page 37 of the Perkin-Elmer specification correctly? These units change resistance at the rate of up to 10% per year? The useful life expectancy is around 1000 hours? Wow, the guys who sell preamps with these volume controls have a better racket going than the phonograph cartridge people used to.

The average phonograph stylus lasts about 1000 hours, too.

As I said, I'm really very happy with my twenty-year old Penny & Giles fader. I just checked it for tracking and overall resistance. Dang if that piece of junk isn't still within 1% of spec after two decades of constant use.

Oh, and I checked with Penny & Giles. The wipers on their faders do NOT use a "feather weight" wiper system, and contact bounce doesn't occur until the AC current through the pots exceeds a value that would cause your LDRs to catch fire.

One of the reasons that it still requires a good sized knob to turn it is that the wipers have plenty of pressure on them and there is noticeable friction as a result.

The Clarostat factory in Mexico told me the same thing. Conductive plastic potentiometers won't work unless there is considerable pressure on the wipers. It's actually a design objective to figure out how to make the element as small as possible so that the applied torque can be reduced. The brand new Clarostat precision pots that I just bought for my new microphone preamp came straight out of the box within 1% for overall resistance and matching each other within 0.1%. Not bad for a couple of precision conductive plastic pots that cost $25 USD delivered to my door by Newark.

I don't know where you get your information, but the manufacturers of the pots seem to think you are misinformed.

[georgehifi]

chewrock, mine are'nt the Perkinelmer ones, mine are from a different company, also I told you they have been on now for 2 years 24/7, are you deaf?, not just mine but all of my customers, and all are as good now as the day they were built. As for the Perkinelmer VTL5C3 lasting only 41 days, you are scare mongering, if you use them as I have outlined, the life should be as long as my units, which so far is 17500 hrs and still going strong.
As for all your negative comments, it's bizzare that someone thinks they can give ANY constructive input when they have not even listened to or built one, and who admits they listen to oxidized pots that are over 20 years old.