Lightspeed Attenuator a new passive preamp - Page 399 - diyAudio
Go Back   Home > Forums > Source & Line > Analog Line Level

Analog Line Level Preamplifiers , Passive Pre-amps, Crossovers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th February 2011, 10:57 PM   #3981
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
I just salvaged parts from a HP 3420B and found an aluminum block that seems to include two pairs of large LDRs.
Each pair's LDRs are connected by a tunnel with a lamp in the middle.
I post a photo later.

Last edited by Bernhard; 8th February 2011 at 11:00 PM.
  Reply With Quote
Old 8th February 2011, 11:02 PM   #3982
Blues is offline Blues  United States
Lightning In A Bottle
diyAudio Member
 
Blues's Avatar
 
Join Date: Sep 2003
Location: The Milky Way
The LEDs on the optocouplers of the Warpspeed are operated at more acceptable voltage/current levels anywhere you desire the volume control. At or near extremes on the Lightspeed will send it past the specified maximum 50mW...try it there for a length of time and you will lose the optocouplers. Keep it at pot mid-point please...

By comparison the Warpspeed actually has typical resistances on its listening range at very much lower levels than where the the Lightspeed operates. This is why the Lightspeed prefers higher input impedance amps. By this, the Lightspeed is more similar to typical high R pots used for passive volume control.

It's a solution and it is imperfect (which one is perfect anyway?) but imho closer to perfection than others. It will remain a riddle how it is done though, for now...
__________________
Life simplified! Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html
  Reply With Quote
Old 9th February 2011, 12:09 AM   #3983
ua100k is offline ua100k  United States
diyAudio Member
 
ua100k's Avatar
 
Join Date: Dec 2009
Location: Bernardsville, NJ
Quote:
Originally Posted by udailey View Post
Dead silence is achieved by pumping up the resistance of the series LDRs to extremes which emulates very high resistance pots.
Uriah
Several points on this.
A series and shunt resistors forms a voltage divide. Increasing the series and reducing the shunt at the same time will bring the division to a fraction of the input voltage. This is how the "Dead" silence is achieved. Not by just increasing the series resistance. If you have a series and shunt LDR and remove the power supply, this would still be voltage divider and you would theoretically get 50% of the voltage out - with not load. Depending on the input impedance of the load, the voltage division will change.

Second point. Turning "off" the LED will leave the LDR at the highest resistance. This is a natural state, not pumped up. In this state the LDR (depending on which you are using) will have about 1 Megaohm of resistance.

Quote:
Originally Posted by udailey View Post
The higher the resistance the higher the Johnson noise and the higher the resistance the more roll off you get of high frequencies.
Uriah
Johnson noise is proportional to thermal values in resistors, that is power dissipation, and voltage. The greater the resistance, the lower the power dissipation and the lower the noise. The voltage across the LDR will change according to its role - shunt, series, and the load. This would be a constant regardless of design - if the design uses a 2 LDR's in a voltage divider.

The ability to fine tune the current, hence the LED and the Light will be the ultimate decision on how to design the circuit. Going even further, the noise on the voltage of the LED will have more effect the the Johnson noise.

As a final note though, we have to pick our poison as all solutions will have some trade offs, some of them subjective.
  Reply With Quote
Old 9th February 2011, 01:04 AM   #3984
Blues is offline Blues  United States
Lightning In A Bottle
diyAudio Member
 
Blues's Avatar
 
Join Date: Sep 2003
Location: The Milky Way
Although the Lightspeed is a voltage divider, the range of operation is limited by the power delivery design to the LEDs -it still operates where amps still has enough voltage at the input to amplify and be heard.

I don't think Johnson Noise should even be considered, unless someone hears some kind of white noise coming from the volume control without the music playing.
__________________
Life simplified! Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html
  Reply With Quote
Old 9th February 2011, 01:10 AM   #3985
Blues is offline Blues  United States
Lightning In A Bottle
diyAudio Member
 
Blues's Avatar
 
Join Date: Sep 2003
Location: The Milky Way
And to add...the series LDR does not need to go dark or the shunt LDR to go very low for the Warpspeed to go dead silent...just the correct ratio of series/shunt R.
__________________
Life simplified! Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html
  Reply With Quote
Old 9th February 2011, 01:43 AM   #3986
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
I suppose Johnson Noise is not going to be audible but certainly it is changed (increased/decreased) by resistance.
Vn=SquareRoot(4KTRB) where k is Bozeman's constant, B is bandwitdth, T is absolute temp, R is the resistance. Its a pretty low amount of noise until we take the resistance up into and above megohms and then when added to any other noise in the circuit it really can have an effect.
This is my understanding from Self's Small signal book Page 10 Table 1.2 and he is talking about plain resistors as well as pots.
At anyrate, I feel like I took the bait to start talking about another's product on the Lightspeed thread.. again.
1 Megohm when turned off? Thats not a NSL32SR2 or an NSL32SR3. Sounds like a NSL32 or NSL32SR5, if its a Silonex Audiohm product. Ooh, or a combo of one of those for series and SR2 for shunt..

Cant wait to see pics of that massive optocoupler from HP. From a printer? That would make sense. Sounds fun
Uriah
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com

Last edited by udailey; 9th February 2011 at 01:46 AM.
  Reply With Quote
Old 9th February 2011, 02:32 AM   #3987
Blues is offline Blues  United States
Lightning In A Bottle
diyAudio Member
 
Blues's Avatar
 
Join Date: Sep 2003
Location: The Milky Way
I'll repeat, the Lightspeed's listening range has the series/shunt combination at higher R values, 4k to 5k on my version with the volume pot at midpoint. So if J Noise is a factor, which I doubt even with the Lightspeed, it is more affected.

At any rate, I don't need bait to get you hooked...in fact you're the one who tossed a fishing line. You can choose not to answer if you feel you are being baited...
__________________
Life simplified! Leap into the Warpspeed wormhole... http://www.6moons.com/audioreviews/warpspeed/1.html
  Reply With Quote
Old 9th February 2011, 10:07 AM   #3988
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
Diameter of each plate is 22mm.

If you can get a hp 3420b cheap somewhere...

Click the image to open in full size.
  Reply With Quote
Old 9th February 2011, 10:13 AM   #3989
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
boyz - isn't this George's thread ?

I can understand and support process of searching for even better alternatives , but something is fishy smelling here

cordially

ZM
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote
Old 9th February 2011, 11:33 AM   #3990
soongsc is offline soongsc  Taiwan
diyAudio Member
 
soongsc's Avatar
 
Join Date: Mar 2005
Location: Taiwan
I agree, if there are technical issues regarding the Lightspeeds, they can present data. With no data, I think other products are really should have their own thread.
__________________
Hear the real thing!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 01:47 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2