Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Lightspeed Attenuator a new passive preamp
Lightspeed Attenuator a new passive preamp
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 1st December 2013, 01:16 PM   #5171
wapo54001 is offline wapo54001  United States
diyAudio Member
 
Join Date: Nov 2008
Here is a question for the folks who have long experience with multiple copies of the Silonex LDR -- what is the maximum current you feel comfortable applying to the LDR on a permanent, continuous basis that will not affect the characterisitics of the LDR over the long term?
  Reply With Quote
Old 1st December 2013, 07:19 PM   #5172
georgehifi is offline georgehifi  Australia
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
My prototype of the production Lightspeed Attenuator MKII has now been on 24/7 for 8 years and is still in perfect calibration. Anyone who pushes them past 20mA is asking for a shortened life and drift problems over time, I have done/found this pushing them to 25mA on test.

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 1st December 2013, 11:58 PM   #5173
wapo54001 is offline wapo54001  United States
diyAudio Member
 
Join Date: Nov 2008
Quote:
Originally Posted by georgehifi View Post
My prototype of the production Lightspeed Attenuator MKII has now been on 24/7 for 8 years and is still in perfect calibration. Anyone who pushes them past 20mA is asking for a shortened life and drift problems over time, I have done/found this pushing them to 25mA on test.

Cheers George
George, you have said this in the past but, do you turn your pot to miminum and that drives the shunt at 20ma and leave it that way for days on end? If you do something like that, your example can be construed as an endorsement for 20ma being the level at which everything remains stable. I'm looking for a value that can left set that way whenever the system is not being used.

I've just come from my workshop and I was driving an LDR which delivered 50 ohms at just under 4 milliamps. At 11 milliamps, it was measuring 34 ohms. That device happens to be the best unit I've gotten from Uriah out of maybe 35 devices that I've bought for testing and I don't have a match for it, it's the only one that will deliver that low a resistance at that current.

Initially, I had my board running at 9.9 milliamps maximum, but I decided that loosening the tolerance just a little to 11ma would make a much higher percentage of LDRs workable in my system. I still plan to use the lesser performing LDRs in the series position and the better performing LDRs in the shunt positions.

I'd like to take the board to 15ma, but unless I get strong corroboration that leaving an LDR at 15ma does nothing, I'll stay at 11 milliamps maximum.
  Reply With Quote
Old 2nd December 2013, 12:05 AM   #5174
georgehifi is offline georgehifi  Australia
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Quote:
Originally Posted by wapo54001 View Post
George, you have said this in the past but, do you turn your pot to miminum and that drives the shunt at 20ma and leave it that way for days on end? If you do something like that, your example can be construed as an endorsement for 20ma being the level at which everything remains stable. .
Yes both min and max so I can gauge both shunt and series for their longevity. Also the use of NSL32SR2/S will give you a far better low impedance at this 20mA than all others will.
And if you use the S version in bulk they come from the same batch and give you the ablity to quad match, which is also a plus as I've stated many times.

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 2nd December 2013, 01:49 AM   #5175
jameshillj is offline jameshillj  Australia
diyAudio Member
 
Join Date: Feb 2005
Location: Melbourne
Please excuse me for 'butting in', but what is the importance/significance of operating the LDRs at less than 50 ohms resistance?
  Reply With Quote
Old 2nd December 2013, 02:38 AM   #5176
georgehifi is offline georgehifi  Australia
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Quote:
Originally Posted by jameshillj View Post
Please excuse me for 'butting in', but what is the importance/significance of operating the LDRs at less than 50 ohms resistance?
Lower minimum levels especially for/on high efficiency speakers/systems, like horns.

Cheers George
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 2nd December 2013, 06:37 PM   #5177
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
Wapo, In my Lighter Note I use LM334 which wont deliver greater than 10mA. I have had one customer complain of LDR failure that I thought was due to LED failure. Like you noted we dont need 20mA to get to 40 ohms which is where I think it ought to be limited to. I feel that driving them into resistances lower than 40 is where the damage starts to occur. Maybe you could just parallel another shunt LDR to get 20R or a few more to get 10R which could give you 60dB of attenuation with a series of around 10k. Most of the time you could turn the paralleled LDRs off. The most common complaint is the min volume and when they have an efficient system there is no cure besides lower shunt resistance and higher series resistance. However, higher series resistance is not the best cure because of resistance wavering about and also because the sound gets kind of mushy at higher resistances compared to my favorite of 6k.
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com

Last edited by udailey; 2nd December 2013 at 06:55 PM.
  Reply With Quote
Old 2nd December 2013, 08:03 PM   #5178
wapo54001 is offline wapo54001  United States
diyAudio Member
 
Join Date: Nov 2008
Quote:
Originally Posted by udailey View Post
Wapo, In my Lighter Note I use LM334 which wont deliver greater than 10mA. I have had one customer complain of LDR failure that I thought was due to LED failure. Like you noted we dont need 20mA to get to 40 ohms which is where I think it ought to be limited to. I feel that driving them into resistances lower than 40 is where the damage starts to occur. Maybe you could just parallel another shunt LDR to get 20R or a few more to get 10R which could give you 60dB of attenuation with a series of around 10k. Most of the time you could turn the paralleled LDRs off. The most common complaint is the min volume and when they have an efficient system there is no cure besides lower shunt resistance and higher series resistance. However, higher series resistance is not the best cure because of resistance wavering about and also because the sound gets kind of mushy at higher resistances compared to my favorite of 6k.
Uriah, thanks for the informative response.

If my spreadsheet is set up properly, with a load of 10K, a pot of 10K, and a source of 200R, a 40 ohm shunt LDR will give me 48db of attenuation, and a second paralleled device creating a 20 ohm shunt will give me 54db. A third paralleled shunt LDR gives 13.3 ohms and almost 58db of attenuation. My board is set up so that a user could select one, two, or three LDRs on the shunt side simply by swapping one resistor in the power supply and selecting the proper load LED (or zener, havenít decided which to use) to go in series with the series LDR which will always be a single unit.

But thereís really no practical way to go below about 15 ohms in shunt, and the only way to get more attenuation is to increase series resistance. I am curious about how much resistance wavering is too much in your opinion. Is +/- 100 ohms at 10K too much? With my feedback control system I think I can do +/- 50 at 10K but havenít had the chance to test my latest software yet. Itís turning out that in control software the KISS principle definitely applies Ė donít try to get fancy because the less code the better.

Your favorite resistance of 6K Ė is that system impedance or series resistance? I couldnít tell from your remarks
  Reply With Quote
Old 3rd December 2013, 08:52 AM   #5179
AndrewT is offline AndrewT  Scotland
R.I.P.
 
Join Date: Jul 2004
Location: Scottish Borders
Quote:
Originally Posted by udailey View Post
......................... However, higher series resistance is not the best cure because of resistance wavering about and also because the sound gets kind of mushy at higher resistances compared to my favorite of 6k.
Has anyone reported this "sound" or behaviour when using >10k?
__________________
regards Andrew T.
  Reply With Quote
Old 3rd December 2013, 09:43 AM   #5180
georgehifi is offline georgehifi  Australia
diyAudio Member
 
georgehifi's Avatar
 
Join Date: Sep 2003
Location: Manly Australia (Jewel of the Pacific)
Send a message via MSN to georgehifi
Quote:
Originally Posted by AndrewT View Post
Has anyone reported this "sound" or behaviour when using >10k?

Voodoo!
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote

Reply


Lightspeed Attenuator a new passive preampHide 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

Forum Jump


New To Site? Need Help?

All times are GMT. The time now is 12:20 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki