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 10th February 2011, 01:29 PM   #4001
jonclancy is offline jonclancy  United Kingdom
diyAudio Member
 
Join Date: Oct 2002
Location: UK
It was only a matter of time...
__________________
John Linsley Hood Ripple Eater GB Part One made 729 for Cancer Research UK. Thanks for your support!!!
  Reply With Quote
Old 10th February 2011, 05:31 PM   #4002
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
Okay, Jon! HaHa!

banbadoo, I am wondering if the increase in volume is drastic or just jumpy. I can see this happening with LDRs that have been burnt a little. So maybe in soldering them in you did shunts first and burnt them a little, then got a bit better at soldering them and did a fine job on series. When they get burnt its possible to drive them low in resistance but then have them jump up to a high level that they wont move from til you drive them lower in resistance again. Just a possibility. I am about out of ideas. I thought initially you probably just needed 100k, or as Ryelands said, that the track was dirty.. both problems would have been likely fixed with the 100k. Well, keep us posted on the second set of LDRs. I know you were probably careful with them but be even extra careful this time and be careful on all 4 of their leads.
Its just this way:
Apply flux to pad and leads.
Heat the pad/not the lead.
Apply solder to the iron while its still on the pad.
Quickly roll over to the lead and as soon as it jumps UP the lead a little you need to remove the iron.
Blow on the leads.
Wish you luck and congrats on your big knob.
Uriah
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
  Reply With Quote
Old 10th February 2011, 07:26 PM   #4003
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
Sick units
__________________
Avatar : Production Lightspeed Attenuator
www.lightspeedattenuator.com
  Reply With Quote
Old 11th February 2011, 04:11 PM   #4004
blue lander is offline blue lander  United States
diyAudio Member
 
Join Date: Jul 2009
I've been using a Lightspeed Attenuator for about a half a year now, and I have a confession to make: I just didn't like it. It's much clearer than a pot or stepped attenuator, but it's always had a "hollow" sound to it that really bothers me. I've the LDA by itself, with a B1 and with a DCB1. I've tried it with 3 different amplifiers, and with two different sets of speakers. Everybody loves these things so I assumed I had made some mistake when I built it. But I couldn't get to sound right no matter how much I fussed with it.

Yesterday I hooked the LDA up between my PC and amplifier to listen to some FLAC. Usually I never needed to turn the volume up on the LDA more than 1/4th the way to get full volume. But I had left the volume on the PC down at 18% or something like that, so I had to turn the LDA up to 50% or so...

...and the hollowness that had been bugging me completely went away! If I turn the PC volume up and the LDA volume down it comes back.

So I'm thinking of adding some additional resistance to the LDA so I can run it in the 50%-60% range rather than 20%-30%. I'll try using the 68r and 1k values recommended in that buildanamp.com article to see if that helps.
  Reply With Quote
Old 11th February 2011, 06:38 PM   #4005
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
Hi blue lander
If you are not using boards purchased from buildanamp.com then DONT switch to 68R resistors. You will burn your LDRs. The 68R in my near-lightspeed circuit are aided by a 200R trimmer in the protection of the LDRs.
I can tell you my assumption. LDRs really dont do well with higher than 2.5V or so going through them. When the volume it turned up on your computer it is outputting higher than 2.5V. This is my guess. I have put 6V through them with a tubed pre and the distortion is audible at this point. I have not tested with lower voltages but graphs posted earlier in this thread by Mr Pass and old test data by Silonex shows that it is better to add a gain stage AFTER the LDRs or to use unity gain devices if you want to stick something in front of them.
Its just my guess but I know that in my system I keep the volume at half on the computer.
Now, maybe its not this at all. Another thing it could be is that your Lightspeed has a resistance curve that looks like a smile. Usually the lowest Rtot of the Lightspeed is at around mid-volume. You might find that its the Rtot you are enjoying. If you want to try a lower Rtot then you would increase the value of those resistors feeding the LDRs and increase the Voltage feeding them. You could try 6,7,8V if you are using an LM317 to feed or some other variable regulator. Remember this: when you are turning the lightspeed's volume control you do not want the minimum resistance of any of the LDRs to go lower than 40R. This is where changing the value of the resistors feeding the LDRs comes into play because they will keep the LDRs from going below 40R but the higher voltage you feed them then the higher resistance you will need to keep above 40R. If I were experimenting to find a solution and if I thought it was Rtot that was sounding better for you, I would build up a protoboard to hold a few trimmers that would be in series with the protection resistors and then I would dial up the voltage until I got something like 4-7k Rtot and try that out. Rtot=total resistance between input and ground.
Uriah
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.com
  Reply With Quote
Old 14th February 2011, 08:04 PM   #4006
pubul57 is offline pubul57  United States
diyAudio Member
 
Join Date: Feb 2009
Default Walwart versus Battery Power

Any experimentation on this front and effect, or not, on sound quality? Any recommended rechargable battery systems from those that have tried it (U.S.)
  Reply With Quote
Old 18th February 2011, 03:32 PM   #4007
bambadoo is offline bambadoo  Norway
diyAudio Member
 
Join Date: Feb 2003
Location: West Coast of Norway
Finished my second lighspeed earlier today. I finally managed to "tweak" it so the volume control is not so sensitive. It feels more "linear" turning til knob..
But this one have a severe channel imbalance. Have to turn the balance knob during volume increase/decrease alot. Infact at some listening values the balance (4.7kohm pot) is not enough. I will maybe try a 10kohm for this.

My speakers are approx 97 dB sensitive and at the lowest volume setting the sound is at "normal" listening level.
Is it possible to adjust this with another resistor in series with the 100k pot?
I notice ~1.6Vdc from the psu to the lightspeed pcb at lowest volume setting. 5v at maximum.
I am using (this time) an alps 100k dual log.

I was very careful soldering .....

Resistors on the pcb is now 180ohm and 8.6kohm.
  Reply With Quote
Old 18th February 2011, 03:49 PM   #4008
Tripmaster is offline Tripmaster  United Kingdom
diyAudio Member
 
Tripmaster's Avatar
 
Join Date: Feb 2008
Location: UK
Quote:
Originally Posted by bambadoo View Post
Finished my second lighspeed earlier today. I finally managed to "tweak" it so the volume control is not so sensitive. It feels more "linear" turning til knob..
But this one have a severe channel imbalance. Have to turn the balance knob during volume increase/decrease alot. Infact at some listening values the balance (4.7kohm pot) is not enough. I will maybe try a 10kohm for this.

My speakers are approx 97 dB sensitive and at the lowest volume setting the sound is at "normal" listening level.
Is it possible to adjust this with another resistor in series with the 100k pot?
I notice ~1.6Vdc from the psu to the lightspeed pcb at lowest volume setting. 5v at maximum.
I am using (this time) an alps 100k dual log.

I was very careful soldering .....

Resistors on the pcb is now 180ohm and 8.6kohm.
Just an idea...As you have such sensitive speakers, are you able to reduce the gain on your amplifier?
  Reply With Quote
Old 18th February 2011, 04:16 PM   #4009
bambadoo is offline bambadoo  Norway
diyAudio Member
 
Join Date: Feb 2003
Location: West Coast of Norway
Of course but that is nok what I was hoping for. (my former speakers were 108dB )

In fact - I don't think I have that much gain.

I may reduse the output of the dac. I think it is 2.5vrms.

The amps are QuadII, preamp is Audio Note m3, dac is Audio Note dac2.1. Speakers are diy.
  Reply With Quote
Old 18th February 2011, 07:17 PM   #4010
udailey is offline udailey  United States
diyAudio Member
 
Join Date: Mar 2008
Its a pain when there is a lot of gain and then efficient speakers. One solution we have found on this forum is to stick a 10R-100R trimmer in series with the 5V that feeds the 100k pot. I know this sounds nuts but it works. You tweak the trimmer til you get a Rtot that is quieter at min volume. This trimmer can dramatically change Rtot so get a 20-25 turn trimmer so you can have great control over it.
Another solution is to stick a 100k pot AFTER the first 100k pot. You would put it on the line that feeds the dual series LDRs. The 100k trimmer goes to ground. At minimum volume you start to tweak the 100k trimmer and the lower its resistance the higher the max resistance of the series LDRs. So you have your shunts at very low resistance and you have your series at high resistance at min volume and you should get respectable low volume this way.
Uriah
__________________
purchase LDRs anytime Also try my Resistor Replacers or LDR based Input Selector Email me. diyldr@gmail.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 06:42 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