Lightspeed Attenuator a new passive preamp - Page 23

Panelhead · 21st September 2006, 01:39 AM

I think if you guys get together and order from RS you will be very happy. My sorted LDR's are all over the place, both in slope and offset. There were matched at three current levels.
The exponetial slope needed for atttenuation makes matching much less critical than you might expect. I checked some stereo pots and was shocked at how poorly they tracked. Some were 50% at middle range, and these were expensive conductive plastic.
My recommendation is two use two control stereo pots, and not the trimmer circuit. This way a small imbalance is easily corrected. I use the two controls when chasing problems from all the diy and modified gear in my system. Sometimes there are lots of gremlins.
I keep wanting to add a buffer after the Lightspeed clone. Thinking of a simple jfet or BJT with degeneration. But am completely happy with the sound as it is.

George

EUVL · 21st September 2006, 04:06 AM

There are a number of possible sources in Europe, of which Banzai is one. RS (UK) has the best price so far. But if no one in the UK is volunteering, there would be no group buy. As mentioned, I already got 25 SR3s from RS Germany, so I have no urgent need.

George put it very well, the advantage of the Group Buy is not only a bit of saving, but more importantly the better match.

Patrick

a333bt · 22nd September 2006, 10:09 PM

Hi,
i am also interested in group buy.

regards, Bostjan

JoshK · 25th September 2006, 09:50 PM

This seems to be an ideal way to do a multichannel attenuator with only a stereo pot. You just have to match as many LDRs as you have channels (not sure how hard that will be).

I really want to give this a try my my multiamped system. I already have a motorised remote controlled 100K pot. Is there a more clever way to do balanced channels then a shunt for each leg?

ErikdeBest · 25th September 2006, 10:29 PM

Quote:

Is there a more clever way to do balanced channels then a shunt for each leg?

YES! Imagine a shunt regulator: a series resistor and a adjustable shunting resistor to ground. Now imagine two of those, one for + and one for -. Now, instead of connecting the shunt resistors to ground, connect both ends to each other, so that there is no connection to gnd anymore. Now you can change the two independent shunt resistors for one!

I know, I picture says a thousand words, but I don't have one on hand right now.

Erik

blu_line · 26th September 2006, 05:03 AM

I am in for a grup buy !

Currently i am,also , building a multichannel amp and need to tackle the volume control section as previous posters mentioned.

6-10 will do fine !

grtz

Simon

JoshK · 26th September 2006, 01:31 PM

Quote:

Originally posted by ErikdeBest

YES! Imagine a shunt regulator: a series resistor and a adjustable shunting resistor to ground. Now imagine two of those, one for + and one for -. Now, instead of connecting the shunt resistors to ground, connect both ends to each other, so that there is no connection to gnd anymore. Now you can change the two independent shunt resistors for one!

I know, I picture says a thousand words, but I don't have one on hand right now.

Erik

So if I understand you correctly you are putting a "T" between the legs? Voltage dividing between the two legs and then shunting that to ground. This would require 3 LDRs if I understand this correctly? One in series with each leg and one from the voltage dividing node to ground.

ErikdeBest · 26th September 2006, 02:04 PM

Hi JoshK

Here is a picture (post 10), worth a thousand from my confusing english words.

How to connect a pot balanced

You see that you will need just one LDR per channel + 2 high precision resistors.

Erik

EUVL · 26th September 2006, 05:37 PM

> Nelson Pass : I don't trust those figures, and I would have to run them myself for these parts, as I am unaware of any big advances in Cadmium Sulfide cells. My examples had large distortion at ordinary line levels.

According to information from both Silonex and Perkin Elmer, the amount of distortion depends greatly on material type as well as voltage rating / level. There are types from Silonex with much higher distortions.

But I have no data to support or disclaim the Silonex data. The LDRs are there, just no time to measure as yet. I am also not for or against LDRs, but I am most curious to find out.

Patrick

wineds · 1st October 2006, 11:55 PM

Here is a link to local preamp shootout including a lightspeed clone for those who might be interested http://www.dtvforum.info/index.php?s...ic=36129&st=80

I have no relationship with George, I only corresponded with him for the first time yesterday.

The Lightspeed clone was up against some very well regarded pres and did very well.

Cheers,

Paul

PS: Starts at about post 88

21st September 2006, 01:39 AM	#221
Panelhead diyAudio Member Join Date: Dec 2002 Location: Houston	Group Buy I think if you guys get together and order from RS you will be very happy. My sorted LDR's are all over the place, both in slope and offset. There were matched at three current levels. The exponetial slope needed for atttenuation makes matching much less critical than you might expect. I checked some stereo pots and was shocked at how poorly they tracked. Some were 50% at middle range, and these were expensive conductive plastic. My recommendation is two use two control stereo pots, and not the trimmer circuit. This way a small imbalance is easily corrected. I use the two controls when chasing problems from all the diy and modified gear in my system. Sometimes there are lots of gremlins. I keep wanting to add a buffer after the Lightspeed clone. Thinking of a simple jfet or BJT with degeneration. But am completely happy with the sound as it is. George

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	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

21st September 2006, 04:06 AM	#222
EUVL diyAudio Member Join Date: Oct 2003	There are a number of possible sources in Europe, of which Banzai is one. RS (UK) has the best price so far. But if no one in the UK is volunteering, there would be no group buy. As mentioned, I already got 25 SR3s from RS Germany, so I have no urgent need. George put it very well, the advantage of the Group Buy is not only a bit of saving, but more importantly the better match. Patrick

22nd September 2006, 10:09 PM	#223
a333bt diyAudio Member Join Date: Jun 2004 Location: Vodice	Hi, i am also interested in group buy. regards, Bostjan

25th September 2006, 09:50 PM	#224
JoshK diyAudio Member Join Date: May 2004 Location: Toronto, ON	This seems to be an ideal way to do a multichannel attenuator with only a stereo pot. You just have to match as many LDRs as you have channels (not sure how hard that will be). I really want to give this a try my my multiamped system. I already have a motorised remote controlled 100K pot. Is there a more clever way to do balanced channels then a shunt for each leg?

26th September 2006, 05:03 AM	#226
blu_line diyAudio Member Join Date: Jan 2002 Location: The Netherlands	I am in for a grup buy ! Currently i am,also , building a multichannel amp and need to tackle the volume control section as previous posters mentioned. 6-10 will do fine ! grtz Simon

26th September 2006, 02:04 PM	#228
ErikdeBest diyAudio Member Join Date: Mar 2003 Location: Itoculo	Hi JoshK Here is a picture (post 10), worth a thousand from my confusing english words. How to connect a pot balanced You see that you will need just one LDR per channel + 2 high precision resistors. Erik

26th September 2006, 05:37 PM	#229
EUVL diyAudio Member Join Date: Oct 2003	> Nelson Pass : I don't trust those figures, and I would have to run them myself for these parts, as I am unaware of any big advances in Cadmium Sulfide cells. My examples had large distortion at ordinary line levels. According to information from both Silonex and Perkin Elmer, the amount of distortion depends greatly on material type as well as voltage rating / level. There are types from Silonex with much higher distortions. But I have no data to support or disclaim the Silonex data. The LDRs are there, just no time to measure as yet. I am also not for or against LDRs, but I am most curious to find out. Patrick

1st October 2006, 11:55 PM	#230
wineds diyAudio Member Join Date: Apr 2006 Location: Melbourne	Here is a link to local preamp shootout including a lightspeed clone for those who might be interested http://www.dtvforum.info/index.php?s...ic=36129&st=80 I have no relationship with George, I only corresponded with him for the first time yesterday. The Lightspeed clone was up against some very well regarded pres and did very well. Cheers, Paul PS: Starts at about post 88

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)